Petrogenesis of the Late Cretaceous–Early Paleocene High‐Si Igneous Rocks in the Western Part of Southern Lhasa Terrane: Implications for the Tectonic Setting and Mineralization

Abstract 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 Neo‐Tethys 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.