论文部分内容阅读
Four dunite xenoliths from the Tietonggou intrusion of western Shandong,China,were subjected to SHRIMP zircon U-Pb dating to constrain timing of the North China Craton(NCC) destruction,a topic of much controversy.Cathodoluminescence images revealed that 15 of the 18 zircon grains from the xenoliths display striped absorption.The rest showed oscillatory growth zoniation.All the zircons had variable contents of Th(49-3569 ppm;average,885 ppm) and U(184-5398 ppm;average,1277 ppm),and variable Th/U ratios(0.15-2.04).These zircon characteristics indicate a magmatic origin.The zircon age data can be divided into five groups:131-145,151-164,261-280,434-452,and 500-516 Ma.Group I(131-145 Ma) is consistent with timing of formation of the Tietonggou high-Mg diorites.Group II(151-164 Ma) is similar in age to Middle-Late Jurassic magmatism in the eastern NCC,which included both mantle-derived and intensive crust-derived magmatism.Group III(261-280 Ma) is similar in age to the Emeishan large igneous province,and Group IV(434-452 Ma) is similar in age to Paleozoic high-silica magmatism in the eastern NCC.Group V(500-516 Ma) may correspond to the global Pan-African event.Results indicate repeated modification of lithospheric mantle in the eastern NCC,and suggest that the most intensive modification occurred in the late Mesozoic(131-164 Ma).
Four dunite xenoliths from the Tietonggou intrusion of western Shandong, China, were subjected to SHRIMP zircon U-Pb dating to constrain timing of the North China Craton (NCC) destruction, a topic of much controversy. Cathodoluminescence images revealed that 15 of the 18 zircon The grains from the xenoliths display striped absorption. the restuted oscillatory growth zoniation. All the zircons had variable contents of Th (49-3569 ppm; average, 885 ppm) and U (184-5398 ppm; average, 1277 ppm), and variable Th / U ratios (0.15-2.04). These zircon characteristics indicate the magmatic origin.The zircon age data can be divided into five groups: 131-145, 151-164, 261-280, 434-452, and 500-516 Ma.Group I (131- 145 Ma) is consistent with timing of formation of the Tietonggou high-Mg diorites. Group II (151-164 Ma) is similar to age to Middle-Late Jurassic magmatism in the eastern NCC, which includes both mantle-derived and intensive crust- derived magmatism.Group III (261-280 Ma) is similar in age to the Emeishan large igneou s province, and Group IV (434-452 Ma) are similar to age to Paleozoic high-silica magmatism in the eastern NCC. Group V (500-516 Ma) may correspond to the global Pan-African event. Results highlight modification of lithospheric mantle in the eastern NCC, and suggest that the most intensively involved in the late Mesozoic (131-164 Ma).