A5: THE NATURE AND TECTONIC SIGNIFICANCE OF THE CARTHAGE COLTON SHEAR ZONE: ADIRONDACK MOUNTAINS, NEW YORK STATE.
Eric Lee Johnson
Hartwick College
Department of Geology and Environmental Science
Oneonta, NY 13820
Johnsone@hartwick.edu
ABSTRACT
This trip will examine the nature and geologic significance of the Carthage-Colton Shear Zone (CCSZ) and late to post-Ottawan intrusive activity along this zone. The CCSZ marks the boundary between the Central Metasedimentary Belt and the Central Granulite Terrane (Frontenac-Adirondack Belt). The significance of this shear zone and the bounding terranes has been a matter of continued debate. This trip will analyze field, geothermometric, and geochronologic relationships along several transects across the CCSZ with the goal of better elucidating the nature and timing of this complex and enigmatic structure.

A5: THE NATURE AND TECTONIC SIGNIFICANCE OF THE CARTHAGE COLTON SHEAR ZONE: ADIRONDACK MOUNTAINS, NEW YORK STATE.

STOP 1. Valentine Wollastonite Mine
Discuss field relationships between the Diana Syenite Body and lowland marbles. Basic goal here is to demonstrate that the Diana Syenite intrudes into lowlands marbles and contact metamorphism drove formation of the Wollastonite.
Note that much of the wollastonite body is at best weakly deformed and so lacks Ottawan deformation.

STOP 2. Big Crop Diana Syenite
Look at pegmatites and shear zones that cut the body. These shear zones vary to greenschist facies formed during the end of CCSZ deformation.

STOP 3. Contact Metamorphism of marble at the Diana Contact (route 813).
OHM 2019: There is no route 813, perhaps the author means route 812... Also no location is given so I put this on the place identified in NYSGA trip 1998 A2, stop 3.
Once again show a lack of a strong Ottawan deformation. Note that this type of grain coarsened marble can be found in many locations at or near to Diana Syenite contacts.

STOP 4. Jayville Road
STOP 4. Jayville Road Here we will cross into the Adirondack Highlands for the first time. Variations in the orientation of stretching lineation will mark our passage across the CCSZ. In the Lowlands, stretching lineations are more steeply dipping and oriented to the NW, but once we cross the CCSZ, stretching lineations rotate to near strike parallel orientation (NNW).
OHM 2019: Guesses were made for most of stops A-E, as only A had any mileage given.

STOP 4A. Fault Zone in Diana Syenite.
This zone shows both strong ductile and brittle deformational fabrics. The Diana Syenite Body is vertically stacked by several small thrust faults. (Lowlands)

STOP 4B. Contact between Diana Syenite and the Border Granite
(Lyon Mountain?) Along RR tracks near Topa-da-Hill Road. Is this the Highlands-Lowlands Boundary?

STOP 4C. Long Lake Fault Zone (look up the lake at this major lineament).
This structure is a brittle normal fault that offsets the CCSZ detachment (SEE FIGURE 1). We will encounter this fault once again at STOP 10. At this location, the Long Lake Fault vertically truncates the CCSZ detachment.

STOP 4D. Road south of Jayville Road (ROD and TODD outcrop)
Note that while to the North of Jayville Road we have passed into the Granite, but here to the south and east, we are still in the Diana Syenite Body. A small east-west trending (strike-slip?) fault offsets the CCSZ (Highlands-lowlands boundary) at this location. This fault passes directly through the Jayville Mine (STOP 4E) and continues (at least in topographic expression) to the east passing through the Benson Mine.

STOP 4E. Jayville Mine (stop to look for vonsenite ore)
Here we can visit the mine shaft and discuss the amphibolite matrix for the vonsenite (Fe2+Fe3+2BO5) ore and the origin of the boron. Discuss the Lyon Mountain Granite at this local and the presence of felsic quartz-albite facies dikes. Examine the location of the mine in terms of known brittle and ductile features.

STOP 5. Faulting in the Diana Syenite Body.
Classic mixture of rock types that characterize the faulted contact between the Diana Syenite Body and lowlands paragneisses including the feldspathic quartzite, marble and diopsidite. Note the strong ductile fabric of these rocks that is overprinted by later brittle faulting.

