Late Ottawan ductile shearing and granitoid emplacement in the Hudson Highlands, NY

Abstract

Large-scale, high-grade ductile shearing, migmatization, and the emplacement of a chemically diverse suite of granitoid plutons characterize the late-to post-Ottawan (<1030 to 925 Ma) geologic history of the northernmost New Jersey Highlands and the Hudson Highlands of New York. The ductile shear zones are large (0.5 to 2 km wide, 2-10 km long), subvertical to vertical, and all kinematic indicators consistently show dextral strike-slip deformation. Timing of deformation is broadly constrained to an upper limit of ~1010 Ma based on the SHRIMP U-Pb zircon ages on crosscut metaplutonic rocks and a rough lower limit of ~925 Ma based on hornblende 40 Ar/ 39 Ar age obtained from an undeformed, crosscutting granite pegmatite dike. At least four discrete granitoid suites were emplaced associated with this shearing event that range from A-and S-type granites to calc-alkaline, I-type gabrro and diorite. These are, in order of inferred or radiometric age: (1) the Sterling Forest Granite Sheets (not yet dated), the Mount Eve Granite (1020±4 Ma; Drake et al., 1991), the Canada Hill Granite (1010±6 Ma; Aleinikoff and Grauch, 1990), and the Lake Tiorati Metadiorite (1008±4 Ma). The Sterling Forest Granite Sheets consist of tabular bodies (5-200 m thick) of metaluminous to slightly peraluminous leucogranite (SiO 2 ~75%) with transitional I-and A-type trace element characteristics. The Mount Eve Granite consists of about thirty small stocks (0.2-5 km 2) of metaluminous syenogranite to quartz monzonite with strong A-type chemical signatures (e.g., high Fe, Ba, Zr, Y, HFSE, REE). The Canada Hill Granite is a peraluminous biotite leucogranite with S-type chemical affinities (e.g., high Si, Al, K, low Fe, highly variable REE content) consisting of small stocks (0.1-1 km 2) and sheets (~2-4 m thick) that intimately associated with surrounding migmatitic metapelitic gneisses. The Lake Tiorati Metadiorite consists of small stocks and sheets (max. 1.5 km 2) of mafic rocks (47-51% SiO 2) with strong I-type, calc-alkaline, continental arc chemical signatures (e.g., low Ti, HFSE). Dextral transcurrent shearing and granitoid emplacement is interpreted here to have resulted from a tectonic escape mechanism due to late-to post-Ottawan adjustments within the newly amalgamated Rodinian supercontinent.

Full text

Late Ottawan ductile shearing and granitoid emplacement in the Hudson Highlands, NY
Matthew L. Gorring
1
, Alexander E. Gates
2
, David W. Valentino
3
, Gary S. Solar
4
, and Jeffrey R.
Chiarenzelli
5
,
1
Department of Earth & Environmental Studies, Montclair State University, Upper Montclair, NJ 07043
2
Department of Geological Sciences, Rutgers University, Newark, NJ 07102
3
Department of Earth Sciences, SUNY-Oswego, Oswego, NY 13126
4
Department of Earth Sciences, SUNY-Buffalo, Buffalo, NY 14222
5
Department of Geology, SUNY-Potsdam, Potsdam, NY 13676
Large-scale, high-grade ductile shearing, migmatization, and the emplacement of a chemically
diverse suite of granitoid plutons characterize the late- to post-Ottawan (<1030 to 925 Ma)
geologic history of the northernmost New Jersey Highlands and the Hudson Highlands of New
York. The ductile shear zones are large (0.5 to 2 km wide, 2-10 km long), subvertical to vertical,
and all kinematic indicators consistently show dextral strike-slip deformation. Timing of
deformation is broadly constrained to an upper limit of ~1010 Ma based on the SHRIMP U-Pb
zircon ages on crosscut metaplutonic rocks and a rough lower limit of ~925 Ma based on
hornblende
40
Ar/
39
Ar age obtained from an undeformed, crosscutting granite pegmatite dike. At
least four discrete granitoid suites were emplaced associated with this shearing event that range
from A- and S-type granites to calc-alkaline, I-type gabrro and diorite. These are, in order of
inferred or radiometric age: (1) the Sterling Forest Granite Sheets (not yet dated), the Mount Eve
Granite (1020±4 Ma; Drake et al., 1991), the Canada Hill Granite (1010±6 Ma; Aleinikoff and
Grauch, 1990), and the Lake Tiorati Metadiorite (1008±4 Ma). The Sterling Forest Granite
Sheets consist of tabular bodies (5-200 m thick) of metaluminous to slightly peraluminous
leucogranite (SiO
2
~75%) with transitional I- and A-type trace element characteristics. The
Mount Eve Granite consists of about thirty small stocks (0.2-5 km
2
) of metaluminous
syenogranite to quartz monzonite with strong A-type chemical signatures (e.g., high Fe, Ba, Zr,
Y, HFSE, REE). The Canada Hill Granite is a peraluminous biotite leucogranite with S-type
chemical affinities (e.g., high Si, Al, K, low Fe, highly variable REE content) consisting of small
stocks (0.1-1 km
2
) and sheets (~2-4 m thick) that intimately associated with surrounding
migmatitic metapelitic gneisses. The Lake Tiorati Metadiorite consists of small stocks and
sheets (max. 1.5 km
2
) of mafic rocks (47-51% SiO
2
) with strong I-type, calc-alkaline, continental
arc chemical signatures (e.g., low Ti, HFSE). Dextral transcurrent shearing and granitoid
emplacement is interpreted here to have resulted from a tectonic escape mechanism due to late-
to post-Ottawan adjustments within the newly amalgamated Rodinian supercontinent.
Geological Society of America Annual Meeting, November 7-10, 2004, Denver, CO.