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Solid Earth An interactive open-access journal of the European Geosciences Union

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doi:10.5194/se-2016-147
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
26 Oct 2016
Review status
A revision of this discussion paper was accepted for the journal Solid Earth (SE) and is expected to appear here in due course.
Structural and rheological evolution of the Laramide subduction channel in southern California
Haoran Xia and John P. Platt Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089 - 0740, USA
Abstract. The Pelona schist in the San Gabriel Mountains, southern California, formed in the Laramide subduction channel, exhibits multiple phases of deformation/metamorphism and provides valuable insights into the rheological properties of the subduction channel. Petrological and microstructural analysis indicates that the Pelona schist has undergone three major deformational/metamorphic events. Subduction of volcanic and sedimentary protoliths during D1 was recorded by aligned mineral inclusions in albite and epidote porphyroblasts. Metamorphic temperature and pressure at the end of subduction yielded by Raman spectroscopy of carbonaceous material and Si-in-muscovite barometry were 518.9 ± 19.6 °C and 10.5 ± 0.4 kbar, respectively. During D1 the dominant deformation mechanism was quartz pressure solution, and the estimated shear stress and strain rate were less than 10 MPa and 5.8×10−13 s−1. D2, the first stage exhumation of the Pelona schist along the upper section of the subduction channel during return flow, was recorded by retrogressive metamorphism, isoclinal folding, and a pervasive schistosity that wraps around earlier porphyroblasts. Metagreywacke was deformed mainly by quartz pressure solution and metachert was deformed dominantly by dislocation creep during D2. The shear stress in metagreywacke was less than 10 MPa and that in metachert was between 8.6 and 13.3 MPa, resulting in a strain rate of 1.4×10−13 to 5.5×10−13 s−1. A topography driven model is proposed as the main driving force of D2 exhumation. D3 records normal-sense movement on the Vincent fault, which separates the schist from overlying arc and continental basement. This resulted in the second stage of exhumation, creating a major synform and associated mylonitic fabric in the upper section of the Pelona schist. Conditions at the beginning of D3 were 390°C and 5.8 kbar given by the TitaniQ thermometer and phengite barometer. The deformation was dominated by quartz dislocation creep with a strain rate of ~5.1 ×10−13 s−1 at a shear stress of ~22 MPa.

Citation: Xia, H. and Platt, J. P.: Structural and rheological evolution of the Laramide subduction channel in southern California, Solid Earth Discuss., doi:10.5194/se-2016-147, in review, 2016.
Haoran Xia and John P. Platt
Interactive discussionStatus: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version      Supplement - Supplement
 
RC1: 'Review', Ruth Keppler, 06 Nov 2016 Printer-friendly Version 
AC1: 'Reply to RC1', Haoran Xia, 03 Jan 2017 Printer-friendly Version Supplement 
 
RC2: 'Review of Xia and Platt on “Structural and rheological evolution…”, Solid Earth', Uwe Ring, 16 Nov 2016 Printer-friendly Version 
AC2: 'Reply to RC2', Haoran Xia, 03 Jan 2017 Printer-friendly Version Supplement 
Haoran Xia and John P. Platt
Haoran Xia and John P. Platt

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Short summary
We investigated the Pelona schist, an exhumed subduction complex in southern California associated with the Laramide subduction in Late Cretaceous–Paleocene. Based on field, microstructural and petrologic analyses, we established the deformational and metamorphic history of the Pelona schist and discussed the exhumation process. Then we presented the rheological properties and deformation mechanisms of the Pelona schist during each phase of deformation.
We investigated the Pelona schist, an exhumed subduction complex in southern California...
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