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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 ²⁰⁷U-²⁰⁶Pb 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 (SiO₂?=?71.1-73.4 wt.%), high alkaline (Na₂O?+?K₂O?=?8.10-9.26 wt.%, K₂O/Na₂O?>?1), and low Al₂O₃ (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 ?_Nd(t) values and the (²⁰⁶Pb/²⁰⁴Pb)_t, (²⁰⁷Pb/²⁰⁴Pb)_t, and (²⁰⁸Pb/²⁰⁴Pb)_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: A₂-type, which formed earlier (~1.8-1.6 Ga), and A₁-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.

SUBMITTER: Wang Y

PROVIDER: S-EPMC6952446 | biostudies-literature | 2020 Jan

REPOSITORIES: biostudies-literature

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

Wang Yan Y Yang Yi-Zeng YZ Siebel Wolfgang W Zhang He H Zhang Yuan-Shuo YS Chen Fukun F

Scientific reports 20200109 1

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 207U-206Pb 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 (SiO2 ...[more]

PMID: 31919370

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

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

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