Mesoproterozoic (similar to 1.4 Ga) A-type gneissic granites in the Xilinhot terrane, NE China: First evidence for the break-up of Columbia in the eastern CAOB

摘要

The Precambrian evolution of the Central Asian Orogenic Belt (CAOB) in NE China remains enigmatic. In this paper, we report petrography, zircon U-Pb ages, and major and trace element data of the Precambrian gneissic granites from the Xilinhot Complex in the Xilinhot terrane of the eastern CAOB. Zircons in four gneissic granite samples yielded weighted mean Pb-207/Pb-206 ages of 1397-1360 Ma, suggesting that the Xilinhot terrane is a microcontinental fragment with Precambrian basement rather not a Paleozoic accretionary complex as previously thought. The gneissic granites contain high SiO2 (73.7-78.6 wt%) and K2O (4.1-4.9 wt%) but low Al2O3 (9.5-12.1 wt%), with depleted Sr, Ba, Ti, P, fractionated REE patterns, and strong negative Eu anomaly. These features are comparable to those of A-type granites related to extensional environments. This first discovery for the occurrence of similar to 1.4 Ga A-type granites suggests that the Xilinhot terrane in the CAOB was likely originated from part of the Columbia supercontinent, and re-assembled after the breakup of Columbia during the Mesoproterozoic, probably at ca. 1.4 Ga. (C) 2017 Elsevier B.V. All rights reserved.