NYSGA 2024
New York State Geological Association
95th Annual Meeting
Field Trip Guidebook
Hosted by
Geological Sciences Program at the State University of New York at Oswego
Oswego, NY, 13126
Compiled by
David W. Valentino
Published by the
www.nysgaonline.org

B1: L-VERSES S-TECTONITE FABRIC VARIATIONS WITHIN THE SOUTHERN ADIRONDACK SHEAR ZONE SYSTEM: PROGRESSIVE DEFORMATION ASSOCIATED WITH A SINISTRAL CONJUGATE TO A GRENVILLE SYNTAXIS
David W. Valentino, Dept. of Earth Sciences, SUNY Oswego, Oswego, NY 13126
Gary S. Solar, Dept. of Earth Sciences, SUNY Buffalo, Buffalo, NY 14222
Jeffrey R. Chiarenzelli, Dept. of Geology, SUNY Potsdam, Potsdam, NY 13676
Alexander E. Gates, Dept. of Geological Sciences, Rutgers University, Newark, NJ 07102
Paul Freyer, Dept. of Earth Sciences, SUNY Oswego, Oswego, NY 13126
Rachel E. Price, Dept. of Geological Sciences, Rutgers University, Newark, NJ 07102
INTRODUCTION
This field guide was prepared in tandem with a field guide for the 73th and 75th NYSGA field conferences, and synchronously with an article written for the Memorial Volume to Nicholas Rast, recently published in the Journal of Geodynamics (Gates et al., 2004). Therefore, some parts of this guide are directly related to work presented in the earlier field guides and some parts were prepared for multiple projects; however, the emphasis here is exclusively on new findings in the Adirondacks. We encourage the reader to examine our data presented in the earlier field guides (Gates et al., 2001; Gorring et al., 2003) and summarized in Gates et al. (2004) for further details.
Transpressional strain is found to be related to a variety of tectonic environments. Transcurrent faults with restraining bends produce structures such as thrusts and conjugate faults (Woodcock, 1986). Oblique motion vectors between two tectonic plates result in oblique collision that produces zones of transpressional strike-slip deformation in the hinterland, and belts of thrusting in the foreland (e.g., Woodcock, 1986; Tappionier and Molnar, 1976). As well, zones of transcurrent strain can develop syntaxes in regions of the crust experiencing horizontal escape as the result of rigid indentors in the colliding lithosphere (Tappionier and Molnar, 1977). These structures have been almost exclusively described for rocks that were exhumed from intermediate to shallow levels of the crust. The distribution of strain and the location of faults can be controlled by the presence of pre-existing structures (Dewey and Burke, 1973), or by the juxtaposition of rock bodies with ductility contrasts such as decoupling of cover rocks over deforming crystalline basement (Gates et al., 1999; Valentino et al., 2004).
Dewey and Burke (1973) and Windley (1986) proposed a model for tectonism recorded in the Grenville Province rocks based upon the deep structure of Himalayas and the intensity of tectonism recorded there. Tapponnier and Molnar (1977) proposed that the rigid indentation of India formed a syntaxis (abrupt bend in the general attitude of the orogen) containing conjugate strike-slip faults in the Eurasian continent during the Himalayan Orogeny. Northeast-striking sinistral, transcurrent shear systems accommodate tectonic escape (Tapponnier et al., 1982) in China and southeast Asia, and these fault systems record hundreds to thousands of kilometers of offset over tens of millions of years. There are also smaller, northwest-striking, dextral systems that have been synchronously active with the sinistral zones that form the conjugate pairs to the larger sinistral zones of tectonic escape within the Himalayan syntaxis.
The Grenville Province forms one of the longest and most deeply exhumed areas of continental crust on Earth, extending from Scandinavia, through eastern Canada and inliers in the Appalachian chain, to Texas and Mexico, and perhaps beyond. Grenvillian basement massifs in the northeastern United States form a series of unconnected inliers along the Appalachian orogen (Figure 1). Because of the great spacing and high degree of tectonism associated with the Appalachian tectonic events, correlation of Grenvillian rocks among the massifs are difficult. In addition to widespread granulite-facies metamorphic conditions at about 1.0 Ga, these basement massifs all contain vast volumes of 'A-type' granite bodies whose magma had intruded (ca. 1150 Ma) into older supracrustal rocks (ca. 1250 Ma) of varied character prior to Ottawan deformation (ca. 1040 Ma; e.g., McLelland and Isachsen, 1986). The Grenville Province exposes the deep crustal roots of an ancient mountain range of immense portions, and records the assembly of one of the Earth's few recognized supercontinents, Rodinia. Consequently the Ottawan Orogeny (ca. 1070-1000 Ma) is often cited as a classic example of continent-continent collision and compressive thickening of the crust, with invocation of the Himalayas as a modern tectonic reference frame (Dewey and Burke, 1973; Windley, 1986; McLelland et al. 2001). However, refinement and testing of such a model must address many important components of the orogeny. One of the most significant components in the Himalayas is the massive amount of strike-slip faulting expressed in tectonic escape and the syntaxis (Tapponnier and Molnar, 1977). Whereas compressive tectonics is universally documented in the Grenville orogen, few workers have recognized analogous, large-scale, orogen-parallel deformation (cf. Baer, 1977). Some of the evidence for strike-parallel deformation is described herein, and is much of the basis for the sequence of outcrops listed in this guide.

B1: L-VERSES S-TECTONITE FABRIC VARIATIONS WITHIN THE SOUTHERN ADIRONDACK SHEAR ZONE SYSTEM: PROGRESSIVE DEFORMATION ASSOCIATED WITH A SINISTRAL CONJUGATE TO A GRENVILLE SYNTAXIS
D.W.Valentino, G.S.Solar, J.R.Chiarenzelli, A.E.Gates, P.Freyer, R.E.Price

STOP 1. Calc-silicate gneiss on the north side of the Snowy Mountain Dome (SMD).
Turn left into the overlook parking lot, and walk south on Rt. 30 approximately 0.2 miles to the first roadcut on the west (right) side of the road.
Calc-silicate gneiss with penetrative foliation and folds occurs in outcrops on the west side of Route 30. The foliation is defined by planar aggregates of recrystallized plagioclase, quartz and diopside (Figure 13). Locally the calc-silicate gneiss contains quartzofeldspathic layers that define isoclinal folds, and locally there are recrystallized masses of diopside (some 10 cm in diameter).
The dominant foliation in the outcrop in most places is structurally continuous with penetrative foliation (S2) in the Snowy Mountain dome, and dips moderately northward at this location. Portions of the exposure reveal an earlier foliation (S1) preserved mostly in the hinges of the isoclinal folds (F2) (Figure 13). The S1 foliation does not occur in the rocks of the Snowy Mountain suite, and the S2 foliation dies out away from the Snowy Mountain dome. In a relative sense, the S1 foliation either predates or is synchronous with the intrusion of the Snowy Mountain suite, and the S2 foliation is superimposed on the suite.
D.W.Valentino, G.S.Solar, J.R.Chiarenzelli, A.E.Gates, P.Freyer, R.E.Price

Roadcuts of charnockitic gneiss.
D.W.Valentino, G.S.Solar, J.R.Chiarenzelli, A.E.Gates, P.Freyer, R.E.Price

STOP 2: Charnockitic gneiss on the north side of the SMD.
Park on the right side of Rt. 30 and cross the road to the roadcut on the east (left) side (at the "Southwinds" sign).
The contact between the calc-silicate gneiss of STOP 1 and charnockitic gneiss of the Snowy Mountain suite occurs approximately 1 km northeast of this location, and is concordant with the S2 foliation. Here there is exposure of highly deformed charnockitic gneiss on both sides of the road. The foliation (S2) is defined by planar aggregates of dynamically recrystallized plagioclase and broken grains of hypersthene and augite. The foliation dips moderately northeastward and weak mineral lineations trend shallowly toward the east. Many of the outcrop surfaces reveal augen of plagioclase with core-mantle structure. Dynamically recrystallized tails developed on porphyroclasts of plagioclase merge with the penetrative foliation. The plagioclase augen are interpreted to be relict igneous crystals, possibly original megacrysts. When viewed on outcrop surfaces that are parallel to the lineation and perpendicular to the foliation, the augen appear to be asymmetric defining both σ- and β-porphyroclasts. Additionally, domino structures and Type I S-C fabrics can be viewed on some optimum surfaces. The kinematic indicators are consistent with top toward to the west ductile shearing, or low-angle sinistral considering the shallow plunge of the lineations.
Proceeding south across the Snowy Mountain dome, the penetrative foliation in the charnockitic gneiss progressively dips toward the east and then toward the southeast. There are numerous outcrops along Route 30 that can easily be viewed. Where the southeastern spur of Squaw Mountain intersects Route 30, there is exposure of gabbroic gneiss and megacrystic anorthosite. We will not be stopping at this outcrop during this trip due to time constraints. However, this is a good place to view the transitional compositions and deformation fabrics. The megacrystic anorthosite lacks penetrative deformation at this location, but some parts of the outcrop contain dynamically recrystallized anorthosite with well developed S2 foliation. The gabbroic gneiss contains penetrative foliation and well developed lineations at this location.
The transition from gabbroic- to charnockitic-gneiss occurs approximately 1000 meters northeast along the Squaw Mountain spur. This transition was documented by DeWaard and Romey (1969). Within the charnockitic gneiss branching high-strain zones can be seen (Figure 14). In places, the high-strain zones merge and have tapered terminations, and close inspection will reveal the penetrative foliation. Compositionally, the rocks in the high-strain zones are identical to the bounding charnockitic gneiss, except for the occurrence of minor quartz veins. The high-strain zones have the same general strike as the location foliation, but typically dip steeper northward in this area. Mineral lineations are better developed in the high-strain zones. Shear sense indicators are consistent with the shear sense indicators observed in the charnockitic gneiss with top toward the west ductile flow, or low-angle sinistral. The high-strain zones contain the same metamorphic minerals as the lower-strain charnockitic gneiss.

