Dhofar 1180月球陨石的岩相学和矿物化学研究

Petrographic and mineralogical studies of the lunar meteorite Dhofar 1180.

Dhofar 1180是一块新发现于阿曼地区的月球陨石,属混合岩质月球角砾岩。本文报道了Dhofar 1180的岩相学和矿物化学特征。该陨石含有辉长岩、斜长岩质辉长岩、辉长质斜长岩、橄长岩和微斑熔融角砾岩等多种类型岩屑,同时还存在含钛玻屑和长石质玻屑。主要的晶屑矿物有橄榄石、辉石、斜长石、和金属氧化物。辉长质斜长岩、橄长岩和微斑熔融角砾岩等岩屑中橄榄石相对富镁(Fo_(55～69)),斜长岩质辉长岩岩屑中橄榄石相对富铁(Fo_(31)),含钛玻屑中橄榄石包体成分变化较大(Fo_(7～54))。晶屑橄榄石相对富铁,且成分变化较大(Fo_(2～46))。Fe/Mn摩尔比主要在69～113之间变化(平均值为93),且Fe-Mn摩尔数变化趋势与典型的月球橄榄石一致。辉长质斜长岩、橄长岩、微斑熔融角砾岩等岩屑和含钛玻屑中的辉石相对贫钙,主要为易变辉石(分别为En_(63)Fs_(32)Wo_5,En_(66)Fs_(23)Wo_(11),En_(55)Fs_(38)Wo_7和En_(57)Fs_(35)Wo_8),而斜长岩质辉长岩和辉长岩岩屑中的辉石和晶屑辉石的成分变化比较大(分别为En_(31～33)Fs_(35～48)Wo_(19～34),En_(18～48)Fs_(23～51)Wo_(24～38)+En_(1～9)Fs_(65～86)Wo_(14～26)和En_(11～53)Fs_(23～63) Wo_(6～36),为易变辉石和普通辉石,以及少量三斜铁辉石。含钛玻屑中辉石含有较高的Al_2O_3(2.79%)和TiO_2(1.57%)含量。辉石的Fe/Mn摩尔比主要在50～70之间变化(平均值为63),且其Fe-Mn摩尔数变化趋势也与典型的月球辉石一致。斜长石主要是钙长石,含有少量的Na_2O,An组分范围是91～98。金属氧化物主要为钛铁尖晶石-铬铁矿-尖晶石固溶体,存在少量的钛铁矿。Dhofar 1180的矿物学、岩石学和微量元素地球化学特征与已知的月球陨石和月岩样品有明显的差异,它来自月球表面的一个新的未知地区。对Dhofar 1180的矿物学、岩石学和化学成分的研究将更大地丰富我们对月球表面物质组成和演化的全面认识。

Dhofar 1180 is a newly found lunar meteorite in Oman. Here we report the detailed petrography and mineralogy of this new lunar meteorite with the hope to better understand of the geological processes on the Moon and the chemical composition of the lunar crust. Dhofar 1 180 is a basalt-bearing feldspathic lunar breccia, containing various types of lithic clasts （ gabbro, anorthositic gabbro, gabbroic anorthosite, troctolite, and microporphyritic crystalline impact melt breccia）. Ti-bearing clasts and anorthositic melt clasts were also observed. Major mineral fragments include olivine, pyroxenes, plagioclase, and some opaque oxides. Olivine grains in gabbroic anorthosite, troctolite, and microporphyritic crystalline impact melt breccia are relatively enriched in Mg （Fo55-69 ） , whereas those in anorthositic gabbro are relatively enriched in Fe （ Fo34 ）. Olivine grains in Ti-bearing clasts show a wide compositional range （ Fo7 -54 ）- Olivine fragments in the matrix are generally Fe-rich （ Fo2 -46 ）- Fe/Mn molar ratios in olivine range from 69 to 1 13 with an average of 93, consistent with the lunar olivine trend. Pyroxene grains in gabbroic anorthosite, troctolite, microporphyritic crystalline impact melt breccia, and Ti-bearing clasts are mainly low-Ca pigeonite （ En63 Fs32 Wo5 , En66 Fs23 WoH , En55 Fs3s Wo7 , and En57 Fs35 Wos, respectively）, and those in anorthositic gabbro, gabbro, and the matrix display a wide range of composition En31～33 FS35～48 WO19～34,En18～48 FS23～51 WO24～38＋En1～9 FS65～86 WO14～26,En11～53 FS23～63WO6～36,respectively）, mainly occurring as pigeonite, augite, and trace amounts of pyroxferroite. Pyroxene grains in Ti-bearing elasts contain relatively high Al2O3 （ 2.79% ） and TiO2 （ 1.57% ）. Fe/Mn molar ratios in pyroxene vary from 50 to 70 with an average of 63, in good agreement with the lunar pyroxene trend. Plagioclase grains in Dhofar 1180 are highly anorthitie （An91-98 ）- Opaque oxide minerals include ehromite-spinel-ulvt^spinel solid solution and minor ilmenite. Dhofar 1180 is a unique lunar meteorite that differs petrographically and geochemically from all other lunar meteorites and lunar samples. It comes from a region on the lunar surface that has not been sampled by any other known lunar rocks. Dhofar 1180 thus enhances our understanding of the mineral and chemical compositions of the lunar surface.