Siderophile Element Compositions of Pyroxenes in HED Meteorites: Implications for the Differentiation of Magma Ocean on Vesta

1 Introduction The howardite,eucrite and diogenite(HED)meteorites are ultramafic and mafic igneous rocks and impact-engendered breccias derived from a thoroughly differentiated asteroid 4 Vesta.Diogenites include dunites,

Behavior of Siderophile and Chalcophile Elements in the Subcontinental Lithospheric Mantle beneath the Changbaishan Volcano,NE China

The mantle xenoliths in the Quaternary ChangbaishanVolcano in southern Jilin Province contain spinel-facies lherzolites. The equilibration temperatures for these samples range from 902℃ to 1064℃ based on the two-pyroxene thermometer of Brey and Kohler （1990）, and using the oxybarometry of Nell and Wood （1991）, the oxidation state was estimated from FMQ-1.32 to -0.38 with an average value of FMQ-0.81 （n = 8）, which is comparable to that of abyssal peridotites and the asthenospheric mantle. ThefO2 values of peridotites, together with their bulk rock compositions （e.g., Mg#, Al2O3, CaO, Ni, Co, Cr） and mineral compositions （e.g., Mg# of olivine and pyroxene, Cr# [=Cr/ [Cr＋Al]] and Mg# [=Mg/[Mg＋Fe2~] of spinel）, suggest that the present-day subcontinental lithospheric mantle （SCLM） beneath the Changbaishan Volcano most likely formed from an upwelling asthenosphere at some time after the late Mesozoic and has undergone a low degree of partial melting. The studied lherzolite xenoliths show low concentrations of S, Cu, and platinum group elements （PGE）, which plot a flat pattern on primitive-mantle normalized diagram. Very low concentrations in our samples suggest that PGEs occur as alloys or hosted by silicate and oxide minerals. The compositions of the studied samples are similar to those of peridotite xenoliths in the Longgang volcanic field （LVF） in their mineralogy and bulk rock compositions including the abundance of chalcophile and siderophile elements. However, they are distinctly different from those of peridotite xenoliths in other areas of the North China Craton （NCC） in terms of Cu, S and PGE. Our data suggest that the SCLM underlying the northeastern part of the NCC may represent a distinct unit of the newly formed lithospberic mantle.

Late veneer and the origins of volatiles of Earth

Late veneer is an important paradigm in early Earth and planetary studies.It refers to the late addition of extraterrestrial materials to the Earth’s mantle after the core formation,which leads to the overabundances of highly siderophile elements in the primitive upper mantle.In this review,the origin,evolution,and expansion of the late veneer hypothesis are summarized,including some unresolved problems.I hope this review would be helpful for the new entrants to this field.

Geochemical models of core-mantle differentiation

The core-mantle differentiation process is one of the most significant events in the Earth’s early history,which profoundly affects the Earth’s internal structure.According to the simple core-mantle differentiation mechanism,elements such as iron and nickel should be extracted from silicate to form an iron-rich proto-core,and the residual silicate materials form the proto-mantle.However,the composition of the lower mantle and the core remains controversial,which largely affects the partition of elements,thus the referred differentiation process of the Earth.In recent years,many experimental studies on the partition coefficient of siderophile elements between metal and silicate under high-temperature and high-pressure conditions have put forward new ideas on the issues around Earth’s core-mantle differentiation.Meanwhile,some researchers suggested that the redox state of the Earth’s mantle changes during its formation and evolution,and many isotope geochemistry studies support that some enstatite chondrites have a common nebular precursor as the Earth.These new studies bring dispute on the Earth’s building materials,which dominates the core-mantle differentiation process and largely affects the partitioning behaviors of elements during the core-mantle differentiation.This chapter aims to review recent experimental studies on the siderophile element geochemistry and discussions on the Earth’s building blocks.