Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5784913 | Precambrian Research | 2017 | 86 Pages |
Abstract
Tonalite-trondhjemite-granodiorite (TTG) suite and potassic granite volumetrically expose in the Neoarchean to Paleoproterozoic Taihua complex, Mts. Huashan region, southernmost segment of the Trans-North China Orogen (TNCO). Zircon U-Pb dating on the trondhjemite, granitic gneiss, K-feldspar granite and coarse-grained granite samples show three episodes of magmatism (2.55-2.49Â Ga, 2.33-2.25Â Ga and 1.87-1.80Â Ga) with distinct geochemical features in this area during the Paleoproterozoic. The trondhjemite samples have high SiO2 (67.46-71.73Â wt%), Na2O (4.83-5.95Â wt%), low Mg# (31-40) and HREE contents, with moderate (La/Yb)N values (16.8 to 35.3) and Sr/Y ratios (15.8 to 34). The potassic granite samples show high SiO2 (65.2-75.43Â wt%), K2O (3.9-8.6), low Na2O (1.74-4.17Â wt%), Mg# (2-46) and HREE contents, with moderate to high (La/Yb)N values (10.3 to 226) and Sr/Y ratios (12.8 to 208). All these granitoid samples are characterized by high SiO2 and low Mg#, Cr, Ni with moderate to high (La/Yb)N values and Sr/Y ratios. The absence of evidence of any pre-existing high Sr/Y and La/Yb sources in this region led to that the granitoids probably generated from partial melting of hydrous mafic rocks with garnet and amphibole in the residue. Therefore, partial melting of thickened lower curst is the most likely origin. Combined with previous studies, the first episodic magmatism (2.55-2.49Â Ga) represented by TTG and granitic gneisses with positive whole rock ÆNd(t) and zircon ÆHf(t) values is interpreted as melts from partial melting of juvenile thickened lower crust. The second episodic magmatism (2.33-2.25Â Ga) represented by TTG, granitic gneisses and K-feldspar granite with positive to negative whole rock ÆNd(t) and zircon ÆHf(t) values is suggested as the product of partial melting of both juvenile and pre-existing crustal material. The third episodic magmatism (1.87-1.80Â Ga) is represented by these potassic granites, which is synchronism with the metamorphism recorded in this region and probably resulted from partial melting of pre-existing crustal materials in a syn-orogenic or post-orogenic setting during the collision between the Eastern and Western Blocks of the North China Craton. Multistage continental accretion (at 2.84-2.72Â Ga, 2.57-2.43Â Ga and 2.36-2.25Â Ga) and reworking (at 2.36-2.25Â Ga, 2.19-2.07Â Ga and 1.87-1.80Â Ga) occurred in the southern segment of the TNCO from Neoarchean to Paleoproterozoic. Transformation from an Andean-type continental margin arc setting on the western margin of the Eastern Block to continent-arc-continent collision in the southern TNCO during Late Neoarchean to Late Paleoproterozoic is suggested in this paper.
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Authors
Guo-Dong Wang, Hao Y.C. Wang, Hong-Xu Chen, Bo Zhang, Qing Zhang, Chun-Ming Wu,