Skip to main content

Research Repository

Advanced Search

On the origin of mafic magmatic enclaves (MMEs) in syn-collisional granitoids: evidence from the Baojishan pluton in the North Qilian Orogen, China

Chen, S.; Niu, Yaoling; Sun, W.L.; Zhang, Y.; Li, J.Y.; Guo, P.Y.; Sun, P.

On the origin of mafic magmatic enclaves (MMEs) in syn-collisional granitoids: evidence from the Baojishan pluton in the North Qilian Orogen, China Thumbnail


Authors

S. Chen

Yaoling Niu

W.L. Sun

Y. Zhang

J.Y. Li

P.Y. Guo

P. Sun



Abstract

Mafic magmatic enclaves (MMEs) are abundant in Baojishan syn-collisional granitoids located in the eastern section of the North Qilian Orogen. Zircon U-Pb ages of the host granodiorite (433.7 ± 3.4 Ma) and their MMEs (431.6 ± 2.8 Ma) are the same as the time of the Qilian ocean closing and continental collision at ∼440–420 Ma, indicating that the granitoids represent a magmatic response to the collision between the Qilian-Qaidam block and the Alashan block. The MMEs have the same mineralogy as the host granodiorite except that they are more abundant in mafic phases (e.g., amphibole and biotite) and thus have higher heavy rare earth element (HREE) abundances. Both the host granodiorite and the MMEs have light REE-enriched patterns and relatively flat HREE patterns (i.e., [Dy/Yb]N = 1–1.1). They are enriched in large ion lithophile elements (LILEs; e.g., Rb, K, Pb) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti) and show a varying Sr anomaly (i.e., Sr/Sr* = 0.9–2.2) for the host and a negative Sr anomaly (i.e., Sr/Sr* = 0.4–0.6) for the MMEs. Both the host granodiorite and the MMEs have overlapping and indistinguishable Sr-Nd-Hf isotopic compositions (87Sr/86Sr(i) = 0.7067–0.7082, εNd(t) = −3.9–−3.2, εHf(t) = 1.0–14.7). The extremely high εHf(t) = 14.7 of sample BJS12-06MME likely results from the calculation due to nugget effect of zircons because of the unexpectedly high Hf (3.53 ppm) and too high Zr (128 ppm). All these characteristics are fully consistent with the MMEs being of cumulate origin formed at earlier stages of the same magmatic systems rather than representing mantle melt required by the popular and alleged magma mixing model. The radiogenic Sr and unradiogenic Nd (εNd(t) <0) indicate the contribution of mature continental crust, while variably radiogenic Hf (εHf(t) > 0) for both the MMEs and their host granodiorite manifest the significant mantle input. The apparent decoupling between Nd and Hf isotopes are likely caused by partial melting of recycled terrigenous sediments and the remaining part of the North Qilian ocean crust under the amphibolite facies conditions during the collision.

Citation

Chen, S., Niu, Y., Sun, W., Zhang, Y., Li, J., Guo, P., & Sun, P. (2015). On the origin of mafic magmatic enclaves (MMEs) in syn-collisional granitoids: evidence from the Baojishan pluton in the North Qilian Orogen, China. Mineralogy and Petrology, 109(5), 577-596. https://doi.org/10.1007/s00710-015-0383-5

Journal Article Type Article
Acceptance Date Apr 9, 2015
Online Publication Date Apr 22, 2015
Publication Date Oct 1, 2015
Deposit Date Jun 4, 2015
Publicly Available Date Mar 29, 2024
Journal Mineralogy and Petrology
Print ISSN 0930-0708
Electronic ISSN 1438-1168
Publisher Springer
Peer Reviewed Peer Reviewed
Volume 109
Issue 5
Pages 577-596
DOI https://doi.org/10.1007/s00710-015-0383-5

Files





You might also like



Downloadable Citations