Journal
LITHOS
Volume 248, Issue -, Pages 12-21Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.lithos.2016.01.012
Keywords
Amphibolite; Zircon U-Pb dating; Petrogensis; Accretionary complex; Hualong Group; Central Qilian belt
Categories
Funding
- National Natural Science Foundation of China [41272220]
- Basic Outlay of Scientific Research Work from the Ministry of Science and Technology of China [J1303]
- Geological Survey Project of China [1212010911033]
- Austrian Science Fund (FWF) [J1303] Funding Source: Austrian Science Fund (FWF)
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The Hualong Group, located in the Central Qilian belt, northwest China, consists mainly of schist, amphibolite, quartzite, and marble, ranging from greenschist to amphibolite facies metamorphism. On the basis of the medium-grade metamorphism, the group has been considered to comprise Proterozoic basement rocks. In this study, geochemical, Sr-Nd isotopic, and zircon U-Pb geochronological analyses were performed on lentoid amphibolites from the Hualong Group, to characterize their age, petrogensis, and tectonic setting. Uranium-lead zircon dating of amphibolite revealed a formation age of 456 +/- 2 Ma and a metamorphic age of 440 +/- 1 Ma. Major, trace, and rare earth element data indicate that the amphibolites are predominantly basaltic-andesitic to andesitic rocks, with island arc affinities. The trace element patterns show enrichment in large-ion lithophile elements and depletion in high field strength elements relative to the N-MORB which confirm their island arc signatures. Obviously enriched light REEs ((La/Yb)(N) = 25-16.9) to chondrite normalized REE patterns further support this interpretation. The epsilon(Nd)(t) values for the amphibolites range from 4.6 to + 2.1, indicating subducted sediments as a larger endmember in the source. Geochemical data for these rocks suggest an island arc setting, and the rocks were derived from the depleted mantle that was enriched by melts of subducted sediments in an active continental margin setting at ca. 456 Ma. Together with regional evidence it suggests that the Hualong Group is an accretionary complex that was incorporated into the Central Qilian belt during the 440-400 Ma orogenic event. (C) 2016 Elsevier B.V. All rights reserved.
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