Greenwood Falls Picnic Area. Look at the Diana Syenite Body

STOP 6. Outcrop of diopsidite skarn.
Contact skarn between the Diana Syenite Body and the Balmat Edwards (?) marble. This friable green colored rock is primarily made up of green diopside and grey calcite. (mapped as Tia)
OHM 2019: Because lunch will be one mile down this road, it is apparent that we must no longer be on Route 3. This stop was located by coming back one mile from the picnic area, which was found on the DEC map of Greenwood Creek State Forest.

STOP 7. Diopsidite contact rock (Dia/Tia).
Note on the map that these diopsidic contact skarns are found in the middle of the Diana Syenite Body and along its eastern edge, at the CCSZ detachment. This unit is associated with the contact between the Diana Syenite and the Balmat Edwards Marble.

STOP 8.
Once we pass the last outcrop of green diopsidite, we have left the Adirondack Lowlands and entered the Adirondack Highlands Terrane. Pink leucogranite and hornblende granite outcrops underpin the ridge. Our stop is near the intersection of Route 3 and Sykes Road. The contact between the Leucogranitic gneiss and the Irish Hill Gneiss is well exposed in this outcrop. The Irish HilI Gneiss (Whippoorwill Corners Gneiss of Hall, 1981) consists of calc-silicate gneiss (containing calcite + diopside ± tourmaline) and quartzite with abundant concordant and crosscutting pegmatites.

STOP 9. Hornblende granite.
This stranded small body of granite differs from those that we have seen on Jayville road. Larger exposures of a similar granite can be found to the north in the South Edwards Quadrangle (Eastern Granite Gneiss of Hall 1981). The granite is moderately deformed at this location.

STOP 10. Faulted Block of the Lowlands and Granite Gneiss
STOP 10A. Faulted Block of the Lowlands
Intersection of NY Routes 58 and 3. Park in the small lot at the intersection of Routes 58 and 3. Directly to the north of the parking lot is a small mine adit. We will start by heading north to the old bridge over the Oswegatchie River. Outcrops to the west (down the slope) are of green Irish Hill Gneiss. The outcrops along the road show a strong brittle deformation and a mixture of rock types. This outcrop contains marble (looks very much like Balmat Edwards Type), bleached syenite-granite, and even some diopsidite. Fluorite crystals have been found in vugs and tension gashes in the marble. This outcrop lies on the trace of the Long Lake Lineament (Fault) and movements on this lineament are the logical cause for the strong brittle overprint observed in these rocks. The intriguing thing about this series of outcrops is that the rock types are more like those of the Lowlands Terrane even though we have crossed the CCSZ and are well into the Highlands at this location. Just 100 m west one can find outcrops of Irish Hill Gneiss (Highlands) and to the east (on Route 3) we find pink granite (Highlands Rock) with a strong brittle overprint. This outcrop may represent a block belonging to the Adirondack Lowlands that has been down faulted along the Long Lake Fault (see figure 2).
STOP 10B. Route 3 Granite gneiss and breccia (Long Lake Fault)
Calcite filled breccia in highlands granite gneiss and Irish Hill Gneiss. Both sides of the road.

STOP 11. IHG/Lg contact
Two large road cuts expose (or nearly expose) the contact between the pink leucogranitic gneiss and the calc-silicate Irish Hill Gneiss. Here the Irish Hill Gneiss is cut by many coarse pegmatite bodies. Stop 11a: Irish Hill Gneiss. Stop 11b: Leuco-granitic gneiss. We are now nearly due north of STOP 8 (IHG/Lg contact on Route 3).

STOP 12. Outcrops of strongly deformed leuco-granitic gneiss
(Highlands).

STOP 13 Roadcut into Diana Syenite.
The Diana Syenite (granitic phase) shows strong ductile deformation with well developed c/s fabric. Note also the strong brittle overprint as marked by the abundant and closely spaced joints sets. We have once again crossed the Highlands/Lowlands boundary. Here we will look for kinematic indicators.

