Anatectic origin and geological significance of the Neoarchean ~2.5 Ga charnockite in the Jining area, northern North China Craton

Abstract

The Neoarchean charnockite of Yinshan Block has been a hot topic into understanding the Precambrian geology of the North China Craton. Although there is a broad consensus that the charnockite is usually related to granulite‐facies metamorphism, its petrogenesis and tectonics still remain controversial. We present a comparative study of the petrography, geochemistry, and geochronology of charnockite and intermediate–basic granulite in the Jining area along the northern margin of the North China Craton. Inclusions within hypersthene in charnockite are used to identify the peak granulite facies mineral assemblage, with the formation of charnockite being attributed to anatexis of the protolith associated with this granulite‐facies metamorphism. Anatexis occurred mainly during postpeak isothermal decompression, as inferred from the metamorphic evolution and pressure–temperature conditions (granulite and charnockite record peak pressure–temperature conditions of 750°C–1,000°C and 0.8–1.2 GPa and 850°C–975°C and 0.9–1.0 GPa, respectively) derived from analyses of metamorphic minerals using electron probe microanalysis, combined with previous zircon geochronology. Hypersthene in charnockite is interpreted to be a residual or peritectic mineral phase that was present during anatexis, and the charnockite is inferred to have been crystallized from a melt containing abundant residual minerals. Charnockite has similar geochemical characteristics to those of intermediate–basic granulite but differs in several key ways: (a) The charnockite is strongly depleted in the large‐ion lithophile element Cs, the heat‐producing elements U and Th, and the high‐field‐strength elements Nb, Ta, P, and Ti; (b) it is enriched in Sr; and (c) it exhibits both positive and negative Eu anomalies, which are characteristics of granites formed largely by in situ anatexis. Geochemical constraints indicate that the intermediate charnockite and retrograde metamorphic biotite–hornblende gneiss may both be the product of mantle‐derived magma in a magmatic subduction‐related back‐arc extensional environment. This setting provided a hot spot for metamorphic anatexis, with additional heat being provided by the upwelling of asthenospheric mantle. After the cessation of subduction by ~2,470 Ma, a magmatic arc extensional setting developed in the Jining area. The charnockite was involved in Paleoproterozoic orogenesis in the North China Craton and was strongly modified by a ~1,950‐Ma metamorphism event.

Geochemical Characteristic of Charnockites in North Margin of North China Craton: Indicating the Significiant of the Neoarchean Tecnotic Event

“…Geochemical characteristics indicate that low-Sr charnockite may be related to later metamorphism, whereas high-Sr charnockite were most likely not affected by late metamorphism. The results of geochronology show that the charnockites in the early Precambrian basement are widely affected by the post-metamorphism, and The study results of the geochronology show that the charnockites in the early Precambrian basement are widely affected by the post-metamorphism, and it is related to the regional metamorphism of the northern margin of the NCC at ~2.45 Ga , ~1.95 and ~1.85 (Li et al, 2000;Zhao et al, 2005;Dong et al, 2007;Jian et al, 2008;Wan et al, 2008;Li et al, 2011;Jian et al, 2012;Ma et al, 2013a;Ma et al, 2013b;Ma et al, 2013c;Guo et al, 2012;Liu et al, 2013;Cai et al, 2014;Bai et al, 2015;Xu et al, 2015;Ma et al, 2016;Yang et al, 2016;Shi et al, 2018). Therefore, we selected high Sr samples for corresponding study.…”

“…There are also some Neoarchean-Paleoproterozoic high-grade metamorphic complex rocks widely distributed in the khondalite series Belt and Yinshan Block, more and more studies have shown the metamorphic ages of ~2.5 Ga and ~1.95 Ga are widespread of the NCC (Jian et al,2005(Jian et al, , 2012Ma et al, 2013aMa et al, . 2013bWang et al, 2015;Guo et al, 2001;Wang et al, 2005;Wan et al, 2006Wan et al, , 2009Wan et al, , 2011Wan et al, , 2013aWan et al, , 2013bWan et al, , 2015Santosh et al, 2006Santosh et al, , 2007aSantosh et al, , 2007bXu et al, 2011;Dong et al, 2013;Cai et al, 2014;Ma et al, 2015;Chen et al, 2017;Shi et al, 2018Shi et al, , 2019aShi et al, , 2019bShi et al, , 2019c.…”

“…11b). Shi et al (2019b) studies shown that JN Charnockite has a typical characteristic of anatectic structure, such as the exists universally of sieve texture in garnets that the mineral assemblages of the peak stage of granulite facies metamorphism (Pl+Cpx+Hb+Qtz) are retained. Ma et al (2013a), Zhang et al (2014), Shi et al (2019a) refer to XWLBL Charnockite has the typical characteristics of meta-anatectic mineral.…”

“…The residual mineral phases of pyroxene and garnet have generally sieve texture (Fig. 2d, 2f, 2h, 2l), with melting corrosion structure of Pl+Hb+Qtz mineral assemblages, and raising to a mineral assemblages of granulite facies metamorphism of the stage of prograde metamorphism (Lu et al, 1992(Lu et al, , 1993Shi et al, 2019b ) . Previosly study of traditional calculation of temperature and pressure may suggest that isothermal decompression after peak metamorphism was intimately related to the formation of anatectic charnockites (Shi et al, 2018;Shi et al, 2019a), in which consistent with the anatectic characteristics charnockites in this paper.…”

“…The high-grade crustal of NCC, north margin of the between the Ordos Block and Yinshan Block, is characterized by anatectic charnockite and high-grade metamorphic complex. This anatectic charnockites mainly occurs in Shiguai-Baotou , Gonghudong-Guyang (Dong et al, 2012a;, Xiwulanbulang (Zhang et al, 2014;Shi et al, 2019a), Jining (Shi et al, 2019b(Shi et al, , 2019c, Gehuyao (Zhang et al, 2017), Qian'an (Han et al, 2016) in Northern margin of NCC, and together with granulites, gneiss greenstone and khondalite belt, forming a significant component of the early precambrian metamorphic baseement (Fig. 1).…”