Melilite-derived mineral inclusions in chromite from the Gaositai complex: Implications for an extensional tectonic setting in Early Permian at the north North China Craton

Abstract

The Early Permian mafic-ultramafic concentrically zoned Gaositai intrusion at Chengde, on the northern margin of the North China Craton (NCC), is a cumulative complex emplaced along a giant fracture that penetrates deeply into the continental lithosphere. Melt inclusions are present in chromite crystals from the inner dunite and chromitite zones of the Gaositai complex. The melt inclusions have experienced post-trap crystallization and resulted in multiple mineral phases, including melilite, garnet, phlogopite, magnesite and apatite, which can indicate the liquidus minerals of the primitive magma. The characteristics of the melilite+melanite+clinopyxene assemblage indicate that the primary parental magma was highly undersaturated and derived from an alkali-rich mantle source. The crystallization of phlogopite, magnesite and apatite suggests a primary magma rich in K, H 2 O and CO 2 . When compared with experimental data, the primary magma of the Gaositai intrusion is concordant with a kamafugite magma originating from partial melting of enriched mantle with H 2 O and CO 2 at pressures greater than 2.7 GPa. This magmatic process would have been related to extensional thinning of the continental lithosphere. The Gaositai primary magmas have high Nb/La ratios, which are similar to those of ocean island basalts, but different from arc-related magmas. This suggests that the northern margin of the NCC was not an active continental margin of the Paleo-Asian Ocean subduction zone during the Early Permian: an extensional tectonic setting during the emplacement of the Gaositai intrusion is more likely. Citation:Shao J A, Tian W, Wei C J, Zhu W P. 2016. Melilite-derived mineral inclusions in chromite from the Gaositai complex: Implications for an extensional tectonic setting in

Tectonic evolution of the Middle-Late Permian orogenic belt in the eastern part of the CAOB: Implications from the magmatism in the Changchun-Kaiyuan area

“…Furthermore, more tectonic models have been proposed to explain the tectonic affiliation of the eastern PAO during the Permian. These models include the continental rift model (Shao et al 2015), continent-continent collision model (Zhang et al 2007), post-orogenic extension model (Zhang et al 2007; Zhao et al . 2008), slab break-off model (Yuan et al 2016) and slab roll-back model (Li et al 2016, 2017).…”