Mesoarchean geodynamic regime evidenced from diverse granitoid rocks in the Anshan-Benxi area of the North China Craton

Abstract

The petrogenesis and inner genetic relations of Mesoarchean granitoid rocks have been poorly researched in the Anshan-Benxi (AB) area of the North China Craton. These Mesoarchean granitoids are mainly composed of ~3.14 Ga Lishan trondhjemitic gneisses (LSTG), and 2.95–3.01 Ga Donganshan – Jinjialing trondhjemitic to monzogranitic gneisses (DTMG) and Tiejiashan – Gongchangling high-K granitoid gneisses (TGKG), which show essentially consistent ages of magmatic crystallization.The LSTG are characterized by SiO2 (70.71–73.72 wt%) and Al2O3 (14.25–15.99 wt%) contents, and low MgO (0.46–1.12 wt%) contents with low Mg# values (32–49) and K2O/Na2O values of 0.43 to 0.66, and total rare earth elements (TREE) of 97 to 151 ppm with (La/Yb)N ratios of 14.19 to 83.15. Integrated with Hf–O isotope characteristics from previous research and partial melting simulation, the geochemical characteristics of LSTG indicate that the trondhjemitic magma was generated by the partial melting of the source consisting of dominant ~3.3 Ga juvenile crustal material and some Paleo- to Eoarchean sediments at the lower crust level. In contrast with the LSTG, the DTMG shows higher SiO2 (73.10–75.99 wt%) contents, slightly lower Al2O3 (13.41–15.00 wt%) and MgO (0.21–0.61 wt%) contents with Mg# values (18–48), higher K2O/Na2O values (0.53–1.26) and similar TREE contents of 85 to 162 ppm, (La/Yb)N ratios (30.78–125.02), and εHf(t2) values from −5.38 to 3.16. Detailed petrogenetic investigations suggest that the magma of the DTMG was derived from the partial melting of the source comprising main ~3.3 Ga basaltic material and more Mesoarchean sediments at the lower crust level, then experienced slight plagioclase fractionation crystallization. The TGKG is characterized by the highest SiO2 (72.86–77.57 wt%) concentrations, but the lowest Al2O3 (11.96–14.47 wt%) and MgO (0.01–0.54 wt%) contents with K2O/Na2O values of 0.86 to 2.53 and Mg# values of 2 to 41. The wide TREE contents (142–766 ppm) and (La/Yb)N ratios (6.41–86.87), εHf(t2) value range of −9.71 to −2.14, suggesting that the magma of TGKG formed from the partial melting of abundant Eo- and Paleoarchean recycled sediments and igneous rocks. This petrogenesis of TGKG magma indicates that Eo- to Paleoarchean supracrustal material may exist under the Tiejiashan – Gongchangling area.Integrating previous studies on the AB area, these diverse granitoids record two episodes of major crust growths at ~3.65–3.8 Ga and ~3.3 Ga. Subsequently, the geological processes were dominated by the recycling of ~3.3 Ga basaltic material and Eo- to Paleoarchean crustal materials during ~3.14–2.95 Ga. The petrogenesis of Mesoarchean diverse granitoids indicates that voluminous supracrustal materials with different ages were transferred into the lower crust level during 2.95–3.14 Ga, revealing that pre-subduction buckling convergence may be the most probable Mesoarchean geodynamic regime in the AB area of the North China Craton.