Thermal evolution of northern Salinia using apatite and zircon (U-Th)/He thermochronology
Abstract
Petrology and geobarometry establish a link between the southern Sierra Nevada batholith and Salinia, a fault-bounded terrane confined by the Nacimiento fault on the west and the San Andreas fault on the east. Most reconstructions are limited to the pre-San Andreas offset and do not address the Cretaceous westward transport history as the upper plate of a proposed detachment system. Because the sedimentary rocks deposited on these granitoids are Late Cretaceous to Paleocene, most of this pre-Miocene westward transport must have occurred at or slightly above surface temperatures. Low temperature thermochronology (up to 200 °C) can provide a window into this time period for northern Salinia, which includes outcrops in Ben Lomond, Montara Mountain, Point Reyes, and Bodega Head.
Samples were collected along north-south transects in each granitoid outcrop in northern Salinia. Apatite and zircon mineral separates were then analyzed for (U-Th)/He and modelled using thermal modelling software. In total, we present 16 new zircon (U-Th)/He dates and 12 new apatite (U-Th)/He dates, along with modelled time-temperature histories. Preliminary results for a subset of the samples yield zircon (U-Th)/He dates of ~13 Ma at Montara Mountain, ~75 Ma at Point Reyes, and ~71 Ma at Bodega Head. These preliminary data suggest that the granitoids in Bodega Head and Point Reyes cooled quickly from emplacement temperatures to below 200 °C in less than 30 Myr. This rapid cooling likely represents tectonic removal of overlying material through detachment faulting. The preliminary data from the Montara Mountain granitoid suggests that there was a reheating event in the Miocene. This heating event may be related to the northward migration of the Mendocino triple junction.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T22D..08S
- Keywords:
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- 4302 Geological;
- NATURAL HAZARDS;
- 8106 Continental margins: transform;
- TECTONOPHYSICS;
- 8170 Subduction zone processes;
- TECTONOPHYSICS;
- 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS