Graduate Student Seminars

Please join us for two graduate student seminar presentations this Friday February 16 in rm 155 Geology:

3:30 pm

Khalil Allahyari, PhD candidate

“Tectono-magmatic evolution of the Southern Neo-Tethys and relationships with ophiolites and mineral deposits: Kermanshah ophiolites as a case study, Iran”

In southwest Asia, the southern branch of the Neo-Tethys Ocean was located between the Arabian shield and the Sanandaj–Sirjan continental block of Iran. Ophiolites cropping out along the Main Zagros Thrust Zone mark the suture zone between the Arabian and Sanandaj-Sirjan continental blocks.

Various hypotheses have been proposed for the tectonic evolution of the Arabian-Iranian sector of the Neo-Tethys. Permian to Triassic time has been suggested for the formation of the ocean. Oceanic spreading persisted until the Late Cretaceous, with a NE-dipping intra-oceanic subduction zone present in the northern margin of Arabia from the Early to Late Cretaceous. This subduction persisted until the continental collision with emplacement of ophiolites in Late Cretaceous. After the Late Cretaceous, calc-alkaline and alkaline magmatism peaked in the Eocene on the southern margin of the Sanandaj- Sirjan block.

As an example, the Zagros ophiolites (Kermanshah ophiolites) preserve fragments of tectonically dismembered sequences of mantle, as well as basaltic and boninitic rocks. The geochemistry of these rocks suggest development in a complex geodynamic framework during the Cretaceous, as they include basalts that record the early stage of ocean crust formation at the ocean-continent transition zone, boninites that formed by 5-15% partial melting of depleted mantle after MORB-type melt extraction, and depleted mantle lherzolites and harzburgites that represent residua after removal of boninitic-type melts after 25-30% partial melting in an intra-oceanic arc setting.

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4:00 pm

Michael McConnell, MSc candidate

“A zircon U-Pb, Hf and O isotope investigation of the Karrat Group, Rae craton, west Greenland”

The Karrat Group is a Paleoproterozoic supracrustal sedimentary-volcanic succession in west Greenland. This succession unconformably overlies Archean basement rock of the Rae craton in separate sub-basins ~500 kilometers in total length (~71° to 75°N). The supracrustal belt is truncated by the ~1.90-1.87 Ga Prøven Igneous Complex. The supracrustal sedimentary sequences of eastern arctic Canada are broadly similar to that of the Karrat Group in terms of lithostratigraphy, but correlation with respect to absolute age and provenance analysis remains untested. Here, we present new coupled zircon U-Pb, εHf, and δ18O isotopic data from the Karrat Group to investigate the provenance of eastern Rae craton. Isotopic compositions of zircon were obtained using a combination of SIMS and ICP-MS. The zircon U-Pb ages range from ~3.4 Ga to ~1.8 Ga, the younger of which is interpreted to represent metamorphic resetting. The εHf show wide arrays in Neoarchean and Orosirian zircon, ranging from depleted mantle values to -25, which reflect tectonic events on the Rae craton. Crustal melts for some of the Karrat detrital zircon grains are suggested by high δ18O values (up to 11.4‰). We investigate multiple provenance sources for the Karrat Group that include various parts of the Rae craton and surrounding microcratons, where geochronology is available. Although this study is ongoing, preliminary results suggest local basement derived provenance in addition to sources from western Canada