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Ca. 1050 Ma intra-continental rift-related A-type felsic rocks in the southwestern Yangtze Block, South China TEXT SIZE: A A A
Late Mesoproterozoic igneous rocks have been traditionally thought to mark Grenvillian orogens and are thus widely used for the reconstruction of Rodinia. In the southwestern Yangtze Block, South China, similar to 1050 Ma dacites and rhyolites in Huili and granites in Julin are rich in large ion lithophile elements (LILE; e.g., Rb, Ba, Th and U) and poor in Nb, Ta, and Ti relative to the primitive mantle. These felsic rocks contain similarly high Zr, Hf, Ga, and HREE contents and Ga/Al ratios, and have high calculated zircon saturation temperatures (similar to 900 degrees C in average), thus resembling A-type granitoids. However, the dacites have whole-rock epsilon(Nd(t)) (-7.2 to -4.5) and zircon epsilon(Hf(t)) values (-20.8 to +1.0) much lower than the rhyolites/granites, and were interpreted to be derived from partial melting of an ancient continental crust. In contrast, rhyolites and granites have much higher epsilon(Nd(t)) (-0.4 to +1.8) and epsilon(Hf(t)) (-3.2 to +11.2) values, indicative of their derivation from primary magmas generated by partial melting of newly formed underplating crust, with possibly minor contributions from mantle-derived materials. These A-type felsic rocks have high Y (20-100 ppm) and Nb (10-40 ppm) contents similar to "within-plate" magmatic rocks in the frequently-used Y vs. Nb and Rb vs. Y + Nb plots for tectonic discrimination. Such a feature, in combination with rift-related, coeval mafic rocks in the region, indicates that they have formed in an intra-plate rifting setting. Our work thus argues against the existence of the so-called Grenvillian Orogen in the southwestern Yangtze Block. In view of the subsequent Neoproterozoic arc magmatism (950-730 Ma) in the region, we propose that the similar to 1050 Ma A-type granitoids and coeval mafic rocks were produced under a continental rifting basin that was transformed to an compression setting during early Neoproterozoic. (C) 2017 Elsevier B.V. All rights reserved.
 

Publication name

 PRECAMBRIAN RESEARCH, 309 22-44; SI 10.1016/j.precamres.2017.02.011 MAY 2018

Author(s)

 Chen, Wei Terry; Sun, Wei-Hua; Zhou, Mei-Fu; Wang, Wei

Corresponding author(s) 

 SUN Weihua 
 weihuasun@yahoo.com  
 China Univ Geosci, Sch Earth Sci & Resources, Beijing 100083, Peoples R China. 

Author(s) from IGCAS   CHEN Wei Terry

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