Roadcuts of metanorthosite.
Roadcuts of gabbroic metanorthosite and megacrystic metanorthosite.

STOP 3: "Underview" of the Snowy Mountain Dome
From this location, the entire structure of the Snowy Mountain dome can be viewed. Numerous slide faces expose the shallowly dipping foliation that occurs at the top of the dome (Figure 15). The exposures at the top of Snowy Mountain can be accessed by a popular hiking trail that occurs about 2 km north of this location. The top of Snowy Mountain is underlain by gabbroic gneiss with penetrative S2 foliation. The foliation dips shallowly toward the north and sub-horizontal mineral lineations trend nearly due east. A near vertical outcrop near the top of the mountain reveals abundant shear sense fabrics. Detailed kinematic analysis using porphyroclasts, S-C fabrics and shear bands resulted in dominant shear of top toward the west. However, some domains upward of a few meters thick showed conflicting shear sense of top toward the east. These exposures are the structurally highest part of the dome.

STOP 4: Charnockitic gneiss on the SE side of the Snowy Mountain Dome.
Turn right onto access road for campsites. Drive this road until just into the woods, and park in the wide flat area just before the bridge over Falls Brook. Walk across the bridge and past the metal gate, then plunge into the woods on the right of the access road about 10 meters to the outcrops in the brook that form the falls.
Stop 4 is of highly deformed charnockitic gneiss, the same lithology as Stop 2. However, the penetrative foliation dips moderately toward the southeast due to the position on the Snowy Mountain dome. At this location, and as before, the foliation (S2) is defined by planar aggregates of dynamically recrystallized plagioclase and broken grains of hypersthene and augite, and weak mineral lineations trend shallowly toward the east. Augen of plagioclase have dynamically recrystallized tails, often forming asymmetric kinematic indicators. As well, Type I S-C fabrics are well developed in some domains (Figure 16). Unlike Stop 2, the shear sense determined at this location is top toward the east. But, considering the dip is southerly, and mineral lineations trend easterly, the shear sense can be considered low-angle sinistral.

Jessup River

Roadcuts of quartzo-feldspathic gneiss with granite dikes
Roadcuts of quartzo-feldspathic gneiss with granite dikes on both sides of the road.

Calcite-garnet rock on right, rock painted as a pig on the left.
Roadcut of calcite-garnet rock on the right, with a rock painted as a pig on the left.

Roadcut of steeply-dipping dextrally sheared rocks on the right.

STOP 5A. Garnet amphibolite, calc-silicate rock and quartzo-feldspathic gneiss.
Here, these three rock types and their contacts are seen. The northern portion of the outcrop consists of garnet amphibolite, the next section of the outcrop is calc-silicate rock and the southern portion is fine-grained quartzofeldspathic gneiss. Complex sheath folds with sub-horizontal tight, isoclinal and sheath folds of foliation and compositional layers dominate the rock, particularly in the gneiss (trend to 110°) (Figure 17). Excellent views of the folds are seen on top of the southern part of the outcrop. The contacts between the rock types are also folded in similar fashion. Matrix minerals define lineations that are E-W and subhorizontal, but are variable in orientation due to folding.

STOP 5B. Garnet amphibolite and quartzo-feldspathic gneiss.
Park on the right, just after the guard rail, as you ascend the north slope of Burgess Hill (see location map). The outcrop is a roadcut on the east (opposite) side ofRt. 30 just north of the sign for Lake Pleasant.
Here the garnet amphibolite and garnet-bearing quartzo-feldspathic rock are in sheared contact. The amphibolite has a distinct foliation and lineation that is folded into shallowly inclined tight folds (N dipping axial planes) whose axes are shallowly E-W plunging. The lineation in the amphibolite is shallowly plunging to 112°. The fabric in the quartzo-feldspathic rock is distinct in contrast to the amphibolite, showing a penetrative L>>S tectonite fabric whose lineation plunges shallowly to 112°. The L>>S fabric is defined by both rods of quartz and quartz aggregates, and by tails around garnet. The highly fractured nature of the outcrop offers excellent views of this fabric. The contact between the rock types is distinct due to the color difference, but also because the amphibolite is boudinaged (foliation boudinage) due to apparent contact-parallel shear. The interboudin partitions are in-filled by plagioclase and amphibole (Figure 17).

Top of the hill (garnet amphibolite roadcuts on both sides).

STOP 5C: Overlook of Speculator Mountain, and the PLSZ.
Park on the right side of the road just south of the intersection, and walk to the top of the large roadcut for southerly views of Lake Pleasant and Speculator Mountain, and the PLSZ.
The rock here is sub-horizontally stratified, with the rock at the top of the hill to the north (garnet amphibolite) the lowest stratum, and the base of the outcrop is interlayered amphibolite and granitic gneiss, followed by granitic gneiss with mica 'mats' at the top (at the viewing area). Foliation is subhorizontal here, but, again, the mineral lineation is shallowly E- and W-plunging. The view to Speculator Mountain illustrates the structure of the late history of the PLSZ. The bench on the east side of the mountain is the top of the hanging wall block of a moderately W -dipping normal fault, and the peak of Speculator Mountain is the hanging wall block. This normal fault is defined by fabric with a distinct top-down fabric trajectory (see Figure 10), and defines the zone to be about 100 m thick. This is one of many normal shear zones that cut the E-W fabric that defines the PLSZ, but this one is perhaps the thickest. Most identified are a few centimeters thick (as in Figure 10).

STOP 6: L-S and L>S fabrics in the PLSZ.
The Piseco Lake shear zone is developed in rocks of granitic composition. Dynamically recrystallized feldspars and quartz form spectacular ribbon- and rod-shaped mineral lineations (McLelland, 1984), in addition to mafic phases such as biotite, chlorite and accessory magnetite. In many places, the alignment of ribbons forms the foliation in this outcrop (Figure 18). Individual quartz ribbons have aspect ratios upward of 60: 1. The foliation dips gently southward and the lineations trend about 110°(Figure 18). This location occurs on the southern flank of the map-scale antiform defined by the foliation in the Piseco Lake shear zone. At the western end of the outcrop there are rods of amphibolite (10-30 cm diameter) within the granitic gneiss. In the granitic gneiss, both biotite and chlorite blades form microscopic lineations and foliation parallel to the macroscopic structure. Rare grains of hypersthene have been found, but they always have well developed overgrowth textures that include biotite and chlorite. The biotite and chlorite are the most abundant index minerals in the granitic gneiss, and suggest the deformation was last active under low-grade metamorphic conditions, although probably began at much higher conditions to account for the relict grains of hypersthene.

TOP 7: Shear fabrics of the southern PLSZ.
Park as far off the road as possible. The outcrop for Stop 7 is pavement exposures located within the bed and the gutter on the east side of the road.
This stop consists of a sub-continuous series of pavement exposures located in the road bed, and in the gutter on the east (northeast-bound) side of the road. Due to the nature of this location, the extent of the exposed rock at this stop changes daily, so some or all of the rock described here may be viewable depending upon the time of the season in which the stop is visited (best later in the season).
Here, quartzo-feldspathic gneiss has intense shallowly WSW-plunging lineation and steeply S dipping foliation, both defined by ribbons (generally 1-5 cm long depending upon grain size). Locally, the gneiss has layers (up to 50 cm wide) of coarser-grained fabrics (grains up to 1 cm in diameter). Within the gneiss is lens- to block-shaped, and blunt-ended amphibolite bodies, also with a distinct mineral fabric that is sub-parallel to that of the gneiss. In general, the long dimension of lens-shaped amphibolite bodies are sub-parallel to the host gneiss fabric. The lengths of these bodies are not quantified due to the fact that the outcrop is composed of meter-scale windows through road gravel, but short dimensions are usually exposed showing bodies 10 to 30 cm wide. Fabric in the amphibolite is generally terminated at the boundary of the body, whereas the fabric in the quartzo-feldspathic gneiss drape the amphibolite bodies, showing fabric tails at the blunt ends of the bodies, sub-parallel to the mineral lineation (as porphyroclasts draped by matrix minerals; Figure 19).

