Synchrotron radiation X-Ray diffraction in situ study of fine-grained minerals in shock veins of Suizhou meteorite

Wang

2011

Sci. China Earth Sci.

Self Cite

The occurrence and mineral chemistry of chromite and its high-pressure phase xieite in the Suizhou meteorite were studied by different modern micromineralogical techniques. Three types of occurrences for chromite were observed in the Suizhou L6 chondrite: coarse chromite grains, cluster of chromite fragments in molten plagioclase, and exsolution lamellar chromite in olivine. All the chromite grains of the first two types are remarkably similar in chemical compositions, but the composition of exsolution chromite is inhomogeneous and variable in Al 2 O 3 content. Xieite is a post-spinel CT-phase of chromite firstly found in the Suizhou meteorite. Three types of occurrences of xieite have also been revealed in this meteorite: coarse xieite grains, complex three-zone-grains consisting of the inner xieite, the intermediate lamellae-like CF-phase and the outer chromite phase, and two-phase-grains consisting of xieite and one of the high-pressure silicate minerals lingunite, ringwoodite or majorite. The curved boundary between xieite and the silicate half in two-phase grains is indicative of some partial or even full melting of the silicate phase. EPMA and EDS results show that the compositions of xieite inside/contacting the shock veins are also identical to that of chromite outside the veins. However, some element diffusion appeared in between the xieite and the silicate half in the two-phase grains, namely, some of Al 3+ from lingunite, or Fe 2+ from ringwoodite migrated to xieite, and some of Cr 3+ migrated from xieite to lingunite or ringwoodite. Majorite in two-phase grains shows remarkable decrease of SiO 2 and MgO, and notable increase of Al 2 O 3 and CaO, indicating that its host mineral pyroxene was fully molten and mixed with the surrounding silicate melt of the vein matrix. The complexity in mineral chemistry of these two-phase grains in shock veins can be explained by the much higher shock peak temperature in shock veins (1800-2000°C) than in unmelted main body (~1000°C), and by the much lower density of the silicate minerals (2.6-3.3 g/cm 3 ) than that of chromite (4.43 g/cm 3 ). Being a refractory and a relatively high-impedance material, chromite is chemically more stable and easier to reflect shock wave into the silicate half causing the partial or even full melting of silicate phases, upon which some diffusion of elements between the two phases themselves, or even mixing of molten pyroxene and the surrounding silicate melt. Sci, 2011Sci, , 54: 998 -1010Sci, , doi: 10.1007 Chromite is a common opaque mineral with spinel structure in ordinary chondrites. Based on textures and assemblages, Ramdohr recognized 6 types of chromites in ordinary chondrites [1, 2]: (1) coarse chromite; (2) clusters of chromite aggregates; (3) pseudomorphous chromite; (4) exsolution chromite; (5) chromite chondrules, and (6) myrmekitic (or symplectitic) chromite. The coarse chromite type occurs in the overwhelming majority of ordinary chondrites, achondrites, stony irons, and iron meteorites as coarse euhedral to subhedral ...

show abstract

mentioning

confidence: 99%

Occurrence and mineral chemistry of chromite and xieite in the Suizhou L6 chondrite

Wang

2011

Sci. China Earth Sci.

Self Cite

show abstract

“…6). On the other hand, the coarse‐grained clast assemblage comprises different high‐pressure mineral phases that were formed through solid state transformation of silicate, phosphate, and oxide minerals (Xie et al. 2001, 2003, 2005; Chen et al.…”

Section: Resultsmentioning

confidence: 99%

The distinct morphological and petrological features of shock melt veins in the Suizhou L6 chondrite

Sun

Meteorit & Planetary Scien

2011

Self Cite

Abstract-The morphology and petrology of distinct melt veins in the Suizhou L6 chondrite have been investigated using scanning electron microscopy, electron microprobe analyses, and Raman spectroscopy, synchrotron energy-dispersive diffraction, and transmission electron microscopy. It is found that the melt veins in the Suizhou meteorite morphologically are the simplest, straightest, and thinnest among all shock veins known from meteorites. At first glance, these veins look like fine fractures, but petrologically they are solid melt veins of chondritic composition and consist of fully crystalline materials of two distinct lithological assemblages, with no glassy material remaining. The Suizhou melt veins contain the most abundant high-pressure mineral species when compared with all other veins known in chondrites. Thus, these veins in Suizhou are classified as shock veins. All rock-forming and almost all accessory minerals in the Suizhou shock veins have been transformed to their high-pressure polymorphs, and no fragments of the precursor minerals remain in the veins. Among the 11 high-pressure mineral phases identified in the Suizhou veins, three are new high-pressure minerals, namely, tuite after whitlockite, xieite, and the CF phase after chromite. On the basis of transformation of plagioclase into maskelynite, it is estimated that the Suizhou meteorite experienced shock pressures and shock temperatures up to 22 GPa and 1000°C, respectively. Shearing and friction along shock veins raised the temperature up to 1900-2000°C and the pressure up to 24 GPa within the veins. Hence, phase transition and crystallization of high-pressure minerals took place only in the Suizhou shock veins. Fast cooling of the extremely thin shock veins is regarded as the main reason that up to 11 shock-induced high-pressure mineral phases could be preserved in these veins.

show abstract

Micro-Mineralogical Investigative Techniques

Suizhou Meteorite: Mineralogy and Shock Metamorphism

2015