Major, trace element, and Nd, Sr and Pb isotope studies of Cenozoic basalts in SE China: mantle sources, regional variations, and tectonic significance

Abstract

Introduction. Transtension is a system of stresses that tends to cause oblique extension, i.e. combined extension and strike slip. Syn-volcanic transtensional deformations of the lithosphere may provide two possible scenarios for control of magmatic processes. One scenario assumes ascending sub-lithospheric melts that mark the permeable lithosphere in a transtension area without melting of the lithospheric material; products of volcanic eruptions in such a zone show only the sub-lithospheric mantle material; components of magmatic liquids do not reveal any connection to the lithospheric structure. Another scenario yields a direct control of melting in lithospheric sources in an evolving transtensional structure. In this case, spatial-temporal changes of lithospheric and sub-lithospheric components are a direct indication of the evolving transtensional zone. In this paper, we present arguments in favor of the transtensional origin of the lithosphere-derived melting anomaly along the Wudalianchi volcanic zone, which are based on the study of components in the rocks sampled from the volcanic field of the same name.Analytical methods. Trace elements were determined by ICP-MS using a mass-spectrometer Agilent 7500ce and isotopes using a mass-spectrometer Finnigan MAT 262. The methods used were described in the previous papers by Rasskazov et al. [2011] and Yasnygina et al. [2015]. Major oxides were measured by "wet chemistry".Structural setting of the Wudalianchi zone. This zone extends north-south for 230 km at the northern circuit of the Songliao basin, subsided in the Late Mesozoic -Early Cenozoic (Fig. 1).Timing of volcanism and variations of K2O contents in rocks from the Wudalianchi zone. Rocks, dated back to the Pliocene and Quaternary, show the stepwise increasing K2O content interval along the Wudalianchi zone from the southernmost Erkeshan volcanic field (5.6-5.8 wt %) to the northernmost Xiaogulihe-Menlu volcanic field (2.0-9.5 wt %) (Fig. 2).Spatial-temporal clustering of volcanoes in the Wudalianchi field. In terms of the general Quaternary evolution of volcanism in Asia [Rasskazov et al., 2012], spatial-temporal distribution and compositional variations of volcanic products, we distinguish three time intervals of the volcanic evolution: (1) 2.5-2.0 Ma, (2) 1.3-0.8 Ma, and (3) <0.6 Ma. The Central group of volcanoes showed persistent shifting of eruptions from Wohushan (1.33-0.42 Ma) to to Laoheishan (1720-1721, possibly earlier) to Huoshaoshan (1721) (Figs 3, 4, 5). No spatial-temporal regularity of eruptions in volcanoes of the Erkeshan field and Western and Eastern groups of the Wudalianchi field reflected background activity.Sampling. Representative sampling of rocks from the Wohushan-Huoshaoshan volcanic line was aimed to identify changing geochemical signatures along the whole volcanic line and in the course of eruptions in each volcano (Figs 3, 6, 7). For comparisons, the background volcanoes were also sampled.Silica and alkalis oxides. On the total alkalis-silica (TAS) diagram (Fig. ...

Chalcophile elemental constraints on sulfide-saturated fractionation of Cenozoic basalts and andesites in SE China

“…The Cenozoic volcanic rocks in SE and NE China show different isotopic compositions due to varied SCLM compositions beneath the two regions (e.g., Zou et al, 2000). SE China is underlain by relatively young, middle to late Proterozoic continental lithosphere, whereas NE China is underlain by Archaean to early Proterozoic continental lithosphere (e.g., Chen and Jahn, 1998).…”

“…The volcanic rocks are predominantly basalts and are thought to have been derived from variable mantle sources (Chung et al, 1994;Fan and Hooper, 1991;Zhou and Armstrong, 1982;Zou et al, 2000). It is commonly accepted that basalts in SE China originated from a mixed source involving asthenospheric mantle and EM2, and that those in NE China were derived from a mixed source of asthenospheric mantle and EM1 (e.g.…”

“…It is commonly accepted that basalts in SE China originated from a mixed source involving asthenospheric mantle and EM2, and that those in NE China were derived from a mixed source of asthenospheric mantle and EM1 (e.g. Ho et al, 2000;Zou et al, 2000;Han et al, 2009).…”

K-Ar dating, geochemical and Sr-Nd-Pb isotopic systematics of Paleocene mafic rocks in Central Jiangxi, SE China: Evidence for lithosphere replacement

“…It is noted that the MORB normalized trace element patterns for these samples (Fig. 6) are similar to those of Late Cenozoic basalts in Southeast China (Peng et al, 1986;Flower et al, 1992;Liu et al, 1994;Qi et al, 1994;Chung et al, 1994Chung et al, , 1995Zou et al, 2000;Ho et al, 2003). The MORB-normalized multielement diagrams display small differences, for example the Luokou mafic rocks exhibit weak Rb positive anomalies and minor Ba negative anomalies, while the Tianxinggang rocks show weak Ba positive anomalies and minor Rb negative anomalies.…”

“…Irvine and Baragar (1971). The fields of Cretaceous mafic rocks and basalts (e.g., Lan et al, 1995;Lapierre et al, 1997;Li and McCulloch, 1998;Xiong et al, 2003;Xie et al, 2006) and Late Cenozoic basalts (e.g., Flower et al, 1992;Qi et al, 1994;Liu et al, 1994;Zou et al, 2000) in Cathaysia Block are shown for comparison. …”