RUI: Testing Models for Late Cretaceous to Cenozoic Collisional Magmatism in South-Central Alaska

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Southern Alaska contains economically important mineral deposits that formed during unique episodes of volcanism and magma emplacement some 70 to 50 million years ago. Deposits of copper, zinc, silver, lead, gold, molybdenum and other metals are predicted to form along the margins of large igneous intrusions and along fault zones that cross-cut the igneous rocks but the origin of many of these deposits is not known. This project will document the compositions of igneous rocks and develop models for their origins which will provide a system for predicting the distribution of mineral resources in the northern Talkeetna Mountains region of southern Alaska. This outcome is consistent with a national strategy to 'ensure availability of reliable geologic, geochemical, geophysical, and mineral locality data for the United States' as described by the U.S. Geological Survey Mineral Resources Program. This project will also provide state-of-the-art scientific training for undergraduate students, including international collaboration. The focus of this project will be on 62 to 50 million year old volcanic and plutonic rocks that were emplaced in a terrane suture zone during the final stages of terrane collision. Preliminary radiometric age and geochemical data reveal that these rocks are not typical of continental margin arc systems. The three-year work plan for this project is to produce new geochronologic, geochemical, and field mapping data on these igneous rocks to address the following fundamental questions: What were the source(s) of magmas during and following terrane collision? Can subduction-related arc rocks be distinguished geochemically from post-subduction (collisional) igneous rocks in a systematic manner? Was magmatism related to collisional and/or post-collisional deformation? These questions will be evaluated using major and trace element chemistry (XRF and ICPMS methods); whole rock Nd, Sr, Pb, and Hf isotope and single zircon Hf isotope chemistry (all by LA-MC-ICPMS); and 40Ar/39Ar and zircon U/Pb dating in collaboration with Dr. Sun-Lin Chung at National Taiwan University in Taipei. Field mapping, sample collection, and data synthesis will be completed by the PI and undergraduate students from Allegheny College. The age, geochemical, and isotopic results of this project will be disseminated through NSF-funded web-based databases (NAVDAT, EarthChem) and will provide a basis for assessing the distribution of economic mineral deposits as well as contribute to the long-term goal of establishing well-constrained models for Cenozoic magmatism across southern Alaska.