STOP 14. Shear Zones in the Diana Syenite Complex
The outcrop on the north side of the road show numerous anastomosing shear zones. Sheared Diana contains Hornblende (Cl-rich) + biotite + plagioclase (An) + perthite + quartz + titanite ± Fe-Ti oxide minerals. Relict clinopyroxene rimmed by amphibole and amphibole + chlorite is common as is scapolite replacement of some plagioclase crystals.
Samples SE-TF-8 and SE TF-11 have been dated by the author using U/Pb titanite and 39Ar/40Ar for hornblende. The intrusion age for the Diana Syenite Complex has been dated to 1155 ± 4 Ma (Grant et al. 1986).
In shear zones, titanite replaces Fe-Ti oxides probably via a reaction involving plagioclase feldspar, and calcic amphibole. Titanite is also found in the syenite outside of these shear zones but it is rare. Away from the shear zones, Fe-Ti oxides are common while they are nearly absent in the shear zones. These observations suggest that sphene growth accompanied recrystallization during shearing, and since the recrystallization conditions during shear zone formation range only to the lower amphibolite facies and probably well below the 600-650°C closure temperature for lead in titanite, U/Pb ages are interpreted to represent growth ages and hence the time of shearing.
The U/Pb age for titanite are concordant and constrain the time of titanite growth during shearing to ∼1041 Ma (see figure 5). 39Ar/40Ar data for amphibole from this sample yield a flat spectrum with a plateau age of 979.8 ± 8.6 Ma. The closure temperature for hornblende (Ar) is 500-550°C, and these ages are interpreted to represent cooling ages.
Sample SE-TF 11: (Same outcrop as SE-TF-8) Geochronology data for the SETF-II is shown in figure 6. Three fractions prepared from this sample all yield concordant ages that range from 1054 to 1034 Ma. These ages are interpreted to represent multiple generations of titanite (sphene) growth in the shear zone.

STOP 15. Ultramylonite zone in the Diana Complex.
The small shear zone exposed here shows extremely sharp strain gradients. The core of this shear zone is ultramylonitic and yet within 2-3 meters, the host Diana Syenite retains some igneous texture. It is interesting to note that strain recorded throughout the Diana Syenite Body is highly variable. The DSC is everywhere deformed ranging from coarse-grained augen gneisses with distinct igneous textures preserved (most common) to ultramlyonite. Against this deformational backdrop, the Diana Syenite is cut by sub-meter width shear zones that record low recrystallization temperatures (greenschist-amphibolite facies). In many locations, a strong brittle deformational event is also evident.

STOP 16. Famous Green Diopside skarn outcrop.
This skarn body marks the contact between the granitic gneiss, which exhibits a strong lineation, and the marble. It is interesting to note that the skarn does not show a deformational overprint.

Leucogranitic Gneiss (Lowlands)

STOP 17. Freshly blasted small outcrop of leucogranitic gneiss.
This granite gneiss body outcrops along the eastern margin of the Diana Syenite Body. This granite body is, therefore, a part of the Adirondack Lowlands. Just around the next corner, we will encounter the Diana Syenite.
DANA HILL METAGABBRO
The Dana Hill Metagabbro preserves multiple deformation and veining events ranging from granulite facies ductile to sub-greenschist facies brittle events (see appendix). In many cases, cross-cutting relationships allow for the determination of a sequence of events. To date, six major deformational/veining events have been identified (Johnson et al., 2004; Streepey et al., 2001). At STOP 18 we will examine EVENT 4 shearing. Events 1 through 6 will be examined at stop 20.

STOP 18. The "Zebra" rock outcrop of Dana Hill Metagabbro
(Adirondack Highlands).
The gabbro is cut by multiple cm to sub meter wide EVENT 4 (see appendix) shear zones. The zones typically dip steeply and shear sense, which varies from shear to shear, can be determined by rotation of a preexisting foliation into the zone (see appendix and figure 8).
The typical assemblage consists of amphibole ± clinopyroxene + scapolite + plagioclase + Fe-Ti oxides. Plagioclase compositions are consistent within individual shear zones but range from An05 to An32 between shear zones. Polygonal scapolite forms distinct halos about amphibole and original ilmenite is replaced by titanite in the shear zones. Geochronologic data for this outcrop are presented in Figure 9.
Sphene (titanite) growth is constrained to occur during shearing and U/Pb ages are considered to be cooling ages off of peak Ottawan temperatures of 680-720°C (Streepey et al., 2001). These shear zones are similar in size and type with those found in the Diana Syenite Body (STOP 14) but shearing in these zones takes place at considerably higher temperatures. Sphene (titanite) U/Pb ages for shear zones in the Diana Syenite are considered to be growth ages marking the time of shear zone formation at ∼ 1054-1034 Ma. Shear zones in the Dana Hill Metagabbro at this location record cooling temperatures at 1020 Ma so it is not unreasonable to suggest that the shear zones found in Dana Hill Metagabbro were active at the same time but at very different temperatures. 39Ar/40Ar cooling ages for these shear zones and similar style shear zones in the Dianan Syenite Body overlap indicating that both units cooled through 550°C closure temperature for hornblende at the same time.

