2. Coast Range Volcanics (California) (20 points) The figure below shows the loc
ID: 121299 • Letter: 2
Question
2. Coast Range Volcanics (California) (20 points) The figure below shows the location of a sequence of volcanic rocks in coastal California (in what is termed the California Coast Ranges). These volcanics are thought to be associated with the plate tectonic evolution of the region and the formation of the San Andreas plate boundary. Describe the development of these volcanic rocks, with a focus on the following: 41 (a) [5 pts] what is the timing of eruption for these volcanic rocks, and do they follow any particular patterns; (b) [5 pts] what are their chemical characteristics and what does that tell us about the source region for the magmas that have erupted; SUTTER BUTT 39 CLEAR LAKE SONOMA 38 ERKELEY HILLS (c) [10 pts] Briefly describe the overall plate tectonic MILL NDERSON-COYOTE evolution of the region 37 SAN LUIS (use sketches and QUIEN SABE figures as appropriate) that led to the formation of this volcanic system 8 36 35 34 235 237 239 240Explanation / Answer
a. The volcanic eruption took place in three age and they are grouped in different geographic groups as:
b. In this region, rocks show a wide variety of compositions spanning basalt to andesite and sometimes basalt to rhyolite. Basaltic lava shows an affinity toward the mid-oceanic basalts and doesn't bear any characteristics of arc lavas, they are depleted in Nb and Ta. Ba/Ta ratios range from 36-338 to basalts indicating a similarity between the mid-ocean ridge basalt. The concentration of 87Sr/86Sr in silica suggests the depletions are inherited from the assimilated older continental crust.
c. Lots of Geological history occurred in California as it’s being listed below:
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