Geochemistry and tectonic significance of late Paleoproterozoic A-type granites along the southern margin of the North China Craton

Abstract

The Longwangzhuang pluton is a typical example of Paleoproterozoic A-type granite intrusions at the southern margin of the North China Craton. This pluton is composed of arfvedsonite granite and minor aegirine-augite granites. Samples from both granite types display similar zircon U-Pb ages with 207 U-206 Pb ages of 1612 ± 19 Ma [mean square weighted deviation (MSWD) = 0.66] and 1609 ± 24 Ma (MSWD = 0.5), respectively. The granites exhibit similar high silica (SiO 2 = 71.1-73.4 wt.%), high alkaline (Na 2 o + K 2 o = 8.10-9.26 wt.%, K 2 o/na 2 o > 1), and low Al 2 o 3 (11.8-12.8 wt. %) contents and metaluminous to weakly peraluminous bulk chemistry. The chemical variations of the Longwangzhuang pluton suggest the effects of mineral fractionation. In addition, all samples show typical characteristics of A-type granites, such as high 10000Ga/Al ratios (4.10-7.28), high FeO tot /(FeO tot + MgO) ratios (0.88-0.99), and high Zr (484-1082 ppm), Ce (201-560 ppm), and Y (78-156 ppm) contents. The ε nd (t) values and the (206 pb/ 204 Pb) t , (207 pb/ 204 Pb) t , and (208 pb/ 204 Pb) t ratios of the arfvedsonite granite samples vary from −4.6 to-5.3, 15.021 to 17.349, 15.241 to 15.472, and 33.206 to 36.905, respectively, and those for the aegirine-augite granite sample amount at −0.2, 14.421, 15.175, and 33.706. The distinct and variable Nd and Pb isotope values indicate the presence of heterogeneous protoliths. Based on its geochemistry, its low initial Pb isotope ratios, and its enrichment in Nd isotopes, we infer that the Longwangzhuang A-type granite is the partial melting product of basement rocks such as the Taihua Group gneisses accompanied by some involvement of juvenile material from the mantle. Together with published data from other Paleoproterozoic A-type granite plutons exposed at the southern margin of the craton, our findings suggest that these granites had a similar origin. Furthermore, geochemically, they can be divided into two groups: A 2-type, which formed earlier (~1.8-1.6 Ga), and A 1-type, which formed later (~1.6-1.5 Ga). Combining this information with the variations in whole-rock Nd and zircon Hf isotopic composition at ca. 1.6 Ga, we propose that tectonic transformation from post-orogenic to anorogenic magmatism occurred at the southern margin of the North China Craton at that time.

Statherian (ca. 1714–1680 Ma) Extension-Related Magmatism and Deformation in the Southwestern Korean Peninsula and Its Geological Significance: Constraints from the Petrological, Structural, Geochemical and Geochronological Studies of Newly Identified Granitoids

“…(b) Histogram of zircon model ages (data collected from this study and [9]). (c) ε Hf (t) versus crystallization ages for the Statherian granitoids in the eastern NCC (data collected from [8,10,11], and references therein). (d) ε Hf (t) versus crystallization ages for the Statherian granitoids in the southwestern part of the Yangtze Block (data collected from [39,40]).…”

“…The petrogenesis of the Statherian granitoids in the eastern part of the NCC was also different from that of the Statherian granitoids of the Yangtze Block. In general, most of the Statherian granitoids in the eastern part of the NCC are formed by partial melting of the ancient crust [8], but the Statherian granitoids in the Yangtze Block are formed by fractional crystallization of the juvenile mafic magma [40].…”

“…The last stage of the Wilson cycle-like evolution in the eastern part of the NCC, including the Korean Peninsula, is characterized by the occurrence of extension-related magmatism, sedimentation, and regional anatexis [4,8,9]. The extension-related mag-matism has produced igneous rocks that have mafic to felsic bimodal compositions in the northwestern area of the eastern part of the NCC [10][11][12][13][14], the southern part of the NCC [8,15], and the western part of the Nangnim and Gyeonggi massifs in the Korean Peninsula [9,16] during 1.80-1.60 Ga. Integrated geochemical studies suggest that igneous rocks were formed in post-orogenic and/or anorogenic settings after the continental collision [8,14].…”

“…The extension-related mag-matism has produced igneous rocks that have mafic to felsic bimodal compositions in the northwestern area of the eastern part of the NCC [10][11][12][13][14], the southern part of the NCC [8,15], and the western part of the Nangnim and Gyeonggi massifs in the Korean Peninsula [9,16] during 1.80-1.60 Ga. Integrated geochemical studies suggest that igneous rocks were formed in post-orogenic and/or anorogenic settings after the continental collision [8,14]. It was recently identified that the southwestern part of the Korean Peninsula also underwent the late Paleoproterozoic (1.71-1.68 Ga) magmatism and deformation [17].…”

Geochemical evolution of the Lebowa Granite Pluton in western Bushveld Igneous Complex, South Africa: More insight into the evolution of bimodal A‐type granitoid

“…Conversely, workers believing in geochemical data suggested derivation of A-type granitoids by partial melting of intermediate to felsic crustal sources (e.g., Collins et al, 1982;Creaser et al, 1991;Kaur et al, 2017;Topno et al, 2018;Whalen et al, 1987;Yadav et al, 2016). A crustal source model for the A-type granitoids has also been postulated using isotopic data (whole-rock Sr-Nd-Pb or O-Hf zircon isotopes; e.g., Hill et al, 1996;Wang et al, 2020;Zhang et al, 2007;Zhou et al, 2017). One of the recent ideas that could bridge these two extreme hypotheses is that the A-type granitoids could have formed by partial melting of sialic continental crust caused by the heat derived from voluminous mantle-derived magmas intruded into the shallower crustal depth.…”