Zircon U-Pb dating, geochemical characteristics and tectonic setting of intermediate-basic volcanic rocks from Middle Cambrian Shengou Formation, eastern Qilian orogen

LI Ruibao; PEI Xianzhi; WANG Xing; CHEN Youxin; LI Zuochen; LIU Chengjun; WANG Meng; PEI Lei; ZHANG Yu; YAN Quanzhi; PENG Sizhong; HU Chenguang

2018 Vol. 37, No. 4

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Article navigation > Geological Bulletin of China > 2018 > 37(4): 589-603

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LI Ruibao, PEI Xianzhi, WANG Xing, CHEN Youxin, LI Zuochen, LIU Chengjun, WANG Meng, PEI Lei, ZHANG Yu, YAN Quanzhi, PENG Sizhong, HU Chenguang. Zircon U-Pb dating, geochemical characteristics and tectonic setting of intermediate-basic volcanic rocks from Middle Cambrian Shengou Formation, eastern Qilian orogen[J]. Geological Bulletin of China, 2018, 37(4): 589-603.

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LI Ruibao, PEI Xianzhi, WANG Xing, CHEN Youxin, LI Zuochen, LIU Chengjun, WANG Meng, PEI Lei, ZHANG Yu, YAN Quanzhi, PENG Sizhong, HU Chenguang. Zircon U-Pb dating, geochemical characteristics and tectonic setting of intermediate-basic volcanic rocks from Middle Cambrian Shengou Formation, eastern Qilian orogen[J]. Geological Bulletin of China, 2018, 37(4): 589-603.

Zircon U-Pb dating, geochemical characteristics and tectonic setting of intermediate-basic volcanic rocks from Middle Cambrian Shengou Formation, eastern Qilian orogen

1.
School of Earth Science and Resource, Chang'an University, Xi'an 710054, Shaanxi, China
2.
Key Laboratory of Western Mineral Resource and Geological Engineering of Ministry of Education, Xi'an 710054, Shaanxi, China

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Corresponding author: PEI Xianzhi, peixzh@263.net

Received Date: 07 July 2017

Revised Date: 02 March 2018

Publish Date: 25 April 2018

Abstract

Abstract

There are andesites intercalated with metabasalts in the Mogou area, southeastern Lajishan mélange. Their protoliths are an-desite and basalt belonging to the sub-alkaline tholeiite series. LA-ICP-MS zircon U-Pb dating of the andesite yielded an age of 503.1±6.6Ma, suggesting Middle Cambrian. ∑REE values of basalt are 93.40×10^-6~135.39×10^-6, (La/Yb)_N=2.76~3.64, and δEu=0.87~1.00. The spider diagram of trace elements shows similar characteristics to OIB or continental rift volcanic rock, with no obviously anomaly of δEu and enrichment of incompatible elements. The andesites have lower REE content than basalt, and the negative Eu anomalies are not obvious.The spider diagram of trace elements of andesites show the enrichment of LILEs (Cs, Rb, Ba) and depletion of HFSE (Nb, Ta, Ti). The genetic analysis suggests that the basalt resulted from low degree partial melting of garnet+spinel lherzolites without obvious crustal contamination, and andesite was derived from partial melting of the crust. Tectonic environment discrimination shows that Shengou Formation was formed in a continental rift environment. These data further indicate that southeastern termination of Lajishan belt might not have had a mature system of ocean basin in the central part of Central Qilian block. With the South Qilian Ocean subdcution in the Early Paleozoic, the Shengou Formation was emplaced on the southern margin of central Qilian block as fragments of continental rift lithosphere.
- Qilian orogen /
- Lajishan mélange /
- basalt /
- Shengou Formation /
- continental rift

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