The Paleoproterozoic Continental Evolution in the Southern North China Craton: Constrains from Magmatism and Sedimentati
Recently, increasing lines of evidence for the 2.45–2.00 Ga magmatic rocks and Paleoproterozoic low-grade metasedimentary sequences have been identified, which can provide diagnostic constrains on the debate on the Paleoproterozoic (2.45–2.00 Ga) evolutio
- PDF / 2,314,883 Bytes
- 27 Pages / 595.276 x 790.866 pts Page_size
- 30 Downloads / 183 Views
10
Yanyan Zhou, Qianying Sun, Taiping Zhao, and Chunrong Diwu
Abstract
Recently, increasing lines of evidence for the 2.45–2.00 Ga magmatic rocks and Paleoproterozoic low-grade metasedimentary sequences have been identified, which can provide diagnostic constrains on the debate on the Paleoproterozoic (2.45–2.00 Ga) evolutional regime of the NCC. The widespread 2.45–2.20 Ga magmatisms occurred in the southern NCC mainly include TTG, dioritic-gabbroic gneiss, amphibolite, and high-K granites. The 2.45–2.20 Ga TTG or TTG-like gneisses show variable Mg# values, low Cr, Ni, and high Rb/Sr ratios, suggesting that they most likely derived from partial melting of basaltic lower crust with juvenile materials addition. The 2.45–2.20 Ga dioritic-gabbroic gneisses show the similar geochemical characteristics with adakitic rocks from thickened lower crust. Their eHf(t) and eNd(t) values are variable, and have weak Ta enrichment, and not obvious negative Nb anomalies, suggesting they were produced by partial melting of metasomatized lithospheric mantle. The 2.45–2.20 Ga amphibolites are consistent with magma derivation from MORB-like mantle wedge. The 2.45–2.20 Ga (high-K) calc-alkaline granites are representative of syn-collisional granites, and derived from older crust with variable mixing of a juvenile melt in a subduction-collision related setting. The 2.20–2.00 Ga magmatism reveals a major period of crustal reworking, rather than one of crustal addition. The 2.20– 2.00 Ga monzonites have mixed IAB- and OIB-like geochemical signatures, possibly related to extension and thinning of the lithosphere and upwelling of asthenosphere. The 2.20– 2.00 Ga potassic granites belong to highly fractionated aluminous A-type granite, and formed in an extensional-rift setting. As indicated by the zircon in situ Hf isotopic compositions, the injection of basaltic melt into the crust has been widely considered as an important mechanism to generate silicious melts. The 2.20–2.00 Ga tonalite would be derived from partial melting of delaminated lower crust. The temporal change from mostly 2.45–2.20 Ga low-K igneous rocks (TTG) to 2.20–2.0 Ga mostly high-K igneous rocks in the southern segment of the NCC indicates a tectonic transformation from accretionary orogenesis (ca. 2.30 Ga) to extensional Y. Zhou (&) State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China e-mail: [email protected] Q. Sun T. Zhao Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China C. Diwu State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an, 710069, China © Springer Science+Business Media Singapore 2016 M. Zhai et al. (eds.), Main Tectonic Events and Metallogeny of the North China Craton, Springer Geology, DOI 10.1007/978-981-10-1064-4_10
251
252
Y. Zhou et al.
regimes (ca. 2.10 Ga). On the other hand, provenances, depositional ages and tectonic settings of l
Data Loading...
