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

Abstract

Cam Thuy Permian basalts consisting of thick lava flows and pyroclastic layers appear along both sides of the Song Ma fault zone in Thanh Hoa and in Son La and Ninh Binh provinces, NW Vietnam. The magmatism has been thought to have genetic relationship with Permian volcanism in the Song Da rift zone, which is believed to be part of the Emeishan large igneous province, having been extruded along the Red River shear zone following Paleogene India-Eurasian collision. A set of Cam Thuy volcanic samples including olivine and alkaline basalts was collected in the Lam Son area (Tho Xuan, Thanh Hoa province) to analyze for geochemical major, trace element and Sr-Nd-Pb isotopic composition. The Cam Thuy basalts are high-TiO 2 , CaO, FeO*, moderate MgO and SiO 2 that plot between the Song Da and Emeishan high-and low-Ti basalt distribution fields and closely overlap that of Song Da's high-Ti field. The primitive mantle and chondrite normalized trace element patterns of Cam Thuy basalts are essentially enriched oceanic island basalt (OIB)-like; this feature, together with crustal contamination-free, chondritic Sr, Nd and Pb initial (255Ma) isotopic composition are certainly of asthenospheric origin. These geochemical and isotopic characteristics are closely analogous to those features observed for the Song Da high-Ti basalts, suggesting similarity in their source of origin. Nevertheless, while the Song Da (and Emeishan) magmatism is signified by the presence of both high-and low-Ti basalts, with the latter being derived from heterogeneous and partially crustal-material contaminated sources in the lithospheric mantle, this low-Ti volcanic rock type has yet to be discovered in the Cam Thuy formation.

Geochemistry, zircon U–PB ages and HF isotopes of the Muong Luan granitoid pluton, Northwest Vietnam and its petrogenetic significance

“…Northwest Vietnam, a part of the Indochina Block, is made up of three major tectonic unites, namely: Song Ma and Song Da structural zones, and the Red River Shear Zone (Figure a,b; Hieu et al, ; Hoang et al, ). The Indosinian Orogeny is considered to be multiple subduction–collision events, resulting in the closure of a branch of the Paleo‐tethys (Carter & Clift, ; Carter, Roques, Bristow, & Kinny, ; Faure et al, ; Metcalfe, ).…”

Geochemical fingerprinting of Pleistocene stone tools from the Tràng An Landscape Complex, Ninh Bình Province, Vietnam

“…Based on proximity and previous studies, it was hypothesized that the stone tools made of rounded igneous cobble recovered from archaeological sites at Tràng An could be geochemically attributed to basalt from the Cam Thuy formation. Geochemical data are available for southwestern Cam Thuy basalts [ 52 ], so the decision was made to assess a previously unsampled source of Cam Thuy basalt in the Pù Luông Nature Reserve, roughly 80 km northwest of Tràng An to test this hypothesis.…”

Geochemistry of late miocene-pleistocene basalts in the Phu Quy island area (East Vietnam Sea): Implication for mantle source feature and melt generation

“…higher Nb) accompanying lower SiO 2 may suggest effect of high melting pressure and/or low degrees of partial melting. Arrow shows temporal evolution trend The positive correlation between the Nb/Y and Zr/Y ratios of the two basalt groups distributed along the limit field of ΔNb (ΔNb = 1.74 + log (Nb/Y) -1.92 Log (Zr/Y)) is an index reflecting the melting of mantle sources, the nature of source enrichment or depletion and the possibility of crustal contamination (Fitton et al, 1997;Hoang et al, 2016).The "low alkaline -high silica" basaltic group is characterized by low Nb/Y and low Zr/Y, distributed near the mid-ocean ridge basalt field, both depleted (N-MORB) and enriched mantle (E-MORB) (Kogiso et al, 1998;Relegous et al, 1999) (Figure 9), which is quite similar to the Dak Mil Neogene basalt (Dak Nong province, Western Highlands) (Hoang et al, 2013), that is interpreted to have been derived from a relatively depleted and refractory litho-sphere mantle or from sources that have undergone previous melting. The Phu Quy "high alkaline -low silica" basaltic group is distributed near the Hawaii and North Arch oceanic island basalt fields (after Norman and Garcia, 1999;Frey et al, 2000), and plotted in Pleiku Pleistocene field (Hoang, 2005a, Hoang et al, 2013 (Figure 9).…”