Late paleozoic-triassic tectono-magmatism in the Paleo-Tethys realm, SW China: timing, nature and implications for continental amalgamation and orogenic processes

[Truncated abstract] The Paleo-Tethys orogen in SW China constitutes an important part of the greater Tethyan–Himalayan tectonic domain. This orogen comprises a series of N–S trending, ophiolitic suture zones and flanking magmatic belts that represent the dominant geological feature of the region. The orogen records closure of the Paleo-Tethys and accretion of a series of continental fragments to Asia in the Late Paleozoic and Mesozoic. Many facets of geology of this vast region remain enigmatic. This thesis focuses on the late Paleozoic–Triassic magmatic belts developed across the Jinshajiang orogenic belt that forms the eastern part of the Paleo-Tethys orogen in SW China. Field investigation, petrology and geochemistry studies, integrated with employment of geochronological and isotopic techniques provide critical information. We have identified two distinct suites of plagiogranites within the Jinshajiang ophiolitic mélange, the Dongzhulin trondhjemite and Jiyidu tonalite, which represent rift and subduction settings, respectively, related to opening and closing of the ocean. SHRIMP U–Pb analysis on zircons extracted from the Dongzhulin trondhjemite yields a mean 206Pb/238U age of 347 ± 7 Ma. REE and isotopic characteristics suggest an origin from low pressure partial melting of an amphibolitic protolith. Highly variable in situ Hf isotopic compositions for zircon, together with geologic relations, suggest that this intrusion probably formed near an embryonic spreading centre in a continent–ocean transition setting. The Jiyidu tonalite has a U–Pb zircon age of 283 ± 3 Ma, and geochemical data indicates high Sr/Y, (La/Yb)N, Nb/Ta and low Y, and marked heavy REE depletion