Geochemistry and petrogenesis of Permian ultramafic-mafic complexes of the Jinping–Song Da rift (southeastern Asia)

Abstract

The Jinping–Song Da rift structure in the Emeishan Large Igneous Province is composed of Permian high- and low-Ti volcanic and volcanoplutonic ultramafic-mafic associations of different compositions and genesis. High-Ti picrites, picrobasalts, basalts, and dolerites are enriched in LREE and depleted in HREE and show low Al2O3/TiO2 ratios (~4), commensurate εNd(T) values (+0.5 to +1.1), and low (Th/Nb)PM ratios similar to those of OIB-enriched mantle source. The established geochemical characteristics evidence that the parental melts of these rocks were generated from garnet lherzolite at the depths of garnet stability (~200 to 400 km). Later, high-Mg low-Ti volcanics (komatiites, komatiitic basalts, and basalts) and associating small peridotite-gabbro massifs and komatiite-basalt dikes were produced as a result of ~20% partial melting of depleted water-poor (≤0.03 wt.% H2O) peridotite substratum from the hottest upper part of mantle plume at relatively shallow depths (100–120 km). The LREE-depleted komatiites and komatiitic basalts are characterized by low (Ce/Yb)CH values, 187Re/188Os = 0.05–1.2, 87Sr/86Sr = 0.704–0.706, positive εNd(T) values (+3 to +8), γOs = –0.5 to +0.9, and strong negative anomalies of Ba, K, and Sr on the spidergrams. The scarcer LREE-enriched komatiites, komatiitic basalts, and basalts vary greatly in chemical composition and values of εNd(t) (+6.4 to –10.2), 87Sr/86Sr (0.706–0.712), and γOs (+14.8 to +56), which is due to the different degrees of crustal contamination of parental magmas. The Rb-Sr isotopic age of basaltic komatiite is 257 ± 24 Ma. The Re-Os age determined by analysis of 12 komatiite samples is 270 ± 21 Ma. These data agree with the age of flood basalts of the Emeishan Large Igneous Province. The komatiite-basalt complex of the Song Da rift is still the only Phanerozoic PGE-Cu-Ni-complex of this composition. The geochemistry of accompanying Cu-Ni-PGE-ores confirms their relationship with komatiite-basaltic magmatism.

Triassic tectonics of the Ailaoshan Belt (SW China): Early Triassic collision between the South China and Indochina Blocks, and Middle Triassic intracontinental shearing

“…(e. g. Lepvrier et al, 1997;Trung et al, 2006;Pham et al, 2008;Nguyen et al, 2013) Permian alkaline mafic rocks of the Song Da rift are petrographically and geochronologically similar to those cropping out near Jinping, as already acknowledged (e.g. Wang et al, 2007;Balykin et al, 2010). However, the Tu Lê acidic volcanic and sedimentary rocks and the contemporaneous alkaline granites (e.g.…”

Petrography and geochemistry of Permian basalts of the Cam Thuy formation and their relation to Song Da and Emeishan magmatic rocks

“…)-basalt association in the Nam Muoi, Pa Uon and Deo Chen areas (Fig. 1a) (Polyakov et al, 1991;Balykin et al, 1996Balykin et al, , 2010Chung et al, 1997;Tran Trong Hoa et al, 1998, 2008Hanski et al, 2004;Nguyen Hoang et al, 2004, 2016a.…”

“…Low-Ti rock type is lower in Nb, Ta, lighter rare earth elements and higher in MgO and SiO 2 relative to the high-Ti magma type (Balykin et al, 2010;Xu et al, 2001Xu et al, , 2004. Trace element and isotopic characteristics of the Cam Thuy basalts are essentially oceanic island basalt (OIB)-like, approximated to Song Da high-Ti basalts (Figs.…”

“…Late Permian mafic, ultramafic and felsic pluton-volcanic magmatic fields are widespread in the Song Da rift zone, including Cam Thuy, Vien Nam-Ba Vi, Kim Boi -Hoa Binh, Son La Pass, Bac Yen -Van Yen, Deo Chen, Nam Muoi, Nam So, Sin Ho and other areas (Polyakov et al, 1992(Polyakov et al, , 1996Balykin et al, 1996Balykin et al, , 2010Hoang et al, , 2016aTran et al, 2011 (Figure 1a). Figure 1a.…”

“…Several authors (e.g. Tran et al, , 2002Tran et al, , 2011Hanski et al, 2004;Balykin et al, 2010) have suggested that the Song Da volcanic rocks are geochemically comparable to magmatic rocks in the Emeishan large igneous province (LIP) in SW China, which was formed by melting of deep mantle sources under the influence of a hot, deep-rooted plume (Chung and Jahn, 1995;Chung et al, 1997). The Song Da and Cam Thuy magmatic rocks are thus considered as a portion of Emeishan (E)-LIP that was extruded southeastward between the Song Ma and Red River fault zones following the India-Eurasian collision in the late Paleogene (about 30 Ma) (Chung et al, 1997;Wang et al, 2007;after Gilder et al, 1996).…”