Middle Paleoproterozoic crustal extensional regime in the North China Craton: New evidence from SHRIMP zircon U-Pb dating and whole-rock geochemistry of meta-gabbro in the Anshan-Gongchangling area
华北克拉通古元古代中期伸展体制新证据:鞍山-弓长岭地区变质辉长岩的锆石SHRIM PU-Pb定年和全岩地球化学

This paper reports whole-rock geochemistry and zircon geochronology of Middle Paleoproterozoic meta-gabbro from the Anshan-Gongchangling area, eastern North China Craton. Based on geochemical compositions, the meta-gabbro can be divided into two types. Type 1 is high in FeOT and low in MgO, with TREE contents and (La/Yb)N values of 107.5×10-6~114.0×10-6 and 2.6~2.7. They are not obviously depleted in Nb, P and Ti, and show strong depletion in Cr. Type 2 meta-gabbro is high in SiO2 and low in FeOT, showing a higher (La/Yb)N ratio (6.8) and stronger depletion of Nb compared with type 1 meta-gabbro. SHRIMP dating of type 1 meta-gabbro yielded a weighted mean 207Pb/206Pb age of 2110±30Ma for baddeleyite and magmatic zircon and an upper intercept age of ~2.95Ga for trapped zircon. Type 1 meta-gabbro is formed by strong recrystallization-differentiation of mafic magma staying a long period at a deep magmatic chamber, supporting a conclusion that the North China Craton was in an extensional regime during the Middle Paleoproterozoic period.