COG3 Seminar - Timothy Grove (MIT)

Friday, May 19, 2023 at 10:00am to 11:00am

Building 54, Room 915
21 AMES ST, Cambridge, MA 02139

Title: Wet and Dry Mantle Melting and Fractional Crystallization Processes at Newberry Volcano, Oregon

Abstract: Newberry Volcano in central Oregon, USA is a large (600 km3) back arc volcano behind the Cascades. It contains a 500,000 year history of volcanism. The basalts at Newberry fall into two distinctive groups. The first group is tholeiitic high-alumina olivine basalt and these lavas are diktytaxitic and aphyric. These lavas are dry (< 0.5 wt. % pre-eruptive H2O) with relatively flat primitive chondrite-normalized incompatible element abundance patterns. Similar basalts are erupted widely at rear-arc volcanoes along the Cascades and across the High Lava Plains to the East of Newberry. These basalts evolve by fractional crystallization along tholeiitic iron-enrichment trends. The second group is calc-alkaline and contains 2-4 vol. % olivine, calcic plagioclase and high-Ca clinopyroxene as phenocrysts. These lavas contained 2 to 4 wt. % H2O prior to eruption and show strong enrichment in the light rare earth elements, Ba, and Sr, and deficits in high-field strength elements such as Nb, Ta, Hf and Zr. Basalts with these compositional characteristics evolve by fractional crystallization along calc-alkaline trends of increasing SiO2 and decreasing FeO. Such compositional characteristics are reflecting a contribution from the subducted lithosphere transported to the mantle wedge by an H2O-rich fluid or melt. The tholeiitic basalts are produced by anhydrous adiabatic decompression melting of convecting mantle asthenosphere. Depths and temperatures of tholeiite melt segregation are 50 – 55 km and 1350 oC. The calc-alkaline basalts are produced by hydrous flux melting. Depths of melting for the calc-alkaline primitive melts are near the seismically defined moho (35 – 60) km depth) and 1175 – 1310 oC. Shallow crustal level fractional crystallization of primitive tholeiitic and calc-alkaline basalts creates the compositional spectrum of Newberry lavas. 

About this series: The Chemical Oceanography, Geology, Geochemistry, and Geobiology Seminar [COG3] is a student-run seminar series. Topics include chemical oceanography, geology, geochemistry, and geobiology. Contact for more information and Zoom password.

Event Type


Events By Interest


Events By Audience

Students, Faculty

Events By School

School of Science



Department of Earth, Atmospheric and Planetary Sciences
Contact Email

Add to my calendar

Recent Activity