Major: Geological Science
Academic Affiliation: University of Texas at El Paso
Belinda Gonzalez is an undergraduate Geology student attending the University of Texas at El Paso. She enjoys spending time with her daughter, being outdoors, and film photography. From her RESESS experience, Belinda has gained considerable interest in Geochemistry. Her project has allowed her to understand the methods of chromatography and its implications. Through RESESS, Belinda learned how to perform Pb, Sr, Nd, and Rb isotope column separation on volcanicclastic rocks from Sliderock Mountain, Montana. Under the supervision of lab manager, Emily Verplanck, the samples were run through the thermal ionization mass spectrometer at the University of Colorado in Boulder in order to further analyze the role of the lithosphere in the creation of the magmas.
Origin of Late Cretaceous, continental interior, volcanism in the Rocky Mountain region
During the Late Cretaceous parts of the western U.S. were intruded by small-volume continental volcanism ~1200km inward from the Pacific margin. These intrusions include the Colorado Mineral Belt (COMB) and Sliderock Mountain, Montana. The continental lithosphere in these areas is quite thick, and the mechanisms by which these volcanic rocks were generated and erupted through this lithosphere are not well understood. Determining the source of the magmas seen in the Colorado to Montana area is important because it will aid in the overall understanding of the trigger mechanisms that lead to magmatism in the continental interior. By analyzing volcanic basaltic clasts of late Cretaceous to early Tertiary ages, we can examine potential sources of parental melt and the interaction that the lithosphere has had in the creation of these magmas. In order to better understand the relationship between shallow subduction and magmatism, composition models were generated. Harker Diagrams were created with using data from the North American Volcanic and Intrusive Database (NAVDAT). The space-time-composition plots were confined to a range of 65-80 Ma in order to seek patterns, if any, of volcanic activity in these times frames. NAVDAT was used to focus on predetermined geographic selections with similar ages in the western U.S. that include Sliderock Mountain and the COMB. SiO2 was plotted against several oxides and then fitted with a Total Alkali Silica (TAS) diagram to better describe the composition and mineralogy of the volcanic rocks. Here we present new isotopic data for Rb, Sm, Nd, Sr, and Pb from volcanic clasts from Sliderock Mountain. The isotope data was generated using standard column separation procedures and measured using a thermal ionization mass spectrometer (TIMS). We analyzed mafic basalt samples that were LREE (Nd) enriched. Sliderock stratovolcano displays much lower negative εNd values than those shown at the COMB. This indicates the difference between the ages of lithosphere through which they erupted (Archean and Proterozoic respectively). Given that our data show negative εNd values, we suggest that the source of the magmas must lie within an older continental mantle lithosphere, rather than the converting mantle asthenosphere. This indicates that an older continental lithosphere was present at the time of magmatism.