期刊
JOURNAL OF ASIAN EARTH SCIENCES
卷 53, 期 -, 页码 25-37出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jseaes.2011.12.024
关键词
Tibet; Neo-Tethyan ocean; Seamount; Supra-subduction zone; Yarlung Zangbo Suture
资金
- Fundamental Research Funds for the central Universities [2009PY03]
- National Basic Research Program of China [2012CB822000]
- 111 Project of China Grant [B07011]
- China Geological Survey [12112011086037]
Despite more than 30 years' studies in the Yarlung Zangbo Suture Zone (YZSZ), southern Tibet is still a region of discovery and the geological evolution of the Neo-Tethys here remains controversial. In this paper we present the new field observation, petrography, zircon U-Pb dating and geochemistry of the Zhongba mafic rocks in the western segment of the YZSZ. Zircon U-Pb analyses from a diabase using SIMS (Secondary Ion Mass Spectrometry) yielded a concordant age of 125.7 +/- 0.9 Ma. All the Zhongba mafic rocks exhibit LREE enrichment (La-N/Yb-N = 4.7-15.8) without Eu anomalies (delta Eu = 0.97-1.01). Their Primitive-Mantle-normalized trace element patterns are similar to those of the average OIB and Hawaii alkaline basalts, as well as other OIB-type rocks already reported in the central-western YZSZ. These observations lead us to suggest the existence of a series of seamounts within the Neo-Tethys during the Early Cretaceous. These OIB-type rocks could be originated from (1) hotspot mantle; (2) near-ridge seamounts by melting-induced mixing of two distinct mantle sources; (3) late-stage magmatism fed by melts that originated from an asthenospheric window due to slab delamination. Combining literature data from the entire YZSZ, which include studies of the MORB- and IAB-type rocks and mantle peridotites, we prefer the third explanation that the OIB-type rocks represent a late-stage magmatic activity above an intra-oceanic supra-subduction zone within the Neo-Tethys. (C) 2012 Elsevier Ltd. All rights reserved.
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