Publication Date:
2016-07-26
Description:
The initiation time and tectonic responses of paleo–Pacific plate subduction beneath the Eurasian continent remain controversial. In this paper we report on Early Jurassic (201–198 Ma) monzogranite-tonalite association from the southern Zhangguangcai Range, northeastern China. Zircon laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U-Pb dating indicates that the monzogranite and tonalite have identical 206 Pb/ 208 U ages of 201 ± 2 (mean square of weighted deviates, MSWD = 1.2, 2) and 198 ± 3 Ma (MSWD = 3.2, 2), respectively. The monzogranite and tonalite display different geochemical features, suggesting that they were derived from two distinct source regions. The monzogranite displays high SiO 2 , K 2 O, and Rb contents, as well as depleted whole-rock Sr-Nd-Pb isotopic compositions, i.e., Nd (t) = +8.3 to +11.7, with single-stage Nd model ages of 0.30–0.05 Ga. Zircons from the monzogranite also have depleted Lu-Hf isotopic compositions, and these contradictory geochemical features suggest that the monzogranite may be derived from melting of mid-oceanic ridge basalt (MORB)–sediment mélanges in subduction zone. The Na-rich tonalite has lower SiO 2 and higher TiO 2 contents. In combination with their relatively evolved Sr-Nd-Pb isotopic compositions and zircon Lu-Hf isotopic compositions, it can be considered that the tonalite was derived from juvenile basaltic crust in an active continental margin. Considering other Triassic to Jurassic mafic intrusive rocks and I-type granites in the Zhangguangcai Range, we propose that the Early Jurassic monzogranite-tonalite association in the Shihe area was caused by the westward subduction of the paleo–Pacific plate beneath northeastern China.
Print ISSN:
1941-8264
Electronic ISSN:
1947-4253
Topics:
Geosciences
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