18 Tectonics of the Death Valley Region III: A Tribute to Bennie Troxel and Lauren Wright

Tuesday, 15 May 2018
1:30 PM - 3:15 PM
Canyon Room

TIMING AND KINEMATICS OF MESOZOIC BURIAL AND CONTRACTIONAL DEFORMATION IN THE FUNERAL MOUNTAINS METAMORPHIC CORE COMPLEX, DEATH VALLEY NATIONAL PARK, CA

Paper number: 18-6
Program: Symposia Sessions
Time: 2:55 PM – 3:15 PM

Authors

Abstract

Repeated episodes of tectonic activity often obscure and overprint earlier fabrics, making it difficult to recognize structures from the earliest deformational history in a region. The Funeral Mountains metamorphic core complex (FMCC), located in Death Valley, CA, has a complex history of NW-directed extension that is predated by a highly overprinted large-magnitude tectonic burial event. Detailed structural mapping at 1:10,000 scale in the Chloride Cliff region provides evidence for two periods of SE-directed contractional deformation. Initial tectonic burial is interpreted to be Late Jurassic based on a prior Lu-Hf garnet age (158.2 ± 2.6 Ma) associated with a compressional PT path from the Indian Pass area, and new monazite growth ages (176-149 Ma) that show decreasing HREE concentrations, consistent with crystallization during garnet growth. This burial caused Barrovian metamorphism and footwall collapse leading to an inclination of regional stratigraphy to the NW. This event is typified by a well-developed bedding-parallel foliation with local asymmetric structures showing top-SE shear including shear bands and mantled porphyroclasts in schist, and asymmetric strained clasts in the Kingston Peak diamictite. The average stretching lineation associated with this event is 21, 148, indicating SE-directed shortening. This early bedding-parallel foliation is then subsequently folded during the second contractional event (Early Cretaceous?). Elongated clasts within the Kingston Peak diamictite are asymmetrically folded, verging towards the SE, and have an average hinge line orientation of 06, 196. Outcrop scale folds with SE vergence within the Noonday Dolomite, Kingston Peak and Johnnie formations associated with this event have fold axes that trend NNE-SSW. The average stretching lineation on axial planar foliation is 19, 112, consistent with the expected shearing direction from fold orientations. This SE-directed shortening documented here provides the first evidence for shortening associated with development of the metamorphic field gradient from upper amphibolite to sub-greenschist facies, from NW to SE. Although we demonstrate evidence for Late Jurassic shortening and burial, the structures and tectonic load required for metamorphism remains enigmatic.

Geological Society of America Abstracts with Programs. Vol. 50, No. 5

doi: 10.1130/abs/2018RM-314245

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