STOP 8: Variations of L-S, L>S and L»S fabrics of the PLSZ.
Park along the side of the road in "the notch" between East and West Notch Mountains (see location map). The notch is Stop 8, featuring 0.2 miles of continuous exposure on both sides of Powley Road. The exposure on the northwest side (left) is the subject of the stop.
Due to the continuous nature of the exposure in an across-strike direction, the fabrics within the quartzo-feldspathic gneiss may be examined for their variations at about the meter scale. In general, the rock fabrics vary between L-S to L»S tectonite. Foliation intensity is variable, but mostly weak here. Foliation dip varies greatly across strike (moderately to steeply south-dipping), whereas the intensity and orientation of the lineation is consistently sub-horizontally E- and ESE-plunging. Of particular note in this outcrop, in addition to the matrix fabrics, is the pervasive feldspar porphyroclasts. Fabrics drape the porphyroclasts to form tails that are elongate sub-parallel to the matrix mineral lineation (sub-horizontal). Perhaps the cleanest views of the fabrics along the lineation may be seen at the very end (northeast end) of the exposure. We suggest that it is best to leave this spot for last in order to best appreciate the nature of the fabric in these rocks.

STOP 9: Fabric variations in gneiss in the PLSZ
Park along the side of the road avoiding the blind curve. The outcrops for Stop 9 are along the side and gutter of the northwest side of the road just before and at the left-hand curve in the road.
Fabric variations in garnet-bearing quartzo-feldspathic gneiss in the PLSZ. Here the quartzo-feldspathic gneiss fabrics vary from LS to L»S tectonite, whose lineation is shallowly E- to ESE-plunging, and the relatively weak foliation is moderately to steeply S-dipping. Feldspar porphyroclasts are present as at Stop 8. The southwest end of the exposure shows a high density of garnet porphyroclasts within foliation. Locally, garnet is concentrated into 2-3 cm-wide bladed bands, or is apparently flattened. Also locally, garnet occurs in patches or 'clots' 3-5 cm wide and up to 20 cm long.

STOP 10: Mylonitic augen gneiss of the PLSZ.
Park on the side of the road for a set of small low pavement exposures on the left (northwest) side of the road as the top of the hill is approached.
Best views of the fabrics in the quartzo-feldspathic gneiss are seen in the approximately 1.5 meter-long, beautifully polished pavement at the top of the hill. Here the rock has meter-scale mineralogical layers where the northern part is relatively more leucocratic, dominated by feldspar (up to 1 cm wide) and quartz ribbons (up to 3 mm wide). The fabric is intensely strong L-S tectonite throughout the exposure, with a steeply S-dipping foliation, and a sub-horizontal shallowly E-plunging lineation. The fabric may be considered 'textbook' mylonite, with spectacularly grain-size reduced texture in the less leucocratic layer. The mylonitic fabric transects the sharp contact between mineralogical layers at a low angle where it transitions into a more ribbon texture in the leucocratic layer. Of particular note here, besides the intense matrix fabrics, is the penetrative augen (generally 1 to 4 cm long) composed exclusively of aggregates of millimeter-grain-size quartz + feldspar, not single crystals. In every case, augen are draped by the matrix fabric, elongate sub-parallel to the lineation. There are a few much larger of these augen in this rock composed of rounded single feldspar crystals (up to 4 cm long) that are surrounded by aggregate quartz and feldspar (Figure 20).

STOP 11. Ultramylonite of the PLSZ.
Park on the side of the road to view the two small pavement exposures in the bed of the road for Stop 11.
These outcrops are very small (about 1 m or so long each) and isolated, so whether or not these rocks are viewable depends upon many factors including whether or not the road has been re-graded recently. As with STOP 7, the exposure of these rocks is better later in the season. The quartzo-feldspathic gneiss here shows spectacular mylonitic fabrics, as at Stop 10, where foliation and lineation are penetratively parallel across the small exposures (E-W fabrics with steep south dips and sub-horizontal E-plunges). Centimeter-scale textural layers are the highlight of this exposure where 1 to 5 cm wide bands of quartz + feldspar aggregate. Relatively thin layers of these aggregates are seen 'pinched and swelled' lenses. Individual augen of the aggregate are in the less leucocratic layers. We envision these textural variations to illustrate a progression of mylonitization where larger bands progressively become augen. Further, we suggest that the augen are seen kinematically combined, and as they interfered, they may form new aggregate bands. In a manner of speaking, one could say that the fabrics in this rock are snapshots of the progression, and that this rock is mylonite that has been multiply reworked as deformation continued.

STOP 12: L-S tectonite of the PLSZ.
Park on the right side of the road for the road cuts just over the top of the hill.
The quartzo-feldspathic gneiss here is spectacular L-S tectonite, whose foliation is moderately SSW-dipping, and whose lineation is shallowly W-plunging. As at Stop 10, augens are aggregates of fine-grained feldspar + quartz, and some here have asymmetric delta tails that show sinistral offset (see Figure 9B). Pavement outcrop at the top of the western roadcut show excellent three-dimensional views of the fabric.

STOP 13A: East of the gorge.
Turn left onto Gray Wilmurt Road just after a sharp right-hand curve in Rt. 8. Cross a bridge over the West Canada Creek and park at the intersection with Jones Road. Walk back toward the bridge over West Canada Creek and down the hill to the outcrop just east (upstream) of the bridge (see location map). The outcrop forms a small water fall on the creek.
The Piseco Lake shear zone traces westward through the West Canada Creek basin. Some of the best continuous exposures occur in the Ohio Gorge near Wulmurt. The last stops for this field trip are in highly deformed granitic gneiss in the gorge. During periods of high water, the exposures at the eastern and western end of the gorge may be covered or not easily accessed. Permission is needed from the landowner at Stop 13A.
The West Canada Creek forms a small waterfall at the upstream part of this outcrop. Pavement exposures reveal the L-S and LS deformation fabric in granitic gneiss (Figure 21). Foliation is gently dipping and the lineations are subhorizontal. In the region immediately down-stream of the falls, the foliation is defined by planar aggregates of recrystallized K-feldspar and quartz that alternate with dark layers containing abundant chlorite and minor biotite. The dominant fabrics are cross cut by at least three small high-strain zones. Two are steeply dipping and strike about east-west, and the third strikes south and dips moderately westward. One of the steeply dipping high-strain zones occurs in the vertical face at the southern side of the outcrop. Another occurs at the western limit of the outcrop close to the water. The north-south striking zone occurs in the low ledge near the falls. This small shear zone contains deformed pegmatite, and cross cuts the PLSZ foliation and lineation (Figure 10). Shear sense is top down to the west or normal. The other high strain zones both contain evidence for oblique sinistral shear.

STOP 13B: Western limit of the outcrop belt in the Ohio Gorge.
Park on the right shoulder just after a steep downhill drive. Walk upstream along West Canada Creek to the first bedrock exposures for the westernmost outcrops in the Ohio Gorge, and Stop 13B.
At this location the north dipping foliation of the Piseco antiform can be viewed in addition to the typical variation in L-S and LS fabrics at the outcrop scale. Again, the foliation is defined by planar aggregates of dynamically recrystallized feldspars and quartz. Quartz also occurs in greatly attenuated ribbons, as seen at other locations during this field trip. Of particular interest at this location, are abundant kinematic indicators that are easily observed. Outcrop surfaces that are perpendicular to the foliation and parallel to the lineation reveal asymmetric augen of K-feldspar and plagioclase forming both σ- and β-type shear sense indicators with most showing top toward the west displacement (Figure 9A). Since the mineral lineations are subhorizontal, the shear sense is considered to be low-angle sinistral at this location. The abundant large (cm-size) porphyroclasts of feldspar provide some information about the protolith for the PLSZ rocks in this region. The relict grains are most likely the remains of megacrysts from an original granite.

