Water-Flux Melting of Amphibolite in Paleozoic Leucogranite from the North Qinling, Central China: Implication for Post Collisional Setting

Abstract

Paleozoic granites can provide important insights of crustal differentiation and collision process of the North Qinling terrane. The Dafanggou leucogranites that intruded in the Qinling Complex is a Paleozoic granite with zircon U-Pb age of 404±6.4 Ma (MSWD=0.13, n=9). The leucogranites display moderate SiO₂ (68.4 wt.% to 71.7 wt.%) content and high Na₂O/K₂O (1.07 to 2.74) and Sr/Y (42 to 65) ratios, and low A/CNK (1.04 to 1.08) and Rb/Sr (0.09 to 0.16) ratios. Combined with negative ε _Nd(t) (−10.4) and ε _Hf(t) (− 9.35 to −0.25) values and ancient T _DM2 ages (1.2 to 1.7 Ga), suggesting the leucogranite are derived from ancient amphibolitic crust in the Qinling Group. In addition, the absence of coeval mafic igneous rocks or mafic enclaves occurred in the Dafanggou pluton and the low T _Zrn (∼700 °C) of leucogranites preclude that the leucogranites derived from high temperature dehydration melting of amphibolite. Thus, we propose that the occurrence of the Dafanggou leucogranite indicates that water-flux melting of middle-lower crust in postcollision setting may be a potential model for the genesis of granites in collisional orogenic belt.

Keywords

leucogranite / North Qinling / Late Paleozoic / crustal differentiation / zircon Lu-Hf isotope

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