Recycled oceanic crust in the source of 90-40 Ma basalts in North and Northeast China: Evidence, provenance and significance

The roles of subduction of the Pacific plate and the big mantle wedge (BMW) in the evolution of east Asian continental margin have attracted lots of attention in past years. This paper reviews recent progresses regarding the composition and chemical heterogeneity of the BMW beneath eastern Asia and geochemistry of Cenozoic basalts in the region, with attempts to put forward a general model accounting for the generation of intraplate magma in a BMW system. Some key points of this review are summarized in the following. (1) Cenozoic basalts from eastern China are interpreted as a mixture of high-Si melts and low-Si melts. Wherever they are from, northeast, north or south China, Cenozoic basalts share a common low-Si basalt endmember, which is characterized by high alkali, Fe 2 O 3 T and TiO2 contents, HIMU-like trace element composition and relatively low 206Pb/204Pb compared to classic HIMU basalts. Their Nd-Hf isotopic compositions resemble that of Pacific Mantle domain and their source is composed of carbonated eclogites and peridotites. The high-Si basalt endmember is characterized by low alkali, Fe 2 O 3 T and TiO2 contents, Indian Mantle-type Pb-Nd-Hf isotopic compositions, and a predominant garnet pyroxenitic source. High-Si basalts show isotopic provinciality, with those from North China and South China displaying EM1-type and EM2-type components, respectively, while basalts from Northeast China containing both EM1- and EM2-type components. (2) The source of Cenozoic basalts from eastern China contains abundant recycled materials, including oceanic crust and lithospheric mantle components as well as carbonate sediments and water. According to their spatial distribution and deep seismic tomography, it is inferred that the recycled components are mostly from stagnant slabs in the mantle transition zone, whereas EM1 and EM2 components are from the shallow mantle. (3) Comparison of solidi of garnet pyroxenite, carbonated eclogite and peridotite with regional geotherm constrains the initial melting depth of high-Si and low-Si basalts at and ~300 km, respectively. It is suggested that the BMW under eastern Asia is vertically heterogeneous, with the upper part containing EM1 and EM2 components and isotopically resembling the Indian mantle domain, whereas the lower part containing components derived from the Pacific mantle domain. Contents of H2O and CO2 decrease gradually from bottom to top of the BMW. (4) Melting of the BMW to generate Cenozoic intraplate basalts is triggered by decarbonization and dehydration of the slabs stagnated in the mantle transition zone.

Generation of Cenozoic intraplate basalts in the big mantle wedge under eastern Asia

The highly siderophile elements (HSE) consist of the Platinum Group Elements (PGE: Ru, Rh, Pd, Os, Ir, Pt) along with rhenium and gold. These transition elements show relative chemical inertness and high market values, which respectively earned them the additional names of noble metals and precious metals.

The HSE show a very pronounced affinity for iron metal, which translates into metal/silicate partition coefficients similar to or higher than 10,000 over large ranges of both pressure and temperature (e.g., O’Neill et al. 1995; Borisov and Palme 2000; Ertel et al. 1999, 2001, 2006, 2008; Fortenfant et al. 2003, 2006; Brenan et al. 2005; Cottrell and Walker 2006; Brenan and McDonough 2009; Laurenz et al. 2010; Mann et al. 2012; see Brenan et al. 2016, this volume for detailed review). Consequently, the HSE are thought to have been efficiently sequestered within the metallic core of our planet during the metal–silicate differentiation of Earth, leaving the silicate counterpart almost HSE-barren. Investigations of mantle peridotites since the 1970s revealed ng.g−1 level abundances as well as close-to-chondritic proportions of the HSE (Chou 1978; Jagoutz et al. 1979; Mitchell and Keays 1981; McDonough and Sun 1995; Becker et al. 2006; Fischer-Godde et al. 2011). Such abundances and inter-HSE fractionations are not predicted for the silicate Earth left after separation of the metallic core for low- or high-pressure core–mantle differentiation (see Brenan et al. 2016, this volume). The close agreement between the osmium isotopic compositions of fertile mantle peridotites and those of chondritic meteorites (Walker et al. 2002a), which requires nearly identical Re/Os ratios in these two reservoirs, provides particularly convincing evidence that the mantle’s HSE content cannot simply represent the residue left after core formation. …

Highly Siderophile Element and 187Os Signatures in Non-cratonic Basalt-hosted Peridotite Xenoliths: Unravelling the Origin and Evolution of the Post-Archean Lithospheric Mantle

The major and trace elements and H2O contents of minerals in peridotite xenoliths hosted by the Cenozoic basalts in Northeast China (NEC) were evaluated using electron microprobe, laser-ablation inductively coupled plasma–mass spectrometry and Fourier transform infrared spectroscopy, respectively. Although a potential loss of H during the xenoliths' ascent cannot be excluded for olivine, orthopyroxene (opx) and clinopyroxene (cpx) largely preserved the H2O contents of their mantle source in all of the samples, as inferred from (1) the homogenous H2O contents within single pyroxene grains and (2) the equilibrium H2O partitioning between cpx and opx. No OH was detected for pyroxenes of peridotite xenoliths from the north part of NEC (NNEC). Combined with previously published data from the North China Craton (NCC) and the South China Block (SCB), the regional heterogeneity in the water contents in the Cenozoic lithospheric mantle beneath the whole Eastern China has been revealed. The lithospheric mantle beneath the NNEC is completely dry. The “bulk” water contents of the lithospheric mantle of the south part of NEC and the NCC have similar ranges and average values, whereas those of the SCB are much higher (12–195 ppm, average 90 ± 45 ppm for whole rock). The regional variations in the H2O content of the Cenozoic lithospheric mantle of Eastern China cannot be caused by partial melting, mantle metasomatism, or variations in redox state. We propose that the lithospheric mantle beneath the different regions of Eastern China may have distinct origins and may have undergone distinct geodynamic processes.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015JB012105

Regional heterogeneity in the water content of the Cenozoic lithospheric mantle of Eastern China

https://espace.library.uq.edu.au/view/UQ:363965/UQ363965_OA.pdf

Composition of the Tarim mantle plume: Constraints from clinopyroxene antecrysts in the early Permian Xiaohaizi dykes, NW China

Petrology, geochemistry and Re-Os isotopes of peridotite xenoliths from Yantai, Shandong Province: Evidence for Phanerozoic lithospheric mantle beneath eastern North China Craton

Hong Zhang

Papers

Petrology, geochemistry and Re-Os isotopes of peridotite xenoliths from Yantai, Shandong Province: Evidence for Phanerozoic lithospheric mantle beneath eastern North China Craton