Recycling lower continental crust in the North China craton

Abstract

Foundering of mafic lower continental crust into underlying convecting mantle has been proposed as one means to explain the unusually evolved chemical composition of Earth's continental crust, yet direct evidence of this process has been scarce. Here we report that Late Jurassic high-magnesium andesites, dacites and adakites (siliceous lavas with high strontium and low heavy-rare-earth element and yttrium contents) from the North China craton have chemical and petrographic features consistent with their origin as partial melts of eclogite that subsequently interacted with mantle peridotite. Similar features observed in adakites and some Archaean sodium-rich granitoids of the tonalite-trondhjemite-granodiorite series have been interpreted to result from interaction of slab melts with the mantle wedge. Unlike their arc-related counterparts, however, the Chinese magmas carry inherited Archaean zircons and have neodymium and strontium isotopic compositions overlapping those of eclogite xenoliths derived from the lower crust of the North China craton. Such features cannot be produced by crustal assimilation of slab melts, given the high Mg#, nickel and chromium contents of the lavas. We infer that the Chinese lavas derive from ancient mafic lower crust that foundered into the convecting mantle and subsequently melted and interacted with peridotite. We suggest that lower crustal foundering occurred within the North China craton during the Late Jurassic, and thus provides constraints on the timing of lithosphere removal beneath the North China craton.

Late Triassic high-Mg andesite/dacite suites from northern Hohxil, North Tibet: Geochronology, geochemical characteristics, petrogenetic processes and tectonic implications

“…The compositional disequilibrium characteristics of the augites suggest that the Hohxil high-Mg andesites were likely derived by interaction between melts and mantle (e.g., Rapp et al, 1999;Yogodzinski and Kelemen, 1998). However, the origin of the melts requires further clarification, given that similar melts have been attributed to partial melting of delaminated or subducted continental crust (e.g., Gao et al, 2004;Wang et al, 2006bWang et al, , 2008cXu et al, 2008), subducted basaltic oceanic crust, or sediments (e.g., Kay et al, 1993;Kelemen et al, 2003;Shimoda et al, 1998;Tatsumi, 2001;Tatsumi and Hanyu, 2003;Yogodzinski and Kelemen, 1998;Yogodzinski et al, 1994Yogodzinski et al, , 1995.…”

“…5-7). There are different models accounting for the petrogenesis of such highMg andesite-adakitic rock suites, including assimilation fractional crystallization (AFC) or fractional crystallization (FC) from parental basaltic magmas (Castillo et al, 1999;Macpherson et al, 2006), magma mixing between felsic and basaltic magmas (e.g., Streck et al, 2007), and interaction between melts and mantle (e.g., Gao et al, 2004; (Rapp et al, 1999(Rapp et al, , 2003, and references therein). The fields for delaminated lower crust, subducted oceanic crust, and thickened lower crust-derived adakitic rocks are after Wang et al (2006a, b).…”

Constraints from melt inclusions and their host olivines on the petrogenesis of Oligocene-Early Miocene Xindian basalts, Chifeng area, North China Craton

“…So far, two extreme models exist: the delamination model (e.g., Wu et al 2000Wu et al , 2003Gao et al 2002Gao et al , 2004Gao et al , 2008Chu et al 2009) and the thermal-mechanical erosion model (e.g., Griffin et al 1998;Menzies and Xu 1998;Xu 2001;Menzies et al 2007). In the delamination model, the thickened eclogitic lower crust, together with the lithospheric mantle below, delaminates into the convection mantle.…”

Big insights from tiny peridotites: Evidence for persistence of Precambrian lithosphere beneath the eastern North China Craton

“…Formation of dense, lower crustal eclogites and garnet clinopyroxenites, during Mesozoic crustal thickening, gave rise to gravitational instability through which the lower portion of lithosphere may have foundered en masse into the asthenosphere, leading to the production of new lithospheric mantle by passive upwelling and melting of hot asthenospheric material. This sequence of events is recorded in the Late Jurassic Xinglonggou high-Mg andesites, and later in the Early Cretaceous Sihetun high-Mg basalts, which have been interpreted to be derived from melting of eclogitic lower crust and mantle that was hybridized by eclogitic melts, respectively (Gao et al, 2004. Moreover, the Fuxin alkali basalts were derived by melting of asthenospheric mantle at a shallow depth (b65 km; Zhang and Zheng, 2003), implying an already thinned lithosphere by the time of eruption (~100 Ma).…”