Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8912682 | Precambrian Research | 2018 | 54 Pages |
Abstract
The origin of magmatic episodes between final assembly and initial breakup of Rodinia is crucial for deciphering geodynamic transition and continental crust growth processes. However, few igneous rocks were identified during the quiescent time from 900â¯Ma to 830â¯Ma in the Tarim Craton. Along its northwestern margin, our field investigations identified abundant granitic debris in the Cryogenian Qiaoenbrak Group. Zircon U-Pb age determination revealed crystallization age at ca. 850â¯Ma. Detrital zircon crystals within Cryogenian to Ediacaran clastic rocks and schists of the basement Aksu Group also contain a major population having crystallized at ca. 860-840â¯Ma. Thus, we suggest that a hitherto unknown major magmatic event occurred ca. 850â¯Ma ago in northern Tarim. Granite gravels exhibit typical fractionated granite features, with high values of SiO2 (73.1-75.7â¯wt%), alkali oxides (Na2Oâ¯+â¯K2Oâ¯=â¯7.8-8.7â¯wt%) and Na2O/K2O (avg. 1.3â¯wt%), and low values of P2O5 (â¤0.04â¯wt%) and A/CNK (0.87-1.01), together with Rb, Th, U and K enrichment, and depletion in Nb, Ta, Sr, P, Ti and Eu, negative Eu anomalies (δEuâ¯=â¯0.21-0.74) and fairly low Ga/Al ratios. Including detrital crystals, ca. 850 Ma zircon crystals display a large range of εHf(t) values from â17.0 up to +11.6. Elemental and zircon Hf isotopes suggest that granites were derived from melting of juvenile lower crust, with addition of reworked upper crust and mantle-derived melts. We propose (1) before ca. 850â¯Ma, arc-continental collision setting related to southward accretionary assembly along Tarim margin, (2) progressive assembly of Tarim Craton, and (3) position of Tarim Craton within Rodinia supercontinent probably closer to North India Block than to Australia at ca. 850â¯Ma.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
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Authors
Guanghui Wu, Yang Xiao, Bernard Bonin, Debo Ma, Xin Li, Guangyou Zhu,