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Analysis of the thermal metamorphism of the ordinary chondrites is a key premise for gaining insights into the accretion and heating of rocky bodies in the early solar system. Such an analysis also represents an essential condition for constraining the early thermal and evolutionary histories of asteroids and terrestrial planets. Classifying ordinary chondrites into petrologic type (type 3–6) is the criterion for studying the thermal metamorphism of their parent bodies. However, the boundary between the unequilibrated (type 3) and equilibrated (type 4–6) chondrites is ambiguous at present, thus, limiting the understanding of their thermal metamorphism. In this study, the petrology, mineralogy and chemical composition of a set of seven ordinary chondrites with different degrees of thermal metamorphism collected from Grove Mountains (Antarctica) have been studied. The results demonstrated that these chondrite samples were L3.7, L3.8, L3.9, L3.9/4, L4, L5 and L6 type meteorites, with optimal correlations of Si, Mg, Fe, Mn and Ca with equilibrium degree of the olivine and low-calcium pyroxene and petrologic type. In this respect, the multi-parameter classification standard PMD (SiO2)-PMD (MgO)-PMD (MnO)-PMD (CaO) based on the percent mean deviation (PMD) of the chemical compositions of the olivine and low-calcium pyroxene was proposed to distinguish between the unequilibrated and equilibrated meteorites. The proposed standard exhibited high "resolution" in terms of classification, thus, also deepening the understanding of the effect of the silicate mineral composition in the thermal metamorphism of chondrites.

Howardite-Eucrite-Diogenite (HED) meteorite clan is a potential group of planetary materials which provides significant clues to understand the formation and evolution of the solar system. Grove Mountains (GRV) 13001 is a new member of HED meteorite, recovered from the Grove Mountains of Antarctica by the Chinese National Antarctic Research Expedition. This research work presents a comprehensive study of the petrology and mineralogy, chemical composition, noble gas isotopes, cosmic-ray exposure (CRE) age and nominal gas retention age for the meteorite GRV 13001. The output data indicate that GRV 13001 is a monomict basaltic eucrite with typical ophitic/subophitic texture, and it consists mainly of low-Ca pyroxene and plagioclase with normal eucritic chemical compositions. The noble gas based CRE age of the GRV 13001 is approximately 29.9 ± 3.0 Ma, which deviates from the major impact events or periods on the HED parent body. Additionally, the U,Th-4He and 40K-40Ar gas retention ages of this meteorite are ~2.5 to 4.0 Ga and ~3.6 to 4.1 Ga, respectively. Based on the noble gases isotopes and the corresponding ages, GRV 13001 may have experienced intense impact processes during brecciation, and weak thermal event after the ejection event at approximately 30 Ma.

We report a petrography, mineral chemistry, oxygen and chromium isotopic study of Grove Mountains (GRV) 020043 together with a subset of other acapulcoites and lodranites. GRV 020043 is a petrologic type 4 chondrite, with chondrules of diverse types and sizes, and is composed of low-Ca pyroxene (40 vol.%), olivine (24 vol.%), diopside (8 vol.%), plagioclase (10 vol.%), Fe-Ni metal (kamacite and taenite), troilite and some accessory minerals (chromite and apatite). The olivine in GRV 020043 has an average fayalite content (Fa) of 10.7 mol.% with the low-Ca pyroxene having an average ferrosilite content (Fs) of 10.8 mol.%. The whole rock oxygen isotopic composition of GRV 020043 is +3.226 ± 0.267‰, +0.797 ± 0.131‰, and −0.927 ± 0.017‰ for δ18O, δ17O, and Δ17O, respectively, with a bulk chromium isotopic compositions of e54Cr = −0.48 ± 0.10. These characteristics of GRV 020043 are different from all established or ungrouped chondrites but agree with those of the acapulcoite-lodranite clan. We therefore suggest that GRV 020043 represents the chondritic precursor of acapulcoite-lodranite parent body. The similarity of bulk oxygen and chromium isotopic compositions among GRV 020043, Acapulco, Northwest Africa (NWA) 468 (metal-rich lodranite), NWA 8118 (lodranite), NWA 8287 (acapulcoite), and NWA 8422 (lodranite) indicates that they originated from a common oxygen and chromium reservoir in the protoplanetary disk or may have derived from a parent body with a differentiated multilayer structure.

Ureilites share the characteristics of differentiated meteorites and of primary chondrites. GRV 024237 is a ureilite, which was found in the 19th Chinese National Antarctic Research Expedition (CHINARE), at the No. 4 moraine, Grove Mountains, Antarctica. GRV 024237 consists mainly of coarse-grained olivine (60 vol%), pigeonite (30 vol%) and opaque minerals (10 vol%). Tri-junction texture between olivine and pigeonite is common. Carbonaceous materials with minor amounts of troilite and nickel-iron metal were observed as interstitial phases. The Fa value of olivine composition varies from 6.2 to 16.8 from rim to core, but pyroxene is homogeneous in composition, with Fs 14.0 to 15.5. Both olivine and pyroxene have normal extinctions. Net-like iron or limonite veins filled in the fractures of olivine and pyroxene, and no diamond was observed. Based on petrographic and mineralogical features, GRV 024237 is a Type I and Group 2 monomict ureilite.

