Age,Petrogenesis And Tectonic Implications Of Gaoligong(Meta-) Magmatic Rocks In The Western Yunnan Province

Micro-block is a relatively small-scale,rigid,geological block with a consistent motion or behavior in present-day space.Clarifying the behavior of micro-blocks during the supercontinent cracking and orogenic process of accretionary orogenic belt is the basis for a deep understanding of plate tectonics theory.Tibetan plateau and its eastern extension-western Yunnan province are formed by a series of(micro-)blocks under the control of the multi-stage Tethys evolution.In order to clarify the behavior of the Tengchong micro-block during supercontinent cracking and orogenic process of accretionary orogenic belt,the(meta-)magmatic rocks in the Gaoligong belt within the Tengchong micro-block were used as research to study the age,petrogenesis and tectonic implications of these rocks.The results of zircon U-Pb chronology indicate that the age of Gaoligong(meta-)magmatic rocks are: early Palaeozoic(444-427Ma),early Cretaceous(122-111Ma),late Cretaceous(72-66Ma),and Eocene(42Ma).The results of whole-rock geochemistry and mineral electron probe analysis indicate that:(1)Late Ordovician S-type granites were formed by vapour-saturated muscovite melting and muscovite dehydration melting of(meta-)sediments in a high pressure and low temperature environment;Early Silurian A-type granite was formed by low-pressure melting of crustal material and had a high forming temperature.(2)Early Cretaceous diabases were the product of partial melting of the mantle wedges transformed by subduction fluids;Early Cretaceous granodiorites were the product of magmatic mixing;Early Cretaceous monzogranite experienced a low degree of partial melting and was formed in a high pressure and low temperature environment.(3)Late Cretaceous S-type granites were formed by muscovite dehydration melting of(meta-)sediments in a high pressure and low temperature environment.(4)Eocene S-type pegmatite was formed by vapour-saturated muscovite melting of(meta-)sediments in a high pressure and high temperature environment.Combining with the magmatism events reported on the area,we can conclude that:(1)The area from late Ordovician to early Silurian should be in the tectonic setting of the thickened lithospheric delamination,asthenosphere upwelling,and crust extension following the subduction-collision process of the Prototethys.(2)Early Cretaceous magmatism formed at the end of the Mesotethys subduction when the crust-mantle interaction gradually weakened.(3)Late Cretaceous magmatism formed in the tectonic setting of the crust thickening in the hinterland induced by the Neotethys subduction.(4)Eocene magmatism formed in the tectonic setting of asthenosphere upwelling and crust extension following the break-off of the Neotethys slab.