B2: VARIATIONS IN L- AND S-TECTONITE ON THE NORTHERN BOUNARY OF THE PISECO LAKE SHEAR ZONE, ADIRONDACK MOUNTAINS, NY
Damian Piaschyk
Department of Geology and Planetary Science
University of Pittsburgh
Pittsburgh, PA 15260
David Valentino
Department of Earth Sciences
State University of New York at Oswego
Oswego, NY 131263
Gary Solar
State University of New York
College at Buffalo
Buffalo, NY 14222
Jeffrey R. Chiarenzelli
Department of Geology
State University of New York at Potsdam
Potsdam, NY 13676
INTRODUCTION
The subject of this field trip is the variation in deformation fabrics along the northern margin of the Piseco Lake shear zone (Gates et al., 2004) with special emphasis on the development of L-tectonite domains at various scales. To some extent, but on a much more regional scale, this was also the emphasis of field guide for the 76th NYSGA field conference (Valentino et al., 2004). The current field guide covers a geology field trip that is a continuation of the earlier field trip with overlap of a few field stops.
The Piseco Lake shear zone (Figure 1) is a major Grenvillian structure that is 10 to 20 kilometers wide and strikes generally east -west in the southern Adirondacks. Kinematic analysis in the zone demonstrated dominantly low-angle sinistral shear (Gates et al., 2004). For the current study, an area of 42 square kilometers was mapped in detail and the study area spans the northern limit of the Piseco Lake zone in the area of the West Canada Creek basin (Figures 1 & 2). The objective of this study was to document the detailed rock fabric variation within the shear zone, within the transition zone and within the wall rocks to the shear zone. This study was designed to better understand the strain and metamorphic history associated with this major Adirondack structure, and document the geographic distribution of L- and L-S tectonites that were previously reported (McLelland, 1984; Chiarenzelli et al., 2000; Gates et al., 2004).

B2: VARIATIONS IN L- AND S-TECTONITE ON THE NORTHERN BOUNARY OF THE PISECO LAKE SHEAR ZONE, ADIRONDACK MOUNTAINS, NY

STOP 1. S>L Granitic gneiss with strong gneissic texture
Exposures of course granitic gneiss with well developed gneissocity can be seen in the high-wall of this old quarry. This stop demonstrates S>L fabric, lineation area weakly developed and foliation dominates. (Figure 5). The grain size is uniform and few kinematic indicators are present. The foliation is penetrative and is defined by planes of K-feldspar and biotite and dips to the northwest. The lineations are defined by streaks of biotite and plunge to the southwest.

STOP 2. L-S and S>L Dioritic Gneiss
The southern most part of the outcrop demonstrates L-S fabric (Figure 6). Lineations are about equal to foliation in intensity. Rods of hornblende define the linear fabric, which plunges to the southwest. Plagioclase and quartz define the foliation. In thin sections of this outcrop a ceased reaction is preserved. The hornblende crystals were breaking down to form biotite in a retrograde reaction. The northern most part of the outcrop demonstrates S>L fabric with gneissic textures, similar to the previous stop. Some small faults with 15cm of displacement and boudins are also preserved at the northern end of the outcrop (Figure 6). Garnets are also visible at the northern end of the outcrop but were not observed at the southern end in hand sample or thin section.

STOP 3A. East of the Ohio Gorge.
The West Canada Creek forms a small waterfall at the upstream part of this outcrop. Pavement exposures reveal the L-S and L>S deformation fabric in granitic gneiss (Figure 7). Foliation is gently dipping and the lineations are subhorizontal. In the region immediately down-stream of the falls, the foliation is defined by planar aggregates of recrystallized K-feldspar and quartz that alternate with dark layers containing abundant chlorite and minor biotite. The dominant fabrics are cross cut by at least three small high-strain zones. Two are steeply dipping and strike about east-west, and the third strikes south and dips moderately westward. One of the steeply dipping high-strain zones occurs in the vertical face at the southern side of the outcrop. Another occurs at the western limit of the outcrop close to the water. The north-south striking zone occurs in the low ledge near the falls. This small shear zone contains deformed pegmatite, and cross cuts the Piseco Lake shear zone foliation and lineation. Shear sense is top down to the west or normal. The other high-strain zones both contain evidence for oblique sinistral shear.

STOP 3B. East end of the Ohio Gorge.
The east end of the Ohio gorge demonstrates L>>S and L-S fabrics. The gorge contains granitic gneiss that varies only in the proportion of quartz, K-feldspar, plagioclase, biotite, and chlorite. The L-S domains have the larges grain size with numerous δ and σ shear sense indicators. The L-S domains also demonstrate lineation about 1 to 5 cm long, .5-2 cm wide, and 1-3 lineations per cm. The L>S domains have a smaller grain size then the L-S domains. The L>S domains demonstrate more lineations and less shear sense indicators, lineations are 1-6 cm long, .5-2 cm wide, and 3-5 lineations per cm. A contact between L>S and L-S can be observed (Figure 8). West of the fabric contact is an oblique left normal fault about 5 cm wide. This fault crosscuts the metamorphic fabrics strikes north south and dips to the east. Farther west is a .5 m wide pegmatite that strikes northwest southeast and dips southwest that also crosscuts metamorphic fabric. The pegmatite is composed of quartz, K-feldspar, and minor chlorite with grains about 1 to 3 cm in size.

STOP 3C. West end of the Ohio Gorge.
Stop 3C requires a .75-kilometer traverse west along the ridge of the Ohio gorge. Please WATCH YOUR STEP because the walls of the gorge are vertical and a fall would likely result in serious injury or worse.
The west end of the Ohio gorge also demonstrates L>S and L-S domains. Another ductile normal fault can also be observed. The ductile normal fault is much larger then the one observed at the east end of the gorge (Figure 9).

STOP 4A. L>>S Granitic Gneiss
Excellent outcrops on the northern side of a small hill just east of the parking area. Follow the dirt road to a path through the woods, and then head up hill to the south to the outcrops. This outcrop of granitic gneiss contains domains of L>S and L>>S. The L>S domains contain large and numerous σ-type shear sense indicators, some δ-type are present but are much less frequent. The porphyroclasts are large about 1-3 cm and the recrystallized porphyroclastic material is often wrapped with a quartz ribbons (Figure 10). The interpreted shear sense is low-angle and left lateral. The granitic gneiss is composed of quartz, K-feldspar plagioclase, and minor chlorite and biotite. The foliation strikes east west and dips to the south.

STOP 4B. Mafic Gneiss and L>>S Cigar Shaped Domain
This stop requires about 2.5 kilometers of traverse at a bearing of about 280º. The traverse will cross a few small streams and under brush can be thick in places. There is no trail to follow, so PLEASE STAY WITH THE GROUP.
Mafic Gneiss. This outcrop is a rare mafic gneiss composed of biotite, hypersthene, plagioclase, quartz and ilmenite. The fabric is L>S, lineations are defined by rods of plagioclase and streaks of biotite. The grains size is very small about 0.5mm. This rock unit borders the L>>S domain which can be seen at the next outcrop.
L>>S Cigar-Shaped Domain. The final stop is a spectacular L-tectonite (Figure 11). The outcrop is granitic gneiss composed of quartz, K-feldspar, plagioclase, and fabric forming chlorite and biotite. Foliation is hard to see in hand sample but can be seen if stained for plagioclase and K-feldspar. Figure 11 – Rock sample from STOP 4C with three mutually perpendicular cuts to reveal the internal fabric. Quartz rods and recrystallized aggregates of K-feldspar define the penetrative lineations, and foliation does not exist in this specimen. The dark minerals are primarily chlorite and biotite, and they too define a microscopic lineation as demonstrated by Price et al. (2003).