A combined Raman spectroscopy and electron probe microanalysis study of the heavily shocked Grove Mountains (GRV) 052049 meteorite revealed the largest chemical fractionation of natural ringwoodite, and composition-dependent variation of the intensities and/or wavenumbers of Raman bands. With Fa content [atomic ratio of Fe/(Fe+Mg)] of ringwoodite varying from 27.8 to 81.6 mol%, the peak position of the single band around 290 cm−1 (SB1), which relates to the SiO4 translation mode, shifts from 296.0 to 284.6 cm−1, and one of the doublets around 790 cm−1 (DB1), which relates to the symmetric stretching of SiO4, shifts from 796.3 to 782.7 cm−1. In addition, the relative intensities of SB1 and the other band of the doublet around 840 cm−1 (DB2), which relates to asymmetric stretching of SiO4, increases with Fa content. Based on the paired Raman-EPMA data, single-peak and two-peak calibrations were established, which can be used to derive Fa contents of ringwoodite from the Raman spectra. The accuracy of Raman-derived Fa content of ringwoodite is better than ±5 mol%. The correlation of SB1 intensity with the Fa content of ringwoodite suggests that the vibration of SB1 is enhanced with the substitution of Mg2+ by Fe2+. The correlation between Raman spectra and the chemical composition of ringwoodite have potential applications in on-line measurement of high-pressure experiments and in situ mineralogical determination in future planetary explorations.

Petrography and mineral chemistry of two new ureilites, GRV 021512 and 022931, from the Grove Mountains, Antarctica, are reported in this paper. GRV 021512 exhibits a typical ureilite texture, and consists of 48.3% olivine, 9.4% pigeonite and 38.1% carbonaceous interstitial material and/or reduction product. GRV 022931 has a cataclastic porphyritic texture, and consists of 19.1% olivine and 14.1% pigeonite embedded in 66.3% carbonaceous interstitial material and/or reduction product. The coarse-grained olivine and pigeonite in both meteorites have homogeneous cores, and they are FeO-rich within the range of the ferroan subgroup (subgroup I) of olivine-pigeonite ureilites. All olivine grains of the meteorites show reduction zones along boundaries and cracks. Abundant diamond coexists with graphite as graphite-rich patches and veins in the carbonaceous interstitial material. Petrogenesis of both meteorites and the origin of diamond are discussed.

Twenty-four refractory inclusions (40-230 μm, with average of 86 ± 40 μm) were found by X-ray mapping of 18 ordinary chondrites. All inclusions are heavily altered, consisting of finegrained feldspathoids, spinel, and Ca-pyroxene with minor ilmenite. The presence of feldspathoids and lack of melilite are due to alteration that took place under oxidizing conditions as indicated by FeO-ZnO-rich spinel and ilmenite. The pre-altered mineral assemblages are dominated by two types: one rich in melilite, referred to as type A-like, and the other rich in spinel, referred to as spinel-pyroxene inclusions. This study and previous data show similar type and size distributions of refractory inclusions in ordinary and enstatite chondrites. A survey of refractory inclusions was also conducted on Allende and Murchison in order to make unbiased comparison with their counterparts in other chondrites. The predominant inclusions are type A and spinel-pyroxene, with average sizes of 170 ± 130 μm (except for two mm-sized inclusions) in Allende and 150 ± 100 μm in Murchison. The relatively larger sizes are partially due to common conglomerating of smaller nodules in both chondrites. The survey reveals closely similar type and size distributions of refractory inclusions in various chondrites, consistent with our previous data of other carbonaceous chondrites. The petrographic observations suggest that refractory inclusions in various groups of chondrites had primarily formed under similar processes and conditions, and were transported to different chondrite-accreting regions. Heterogeneous abundance and distinct alteration assemblages of refractory inclusions from various chondrites could be contributed to transporting processes and secondary reactions under different conditions.

We report the petrography, mineral chemistry and oxygen isotopic composition of GRV 99027, a new Martian meteorite recently collected during the 16th Chinese Antarctic Research Expedition. This meteorite consists of two textural regions. The interstitial region is characterized by the presence of plagioclase and phosphate, and higher FeO contents of olivine and orthopyroxene, in comparison with the poikilitic region. All of the observations are similar to the three known Martian lherzolites. We classify GRV 99027 as the fourth sample of Martian lherzolite.

Grove Mountains (GRV) 020090 is an enriched lherzolitic shergottite, distinct from other lherzolitic shergottites, except RBT 04262/1. Its characteristics include high abundance of plagioclase (24.2 vol% in the nonpoikilitic area), presence of K-feldspar, common occurrence of baddeleyite, high FeO contents of olivine (bimodal peaks at Fa 33 mol% and Fa 41 mol%) and low-Ca pyroxenes (bimodal peaks at Fs 23.8–31.7 mol% and Fs 25.7–33.9 mol%), and significant LREE enrichment of phosphates (500–610 × CI). The bulk composition of GRV 020090 suggests derivation from partial melting of an enriched reservoir. However, the REE patterns of the cores of pigeonite oikocrysts and the olivine chadacrysts are indistinguishable from those of GRV 99027 and other moderately depleted lherzolitic shergottites, and reveal a LREE-depleted pattern of the primordial parent magma. We propose that the primordial parent magma of GRV 020090 was derived from a moderately depleted Martian upper mantle reservoir, and later the residual melt was contaminated by oxidized and enriched Martian crustal materials as it ascended up to the subsurface. GRV 020090 and RBT 04262/1 may have sampled an igneous unit different from other lherzolitic shergottites.