Major element, trace element, and Sr, Nd and Pb isotope studies of Cenozoic basalts from the South China Sea

Abstract

The whole rock K-Ar ages of basalts from the South China Sea basin vary from 3.8 to 7.9 Ma, which suggest that intra-plate volcanism after the cessation of spreading of the South China Sea (SCS) is comparable to that in adjacent regions around the SCS, i.e., Leiqiong Peninsula, northern margin of the SCS, Indochina block, and so on. Based on detailed petrographic studies, we selected many fresh basaltic rocks and measured their major element, trace element, and Sr-Nd-Pb isotope compositions. Geochemical characteristics of major element and trace element show that these basaltic rocks belong to alkali basalt magma series, and are similar to OIB-type basalt. The extent of partial melting of mantle rock in source region is very low, and magma may experience crystallization differentiation and cumulation during the ascent to or storing in the high-level magma chamber. Sr-Nd-Pb isotopic data of these basaltic rocks imply an inhomogeneous mantle below the South China Sea. The nature of magma origin has a two end-member mixing model, one is EM2 (Enriched Mantle 2) which may be originated from mantle plume, the other is DMM (Depleted MORB Mantle). Pb isotopic characteristics show the Dupal anomaly in the South China Sea, and combined with newly found Dupal anomaly at Gakkel ridge in Arctic Ocean, this implies that Dupal anomaly is not only limited to South Hemisphere. In variation diagrams among Sr, Nd and Pb, the origin nature of mantle below the SCS is similar to those below Leiqiong peninsula, northern margin of the SCS and Indochina peninsula, and is different from those below north and northeast China. This study provides geochemical constraints on Hainan mantle plume.Cenozoic alkali basalt, Dupal anomaly, Hainan mantle plume, the South China Sea, geochemistry.

Petrogenesis of Late Cenozoic basalts from North Hainan Island: Constraints from melt inclusions and their host olivines

“…Having erupted in a continental intra-plate tectonic setting (Yan et al, 2008), the second hypothesis can be ruled out for the Hainan basalts and, as discussed in Section 5.3 there is little evidence for crustal contamination in the Hainan basalts (Zou and Fan, 2010). Therefore, we argue that a recycled gabbro component was involved in the source region of the Hainan basalts.…”

“…Cenozoic continental intra-plate basalts are widespread in Southeast China, the South China Sea Basin and the Indo-China Peninsula (Zhou and Armstrong, 1982;Hoang et al, 1996;Chung et al, 1997;Zhou and Mukasa, 1997;Hoang and Flower, 1998;Ho et al, 2000Ho et al, , 2003Zou et al, 2000;Fedorov and Koloskov, 2005;Yan et al, 2008;Zou and Fan, 2010;Wang et al, 2012Wang et al, , 2013Fig. 1a), defining a potentially 'diffuse' igneous province in Southeast Asia (Hoang et al, 1996).…”

Opening and evolution of the South China Sea constrained by studies on volcanic rocks: Preliminary results and a research design

“…K-Ar dating of the samples dredged from the north slope of East Reed bank yield very young ages of 2.7-0.4 Ma [51]. Yan et al [52] reported K-Ar ages of basalts from the same area which range from 7.91-3.80 Ma.…”

“…From the limited distribution of volcanism and available seismic profiles in the northern margin of the SCS, the South China continental margin does not share these characteristics, perhaps implying that the opening of the SCS was not caused by a mantle plume [52]. Likewise, the fact that all the OIB-type basalts were emplaced during the post-spreading stage, even if these rocks resulted from melting of the Hainan plume, suggests that the mantle plume may not be responsible for the opening of the SCS.…”

Tracing the life history of a marginal sea—On “The South China Sea Deep” Research Program

“…Judging from the data available up to now, magmatic activities in the SCS occurred mostly after but only rarely before spreading. All the trawled basalt samples form the SCS postdate the oceanic crust and should represent the products of post-spreading magmatism [26][27][28]. The most prominent post-spreading magmatism includes the volcanic sea-mount chains in the deep basin, many of which are ranged along the relict spreading ridges and lacking a systematic investigation.…”