Late Paleoproterozoic charnockite suite within post-collisional setting from the North China Craton: Petrology, geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes

Journal article

Authors / Editors

Rajesh, Hariharan

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Publication Details

Author list: Yang QY, Santosh M, Rajesh HM, Tsunogae T

Publisher: Elsevier

Place: AMSTERDAM

Publication year: 2014

Journal: Lithos: Journal of Petrology, Mineralogy and Geochemistry (0024-4937)

Journal acronym: LITHOS

Volume number: 208

Start page: 34

End page: 52

Number of pages: 19

ISSN: 0024-4937

Languages: English-Great Britain (EN-GB)

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Abstract

Charnockites (pyroxene-bearing granitoids) of magmatic origin in diverse tectonic settings and ranging in age from Mesoarchean to Cretaceous constitute important components of the continental crust. Here we report charnockites displaying both magnesian and ferroan compositions associated with gabbros from an AMCG (anorthosite-mangerite-charnockite-granite) suite in the North China Craton. The orthopyroxene in the magnesian charnockite is characterized by moderate X-Mg of 0.63-0.65 (Wo(1-2)En(62-63)Fs(35-36)), and low Al2O3 content of 0.59-0.71 wt.%. The magnesian chamockites show medium- to high-K contents, and high Mg# (similar to 47-69) similar to that of gabbros, whereas the Mg# of the ferroan charnockites is low (similar to 6-28). The ferroan charnockites are alkali-calcic to alkalic, and weakly peralkaline to metaluminous, whereas the magnesian charnockites are calcic to calc-alkalic, and metaluminous. Although magnesian chamockites are in general considered to have formed in subduction setting, the medium- to high-K contents, high Mg# values with a wide range, and the highly negative epsilon Hf values of the zircons in these rocks (-8.4 to -13.6), suggest inheritance of the arc signature from the melting of ancient arc-related crustal material. The ferroan charnockites show tholeiitic affinity and define a common differentiation trend with the gabbroic anorthosites and likely represent fractionated end-members with or without crustal interaction in a post-collisional rift setting. We present U-Pb age data from zircon grains on seven samples including two ferroan chamockites, three magnesian chamockites, one gabbroic enclave in magnesian charnockite and one gabbroic anorthosite which show emplacement ages of 1748.8 +/- 6.4 Ma, 1747.1 +/- 9.5 Ma, 1756.4 +/- 7.3 Ma, 1756.7 +/- 9.2 Ma, 1731 +/- 17 Ma, 1731.6 +/- 8.2 Ma and 1746.5 +/- 73 Ma respectively. The negative epsilon Hf values (-1.2 to -13.6) of zircon grains from these rocks and the older crustal model ages ranging from Mesoarchean to Paleoproterozoic suggest that the magma sources of these rocks involved the melting of ancient crustal components. The age data suggest that the magmatic suite was emplaced within a relatively short time interval between 1.73 and 1.76 Ga, during late Paleoproterozoic, placing the rocks suite in a post-collisional scenario, following the amalgamation between the Eastern and Western Blocks of the North China Craton along the Trans-North China Orogen at ca. 1.85-1.80 Ga. (C) 2014 Elsevier B.V. All rights reserved.

Keywords

Chamockite, geochemistry, Lu-Hf isotopes, North China Craton, Zircon U-Pb geochronology

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