3 The Southern Adirondack Sinistral Transpressive Shear Systemp
David Valentino
Department of Earth Sciences
State University of New York at Oswego
Oswego, NY 131263
Jeffrey R. Chiarenzelli
Department of Geology
State University of New York at Potsdam
Potsdam, NY 13676
Damian Piaschyk
Pennsylvania General Energy
120 Market Street
Warren, Pennsylvania
Lindsay Williams
Robert Peterson
Department of Earth and Environmental Sciences
Rutgers University
Newark, New Jersey
IABSTRACT
The southern Adirondack mountains of New York are underlain by metaigneous and metasedimentary rocks that were deformed in a system of mostly sinistral shear zones (the southern Adirondack shear system) during the late stage of the Ottawan orogeny. At all scales, the shear system is generally east-west striking and contains generally east-west trending (080 o to 120o ) subhorizontal mineral elongation lineations and variably developed foliation (shallow to steeply dipping). The shear system is identified by the Snowy Mountain dome-Moose River plain shear system in the north, and the Piseco Lake domes and shear zone (PLsz) in the south.
The Snowy Mountain anorthosite body, and related AMCG rocks, occur within a structural dome (Snowy Mt. dome, SMD) approximately 15 km across. The SMD is defined by a concentric mantle of variably foliated noritic-, gabbroic-, and charnockitic-gneisses. Kinematic analysis was performed on rocks around SMD. The northeast and northwest flanks of the dome yielded a dominant shear sense of top westward, while on the southeast and southwest flanks resulted in a top eastward shear sense. The foliation is penetrative in the dome flanks, but is progressively weaker developed toward the interior anorthosite and in the supracrustal rocks that overly the dome. The foliation that wraps around SMD, narrows into the sinistral Moose River Plain shear zone (MRPz) to the west. Opposing shear sense on opposite flanks of the SMD suggests that sinistral ductile flow occurred around the anorthosite.
The Piseco Lake shear zone (PLsz) is a trans-Adirondack east-west structure, up to 20 km wide, defined by the regional fabric including a penetrative lineation, and foliation attitude and intensity that varies across the zone. The trend of lineations within the zone are subparallel to lithologic contacts and also parallel to subhorizontal regional lineation. The zone is developed primarily within highly deformed coarse-grained granitic rocks whose chemistry suggests an arc affinity. New field results indicate that the structure has two domains including a steeply dipping (5-7 km wide) mylonite zone (southern domain) that merges across strike with a broad open foliation arch (Piseco antiform or domes, northern domain). Sinistral kinematic indicators are common in both the steeply dipping mylonite domain and the flanks of the domes. Locally, the trend of the dome axis is asymmetric to the adjacent mylonite zone, and consistent with sinistral shear. The combination of steeply dipping mylonite with transcurrent strain history and adjacent domes suggests overall sinistral transpression. Metamorphic mineral assemblages from hypersthene to chlorite define the Piseco fabrics, indicating structural development over a wide temperature range (high to low) or reactivation at lower temperature conditions. Small (dm-scale ) north-striking extensional ductile shear zones occur through out the area, crosscutting the fabrics of the Piseco and Snowy Mountain structures.
The entire southern Adirondack shear system spans from a part of the Adirondacks dominated by AMCG suite rocks to a part dominated by granitoids with probable arc affinity. Based on the magnitude of the structures and the special association with rocks of different Adirondack terranes, this shear system may be a tectonic boundary separating the edge of Laurentia and older ca.1350 Ma tonalities and related arc supracrustal rocks exposed to the south. The location of the proposed suture served as a strike-slip escape structure as part of a Himalayan-type syntaxis in the late stage of the Ottawan orogeny.

Assembly Point

3 The Southern Adirondack Sinistral Transpressive Shear Systemp

STOP 1: Calc-silicate gneiss on the north side of the Snowy Mountain Dome (SMD)
STOP 1: Calc-silicate gneiss on the north side of the Snowy Mountain Dome (SMD) Calc-silicate gneiss with penetrative foliation and folds occurs in outcrops on the west side of Route 30. The foliation is defined by planar aggregates of recrystallized plagioclase, quartz and diopside (Figure 30). Locally the calc-silicate gneiss contains quartzofeldspatic layers that define isoclinal folds, and locally there are recrystallized masses of diopside (some &>10 cm in diameter).
The dominant foliation in the outcrop in most places is structurally continuous with penetrative foliation (S2) in the Snowy Mountain dome, and dips moderately northward at this location. Portions of the exposure reveal an earlier foliation (S 1) preserved mostly in the hinges of the isoclinal folds (F 2) (Figure 30). The S 1 foliation does not occur in the rocks of the Snowy Mountain suite, and the S 2 foliation dies out away from the Snowy Mountain dome. In a relative sense, the S 1 foliation is either predates or is synchronous with the intrusion of the Snowy Mountain suite, and the S 2 foliation is superimposed on the suite.

STOP 2: Charnockitic gneiss on the north side of the SMD
The contact between the calc-silicate gneiss of STOP 1 and charnockitic gneiss of the Snowy Mountain suite occurs approximately 1 km northeast of this location, and is concordant with the S 2 foliation. Here there is exposure of highly deformed charnockitic gneiss on both sides of the road. The foliation (S 2) is defined by planar aggregates of dynamically recrystallized plagioclase and broken grains of hypersthene and augite (Figure 31). The foliation dips moderately northeastward and weak mineral lineations trend shallowly toward the east. Many of the outcrop surfaces reveal augen of plagioclase with core-mantle structure. Dynamically recrystallized tails developed on porphyroclasts of plagioclase merge with the penetrative foliation. The plagioclase augen are interpreted to be relict igneous crystals, possibly original megacrysts. When viewed on outcrop surfaces that are parallel to the lineation and perpendicular to the foliation, the augen appear to be asymmetric. Domino structures and Type I S-C fabrics can be viewed on some optimum surfaces. The kinematic indicators are consistent with top toward to the west, low-angle sinistral shear.
Proceeding south across the Snowy Mountain dome, the penetrative foliation in the charnockitic gneiss progressively dips toward the each and then toward the southeast. There are numerous outcrops along Route 30 that can easily be viewed. Where the southeastern spur of Squaw Mountain intersects Route 30, there is exposure of gabbroic gneiss and megacrystic anorthosite. We will not be stopping at this outcrop during this trip due to time constraints. However, this is a good place to view the transitional compositions and deformation fabrics. The megacrystic anorthosite lacks penetrative deformation at this location, but some parts of the outcrop contain dynamically recrystallized anorthosite with well developed S 2 foliation. The gabbroic gneiss contains penetrative foliation and well developed lineations at this location.
The transition from gabbroic- to charnockitic-gneiss occurs approximatley 1000 meters northeast along the Squaw Mountain spur. This transition was documented by DeWaard and Romey (1969). Within the charnockitic gneiss branching high-strain zones can be seen (Figure 32). In places, the high-strain zones merge and have tapered terminations, and close inspection will reveal the penetrative folation. Compositionally, the rocks in the high-strain zones are identical to the bounding charnockitic gneiss, except for the occurrence of minor quartz veins. The high-strain zones have the same general strike as the location foliation, but typically dip steeper northward in this area. Mineral lineations are better developed in the high-strain zones. Shear sense indicators are consistent with the shear sense indicators observed in the charnockitic gneiss with top toward the west ductile flow, or low-angle sinistral. The high-strain zones contain the same metamorphic minerals as the lower-strain charnockitic gneiss.

STOP 3: “Underview” of the Snowy Mountain Dome
From this location the crest of the Snowy Mountain dome can be viewed. Numerous slide faces expose the shallowly dipping foliation that occurs at the top of the dome (Figure 33). The exposures at the top of Snowy Mountain can be accessed by a hiking trail that occurs about 2 km north of this location. The top of Snowy Mountain is underlain by gabbroic gneiss with penetrative S2 foliation. The foliation dips shallowly toward the north and subhorizontal mineral lineations trend nearly due east. A near vertical outcrop near the top of the mountain reveals abundant shear sense fabrics. Detailed kinematic analysis using porphyroclasts, S-C fabrics and shear bands resulted in dominant shear of top toward the west. However, some domains upward of a few meters thick showed conflicting shear sense of top toward the east. These exposures are the structurally highest part of the dome available.

STOP 4: Charnockitic gneiss on the southeast side of the Snowy Mountain Dome
Stop 4 is of highly deformed charnockitic gneiss, the same lithology as Stop 2. However, the penetrative foliation dips moderately toward the southeast due to the position on the Snowy Mountain dome. At this location, and as before, the foliation (S 2) is defined by planar aggregates of dynamically recrystallized plagioclase and broken grains of hypersthene and augite, and weak mineral lineations trend shallowly toward the east. Augen of plagioclase have dynamically recrystallized tails often forming asymmetric kinematic indicators. As well, Type I S-C fabrics are well developed in some domains (Figure 34). Unlike Stop 2, the shear sense determined at this location is top toward the east. But, considering the dip is southerly, and mineral lineations trend easterly, the shear sense can be considered low-angle sinistral.

STOP 5A: Garnet amphibolite, calc-silicate rock and quartzo-felspathic gneiss
Rocks of each outcrop for Stop 5 are typical of rocks that occupy the zone between the SMD to the north (STOPS 1 to 4) and the Piseco Lake shear zone to the south (STOPS 6 to 13).
Here, these three rock types and their contacts are seen. The northern ¼ of the outcrop consists of garnet amphibolite, the next ~ 0.25 of the outcrop is calc-silicate rock and the southern 0.5 is fine- grained quartzo-feldspathic gneiss. Complex sheath folds with sub-horizontal tight, isoclinal and sheath folds of foliation and compositional layers dominate the rock, particularly in the gneiss (trend to 110°) (Figure 17). Excellent views of the folds are seen on top of the southern part of the outcrop. The contacts between the rock types are also folded in similar fashion. Matrix minerals define lineations that are E-W and subhoriziontal, but are variable in orientation due to folding.

STOP 5B: Garnet amphibolite and quartzo-feldspathic gneiss
Here the garnet amphibolite and garnet-bearing quartzo-feldspathic rock is in sheared contact. The amphibolite has a distinct foliation and lineation that is folded into shallowly inclined tight folds (N-dipping axial planes) whose axes are shallowly E-W plunging. The lineation in the amphibolite is shallowly plunging to 112°. The fabric in the quartzo-feldspathic rock is distinct in contrast to the amphibolite, showing a penetrative L>>S tectonite fabric whose lineation plunges shallowly to 112°. The L>>S fabric is defined by both rods of quartz and quartz aggregates, and by tails around garnet. The highly fractured nature of the outcrop offers excellent views of this fabric. The contact between the rock types is distinct due to the color difference, but also because the amphibolite is boudinaged (foliation boudinage) due to apparent contact-parallel shear. The inter-boudin partitions are in-filled by plagioclase and amphibole (Figure 35).

