胶-辽-吉活动带中段古元古代早期构造演化:来自牧牛河和大房身岩体的证据

辽吉花岗岩是胶-辽-吉活动带的重要组成部分,它们是限定胶-辽-吉活动带早期构造属性的重要依据.由于辽吉花岗岩的属性一直存在争议,所以胶-辽-吉带的早期构造环境也一直没有定论.通过对牧牛河-大房身地区的辽吉花岗岩(牧牛河岩体和大房身岩体)进行年代学和地球化学分析,以探讨该地区辽吉花岗岩成因和地质意义.锆石U-Pb定年结果...

Early Paleoproterozoic Tectonic Evolution of Central Jiao-Liao-Ji Belt:Evidence from Muniuhe and Dafangshen Plutons

Liaoji granitoids are important constituents of the Jiao-Liao-Ji belt (JLJB), and they provide important constraints on tectonic setting of the JLJB. The tectonic setting of the JLJB is still controversial due to the debate on nature of the Liaoji granitoids. It conducted zircon U-Pb geochronological and geochemical analyses of Liaoji granitoids (Muniuhe and Dafangshen plutons) in the Muniuhe-Dafangshen area, and then discuss the petrogenesis and geological significance of these granitoids. LA-ICP-MS U-Pb zircon dating gives the emplacement age of 2 176±4 Ma and 2 179±4 Ma for Muniuhe and Dafangshen plutons, respectively. Muniuhe and Dafangshen granitoids display similar geochemical characteristics. They have high SiO₂ (72.85%-77.67%), alkalis (K₂O+Na₂O=7.65%-8.86%) and K₂O/Na₂O ratios (0.99-1.83), and low CaO (0.10%-0.92%), MgO (0.03%-0.09%) and Al₂O₃ (11.49%-12.67%) contents. The chondrite-normalized REE patterns of Muniuhe and Dafangshen granitoids show right-dipping linear trends with slightly negative Eu anomalies (Eu/Eu*=0.08-0.56) and high Ga/Al ratios. They are enriched in high field strength elements (HFSEs; e.g., Zr, U and Y) and large-ion lithophile elements (LILEs; e.g., Rb and K), and depleted in Nb, P, Ti and Sr. In addition, they display high Zr saturation temperatures (855-871 ℃ and 850-886 ℃, repectively). Low Nb/Y ratios and high Zr saturation temperatures indicate that the Muniuhe and Dafangshen granitoids have affinities with A₂-subtype granitoids, and they were derived from thinned lower crust. The occurrence of voluminous A₂-subtype granitoids, combined with the newly discovered Na-rich granitoids and calc-alkaline mafic rocks, suggests that the tectonic setting of the JLJB is back-arc basin.