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Precambrian structural geology, petrology, and geochemistry of a polydeformed Helikian mylonite zone in the southeast Adirondack Mountains of New York State
Abstract
The Helikian age rocks adjacent to the village of Whitehall in the SE Adirondack Mountains of New York State are polydeformed upper amphibolite to granulite facies mylonites. These rocks are in no discernible stratigraphic order due to pervasive structural slicing. The preexisting stratigraphy of these rocks, however, is known from equivalent lithologies elsewhere in the Adirondacks. The earliest recognizable deformation event, D1$\sb{\rm S1}$, resulted in the formation of an S1 metamorphic foliation. Two plastic deformation events folded D1$\sb{\rm S1}$. The first D2$\sb{\rm F1}$, resulted in overturned isoclinal folds; these are overprinted by a second more open folding, D3$\sb{\rm F2}$. This folding period was followed by two episodes of ductile faulting. The first episode, D4$\sb{\rm S2}$, produced the current regional foliation S2 and a SE-NW trending lineation. The second episode, D5$\sb{\rm FAULT}$, accentuated the structures formed during D4$\sb{\rm S2}$ and is characterized by ductile fault planes at a variably high angle to S2. D1$\sb{\rm S1}$ is correlative with the pre-folding foliation of the Adirondack Dome. D2$\sb{\rm F1}$ and D3$\sb{\rm F2}$ are correlative with the F$\sb1$ and F$\sb2$ regional isoclinal folding events of the dome, respectively. The first ductile fracture event (D4$\sb{\rm S2}$) and subsequent intrusion and granulite facies metamorphism of gabbro are correlative with the regional F$\sb2$ and F$\sb3$ plastic deformation events. By the end of D4$\sb{\rm S2}$ or regional F$\sb3$, granulite facies conditions vanished. The second ductile fracture event (D5$\sb{\rm FAULT}$) is correlative with the F$\sb4$ and F$\sb5$ regional episodes of more open folding of the Adirondack dome. The transitions in the deformation modes of the study area from pure ductility to ductile fracture during the five purely plastic regional deformation events in the Adirondack Mountains can be explained if the rocks adjacent to the Whitehall strain-hardened faster than the majority of those in the interior of the Adirondack dome.
Subject Area
Geology
Recommended Citation
Stracher, Glenn Blair, "Precambrian structural geology, petrology, and geochemistry of a polydeformed Helikian mylonite zone in the southeast Adirondack Mountains of New York State" (1989). ETD collection for University of Nebraska-Lincoln. AAI8918564.
https://digitalcommons.unl.edu/dissertations/AAI8918564