Title: Plate tectonic reconstructions in the laboratory and in the classroom
Speaker: Dr. Elizabeth Kenderes
Instructional Assistant Professor, Texas A&M University
Abstract: The Sierra Nevada batholith in central California is one of the best studied examples of subduction zone magmatism in the world. This is largely due to excellent exposures of both plutonic and volcanic units originally emplaced during the Mesozoic. It has been long assumed that the east-neighboring White–Inyo Range (WIR) plutons are a simple extension of this magmatism. WIR plutons were emplaced over two magmatic events during the Jurassic and Cretaceous at ca. 180–167 Ma and 102–86 Ma into greenschist facies Neoproterozoic and Cambrian sedimentary units. Both Jurassic and Cretaceous plutons of the WIR are characteristically calc-alkaline like the Sierras. However, the WIR exposes Jurassic age monzonites and Cretaceous aged peraluminous granitoids that are not observed or widely represented in the Sierras. Radiogenic isotopes and trace element data of whole rocks and minerals from these volumetrically limited granitoids provide evidence of magma source variation in the WIR that is not widely observed in the Sierra Nevadas, and provides insights into the tectonic history of the Mesozoic North American Cordillera.
Whole rock ƐNdi values of Jurassic and Cretaceous plutons reflect a change in source from a relatively juvenile sources in the Jurassic (–0.15 to –8.32), to older Paleozoic to Proterozoic crustal sources in the Cretaceous (–18.6 to –20.1). The lower ƐNdi values are atypical of the region and represent the peraluminous granitoids, reflecting melting of upper-crustal Proterozoic sedimentary rocks. Trace element data from monzonites (e.g. Sm/Yb > 4.5 and Sr/Y ratios up to 240) suggest an underplated eclogitized volcanic arc source, supporting previous research that underplating of island arcs is a common process in the formation of the lower continental crust. By integrating geochemical processes with existing tectonic models, we have a better understanding of the tectonic evolution of the region from the Devonian to the Mesozoic.
My research emphasizes the relationship between igneous and metamorphic rocks and plate tectonics. However, traditional petrology courses often understate the relationship. To correct this, I have restructured my courses such that plate tectonics is the framework for understanding the formation of igneous and metamorphic rocks. Using plate tectonics in this context promotes critical thinking, and it also allows students to bridge their understanding to other core courses such as structural geology and tectonics.
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