STOP 5C: Overlook of Speculator Mountain, and the PLSZ
The rock here is sub-horizontally stratified, with the rock at the top of the hill to the north (garnet amphibolite) the lowest stratum, and the base of the outcrop is interlayered amphibolite and granitic gneiss, followed by granitic gneiss with mica ‘mats’ at the top (at the viewing area). Foliation is sub-horizontal here, but, again, the mineral lineation is shallowly E- and W-plunging.
The view to Speculator Mountain illustrates the structure of the late history of the PLSZ. The bench on the east side of the mountain is the top of the hanging wall block of a moderately W-dipping normal fault, and the peak of Speculator Mountain is the hanging wall block. This normal fault is defined by fabric with a distinct top-down fabric trajectory, and defines the zone to be about 100 m thick. This is one of many normal shear zones that cut the E-W fabric that defines the PLSZ, but this one is perhaps the thickest. Most identified are a few centimeters thick (as in Figure 18).

STOP 6A L-S and L>S fabrics in the Piseco dome.
The Piseco Lake zone consists of the northern dome that merges with a steeply dipping shear zones to the south. This series of field stops shows variations in the attitude and type of fabrics that occur in the core of the dome. Stops 6A to 6D are a driving traverse around Piseco Lake, the type location of the Piseco antiform. At all of these localities, dynamically recrystallized feldspars and quartz form spectacular ribbon- and rod-shaped mineral lineations (McLelland, 1984), in addition to mafic phases such as biotite, chlorite and accessory magnetite. In many places, the alignment of ribbons forms the foliation in this outcrop. Individual quartz-ribbons have aspect ratios upward of 60:1. At Stop 6A, the foliation is weakly to moderately developed, and dips shallowly southward at the eastern part of the outcrop (Figure 36), but is steeply dipping at the western end of the outcrop. The transition between these different foliation attitudes is difficult to determine because the intensity of the foliation is variable. Lineations are penetrative on all scales, and consistent in attitude (Trend: 110°; Plunge: 05°). Stop 6A occurs on the southern flank of the map-scale dome portion of the Piseco antiform. At the western end of the outcrop there are rods of amphibolite (10- 30 cm diameter) within the granitic gneiss.

Stop 6 B
There is an apparent Cenozoic fault that traces down the western side of Piseco Lake and has locally displaced parts of the Piseco dome (Figures 13 and 14). At Stop 6B, again the foliation is weakly developed with a penetrative shallowly plunging lineation. However, the foliation, where it can be observed, dips northerly. As you drive southwest along the western side of Piseco Lake, note that the foliation gradually shallows and then dips southerly. There are several outcrops that can be observed where this transition in foliation attitude occurs.

Stop 6 C
The rock fabrics at Stop 6C are similar to those at Stops 6A and 6B, but again the variably developed foliation dips toward the south.

Stop 6D
Stop 6D is located at the intersection of Rts. 8 and 10, and the folation and lineation is penetrative.
Common to all of these field stops is that both biotite and chlorite blades form microscopic lineations and foliation parallel to the macroscopic structure. Rare grains of hypersthene have been found, but they always have well developed overgrowth textures that include biotite and chlorite. The biotite and chlorite are the most abundant index minerals in the granitic gneiss, and suggest the deformation was last active under low- to moderate- metamorphic conditions, although probably began at much higher conditions to account for the relict grains of hypersthene.

STOPS 7: Steeply dipping mylonite zone of the southern PLSZ
Along Powley Road, there are a sub-continuous series of pavement exposures located in the road bed, and in the gutter on the east (northeast-bound) side of the road. Due to the nature of this location, the extent of the exposed rock at this stop changes daily, so some or all of the rock described here may be viewable depending upon the time of the season in which the stop is visited (best later in the season). The best exposures occur along the road between West and East Notch Mountains. All rocks in this region are very similar in mineral content, and vary only in detail with regard to mineral percentage and fabric type and intensity. The rock is dominantly granitic gneiss with intense subhorizontal to shallowly plunging mineral elongation lineation that trends on average about 095°, with steeply dipping generally east-west striking foliation. Both fabric elements are defined by ribbons of quartz, and ribbons of aggregate feldspar and quartz (generally 1-5 cm long depending upon grain size). Intensity of the fabric varies across strike at the 50 cm scale, with local layers of significantly coarser-grained fabrics (grains up to 1 cm in diameter). There are also places where the foliation intensity varies as seen at the field stops around Piseco Lake. Rare amphibolite bodies that are 10’s of cm thick occur within the granitic gneiss (Figure 37). Shear sense indicators are abundant in the granitic rocks and consistently show sinistral shear sense (Figure 11).

STOP 8: Southern extent of steeply dipping mylonite
Here the granitic gneiss fabrics contain both a penetrative foliation and lineation. The foliation is steeply dipping and strikes about east-west. Mineral elongation lineation defined by linear aggregates of quartz and feldspar are subhorizontal. The extent of readily available bedrock exposure diminishes south of this location, so this may be the southern-most exposure of the Piseco Lake shear zone. Note that this location is about 21 kilometers across strike from the northern side of the Piseco dome where the pronounced lineation occurs.

STOP 9: L>>S and L-tectonite in the core of the Piseco antiform
Excellent outcrops on the northern side of a small hill just west of the parking area. Follow the dirt road to a path through the woods, and then head up hill to the south to the outcrops. This outcrop of granitic gneiss contains domains of L>S and L>>S. The L>S domains contain large and numerous σ-type shear sense indicators, some δ-type are present but are much less frequent. The porphyroclasts are large about 1-3 cm and the recrystallized porphyroclastic material is often wrapped with a quartz ribbons (Figure 38). The interpreted shear sense is low-angle and left lateral. The granitic gneiss is composed of quartz, K-feldspar plagioclase, and minor chlorite and biotite. The foliation strikes east west and dips to the south.
Stops 9B and 9C require about 2.5 kilometers of traverse at a bearing of about 280°. The traverse will cross a few small streams and under brush can be thick in places. There is no trail to follow, so PLEASE STAY WITH YOUR GROUP.
Stop 9B there is an outcrop of a rare mafic gneiss composed of biotite, hypersthene, plagioclase, quartz and ilmenite. The fabric is L>S, lineations are defined by rods of plagioclase and streaks of biotite. The grains size is very small about 0.5mm. This rock unit borders the L>>S domain which can be seen at Stop 9C.
Stop 9C is a spectacular L-tectonite (Figure 39) that occurs in a cigar-shaped domain that appears on the geology map of Figure 15. The outcrop is granitic gneiss composed of quartz, K-feldspar, plagioclase, and fabric forming chlorite and biotite. Foliation is hard to see in hand sample but can be seen if stained for plagioclase and K-feldspar.

Stops 9B and 9C
Excellent outcrops on the northern side of a small hill just west of the parking area. Follow the dirt road to a path through the woods, and then head up hill to the south to the outcrops. This outcrop of granitic gneiss contains domains of L>S and L>>S. The L>S domains contain large and numerous σ-type shear sense indicators, some δ-type are present but are much less frequent. The porphyroclasts are large about 1-3 cm and the recrystallized porphyroclastic material is often wrapped with a quartz ribbons (Figure 38). The interpreted shear sense is low-angle and left lateral. The granitic gneiss is composed of quartz, K-feldspar plagioclase, and minor chlorite and biotite. The foliation strikes east west and dips to the south.
Stops 9B and 9C require about 2.5 kilometers of traverse at a bearing of about 280º. The traverse will cross a few small streams and under brush can be thick in places. There is no trail to follow, so PLEASE STAY WITH YOUR GROUP.
Stop 9B there is an outcrop of a rare mafic gneiss composed of biotite, hypersthene, plagioclase, quartz and ilmenite. The fabric is L>S, lineations are defined by rods of plagioclase and streaks of biotite. The grains size is very small about 0.5mm. This rock unit borders the L>>S domain which can be seen at Stop 9C.
Stop 9C is
a spectacular L-tectonite (Figure 39) that occurs in a cigar-shaped domain that appears on the geology map of Figure 15. The outcrop is granitic gneiss composed of quartz, K-feldspar, plagioclase, and fabric forming chlorite and biotite. Foliation is hard to see in hand sample but can be seen if stained for plagioclase and K-feldspar.

