Earth Planetary Science Seminar – Dr. Dawnika Blatter “Geochemistry and petrology of long-lived primitive volcanism at Clear Lake volcanic field, CA, elucidate melt generation sources and conditions in the wake of a migrating slab window”.

Abstract: Clear Lake Volcanic Field (CLVF) is the northernmost and youngest (~8 ka – 2.8 Ma) of six slab window-related volcanic centers distributed along the San Andreas transform fault in the California Coast Ranges. Ongoing geothermal and seismic activity as well as recent geophysical imaging indicate potential for future eruptions, thus the USGS California Volcano Observatory (CalVO) is conducting a multidisciplinary Next Generation hazard assessment.
​New Ar-Ar ages, geochemistry, and petrology refine previous work and indicate that past eruptive activity occurred in 4 intervals, each with its own eruptive styles and compositions: 1. (2.8 – 1.3 Ma) was the most widespread, with dominantly basaltic – andesitic primitive lavas. Sparse adakiticdacites and andesites on the eastern periphery indicate slab melting occurred at the edge of the slab window. 2. (1.2 – 0.8 Ma) produced large volumes (~10.4 km3) of andesites, dacites, and rhyolites focused at Cobb Mtn. and Mt. Hannah. 3. (0.62 – 0.28 Ma) generated large volumes (~32.2 km3) of evolved dacites and rhyolites focused at Mount Konocti and Seigler Mountain. 4. (0.12 – 0.01 Ma)produced small volume (~1.1 km3), dispersed basaltic andesite and andesite focused along two N-S lineaments and in maar eruptions around the lake.
​This presentation will summarize recent findings focused on geochemistry and petrology of the initial phase of volcanism and discuss how our multidisciplinary science can be integrated to determine melting sources and conditions recorded by early CLVF magmatism. The hot (1130-1329 °C), shallow to moderate pressure (0.63-1.47 GPa) melting conditions for these primitive compositions are indicative of the heat delivered to the crust. Over time, this flux led to maturation of the CLVF magmatic system toward the more voluminous and silicic volcanism that characterizes the balance of its subsequent volcanic history and maintains the present-day anomalously high heat flow in the region.

Biography: Dawnika Blatter is a Research Geologist with the USGS California Volcano Observatory (CalVO). She integrates experimental petrology, microbeam analyses, geochemistry, and petrology withfield observations on distribution, timing, and volumes of eruptive products to understand volcanism from magma genesis to eruption. Field-based projects include extensive mapping and sampling across the Mexican Volcanic Belt, work on Cascade arc volcanoes, Aleutian arc volcanoes, and most recently in the Clear Lake Volcanic Field and Mount Shasta region of northern California. She has a BS in Geology from UC Davis and a PhD in Geology from UC Berkeley. She taught geology at DVC for 15 years prior to joining USGS full-time.
* For the Zoom link please email Xueyao Cheng > xc272@stanford.edu