Asish Basu - PhD University of California, Davis 1975









Research Projects





Impact tracers at the Permo-Triassic boundary

We recently reported the occurrence of chondritic meteorite fragments from an end-Permian bed in Graphite peak, Antarctica. This is so far the most direct evidence of a bolide impact at the P-T boundary and is a reasonable interpretation for the mass extinction at the end-Permian, arguably the greatest in the history of life. Graduate student Chakrabarti, recently went to Antarctica for more samples.

Clinoenstatite grains in a P/T breccia from graphite Peak, Antarctica














Braving a blizzard in Coalsack Bluff, Antarctica
















Petrology and geochemistry of continental flood basalts and plume volcanism

Our earlier work on the Siberian traps is being followed up by a detailed Nd-Sr-Hf-Pb isotope and trace element geochemistry of the Deccan volcanics, India. Graduate student Aniki Saha is currently working on this project as a part of her Phd dissertation.

This map shows the major lineaments, radiating out from the region of positive gravity anomaly. Intrusions 1 and 2 (Mundwara Complex) are earlier (68 Ma) than the main pulse of Deccan volcanism at the K-T boundary. Intrusion 8 cuts the main Deccan lava flows and is dated at 65 +/- 0.15.










Photograph of the SFBP in the Putorana region,Siberia.

Notice the beautiful horizontal basalt flows.










These pictures are photomicrographs of fluid inclusions from the Siberian Traps (left) and the Deccan. These bubbles contain He with high 3He/4He ratios, 12 to 13 times the atmospheric ratio. This He isotopic signature characterizes the sources of the Deccan and Siberian continental flood basalts to be in the lower mantle.









Sub-arc mantle geochemistry and devolatilization of the subducting lithosphere beneath Kamchatka

This work is being performed in collaboration with Prof. Gene Yogodzinsky of the University of S. Carolina.





Geochemistry of Archean sandstones from the eastern Indian Craton - the presence of a subduction zone as old as 3.4 Ga

Rounded microcline feldspar grains













Geochemistry of the volcano-sedimentary suite of rocks from the ~ 3.3Ga old Iron Ore Group (IOG) of rocks from the eastern Indian craton

The banded iron formations (BIF) in the IOG are perhaps the least altered among the oldest BIFs in the earth history. Graduate student Chakrabarti is working on this project and results of the preliminary work were presented at the Fall AGU conference in 2003.





Petrogenesis and geochemistry of the Nyirangongo ultrabasic volcanics from Congo, Africa

These samples were collected after the recent explosive volcanism which virtually
destroyed the city of Goma












Thermochronology of the Adirondack Granulites

Sm-Nd isotope systematics of the various lithologies of the Adirondack anorthosite-charnokite suite, as well as single zircon U-Pb analyses, reveal ages of igneous crystallization and the following granulite metamorphism. Internal Sm-Nd mineral isochrons of wollastonite skarns, garnet granulites and meta-anorthosites give a younger range in age of metamorphism. The youngest ages are obtained from 40Ar/39Ar step-heating plateau ages of hornblende and biotite separates of a granulite from the Gore Mountain. This age of 1025 Ma defines the cooling history of the Adirondack high-peaks from 700oC at 1060 Ma to 300oC at 1025 Ma, a cooling rate of 11oC per Ma which is considerably faster than the 2oC per Ma rate generally attributed to these rocks by other workers.

Map of the Adirondack region.


















Hawaii

Preliminary results indicate Lanai,Koolau and Kahoolawe are more closely related than previously thought. As the Molokai fracture zone crosses the Hawaiian trend there is an influx of more-enriched lower mantle plume material. Sr-isotopic systematics indicate significant inclusion of a seawater altered lithospheric component as well. Major element variations observed in basalts (tholeiitic and alkalic) from the Hawaiian Islands, Leeward Islands and Emperor Seamounts appear to be directly linked to the degree of melting of the parent source.

Photograph of recently erupted Aa and Pahoehoe lava.


















Bengal-basin groundwater and submarine groundwater discharge

Our recent work has shown that groundwater is a potentially significant source of Strontium to the oceans equal in magnitude to the dissolved strontium concentration carried to the oceans by the Ganges-Brahmaputra river system.

Map of the Bengal Basin


















Sudbury Impact

We measured the Nd-isotopic systematics of rocks of the Sudbury Complex in Canada. We demonstrated that the igneous rocks in this complex retained a continental crustal Nd-isotopic signature. Therefore, melting of continental crust due to an impact is invoked.



 
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