西北非 7042 中间 Shergottite 的岩石成因、蚀变和冲击历史：火星上含水岩浆作用的证据？,Geochimica et Cosmochimica Acta

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西北非 7042 中间 Shergottite 的岩石成因、蚀变和冲击历史：火星上含水岩浆作用的证据？
Geochimica et Cosmochimica Acta ( IF 4.5 ) Pub Date : 2020-08-01 , DOI: 10.1016/j.gca.2020.05.030
T.V. Kizovski , M.R.M. Izawa , K.T. Tait , D.E. Moser , J.M.D. Day , B.C. Hyde , L.F. White , L. Kovarik , S.D. Taylor , D.E. Perea , I.R. Barker , B.R. Joy

摘要西北非 (NWA) 7042 是一种中性、永固性辉石，由两代橄榄石（早期分带橄榄石 Fo41-76 和后期铁橄榄石型橄榄石 Fo46-56）、复杂分带辉石（En35-64Fs22-46Wo5-34）组成、冲击熔解或蒙脱石化长石 (An5-30Ab16-61Or1-47)，以及附属的磷灰石、磷灰石、钛铁矿、钛磁铁矿、Fe-Cr-Ti 尖晶石、磁黄铁矿和斜铅矿。带状橄榄石颗粒已被广泛修饰，包含显眼的棕色富镁核心，周围环绕着无色、未改变的富铁过度生长边缘。这种结构关系表明，在火星边缘结晶之前，岩心在岩浆温度下发生了变化。NWA 7042 中发射产生的激波脉也横切并取代了几个改变的橄榄石颗粒，表明改变发生在陨石喷射之前。虽然这种类型的橄榄石蚀变在橄榄岩中很少见，但它类似于地球上玄武岩和辉长岩中的氘蚀橄榄石，由残余的富含水的岩浆流体引起。橄榄石蚀变的透射电子显微镜分析没有揭示该过程预期的高温相；然而，NWA 7042 也受到了广泛的陆地风化，这可以解释它们的缺失。NWA 7042 中可能存在氘代改变的橄榄石具有重要意义，因为它是第三颗观察到橄榄石氘代改变的火星陨石（其他是 NWA 10416 和 Allan Hills 77005）。

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Petrogenesis, alteration, and shock history of intermediate shergottite Northwest Africa 7042: Evidence for hydrous magmatism on Mars?

Abstract Northwest Africa (NWA) 7042 is an intermediate, permafic shergottite consisting of two generations of olivine (early zoned olivine Fo41-76, and late-stage fayalitic olivine Fo46-56), complexly zoned pyroxene (En35-64Fs22-46Wo5-34), shock-melted or maskelynitized feldspar (An5-30Ab16-61Or1-47), and accessory merrillite, apatite, ilmenite, titanomagnetite, Fe-Cr-Ti spinels, pyrrhotite, and baddeleyite. The zoned olivine grains have been pervasively modified, containing conspicuous brown Mg-rich cores surrounded by colorless, unaltered Fe-rich overgrowth rims. This textural relationship suggests that the cores were altered at magmatic temperatures prior to crystallization of the rims on Mars. Launch-generated shock veins in NWA 7042 also crosscut and displace several of the altered olivine grains indicating that alteration occurred before ejection of the meteorite. While this type of olivine alteration is rare in shergottites, it is similar to deuterically altered olivine in basalts and gabbros on Earth, caused by residual water-rich magmatic fluids. Transmission electron microscopy analysis of the olivine alteration did not reveal the high-temperature phases expected from this process; however, NWA 7042 has also been subjected to extensive terrestrial weathering, which may explain their absence. The potential presence of deuterically altered olivine in NWA 7042 has significant implications, as it is the third martian meteorite where deuteric alteration of olivine has been observed (the others being NWA 10416, and Allan Hills 77005). The different mantle sources for the parental melts of these three meteorites would suggest many, if not all martian mantle reservoirs have the potential to produce water-rich magmas.

更新日期：2020-08-01

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