Abstract:
We report the petrology, whole-rock geochemistry, zircon LA-ICP-MS U–Pb chronology and zircon Hf isotopic data of Daxigou granitoids (western part of the Kuluketage Block, NW China) to evaluate their likely petrogenesis and tectonic setting. Zircons from syenogranite can be divided into two groups: 1) those that display oscillatory zoning and high Th/U ratios (average = 1.38), implying their magmatic origin and 2) those that exhibit weak zoning and extremely high U and Pb contents but low Th/U ratios (average = 0.35), resembling zircons that experienced hydrothermal alteration. The zircon LA-ICP-MS U–Pb dating of the two groups of zircons yielded weighted mean ages of 1830 ± 12 Ma (MSWD = 0.78) and 1798 ± 21 Ma (MSWD = 1.6) respectively.
The Daxigou granitoids belong mostly to normal-K and sodium-rich metaluminous calc-alkaline type, systematically enriched in LREE and large ion lithophile elements (LILE, e.g., K, Ba and Rb), but significantly depleted in high field strength elements (HFSE, e.g., Ti, P, Nb, Ta and U). Their εHf(t) values and two-stage Hf model ages range from –7.16 to –5.03 and 2.69 to 2.76 Ga, respectively. Taken together, it is suggested that Daxigou granitoids are of I-type affinity and that they were derived by partial melting of a Neoarchaean TTG (e.g., Tuoge Complex) rocks in a continental-arc environment. These new data, combined with previous regional geological studies, demonstrate that a series of Palaeoproterozoic (c. 2.0–1.8 Ga) tectono-magmatic events occurred in Kuluketage Block during the assembly of Columbia.
