论文部分内容阅读
A suite of ~1.84–1.92 Ga metamafic dykes within the paragneiss suite(khondalite) of the Quanji massif in NW China, has been chosen in this study for further understanding the tectonic evolution and possible links to the global Columbia supercontinent. Occurrence and field relations suggest that they were formed coevally with a previous studied ~1.83–1.85 Ga metamafic dyke swarms. Whole-rock major and trace elemental geochemistry suggests precursor magma of the amphibolites being generated from a volcanic arc-related tectonic setting rather than a back-arc environment where the metamafic dyke swarms were emplaced. The metamafic dykes show enrichment of LREE and strongly negative anomalies for Ta-Nb, Zr-Hf and Ti, have high SiO_2(49.3 wt.%–52.5 wt.%) but low MgO(6.40 wt.%–7.76 wt.%) contents and Mg~#(Mg~#=[100×(MgO/40.3)]/[MgO/40.3+FeO/71.8]) values(45.7–52.1), suggesting evolved precursor magma. The high values of La/Ta(22.2–42.8) and La/Nb(1.71–2.47), mildly negative εNd(t) values(-2.51–0.15), with depleted mantle model ages(TDM) of 2.45–2.84 Ga, suggest that their precursor magmas were possibly derived from a subduction-related fluid metasomatized Archean sub-continental lithospheric mantle. This study provides further evidence for oceanic plate subduction prevailing before or around ~1.85 Ga, which confirms a prolonged subduction-accretion-collision history in the NW China which is possibly linked to the assembly of the Columbia supercontinent.
A suite of ~ 1.84-1.92 Ga metamafic dykes within the paragneiss suite (khondalite) of the Quanji massif in NW China, has been chosen in this study for further understanding the tectonic evolution and possible links to the global Columbia supercontinent. Occurrence and field relations suggest that they were formed coevally with a previous studied ~ 1.83-1.85 Ga metamafic dyke swarms. Whole-rock major and trace elemental geology suggests precursor magma of the amphibolites being generated from a volcanic arc-related tectonic setting rather than a back-arc environment The metamafic dykes swarms were emplaced. The metamafic dykes show enrichment of LREE and strongly negative anomalies for Ta-Nb, Zr-Hf and Ti, have high SiO 2 (49.3 wt.% - 52.5 wt.%) but low MgO % - 7.76 wt.%) Contents and Mg ~ # (Mg ~ # = [100 × (MgO / 40.3)] / [MgO / 40.3 + FeO / 71.8]) values (45.7-52.1), suggesting evolved precursor magma The high values of La / Ta (22.2-42.8) and La / Nb (1.71-2.47), mildly negative εN d (t) values (-2.51-0.15), with depleted mantle model ages (TDM) of 2.45-2.84 Ga, suggest that their precursor magmas were possibly derived from a subduction-related fluid metasomatized Archean sub-continental lithospheric mantle. This study provides even evidence for oceanic plate subduction before or around ~ 1.85 Ga, which confirms a prolonged subduction-accretion-collision history in the NW China which is possibly possibly linked to the assembly of the Columbia supercontinent.