Geochemistry and LA-ICP-MS zircon U-Pb age of Late Carboniferous Shalazhashan pluton on the northern margin of the Alxa Block, Inner Mongolia and their implications

The Wenduermaodao biotite granodiorite pluton is located in Shalazhashan on the northern margin of the Alxa Block. LA-ICP-MS U-Pb dating of zircons from the pluton yielded an age of 301±2Ma, which indicates that the pluton is a Late Carboniferous intrusion. According to the geochemical analysis, the Wenduermaodao pluton has high SiO2 (67.23%~72.57%), K2O(1.14 %~6.13%) and Al2O3(13.67%~17.29%), suggesting that it is calc-alkaline and peraluminous (A/CNK=0.98~1.10). This intrusion has low REE content (38.86×10-6~74.39×10-6) with a relative enrichment of LREE and week Eu anomalies (δEu=0.9~1.3). The primitive mantle normalized trace element patterns are characterized by the enrichment of the LILE (Rb, Th, K) and depletion of HFSE (Nb, Ta, P, Ti), showing the features of I-type granite. Combined with regional geology, the authors hold that the pluton was emplaced in a subduction setting and derived from mixed sources of oceanic crust and juvenile crust, and the subduction of Paleo Asian plate beneath the northern Alxa Block took place at 301Ma or earlier.