The Gaojiacun Mafic-Ultramafic Complex (Sichuan, SW China):Neoproterozoic Magmatic Activity at the Western Margin of the Yangtze Craton

摘要

The Neoproterozoic Gaojiacun intrusive complex (GIC) is composed of one big intrusion (ca.9 × 7.5 km) and numerous satellite intrusions, emplaced in the low-grade schists of the Neoproterozoic Yanbian Group. The main intrusion is concentrically zoned, with peridotite bodies + leucogabbroids in its core (inner zone) and the sequence: olivine hornblende gabbronorite - porphyric pyroxene hornblende gabbronorite (transitional zone) - pyroxenehornblende gabbronorite + hornblende gabbro + diorite (outer zone), towards the margins. The satellite intrusions are composed either of a single rock type (peridotite, gabbro, diorite or granite) or of different rock types (peridotite + diorite + granite).Upper crustal contamination is evidenced by the occurrence of numerous metamorphic enclaves,migmatites and mixed rocks in the outer zone of the main intrusion and in the satellite intrusions.Hornblende (often oikocrystic) is present in all mafic and ultramafic rocks. Cu-Ni (-PGE) deposits occur in several satellite intrusions, hosted in peridotite. The geochemical and mineralogical features of GIC support the presence of a subduction zone at the western edge of the Yangtze Craton. A feeder-related genesis of the satellite intrusions is inferred.