STOP 10. Northern limit of Piseco zone fabrics: granitic gneiss with well developed gneissocity
Exposures of course granitic gneiss with well developed gneissocity can be seen in the high-wall of this old quarry. This stop demonstrates S>L fabric, lineation area weakly developed and foliation dominates. (Figure 40). The grain size is uniform and few kinematic indicators are present. The foliation is penetrative and is defined by planes of K-feldspar and biotite and dips to the northwest. The lineations are defined by streaks of biotite and plunge to the southwest.

STOP 11. L-S and S>L Dioritic Gneiss
The southern most part of the outcrop demonstrates L-S fabric. Lineations are about equal to foliation in intensity. Rods of hornblende define the linear fabric, which plunges to the southwest. Plagioclase and quartz define the foliation. In thin sections of this outcrop a ceased reaction is preserved. The hornblende crystals were breaking down to form biotite in a retrograde reaction. The northern most part of the outcrop demonstrates S>L fabric with gneissic textures, similar to the previous stop. Some small faults with 15 cm of displacement and boudins are also preserved at the northern end of the outcrop. Garnets are also visible at the northern end of the outcrop but were not observed at the southern end in hand sample or thin section.

STOP 12A: The PLSZ at the Ohio Gorge of West Canada Creek - East of Gorge
The Piseco Lake shear zone traces westward through the West Canada Creek basin. Some of the best continuous exposures occur in the Ohio Gorge near Wilmurt. The last stops for this field trip are in highly deformed granitic gneiss in the gorge. During periods of high water, the exposures at the eastern and western end of the gorge may be covered or not easily accessed. Permission is needed from the landowner at Stops 12A and 12B.
The West Canada Creek forms a small waterfall at the upstream part of this outcrop. Pavement exposures reveal the L-S and L>S deformation fabric in granitic gneiss (Figure 21). Foliation is gently dipping and the lineations are subhorizontal. In the region immediately down-stream of the falls, the foliation is defined by planar aggregates of recrystallized K-feldspar and quartz that alternate with dark layers containing abundant chlorite and minor biotite. The dominant fabrics are cross cut by at least three small high-strain zones. Two are steeply dipping and strike about east- west, and the third strikes south and dips moderately westward. One of the steeply dipping high- strain zones occurs in the vertical face at the southern side of the outcrop. Another occurs at the western limit of the outcrop close to the water. The north-south striking zone occurs in the low ledge near the falls. This small shear zone contains deformed pegmatite, and cross cuts the PLsz foliation and lineation (Figure 18). Shear sense is top down to the west or normal. The other high strain zones both contain evidence for oblique sinistral shear.

STOP 12B: Western limit of the outcrop belt in the Ohio Gorge
At this location the north dipping foliation of the Piseco antiform can be viewed in addition to the typical variation in L-S and L>S fabrics at the outcrop scale. Again, the foliation is defined by planar aggregates of dynamically recrystallized feldspars and quartz. Quartz also occurs in greatly attenuated ribbons, as seen at other locations during this field trip. Of particular interest at this location, are abundant kinematic indicators that are easily observed. Outcrop surfaces that are perpendicular to the foliation and parallel to the lineation reveal asymmetric augen of K-feldspar and plagioclase forming both - and -type shear sense indicators (Figure 41) with most showing top toward the west displacement. Since the mineral lineations are subhorizontal, the shear sense is considered to be low-angle sinistral at this location. The abundant large (cm-size) porphyroclasts of feldspar provide some information about the protolith for the PLSZ rocks in this region. The relict grains are most likely the remains of megacrysts from an original granite.

4 THE PISECO LAKE SHEAR ZONE A SHAWINIGAN CRYPTIC SUTURE IN THE SOUTHERN ADIRONDACK MOUNTAINS, NEW YORK
David W. Valentino
Department of Atmospheric and Geological Sciences
SUNY Oswego,
Oswego, NY 13126
david.valentino@oswego.edu
Jeffrey R. Chiarenzelli
Department of Geology
St. Lawrence University
Canton, NY 13617
jchiaren@stlawu.edu
ABSTRACT
This field trip was first run in 2005 for NYSGA and was reorganized for the 2018 NYSGA-NEIGC joint field conference to show progress in our understanding of the complex geology of the southern Adirondacks. However, in 2018 the trip canceled just prior to the conference due to the sudden tragic loss of Dr. Brian Hough that occurred a few days before the conference. Brian was a colleague of the lead author. Four years later the trip is finally being run again, and it is dedicated to the memory of Brian. Although his tenure at SUNY Oswego was not long, and was tragically cut-short, the impact that he had on many student and colleagues will last a lifetime.
Highly deformed Piseco granitic gneisses occur in an arching east-west transpressional ductile shear zone (Piseco Lake shear zone) that spans the width of the exposed southern Adirondacks. The highly deformed granitic gneisses have restricted silica content, are metaluminous, alkali-calcic to calc-alkalic, continental arc trace element signatures. These granitic rocks intruded supracrustal gneisses resulting in extensive Shawinigan partial melting. The Piseco Lake shear zone (20-30 km wide) formed in this belt of granitic rocks and correlate with a pronounced arcuate-shaped high magnetic anomaly. The magnetic anomaly extends well beyond the exposed Adirondack basement window.
The shear zone is 20-30 km wide and is believed to be the location of a cryptic suture because it occurs between the Adirondack Highlands (underlain primarily by anorthosite and related granitic rocks, AMCG suite) and the Southern Adirondack Terrane (underlain by calc-alkaline tonalitic arc rocks) (Valentino et al., in press). Within the shear zone, the original megacrystic granite contains lineated quartz and rodded feldspar aggregates up to a meter long in places. Along the axis of the shear zone there are thick (1-2 km), subvertical zones of granitic L-S and L-tectonites.
The northern domain of the zone is defined by large foliation domes that are cored by L-tectonite. The southern limbs of the domes steepen toward the south and merge with a wide zone (up to 15 km) of steeply dipping granitic mylonite. Overall, the shear system (domes and steep mylonite zone) forms the core of a region of intense ductile deformation with left-lateral kinematic indicators and subhorizontal E-W ribbon lineations.
The Piseco granitic suite are highly deformed suture-stitching arc plutons that intruded within a sinistral, oblique-convergent, shear system in the deep crust during the Shawinigan orogeny. This is ductile shear zone is the most continuous and largest in the entire Adirondack massif. The shear zone, associated granitic rocks, and the magnetic anomaly abruptly trends toward the south in the eastern Adirondacks. Just beyond this location, the magnetic anomaly appears to be truncated by a branch of the NY-AL magnetic lineament. Following the trace of the magnetic anomaly toward the west, suggests that the shear zone continues for a considerable distance beyond the Adirondack window. It’s magnitude, in addition to the magnitude and extend of the associated magnetic anomaly, suggests that the Piseco shear zone penetrates the Moho.
The current field trip is an update on our very long research project, and it’s geared toward an undergraduate student audience. All field locations were picked to accommodate large student groups. Sampling is generally prohibited by NYS law in the Adirondack Park, and we encourage future instructors to help preserve the field locations presented herein by showing and discussing, and not removing the spectacular bedrock features. Note that the field guide included here in was pirated and modified from the Friends of the Grenville field conference run by D. Valentino, J. Chairenzelli, D. Piaschyk, L. Williams and R. Peterson in 2008.

A3:THE PISECO LAKE SHEAR ZONE: A SHAWINIGAN CRYPTIC SUTURE IN THE SOUTHERN ADIRONDACK MOUNTAINS, NEW YORK

Meeting Point - Charlie Johns Store

STOP 1. Supracrustal rocks of the Adirondack Highlands, just north of the Piseco Lake shear zone
There are several rock types that can be observed at this outcrop, along with the contacts and primary compositional layering. The northern ¼ of the outcrop consists of garnet amphibolite, the next ∼ ¼ of the outcrop is calc-silicate gneiss and the southern ½ is fine-grained quartzo-feldspathic gneiss locally interlayered with highly folded marble (Figure 7). Complex sheath folds with sub-horizontal tight, isoclinal and sheath folds of foliation and compositional layers dominate the rock, particularly in the gneiss (trend to 110o). Excellent views of the folds are seen on top of the southern part of the outcrop. The contacts between the rock types are also folded in similar fashion. Matrix minerals define lineations that are E-W and sub-horizontal, but are variable in orientation due to folding. Overall, the diverse lithologies and style of deformation are typical for the supracrustal rocks located north of the Piseco Lake granitoids. At this point, note that primary compositional layering is preserved at this outcrop.

