Constraining the Sediment Source and Dispersal Patterns of the Miocene Coachella Fanglomerate Along the Mission Creek Fault Strand of the Southern San Andreas Fault System Using Detrital Geochronology and Clast Geochemistry Provenance Analysis
Abstract
Sedimentary strata deposited across tectonic structures serve as valuable strain markers for strike-slip fault restorations, requiring robust provenance comparisons for reliable across-fault correlations. We report new sedimentology and detrital provenance data from the upper Miocene Coachella Fanglomerate and Bear Canyon Conglomerate, two formations located 200 km apart on opposite sides of the Mission Creek fault strand of the southern San Andreas Fault system (California, USA), to test their paleogeographic connection and proposed fault restorations. Widely accepted fault reconstructions have correlated the source of the Coachella Fanglomerate to the Chocolate Mountains, however other studies suggest a compositional similarity with the Bear Canyon Conglomerate located farther south in the South Chocolate or Cargo Muchacho Mountains. These competing interpretations imply up to 40 km difference in restored fault slip since 6 Ma. The Coachella Fanglomerate is composed of crudely stratified, poorly sorted white and reddish tan cobble to boulder conglomerate and lenticular coarse-grained sandstone interpreted as braided fluvial and alluvial deposits. Clasts within the white beds of the Coachella Fanglomerate are dominantly granite, chlorite-epidote schist, and feldspathic monzonite, whereas the reddish tan beds consist of predominantly silicic to intermediate volcanic clasts. The Bear Canyon Conglomerate is a poorly sorted, crudely stratified reddish tan cobble to boulder alluvial-fluvial conglomerate and sandstone. Clasts include a wide variety of volcanic clasts with an upsection increase in metamorphic and igneous clasts. The most striking compositional similarity between the two formations are the chlorite-epidote schist and feldspathic monzonite found in the uppermost section of the Bear Canyon strata and the white beds of the Coachella Fanglomerate. Based on paleoflow measurements from imbricated cobbles and trough cross-bedding, both deposits show a general north-directed paleoflow. Additional analysis of the detrital zircon U/Pb geochronology age spectra and modal analysis of sandstone compositions will further refine the provenance of the Coachella Fanglomerate to constrain the long-term faulting history along the southern SAF during the past 6 Ma.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP53D1896G
- Keywords:
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- 1051 Sedimentary geochemistry;
- GEOCHEMISTRYDE: 1824 Geomorphology: general;
- HYDROLOGYDE: 1862 Sediment transport;
- HYDROLOGYDE: 8169 Sedimentary basin processes;
- TECTONOPHYSICS