Structural evolution of the Sagaing Fault and Mogok metamorphic complex, Burma

M.P. Searle in collaboration with A. Mitchell (Ivanhoe Mining, Rangoon)

The Mogok Metamorphic belt in Burma contains a variety of andalusite and sillimanite bearing metamorphic rocks, pre-collisional granites and granodiorites, and post-collision garnet + tourmaline bearing leucogranites. Some of the World’s best gem-quality rubies and sapphires also come from the Mogok belt. U-Th-Pb dating of monazite, xenotime and thorite reveal at least two phases of metamorphism, one pre-59 Ma the age of cross-cutting post-kinematic biotite granite dykes, the second spanning Late Oligocene to Eocene (37-29 Ma) with intrusion of garnet-tourmaline leucogranites at 45.5 and 24.5 Ma. The youngest ages of leucogranites that are cut by the right-lateral Sagaing Fault provide a maximum time constrain on initiation of the fault, a major plate boundary along the eastern margin of the indenting Indian plate. This project aims to unravel the thermal evolution of the Burmese crust before during and after the collision and accretion of the Indian plate.

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Structural evolution of the Mae Ping Fault and metamorphic core complexes, Northern Thailand

M.P. Searle in collaboration with C.K. Morley (PTTE, Bangkok)

The 500 km long NW-SE aligned Mae Ping Fault in NW Thailand splays off the Sagaing fault in Burma shows approximately 150 km of left-lateral motion. It is part of a network of regional strike-slip faults across Southeast Asia that is related to continental extrusion of Indochina since the India-Asia collision. There is great debate over the scale and timing of this extrusion of Indochina. Thus it is important to constrain the timing of metamorphism and melting in metamorphic rocks exhumed along the fault (Lansang gneiss), as well as the timing of cooling and exhumation from U-Pb, 40Ar/39Ar and Fission track dating. Spectacular ductile mylonites occur along the fault in the Lansang National park. This project aims to constrain the geological offsets and timing of motion along the Mae Ping Fault, as well as dating metamorphism in the metamorphic core complexes of North Thailand (eg: Doi Inthanon, Doi Suthep gneisses).

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Petrogenesis and timing of the Malay tin granite belt

M.P. Searle in collaboration with A. Mitchell (Ivanhoe Mining, Rangoon) and M.J. Whitehouse (Stockholm)

Three contrasting granite belts have been defined in South-east Asia across southern Thailand, the Malay peninsula and Sumatra: the Western province (Cretaceous I- and S-types), the Central Main Range province (mainly Triassic S-types) and the Eastern province (mainly Permo-Triassic I-types). The Phuket suite of granites in southwest Thailand includes both hornblende- and biotite-bearing granites and more evolved biotite- and muscovite (± garnet and tourmaline) granites, interpreted as resulting from fractional crystallization of a subduction-related granite melt, subsequently affected by crustal thickening, remobilization and hydrothermal alteration. Abundant pegmatite veins contain tin-tungsten mineralization. This project aims to obtain precise U-Th-Pb zircon and monazite ages from each belt across the Malay tin granite province. We have preliminary ages from the Phuket tin granites in SW Thailand, the Central belt granites from Kuala Lumpur (Malaysia) and the Eastern belt granites from Tioman Island.

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Geology of the Andaman-Nicobar Islands, and origin of the Andaman Ophiolite

M.P. Searle in collaboration with A. Carter (UC, London), R. Pedersen (Bergen)

The Andaman Ophiolites form the basement of the Andaman Islands, part of the outer forearc to the Sumatra-Java Volcanic arc. Two recently active volcanoes, Barren Island and Narcondam Island are the northern extension of the Sumatra-Java arc. In the eastern part of the Andaman Islands, upper mantle harzburgite and dunite are overlain by a cumulate peridotite-gabbro complex and high-level intrusives including both tholeiitic and calc-alkaline volcanic rocks. The upper crust in the South Andaman ophiolite shows a prominent trondhjemite-diorite-andesite volcanic suite, suggesting arc volcanism build onto ocean crust. This project is presently mapping out the ophiolite complex and overlying sedimentary rocks (Andaman ‘flysch’; Archipelago Group etc) and dating the felsic components of the ophiolite crustal section and arc volcanic rocks above, using U-Pb zircon dating.

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