STOP 2A
The Piseco Lake shear zone includes the northern foliation domes that merge with the steeply dipping shear zones to the south. This series of field stops shows variations in the attitude and type of fabrics that occur in the core of the dome at Piseco Lake. Stops 2A to 2D are a driving traverse around Piseco Lake, the type location of the Piseco antiform. At all of these localities, dynamically recrystallized feldspars and quartz form spectacular ribbon- and rod-shaped mineral lineations (McLelland, 1984), in addition to accessory biotite and magnetite. In many places, the alignment of ribbons forms the foliation in this outcrop. Individual quartz-ribbons have aspect ratios upward of 60:1. At Stop 2A, the foliation is weakly to moderately developed, and dips shallowly southward at the eastern part of the outcrop, but is steeply dipping at the western end of the outcrop. The transition between these different foliation attitudes is difficult to determine because the intensity of the foliation is variable. Lineations are penetrative on all scales, and consistent in attitude (Trend: 110°; Plunge: 05°). Stop 6A occurs on the southern flank of the map-scale dome portion of the Piseco antiform. At the western end of the outcrop there are rods of amphibolite (10-30 cm diameter) within the granitic gneiss.
There is an apparent Mesozoic fault that traces down the western side of Piseco Lake and has locally displaced parts of the Piseco dome (Figure 3). At Stop 2B, again the foliation is weakly developed with a penetrative shallowly plunging lineation. However, the foliation, where it can be observed, dips northerly. As you drive southwest along the western side of Piseco Lake, note that the foliation gradually shallows and then dips southerly. There are several outcrops that can be observed where this transition in foliation attitude occurs. The rock fabrics at Stop 2C are similar to those at Stops 2A and 2B, but again the variably developed foliation dips toward the south. Stop 2D is located at the intersection of Rts. 8 and 10, and the foliation and lineation is penetrative.
Common to all of these field stops is that biotite and sometimes chlorite blades form microscopic lineations and foliation parallel to the macroscopic structure. Rare grains of hypersthene have been found, but they always have well developed overgrowth textures that include biotite and chlorite. The biotite and chlorite are the most abundant index minerals in the granitic gneiss, and suggest the deformation was last active under low- to moderate- metamorphic conditions, although probably began at much higher conditions to account for the relict grains of hypersthene.

STOP 2B:
The Piseco Lake shear zone includes the northern foliation domes that merge with the steeply dipping shear zones to the south. This series of field stops shows variations in the attitude and type of fabrics that occur in the core of the dome at Piseco Lake. Stops 2A to 2D are a driving traverse around Piseco Lake, the type location of the Piseco antiform. At all of these localities, dynamically recrystallized feldspars and quartz form spectacular ribbon- and rod-shaped mineral lineations (McLelland, 1984), in addition to accessory biotite and magnetite. In many places, the alignment of ribbons forms the foliation in this outcrop. Individual quartz-ribbons have aspect ratios upward of 60:1. At Stop 2A, the foliation is weakly to moderately developed, and dips shallowly southward at the eastern part of the outcrop, but is steeply dipping at the western end of the outcrop. The transition between these different foliation attitudes is difficult to determine because the intensity of the foliation is variable. Lineations are penetrative on all scales, and consistent in attitude (Trend: 110°; Plunge: 05°). Stop 6A occurs on the southern flank of the map-scale dome portion of the Piseco antiform. At the western end of the outcrop there are rods of amphibolite (10-30 cm diameter) within the granitic gneiss.
There is an apparent Mesozoic fault that traces down the western side of Piseco Lake and has locally displaced parts of the Piseco dome (Figure 3). At Stop 2B, again the foliation is weakly developed with a penetrative shallowly plunging lineation. However, the foliation, where it can be observed, dips northerly. As you drive southwest along the western side of Piseco Lake, note that the foliation gradually shallows and then dips southerly. There are several outcrops that can be observed where this transition in foliation attitude occurs. The rock fabrics at Stop 2C are similar to those at Stops 2A and 2B, but again the variably developed foliation dips toward the south. Stop 2D is located at the intersection of Rts. 8 and 10, and the foliation and lineation is penetrative.
Common to all of these field stops is that biotite and sometimes chlorite blades form microscopic lineations and foliation parallel to the macroscopic structure. Rare grains of hypersthene have been found, but they always have well developed overgrowth textures that include biotite and chlorite. The biotite and chlorite are the most abundant index minerals in the granitic gneiss, and suggest the deformation was last active under low- to moderate- metamorphic conditions, although probably began at much higher conditions to account for the relict grains of hypersthene.

STOP 2C
The Piseco Lake shear zone includes the northern foliation domes that merge with the steeply dipping shear zones to the south. This series of field stops shows variations in the attitude and type of fabrics that occur in the core of the dome at Piseco Lake. Stops 2A to 2D are a driving traverse around Piseco Lake, the type location of the Piseco antiform. At all of these localities, dynamically recrystallized feldspars and quartz form spectacular ribbon- and rod-shaped mineral lineations (McLelland, 1984), in addition to accessory biotite and magnetite. In many places, the alignment of ribbons forms the foliation in this outcrop. Individual quartz-ribbons have aspect ratios upward of 60:1. At Stop 2A, the foliation is weakly to moderately developed, and dips shallowly southward at the eastern part of the outcrop, but is steeply dipping at the western end of the outcrop. The transition between these different foliation attitudes is difficult to determine because the intensity of the foliation is variable. Lineations are penetrative on all scales, and consistent in attitude (Trend: 110°; Plunge: 05°). Stop 6A occurs on the southern flank of the map-scale dome portion of the Piseco antiform. At the western end of the outcrop there are rods of amphibolite (10-30 cm diameter) within the granitic gneiss.
There is an apparent Mesozoic fault that traces down the western side of Piseco Lake and has locally displaced parts of the Piseco dome (Figure 3). At Stop 2B, again the foliation is weakly developed with a penetrative shallowly plunging lineation. However, the foliation, where it can be observed, dips northerly. As you drive southwest along the western side of Piseco Lake, note that the foliation gradually shallows and then dips southerly. There are several outcrops that can be observed where this transition in foliation attitude occurs. The rock fabrics at Stop 2C are similar to those at Stops 2A and 2B, but again the variably developed foliation dips toward the south. Stop 2D is located at the intersection of Rts. 8 and 10, and the foliation and lineation is penetrative.
Common to all of these field stops is that biotite and sometimes chlorite blades form microscopic lineations and foliation parallel to the macroscopic structure. Rare grains of hypersthene have been found, but they always have well developed overgrowth textures that include biotite and chlorite. The biotite and chlorite are the most abundant index minerals in the granitic gneiss, and suggest the deformation was last active under low- to moderate- metamorphic conditions, although probably began at much higher conditions to account for the relict grains of hypersthene.

STOP 2D

STOP 3. Steeply dipping mylonite zone of the southern PLsz
Along Powley Road, depending on the time of year and the amount of road maintenance, there are a sub-continuous series of pavement exposures located in the road bed, as well as in the gutter on the east (northeast-bound) side of the road. Due to the nature of this location, the extent of the exposed rock at this stop changes yearly, so some or all of the rock described here may be viewable depending upon the time of the season in which the stop is visited (best later in the summer). The best exposures occur along the road between West and East Notch Mountains.
All rocks in this region are very similar in mineral content, and vary only in detail with regard to mineral percentage and fabric type and intensity. The rock is dominantly granitic gneiss with intense subhorizontal to shallowly plunging mineral elongation lineation that trends on average about 095 o, with steeply dipping generally east-west striking foliation. Both fabric elements are defined by ribbons of quartz, and ribbons of aggregate feldspar and quartz (generally 1-5 cm long depending upon grain size). Intensity of the fabric varies across strike at the 50 cm scale, with local layers of significantly coarser-grained fabrics (grains up to 1 cm in diameter). There are also places where the foliation intensity varies as seen at the field stops around Piseco Lake. Rare amphibolite bodies that are 10’s of cm thick occur within the granitic gneiss. Shear sense indicators are abundant in the granitic rocks and consistently show sinistral shear sense.

STOP 4. Southern extent of steeply dipping mylonite
Here the granitic gneiss fabrics contain both a penetrative foliation and lineation. The foliation is steeply dipping and strikes about east-west. Mineral elongation lineation defined by linear aggregates of quartz and feldspar are subhorizontal. The extent of readily available bedrock exposure diminishes south of this location, so this may be the southern-most exposure of the Piseco Lake shear zone. Note that this location is about 21 kilometers across strike from the northern side of the Piseco dome where the pronounced lineation occurs.

Parking for Stop 5

STOP 5: L>>S and L-tectonite in the core of the Piseco antiform
Excellent outcrops on the northwestern side of a small hill just west of the parking area. Follow the dirt road to a path through the woods, and then head up hill to the south to the outcrops. This outcrop of granitic gneiss contains domains of LS and LS. The LS domains contain large and numerous σ-type shear sense indicators, some δ-type are present but are much less frequent. The porphyroclasts are large about 1-3 cm and the recrystallized porphyroclastic material is often wrapped with a quartz ribbons. The interpreted shear sense is low-angle and left lateral. The foliation strikes east-west and dips gently to the south. Return to the vehicles by following the path. At this point the trip is over. Retrace your trip to Route 8. If you are headed back to Lake George, then follow Route 8 back to Speculator, NY, then turn south on Route 30.