STOP 19. Shear zones in the Lyon Mountain Granite Gneiss.
Sillimanite + quartz + magnetite is a common assemblage in the Lyon Mountain Gneiss (McLelland et al., 2001). At this location, one can see the formation of this assemblage as a consequence of deformation and post deformational fluid flow through the shear zones. In the shear zones, sillimanite needles are both aligned along the developing folia and as radial splays that clearly cross-cut the foliation. In the shear zones, plagioclase feldspar is only present as albite lamellae in exsolved perthite. Bulk and trace element chemistries of this rock both in and outside of the shear zones show some interesting variations (see table 1 RL).
Samples from sheared sillimanite-bearing Lyon Mountain samples (SRCHI and SRCH2) show marked depletions in Ca, Na, and enrichments in K, Rb, and Ba. The proposed mechanism for quartz-sillimanite formation is via the incongruent dissolution of plagioclase feldspar via the reaction:
CaAl2Si2O8 +H2O = Al2SiO5 +SiO2 +Ca(OH)2aq
2NaAlSi3O8 + H2O = Al2SiO5 +5SiO2 + 2Na(OH)aq
REACTIONS 1 AND 2
Slight enrichments in SiO2 Al2O3 can be accommodated by these reactions and the simple removal of Na2O and CaO , but K2O enrichments cannot be caused in this fashion. It appears that potassium was indeed introduced to these samples during and after shearing.
The timing of this fluid infiltration event is constrained to post date emplacement of the granite during syn to late-Ottawan time (∼1050 Ma).

Note the large outcrop of Irish Hill (Whippoorwill Corners) Gneiss.

Roadcut of pink granitic gneiss

Roadcut into pink granitic gneiss (hornblende granite protolith)

STOP 20. DANA HILL METAGABBRO
Park the vans and climb the hill on the north side of the road. On the trail up the hill we will pass several sub-meter width EVENT 4 shear zones.
We return to the Dana Hill Metagabbro to examine the complex deformation of the body. This outcrop along with the outcrops at the top of the hill across the road, exhibit all 6 deformational events (see appendix and fig. 10). We will start at the far end of the outcrop and examine the deformational sequence of events recorded. From the oldest to the youngest, this outcrop preserves EVENT 1 mega-shearing, EVENT 3 hornblende veining, EVENT 4 sub-meter shearing, and EVENT 6 folding and brecciation. EVENTS 2 and 4 can be observed at the top of the hill across the road. Events 3 through 5 take place in the presence of a fluid or fluids that drive scapolite replacement of original plagioclase feldspar in the host metagabbro. In the Diana Syenite Body (Lowlands Terrain), sub meter wide shear zones (dated to 1052-1034 Ma) also exhibit scapolite replacement of plagioclase feldspar. This scapolitization event is widespread in and around the CCSZ from just north of Harrisville to Colton and is present in both the Highlands and Lowlands Terranes. It therefore marks a common event for both terranes.
The goal of this stop is to demonstrate that the Dana Hill Metagabbro Body acted as a rigid block during deformation. In some instances, cumulate igneous textures have been completely preserved while in others the gabbro ranges to ultramylonitic in texture. The resistance to deformation in the Dana Hill Metagabbro resulted in an episodic response to the applied stress leading to discrete pulses of deformation. This body preserves individual and distinct events that record the entire deformational history of the region. The earliest shear zones are massive (30 m wide) and mylonitic to ultramylonitic. These shear zones record recrystallization temperatures in excess of 700°C. Subsequent shearing events are dramatically different, forming sub-meter wide anastomosing shear zones at recrystallization temperatures at or below 700°C. The last deformation events to affect the Dana Hill Metagabbro transition to brittle failure at low to sub greenschist facies conditions. The deformational history is one of an exhuming footwall with deformation beginning in the granulite facies and eventually passing through the brittle-ductile transition at greenshist to sub greenschist facies conditions. We will examine these events and the available geochronologic data for this complex outcrop.