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|Title:||Geochronology and geochemistry of the Neoarchean Lulong Complex in the eastern Hebei Province, North China Craton: implications on regional crustal evolution|
|Citation:||Precambrian Research, 2019; 323:102-125|
|Wei Wang, Fu-Lai Liu, Lei Ji, M. Santosh|
|Abstract:||The Lulong Complex, exposed in the southeastern part of the eastern Hebei Province in the North China Craton (NCC), is mainly composed of meta-basalt, biotite plagioclase gneiss, migmatite, amphibolite and granitoids. Mineral assemblages indicate the rocks in this Complex underwent upper amphibolite facies metamorphism. Zircon U-Pb and Lu-Hf data constrain that both protolith of the biotite plagioclase gneiss and the homogeneous domain of the migmatite formed at 2.53 Ga and were mainly derived from the reworking of 2.8–2.7 Ga crustal source. The similar mineral association, zircon U-Th-Pb systematics and geochemical features suggest that their protolith should be dominated by felsic volcanic sequences with limited contributions from older crust. The protolith of the amphibolite (gabbro or diabase) was metamorphosed at 2477 ± 20 Ma. Geochemistry and zircon Lu-Hf systems indicate that these meta-mafic rocks originated from an enriched subcontinental lithospheric mantle source. The granitoids exposed in the Lulong area yield zircon U-Pb ages of 2507 ± 21 Ma to 2473 ± 38 Ma and record ∼2.5 Ga regional metamorphic event. The initial zircon ¹⁷⁶Hf/¹⁷⁷Hf ratios of the granite are in the range of 0.280640–0.281678 and suggest a complicated source where as those from the granodiorite indicate melting of juvenile crustal materials. Geochemically, the felsic meta-volcanics of the Lulong Complex are comparable to rhyodacite-dacite with calc-alkaline affinities. The granitoids suite comprises 2.47 Ga peraluminous granite, felsic dikes and 2.51 Ga metaluminous granodiorite. All these felsic intrusions are characterized by moderate differentiation of REE patterns and low Sr/Y ratios (<10), indicating relatively shallow depth of sources. Different Th-U-Nb systematics suggests that the granite should not be derived from similar parent magmas with the granodiorite. Based on the result obtained in this study, we propose the following tectonic scenario: (1) the region is underlain by early Neoarchean (2.8–2.7 Ga) crustal basement; (2) only limited contribution of Paleoarchean and other older crustal components to the Neoarchean suites; (3) enriched mantle source beneath this region formed no later than the end of Neoarchean. Combined with the protolith history and subsequent metamorphism and anatexis, our results are consistent with the construction of the NCC through micro-block amalgamation at the end of the Neoarchean. These processes are broadly similar to those in modern subduction systems.|
|Keywords:||Neoarchean; crustal evolution; geochronology; geochemistry; Lulong Complex|
|Rights:||© 2019 Published by Elsevier B.V.|
|Appears in Collections:||Geology & Geophysics publications|
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