Early Cretaceous adakitic lavas and A-type rhyolites in the Songliao Basin, NE China: Implications for the mechanism of lithospheric extension

Much evidence points to a dramatic thinning of East Asian lithosphere during the Mesozoic, but with little precision on when, or over what time scale. Using geochemical constraints, we examine an extensive compilation of dated volcanic samples from Russia, Mongolia and North China to determine when the lithosphere thinned and how long that process took. Geochemical results suggest that magmatism before 107 Ma derived from metasomatised subcontinental lithospheric mantle (SCLM), whereas after 107 Ma, melt predominantly derived from an asthenospheric source. The switch to an asthenospheric magma source at ~107 Ma occurred in both Mongolia and North China (>1600 km apart), whereas in eastern Russia the switch occurred a little later (~85 Ma). Such a dramatic change to an asthenospheric contribution appears to have taken, from beginning to end, just ~30 Myrs, suggesting this is the duration for lithospheric mantle weakening and removal. Subsequent volcanism, through the Cenozoic in Mongolia and North China does not appear to include any contribution from the removed SCLM, despite melts predominantly deriving from the asthenosphere.

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Simultaneous and extensive removal of the East Asian lithospheric root.

Evidence for southward subduction of the Mongol-Okhotsk oceanic plate: Implications from Mesozoic adakitic lavas from Mongolia

Late Mesozoic volcanic rocks are widespread in the Great Xing’an Range (GXR), Northeast (NE) China. However, details of the tectono-magmatic evolution during the Late Mesozoic are poorly understood...

Geochronology and geochemistry of late Jurassic–Early Cretaceous volcanic rocks in the southern Great Xing’an range, NE China: constraints for late Mesozoic tectono-magmatic evolution

Petrogenesis and tectonic implications of Early Cretaceous volcanic rocks from the Shanghulin Basin within the north‐western Great Xing'an Range, NE China: Constraints from geochronology and geochemistry

This paper presents new geochemical and geochronological data of the Late Mesozoic volcanic rocks in East Mongolia. These volcanic rocks belong to high-K calc-alkaline and shoshonitic series and exhibit features of bimodal rocks. The mafic rocks have elevated incompatible trace element concentrations and significantly negative Nb, Ta, and Ti anomalies, with Sr-87/Sr-86(i) and Nd-&(t) values of 0.70502-0.70572 and -1.72459 to +1.720736, respectively, which suggest that the mafic magma was derived from a lithospheric mantle source that might have been metasomatized by subduction-derived fluids, experienced fractional crystallization, and was contaminated by crustal materials. The felsic rocks have similar rare earth element patterns to the mafic rocks but show much more significantly negative Eu and Sr anomalies. The felsic rocks have higher Sr-87/Sr-86(i) values of 0.706496-0.71104 than the mafic rocks but similar Nd-&(t) values (-0.28003 to +2.928506) to the mafic ones. These data indicate that the felsic rocks originated from partial melting of a crustal source that is dominated by juvenile mafic rocks. Our new K-Ar dating, together with previous data, shows that the Late Mesozoic volcanism in East Mongolia took place during the Late Jurassic-Early Cretaceous between ca. 155 and 99 Ma. The model of back-arc extension, possibly induced by slab rollback of the westward subducted Pacific Plate and the subduction zone retreat, can explain the geodynamic setting and the eastward younging trend of the Late Mesozoic volcanism in East Mongolia and in adjacent NE China.

Zhang Fochin

Papers

Petrogenesis and tectonic implication of the Late Mesozoic volcanic rocks in East Mongolia