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Abstract: The Andaman ophiolites form the basement of the Andaman Islands, which is a part of the outer forearc that links the Indo-Burma accretionary complex to the north with the Java-Sumatra trench-arc system to the SE. Upper mantle harzburgite and dunite are overlain by a cumulate peridotite-gabbro complex, highlevel intrusive rocks and a tholeiitic volcanic series. The upper crust in the South Andaman ophiolite shows also a prominent andesite-dacite volcanic suite, suggesting arc volcanism built onto ocean crust. U-Pb zircon dating of a trondhjemitic rock from Chiriya Tapu in South Andaman Island using laser ablation inductively coupled mass spectrometry reveals an age of crustal formation of 95 ± 2 Ma. The trondhjemites have geochemistry comparable with that of plagiogranites associated with ophiolite complexes, and ε^sub Nd^ values around +7 further confirm that they are derived from depleted mantle melts. Basaltic pillow lava and basaltic dykes that cut the trondhjemites have mid-ocean ridge basalt-like trace-element geochemistry. The new data show that the Andaman volcanic arc was built on Cenomanian ophiolite-oceanic crust and that subduction was initiated at this time along Tethys, at least from Cyprus through Oman to the Andaman Islands.
Ophiolite complexes preserved within and adjacent to the main India-Asia collision zone provide us with some idea concerning the composition and structure of the oceanic crust that lay between the continental plates. Along the Himalaya-South Tibet suture zone several ophiolites are found, but only a few of these preserved ophiolites were obducted onto the Indian continental margin (e.g. Searle et al. 1997; Corfield et al. 2001). U-Pb zircon dating of the Spontang ophiolite in Ladakh reveals that the oceanic crust formed during the Mid-Jurassic (177 ± 1 Ma) but an andesitic island arc was formed during the Late Cretaceous (88 ± 5 Ma) contemporaneous with the initiation of obduction onto the passive Indian continental margin (Pedersen et al. 2001). Ophiolite complexes along the Indus suture zone in southern Tibet are thought to be mainly Early Cretaceous in age from limited U-Pb dating in the Xigase ophiolite (Gopel et al. 1984; Malpas et al. 2003). Dismembered ophiolites marking the India-Asia suture zone are sporadically present around the Namche Barwa East Himalayan syntaxis and along several belts to the south in Burma (Fig. 1).
Along the...