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Minerals 2018, 8(6), 228; https://doi.org/10.3390/min8060228

Dual Geochemical Characteristics for the Basic Intrusions in the Yangtze Block, South China: New Evidence for the Breakup of Rodinia

1
CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China
2
State Key Laboratory of Continental Dynamics, Northwest University, Xi’an 710069, China
3
Chengdu Center, China Geological Survey, Chengdu 610081, China
4
College of Civil Engineering, Anhui Jianzhu University, Hefei 230601, China
*
Authors to whom correspondence should be addressed.
Received: 17 March 2018 / Revised: 17 May 2018 / Accepted: 21 May 2018 / Published: 28 May 2018
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Abstract

Neoproterozoic intraplate magmatic rocks are widespread in the Yangtze Block (YZB). The contrasting interpretations on their petrogenesis and tectonic evolution induce stimulating discussions on the coeval tectonic setting, including the two competing models of rift-related (R-model) and arc-related (A-model). Their main evidence is dominantly from felsic magmatic rocks. In contrast, the less evolved basic rocks are more suitable for tectonic setting discrimination. Here we study the Longtanqing basic intrusions (LTQ) that are exposed to the central part of the N–S trending Kangdian rift in the western YZB, by detailed geochemical and geochronological investigations. Zircon U–Pb dating of the two diabases from LTQ yield identical ages within error of 777 ± 17 Ma and 780 ± 5.3 Ma, respectively. LTQ rocks are characterized by low SiO2 (49.83–50.71 wt %), high MgO (5.91–6.53 wt %), and Cr (140–150 ppm) contents, supporting the significant mantle affinity. They also display dual geochemical characteristics, including a series of features of continental within-plate basalts (WPB, Ti/V = 37.3–47.5, Zr/Y = 3.4–3.8, Ta/Hf = 0.19–0.23), and the typical signatures of island arc basalt (IAB), such as highly depleted in HFSE and HREE, and enriched in LREE and LILE. Most zircon εHf(t) values are positive (1.6–9.4) while the corresponding Hf depleted mantle model ages (TDM1) range from 1.0 Ga to 1.3 Ga. In combination with the occurrence of inherited zircons (991–1190 Ma), it is suggested that their sources are dominantly derived from the lithospheric mantle that was reconstructed in the late Mesoproterozoic. Thus, LTQ is mainly formed by partial melting of the enriched lithospheric mantle, and subsequently assimilated by a juvenile crust during upwelling. The melt compositions are controlled by different degrees of the crystal fractionation of the dominant clinopyroxene and plagioclase with minor amphibole under high fO2 conditions. Combined with previous geochronological and geochemical data in the YZB, our new results support the theory that the R-model can be responsible for the petrogenesis of Neoproterozoic magmatic rocks in South China. View Full-Text
Keywords: Neoproterozoic magmatism; continental rifting; Rodinia breakup; Yangtze Block Neoproterozoic magmatism; continental rifting; Rodinia breakup; Yangtze Block
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Shu, S.; Yang, X.; Liu, L.; Liu, W.; Cao, J.; Gao, E. Dual Geochemical Characteristics for the Basic Intrusions in the Yangtze Block, South China: New Evidence for the Breakup of Rodinia. Minerals 2018, 8, 228.

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