Late Mesozoic mafic magmatism from the North China Block: constraints on chemical and isotopic heterogeneity of the subcontinental lithospheric mantle

Abstract

Available major, trace element and Sr–Nd isotope data for the late Mesozoic mafic rocks in the eastern North China Block (NCB) show chemical and isotopic differences between rocks from different tectonic units. Such differences are interpreted as signatures inherited from the melted mantle sources, which had experienced distinctive enrichment processes during lithospheric evolution. The subcontinental lithospheric mantle beneath the NCB interior is characterized by long-term light REE (LREE) enrichment and EM1-like Sr–Nd isotopic signatures. Such a lithospheric mantle is mainly composed of chemically refractory peridotites that are common in cratonic regions. In contrast to that of the NCB interior, beneath the northern part of the NCB a relatively chemically fertile mantle was enriched in large ion lithophile elements and LREE and depleted in Nb–Ta and Th–U. It has higher 87Sr/86Sr(i) and εNd(t) than that of the interior of the block, and is interpreted to have been modified by recycled lower continental crust components related to the palaeo-Asian Ocean subduction. The lithospheric mantle beneath the southern NCB has the highest 87Sr/86Sr(i) and the lowest εNd(t), and is chemically transitional between the interior and northern part of the block. Formation of such an enriched lithospheric mantle was closely associated with modification from the subducted Yangtze lower–middle crust during Triassic collision between the North China and Yangtze Blocks. A lithospheric extension–thinning model is proposed to explain the petrogenesis of these late Mesozoic mafic rocks in the eastern North China Block. This process was amplified by effects from surrounding plate interactions, including the rapid northward movement of the palaeo-Pacific Ocean, compressional forces from the Siberian plate, the Tethyan tectonic belt and possibly the Indo-China Block. The resultant forces triggered lithospheric extension, asthenospheric upwelling, and decompressional melting of the enriched mantle sources.

Field relation, geochemistry and origin of the Xinglonggou volcanic rocks in Beipiao area, Liaoning Province (China): Reappraisal on the foundering of lower continental crust of North China Craton

“…This feature is distinguished from those of Mesozoic igneous rocks in the North China Craton (e.g. Chen and Chen, 1997;Fan et al, 2007;Guo et al, 2007) …”

“…12 and 13). Compared with other Mesozoic igneous rocks of the North China Craton, the Xinglonggou volcanic rocks exhibit young and immature characteristics of radiogenic isotopes similar to those of the Late Paleozoic-Mesozoic igneous rocks of the Xing'an-Inner Mongolia Orogenic Belt (Chen and Chen, 1997;Jahn et al, 1999;Wu et al, 2002;Jahn, 2004;Gao et al, 2005;Fan et al, 2007;Guo et al, 2007;Huang et al, 2007). Consequently, it is inferred that the source of the Xinglonggou volcanic rocks is different from those of the Mesozoic igneous rocks of the North China Craton (Figs.…”

“…As a useful ''petrological tool'' deciphering the deep dynamic process, the high-magnesium igneous rocks had attracted considerable attention over the last decade (e.g. Griffin et al, 1998;Zhang et al, 2003Zhang et al, , 2004Gao et al, 2004Gao et al, , 2008Xu et al, 2004;Chen et al, 2007;Fan et al, 2007;Guo et al, 2007;Zhang, 2007). Among these rocks, the Xinglonggou volcanic rocks occurred in western Liaoning Province, the NE part of North China Craton are the only known samples that formed in early or middle Jurassic (Chen and Chen, 1997;Gao et al, 2004).…”

Formation of mafic magmas through lower crustal AFC processes — An example from the Jinan gabbroic intrusion in the North China Block

“…All Mesozoic mafic rocks in NCB show arc-like trace element characteristics, enriched Sr-Nd-Hf isotopic signatures and variable Pb isotopic compositions, which are unlikely to be attributed to crustal contamination or assimilation of asthenosphere-derived magmas such as MORBs and OIBs (e.g., Fan et al, 2007). Also, there was no evidence for the existence of a mantle plume during the Mesozoic beneath the NCB.…”

“…These enrichment processes will accumulate time-integrated evolved isotopic compositions in the subcontinental lithospheric mantle relative to their oceanic counterparts. Many papers have attempted to distinguish between the effects of crustal vs. lithospheric sources and/or contaminants in the petrogenesis of continental mafic magmas, such as those of the Mesozoic mafic rocks in the North China Block (NCB) (e.g., Fan et al, 2007;Gao et al, 2008;Guo et al, 2001;Qian and Hermann, 2010;Yang et al, 2007;Zhang et al, 2002Zhang et al, , 2004.…”