Zhao J.,Northwest University, China |
Zhang C.L.,Northwest University, China |
Guo X.J.,Northwest University, China |
Liu X.Y.,Northwest University, China |
Wang Q.,Institute of Shanxi Geological Survey
Yanshi Xuebao/Acta Petrologica Sinica | Year: 2015
The understanding the tectonic transformation of the North China Craton (NCC) from Late Neoarchean to Early Paleoproterozoic is significant for discussing early crustal evolution in NCC. The Gaijiazhuang granitic pluton is outcropped in Lvliang area of the Trans-North China Orogen (TNCO) in NCC. The ages of 2398 ∼ 2408Ma was obtained using LA-ICPMS zircon U-Pb dating. Thus its petrogenesis and forming tectonic setting can provide us important information for Early Paleoproterozoic evolution of TNCO. The Gaijiazhuang granite was mainly composed of syenogranite, and geochemically characterized by the high Si, K, alkaline and FeOT/MgO, low Ca, Mg, enrichment of LILE such as Rb, Th, U and HFSE as well as depletion of Sr, Ba, P, Ti, with a "seagull-type" pattern of slight REE fractionation between LREE and HREE and strong negative Eu anomaly, showing the features of typical A2-type granite formed in a post orogenic setting. They have positive εNd(t) of 2.0 ∼ 2.3 and narrow raging of tDM2 (2606 ∼ 2629 Ma). Their zircon εHf(t) also show positive values varying from +2.2 to +7.1, and the two-stage model ages is from 2494Ma to 2791 Ma, slightly higher or close to its formation age. All demonstrate that Gaijiazhuang syenogranite was mainly derived from the Mid-late Neoarchean lower crustal materials, and involved minor mantle-derived component. Combined with regional geology and the widespread coeval K-rich granitiods in TNCO, the Gaijiazhuang syenogranite together with the K-rich granitiods represent a tectonothermal event occurred at 2.4Ga due to the partial melting of juvenile lower crustal materials trigged by the mantle upwelling, which resulted from the crustal extension after the ∼ 2.5Ga blocks amalgamation of NCC, suggesting that the NCC has been entered into the extensional tectonic environment during the Early Paleoproterozoic of ∼2.4Ga.