COUPLED MAGMATIC-HYDROTHERMAL RECORDS IN DAXIGOU MASSIF-TYPE ANORTHOSITE: IMPLICATIONS FOR PALEOPROTEROZOIC TECTONOTHERMAL EVENTS IN NORTHWESTERN CHINA

Occurring predominantly in Proterozoic, massif-type anorthosites have long been recognized carrying important significance for the earth evolution of the Earth. Daxigou anorthosite complex, a recently discovered intrusive pluton in Kuluketage block of NW China, locates within a tectonically vital domain between Tarim Craton and Central Asian Orogenic Belt. No detailed studies have been carried out with respect to its isotope geochronology, petrogenesis and tectonic implications in relation to Paleoproterozoic tectonothermal evolution. Here we present in situ LA-(MC)-ICP-MS U-Pb zircon dating and Lu-Hf-Sr-Nd systematics for the anorthosite, syenogranite, and zircon corona around the Fe-Ti oxides for Daxigou complex. The results of separate zircons from anorthosite reveal an emplacement age of ~1818± 9 Ma for Daxigou complex, which is indistinguishable from the magmatic zircon age of its associated syenogranite (1830 ±12 Ma) within analytical uncertainties. The hydrothermally altered zircons found in syenogranite indicated by their high U and Pb contents but low Th/U ratio yield concordant results with 1798 ± 21 Ma. This hydrothermal event is overall consistent with our in situ U-Pb age (1806 ± 5 Ma) for the zircon corona around the ilmenite in thin sections of anorthosite. The rim distributed zircons around the ilmenite grains are possibly due to the interaction of the exsolved baddeleyite from the ilmenite with this late hydrothermal fluid. Major and trace elements, together with Sr-Nd and Lu-Hf isotope, highly suggest Daxigou complex were derived by partial melting of a Neoarchaean TTG rocks or had experienced the assimilation of TTG rocks. Collectively, the documented magmatic-hydrothemral events herein, from 1830 to 1798 Ma, broadly correlates with a series of tectonothermal events along the northern margin of Tarim Craton, which is probably the results of the assembly of Columbia supercontinent resembling that in both the South and North China Craton.