|
|||||
|
|
Late Triassic granitoids of the eastern margin of the Tibetan Plateau: Geochronology, petrogenesis and implications for tectonic evolution |
|
| Authors: | L Xiao HF Zhang JD Clemens QW Wang ZZ Kan KM Wang PZ Ni XM Liu |
| Institution: | aFaculty of Earth Science, China University of Geosciences, 388 Lumo Rd, Hongshan District, Wuhan 430074, China bSchool of Earth Sciences & Geography, CEESR, Kingston University, Penrhyn Rd, Kingston-upon-Thames, Surrey KT1 2EE, UK cGeological Survey Party of Sichuan Province, Chengdu 61500, China dKey Laboratory of Continental Dynamics, Ministry of Education, Northwest University, Xi'an 710069, China |
| Abstract: | Late Triassic granitoids in the Songpan-Garzê Fold Belt (SGFB), on the eastern margin of the Tibetan Plateau, formed at 230 to 220 Ma and can be divided into two groups. Group 1 are high-K calc-alkaline rocks with adakitic affinities (K-adakites), with Sr > 400 ppm, Y < 11 ppm, strongly fractionated REE patterns ((La/Yb)N = 32–105) and high K2O/Na2O (≈ 1). Group 2 are ordinary high-K calc-alkaline I-types with lower Sr (< 400 ppm), higher Y (> 18 ppm) and weakly fractionated REE patterns ((La/Yb)N < 20). Rocks of both groups have similar negative Eu anomalies (Eu/Eu = 0.50 to 0.94) and initial 87Sr/86Sr (0.70528 to 0.71086), but group 1 rocks have higher εNd(t) (? 1.01 to ? 4.84) than group 2 (? 3.11 to ? 6.71). Calculated initial Pb isotope ratios for both groups are: 206Pb/204Pb = 18.343 to 18.627, 207Pb/204Pb = 15.610 to 15.705 and 208Pb/204Pb = 38.269 to 3759. Group 1 magmas were derived through partial melting of thickened and then delaminated TTG-type, eclogitic lower crust, with some contribution from juvenile enriched mantle melts. Group 2 magmas were generated by partial melting of shallower lower crustal rocks. The inferred magma sources of both groups suggest that the basement of the SGFB was similar to the exposed Kangding Complex, and that the SGFB was formed in a similar manner to the South China basement. Here, passive margin crust was greatly thickened and then delaminated, all within a very short time interval ( 20 Myr). Such post-collisional crustal thickening could be the tectonic setting for the generation of many adakitic magmas, especially where there is no spatial and temporal association with subduction. |
| Keywords: | granite K-adakite geochronology geochemistry isotopes songpan-garzê Tibetan Plateau |
| 本文献已被 ScienceDirect 等数据库收录！ | |