TY - JOUR

T1 - Majorite-olivine-high-Ca pyroxene assemblage in the shock-melt veins of Pervomaisky L6 chondrite

AU - Bazhan, Ivan S.

AU - Litasov, Konstantin D.

AU - Ohtani, Eiji

AU - Ozawa, Shin

PY - 2017/6/1

Y1 - 2017/6/1

N2 - High-pressure minerals majorite-pyrope garnet and jadeite were found in the Pervomaisky L6 ordinary chondrite. Majorite-pyrope (79 mol% majorite) was observed within the fine-grained silicate matrix of a shock-melt vein (SMV), coexisting with olivine and high-Ca pyroxene. This is the first report of a garnet olivine high-Ca pyroxene assemblage that crystallized from the melt in the SMV matrix of meteorite. P-T conditions of the formation of the SMV matrix with olivine fragments are 13.5-15.0 GPa and 1750-2150 degrees C, the lowest parameters among all known majorite-bearing (H,L)-chondrites. The estimated conditions include the olivine/(olivine + ringwoodite) phase boundary and there is a possibility that observed olivine is the result of wadsleyite/ringwoodite back-transformation during a cooling and decompression stage. In the framework of this hypothesis, we discuss the problem of survival of the high-pressure phases at the post-shock stage in the meteorites and propose two possible P-T paths: (1) the high-pressure mineral is transformed to a low-pressure one during adiabatic decompression above the critical temperature of direct transformation; and (2) quenching below the critical temperature of direct transformation within the stability field of the high-pressure phase and further decompression. The aggregates with plagioclase composition (Ab(81 1)An(14 9)Or(4.1)) occur in host-rock fragments near (or inside) of the SMV, and have a radial, concentric "spherulite-like" microstructure previously described in the Novosibirsk meteorite, and that is very similar to the texture of tissintite in the Tissint martian meteorite. It is likely that jadeite is related to crystallization of the SMV and could have formed from albitic feldspar (plagioclase) melt at 13.5-15.0 GPa and similar to 2000 degrees C.

AB - High-pressure minerals majorite-pyrope garnet and jadeite were found in the Pervomaisky L6 ordinary chondrite. Majorite-pyrope (79 mol% majorite) was observed within the fine-grained silicate matrix of a shock-melt vein (SMV), coexisting with olivine and high-Ca pyroxene. This is the first report of a garnet olivine high-Ca pyroxene assemblage that crystallized from the melt in the SMV matrix of meteorite. P-T conditions of the formation of the SMV matrix with olivine fragments are 13.5-15.0 GPa and 1750-2150 degrees C, the lowest parameters among all known majorite-bearing (H,L)-chondrites. The estimated conditions include the olivine/(olivine + ringwoodite) phase boundary and there is a possibility that observed olivine is the result of wadsleyite/ringwoodite back-transformation during a cooling and decompression stage. In the framework of this hypothesis, we discuss the problem of survival of the high-pressure phases at the post-shock stage in the meteorites and propose two possible P-T paths: (1) the high-pressure mineral is transformed to a low-pressure one during adiabatic decompression above the critical temperature of direct transformation; and (2) quenching below the critical temperature of direct transformation within the stability field of the high-pressure phase and further decompression. The aggregates with plagioclase composition (Ab(81 1)An(14 9)Or(4.1)) occur in host-rock fragments near (or inside) of the SMV, and have a radial, concentric "spherulite-like" microstructure previously described in the Novosibirsk meteorite, and that is very similar to the texture of tissintite in the Tissint martian meteorite. It is likely that jadeite is related to crystallization of the SMV and could have formed from albitic feldspar (plagioclase) melt at 13.5-15.0 GPa and similar to 2000 degrees C.

KW - jadeite

KW - L6 chondrite Pervomaisky

KW - olivine high-Ca pyroxene majorite-pyrope assemblage

KW - shock-melt vein history

KW - GARNET TRANSFORMATION

KW - (MG

KW - 6 GPA

KW - JADEITE

KW - TEMPERATURES

KW - CALORIMETRIC MEASUREMENTS

KW - CONSTRAINTS

KW - PHASE-RELATIONS

KW - ALBITE

KW - HIGH-PRESSURE MINERALS

UR - http://www.scopus.com/inward/record.url?scp=85020683428&partnerID=8YFLogxK

U2 - 10.2138/am-2017-5892

DO - 10.2138/am-2017-5892

M3 - Article

AN - SCOPUS:85020683428

VL - 102

SP - 1279

EP - 1286

JO - American Mineralogist

JF - American Mineralogist

SN - 0003-004X

IS - 6

ER -