Mafic dykes derived from Early Cretaceous depleted mantle beneath the Dabie orogenic belt: implications for changing lithosphere mantle beneath Eastern China

Abstract

SHRIMP zircon U-Pb geochronological, elemental and Sr-Nd isotopic data from Early Cretaceous mafic dykes in North Dabie orogenic belt elucidate a change of Mesozoic lithospheric mantle in eastern China. The dykes are predominantly dolerite with the major mineral assemblage clinopyroxene þ hornblende þ plagioclase and yield a SHRIMP zircon U-Pb age of 111.6 AE 5.3 Ma. They have a narrow range of SiO 2 from 46.16% to 49.78%, and relative low concentrations of K 2 O (1.07À2.62%), Na 2 O (2.45À3.54%), Al 2 O 3 (13.04À14.07%), and P 2 O 5 (0.42À0.55%) but relatively high concentration of MgO (5.94-6.61%) with Mg # 52-54. All the samples are characterized by enrichment of large ion lithophile elements (LILE, e.g., Ba, Th) and high field strength elements (HFSE, e.g., Nb, Ti). ( 87 Sr/ 86 Sr) i ratios from 0.704 to 0.705, e Nd values from 3.36 to 4.33 and mantle-depletion Nd model ages (T 2DM ) in the range 0.56-0.64 Ga indicate that the magma of the Baiyashan mafic dykes was derived from a young depleted mantle source. This finding is different from previous research on mafic dykes in the age range 120-138 Ma that revealed enrichment of LILE and depletion of HFSE, high initial Sr isotopic ratios and negative e Nd , value which represents an old enriched mantle source. Ours is the first report of the existence of Early Cretaceous depleted mantle in eastern China and it implies that changing of enriched mantle to depleted mantle occurred at ca. 112 Ma, associated with back-arc extension which resulted from the subduction of the Palaeo-Pacific Plate towards the Asian Continent.

An Early Cretaceous garnet-bearing metaluminous A-type granite intrusion in the East Qinling Orogen, central China: Petrological, mineralogical and geochemical constraints

“…Histogram of 3 Nd (120 Ma) values from the Erlangmiao granite, the Paleoproterozoic granitic gneisses (Zhang et al, 1994 and our two unpublished data), the Early Cretaceous granites (Zhou et al, 2008), and the mafic dikes (Chen et al, 2010). of zircon, apatite, and ilmenite.…”

“…8) (Zhou et al, 2008) and Nd model ages (w2.0 Ga) of the Early Cretaceous granites and the formation age of the Paleoproterozoic granitic gneisses are also similar, whereas the 3 Nd (120 Ma) values of the Erlangmiao granite (À6.6 to À9.0) are less negative and its Nd model ages (1.5e1.7 Ga) are younger. Considering the gradually increased role of the asthenosphere during the Early Cretaceous in the QinlingeDabie region (Chen et al, 2010), we infer that partial melting of the Paleoproterozoic granitic gneisses formed Early Cretaceous granites, subsequently, with participation of depleted mantle, continuous partial melting possibly produced the Erlangmiao granite.…”

40Ar–39Ar age and geochemistry of subduction-related mafic dikes in northern Tibet, China: petrogenesis and tectonic implications

“…In contrast, samples from an asthenospheric mantle (e.g. OIB) usually show LILE and HFSE enrichment (Zou et al 2000) and have similar Sr-Nd isotope compositions as a depleted mantle (Chen et al 2011a). The Xiaomiao mafic dikes are characterized by relatively low TiO 2 (0.71-1.64%), enrichment of LILE and LREE and depletion of HFSE such as Nb, Ta, and Ti relative to the primitive mantle ( Figure 5) and resembles a lithospheric mantle.…”

Geochemistry of Early Cretaceous Intermediate to Mafic Dikes in the Jiaodong Peninsula: Constraints on Mantle Source Composition beneath Eastern China

“…Knowledge about the nature and evolution of the lithospheric mantle can give important clues about these geological events. Although numerous papers have already discussed the petrology and geochemistry of xenoliths from mantle perido-tites or mantle-derived intrusive rocks in the NCC (e.g., Gao et al 2002;Zhang et al , 2008Wu et al 2006;Xu et al 2010) and the Dabie-Sulu orogen (e.g., Jahn et al 1999;Wang et al 2005;Liu et al 2008b;Tang et al 2009;Chen et al 2011;Xu et al 2012;Ma et al 2014b;Cai et al 2015), direct information about the mantle beneath the southeastern margin of the NCC during the Early Cretaceous cannot be easily reconciled, because of the scarcity of material that comes from the mantle. However, Early Cretaceous mafic dikes are widely distributed in the Jiaodong Peninsula (Yang et al 2004;Cai et al 2013).…”