摘要
Many Late Cretaceous-Early Paleocene high-silica igneous rocks,associated with Pb-Zn-Ag deposits,were identified in western part of southern Lhasa terrane.The Dajiacuodong muscovite granite as one of the high-silica granites was dated by zircon U-Pb method and determined for whole-rock major and trace elements and zircon trace elements.Combined with previous data of other high-silica igneous rocks,petrogenesis,tectonic setting,and factors controlling Pb-Zn-Ag mineralization were studied.The muscovite granite emplaced at 68.2±0.3 Ma and is peraluminous.All high-silica igneous rocks are S-type and whole-rock CaO,Na_(2)O,and Rb-Sr-Ba and zircon Hf isotopic compositions show that they were formed by partial melting of meta-sedimentary protoliths from the Lhasa terrane basement.Roll-back of the NeoTethys oceanic slab caused melting of the mantle wedge is the trigger for partial melting of basement.Zircon trace elements indicate that the high-silica igneous rocks are reduced and H_(2)O-and F-enriched.These geochemical features and magma sources of the high-silica igneous rocks are comparable with the W-Sn deposit related granites.Shallow emplacement of high-silica granites and coeval volcanic eruption induced rapid escape of fluids.This caused inefficiency of hydrothermal-magmatic interaction,which are reasons to form Pb-Zn-Ag rather than W-Sn deposits.
基金
funded by the National Key R&D Program of China(2021YFC2900100)
the Basic Research Found of Chinese Academy of Geological Sciences(KK2306)
the Geological Survey Program of China Geological Survey(DD20230360 and DD20240078)。
