Fractured conglomerates: Implications of brittle deformation in the Titus Canyon Formation, southwestern Nevada and southeastern California

Christie D Lindemann, Purdue University

Abstract

This study focuses on sub-parallel, clast-scale fracture patterns within conglomerates of Eocene-Miocene synextensional sedimentary strata of the Titus Canyon Formation in the Grapevine and Funeral Mountains of southwestern Nevada and southeastern California. Features including shear fractures and pressure solution depressions, cross-cut by subsequent point-contact deformation and sub-parallel fractures, have also proven to be essential in a understanding the mechanism that produces this systematic deformation. We propose that clast deformation occurs in 2 phases. Phase 1 involves pressure solution processes. Pressure solution depressions are recognized as shallow features that begin to develop at relatively low temperatures of 90±10°C and depths of approximately 2-5 km. With rapid uplift and erosion, Phase 2 conditions emerge and lead to sub-parallel fracture processes. Modeling clasts as Eshelby inclusions with an internally uniform stress field, imply that sub-parallel fracturing occurs with minimum confining pressure in the range of 2 to 30 MPa. This corresponds to relatively shallow depths of less than 1250 meters. With progressive deformation from the same remote stress during Phase 2 conditions, shear factures coalesce from sub-parallel fractures. Through kinematic analysis, we infer strain field orientations consistent with a minimum compressive stress in a NW/SE orientation. Further analysis of shear fractures and slickenlines implies a maximum compressive stress near 225°, 50° SW. Investigation of units below the Titus Canyon Formation show slickenlines with similar orientations that cross-cut ductile fabrics below regional detachments. Units above the Titus Canyon Formation suggest that conditions leading to sub-parallel fractures were either no longer present by Late Miocene time or that younger units were deposited during deformation, but were not exposed to the appropriate conditions required to induce fracturing. Altogether, these data suggest a common source for the stress field responsible for the deformation. Our estimates imply a stress field with a maximum compressive stress oriented near normal to the orientation of sub-parallel regional detachments. This possibly indicate the influence of near-field stresses associated with brittle rupture events on the fault as it was exhumed, or some other driving stress oriented in a similar orientation. We propose the Boundary Canyon detachment fault and Monarch Spring fault as likely candidate sources of this stress field.

Degree

M.S.

Advisors

Ridgway, Purdue University.

Subject Area

Geology|Geophysics

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