Petrogenesis of an early Eocene gabbro–granite complex in Kachang (SW Yunnan) and its implications for Eocene magmatism in the Tengchong terrane of SW China

Major and trace element, zircon U-Pb and Hf-isotope data are reported for mafic intrusions and host granite from the Kachang pluton (North Yingjiang of SW Yunnan) in the Tengchong Terrane, in order to investigate their sources, petrogenesis and tectonic implications. The zircon U-Pb age of the mafic...

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Bibliographic Details
Published in:International geology review 2018-05, Vol.60 (7), p.825-843
Main Authors: Yang, Xingchen, Ye, Peisheng, Ye, Mengni, Wang, Zhen, Luzhou, Yangfan, Chang, Pengyuan
Format: Article
Language:English
Subjects:
Contamination
Data
Dating
Enrichment
Eocene
Fractionation
Gabbro
Geochemistry
Geochronology
Geochronometry
Granite
Isotopes
Lava
Lead
Mafic magma
Magma
Mantle
Melts
Ocean circulation
Petrogenesis
Plutons
Radiometric dating
Rock
Rocks
Silica
Silicon dioxide
Subduction
Subduction (geology)
Temporal variations
Trace elements
Upwelling
Uranium
Zircon
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Summary:Major and trace element, zircon U-Pb and Hf-isotope data are reported for mafic intrusions and host granite from the Kachang pluton (North Yingjiang of SW Yunnan) in the Tengchong Terrane, in order to investigate their sources, petrogenesis and tectonic implications. The zircon U-Pb age of the mafic rocks (~55 Ma) is identical to that of the host granite (56.7 ± 0.6 Ma). The mafic rocks have high MgO concentrations (up to 13.43 wt.%) at low SiO2 contents (low to 42.73 wt.%) and slight negative to positive [epsilon]Hf(t) values (-2.26 to +0.59). They are enriched in LILE and LREEs and depleted in HFSEs, which can be explained as melts derived from a enriched mantle, with some crustal contamination. The host granite have high SiO2 contents (69.18-72.65 wt.%), highly negative [epsilon]Hf(t) values (-9.08 to -5.14), suggesting mainly derived from an ancient crustal source. Field observations, geochronology, geochemistry and zircon Hf isotopic compositions point to a complex petrogenesis, where enriched mantle- and crust-derived magma mixing was coupled with crystal fractionation, thus explaining the genetic link between mafic and felsic magmas, result of mafic magma upwelling triggered by the subduction rollback of the Neotethyan slab. Our new data, along with the data reported (especially zircon U-Pb dating and Lu-Hf isotope data) in the Tengchong Terrane, indicate that the spatial and temporal variations and changing magmatic compositions over time in the Tengchong Terrane closely resemble those of the Lhasa Terrane in southern and central Tibet.
ISSN:0020-6814
1938-2839
DOI:10.1080/00206814.2017.1353446