南极月球陨石MIL05035矿物学、岩石学及演化历史
发布时间：2018-09-04 10:56
【摘要】：月球陨石MIL05035岩石类型上属于普通辉石低钛玄武岩,粗粒辉长结构,无角砾化。主要矿物为辉石(60.2%)、斜长石(27.3%)和橄榄石(6.05%),次要矿物为石英(4.36%)、钛铁矿(1.25%)和陨硫铁(0.84%),含极少量富Ti、Fe尖晶石和磷灰石,广泛发育由钙铁辉石+铁橄榄石+石英组成的后成合晶三相集合体。辉石颗粒具有明显的化学成分不均匀性和出溶片晶,核部相对贫铁钙富镁(Fs30.2-60.8Wo14.2-35.0),边部富铁钙贫镁(Fs47.5-64.9Wo22.8-44.3)。熔长石化斜长石具有微弱的成分环带,边部相对富碱金属元素(Ab9.3-12.3,Or0.31-1.03),核部则相反(Ab7.6-10.6,Or0.12-0.36),含有未熔长石化的残留斜长石。橄榄石具有粗晶橄榄石(Fa95.5-96.6)和后成合晶中细粒橄榄石(Fa88.9-93.5)两种产状。石英具有脉状、团块状和蠕虫状等产状:脉状石英大部分转变为二氧化硅玻璃,核部石英具有较宽的拉曼谱特征峰(448~502cm-1),证明其经历了冲击变质与退变质作用;团块状石英分布于粗粒橄榄石颗粒间或橄榄石与斜长石和辉石接触边界上,与斜长石构成充填结构;蠕虫状石英分布于细粒后成合晶中。粗粒辉石边部铁辉石和后成合晶中辉石成分的继承性、结构上的延续性、光学特征上的冲击暗化现象、与冲击熔脉结构上的相关性和后成合晶中发育与粗粒辉石方向几乎一致的解理等方面的证据,认为后成合晶可能由于铁辉石在冲击压力释放与温度降低后的退变质作用下分解形成。根据岩石矿物结构观察、成分分析和MELTS模拟表明该陨石母岩的岩浆演化过程可能为:母岩浆在温度降低后首先产生极少量钛铁尖晶石、其次是普通辉石和钙长石先后结晶;随着温度下降,贫钙铁普通辉石、铁钙铁辉石和铁普通辉石等在普通辉石边部大量结晶,钙长石边部分异结晶少量培长石或拉长石;随着温度继续下降,早期结晶的普通辉石析出易变辉石等出溶片晶,橄榄石在辉石和斜长石边部结晶;其后,钛铁矿和陨硫铁析出,石英沿橄榄石和钙长石等先结晶矿物裂隙充填。出露月表后强烈的冲击变质作用使斜长石几乎全部转变为熔长石、石英大部分转变为二氧化硅玻璃,并具有一系列面状变形,冲击熔脉发育,冲击变质程度至少为S5。本研究为月球的岩浆演化和冲击变质过程提供了重要证据。
[Abstract]:The MIL05035 rock type of lunar meteorite belongs to ordinary pyroxene low titanium basalt with long structure of coarse grain and no breccia. The main minerals are pyroxene (60.2%), plagioclase (27.3%) and olivine (6.05%), secondary minerals are quartz (4.36%), ilmenite (1.25%) and meteorite (0.84%), and contain a very small amount of Ti,Fe rich spinel and apatite. The post-eutectic three-phase aggregates composed of calcium-ferroxene iron olivine quartz are widely developed. The pyroxene particles have obvious chemical composition inhomogeneity and exsolution tablets, the core is relatively poor in iron, calcium and magnesium (Fs30.2-60.8Wo14.2-35.0), and the edge part is rich in iron, calcium and magnesium (Fs47.5-64.9Wo22.8-44.3). The feldspar plagioclase has a weak composition ring with relatively alkali rich metal elements (Ab9.3-12.3,Or0.31-1.03) in the edge and Ab7.6-10.6,Or0.12-0.36 in the nucleus, which contains the residual plagioclase from the unmelted petrifaction. Olivine has two types of occurrences: coarse olivine (Fa95.5-96.6) and fine olivine (Fa88.9-93.5) in post-syntectic crystal. Most of the vein-like quartz is converted to silica glass, and the nuclear quartz has a wide Raman spectrum characteristic peak (448~502cm-1), which indicates that the quartz has undergone impact metamorphism and retrograde metamorphism. Block quartz distributes between coarse olivine grains or olivine contact boundary with plagioclase and pyroxene and forms filling structure with plagioclase while wormlike quartz distributes in fine post-grain eutectic. The inheritance of pyroxene composition, the continuity of structure, and the impact darkening of optical characteristics in the edge of the coarse pyroxene and the post eutectic. Evidence of the correlation with the structure of the impact melting pulse and the cleavage of the development of coarse-grained pyroxene in the post-eutectic, It is considered that the post-eutectic may be due to the decomposition and formation of ferroxene due to the retrograde metamorphism of impingement pressure release and temperature reduction. According to the observation of rock mineral structure, the composition analysis and MELTS simulation indicate that the magmatic evolution process of the meteorite parent rock may be as follows: the mother magma first produces a very small amount of titaniferrite after lowering the temperature, and then the ordinary pyroxene and calcium feldspar crystallize successively; With the decrease of temperature, the poor calcium iron ordinary pyroxene, the iron calcium iron pyroxene and the iron ordinary pyroxene crystallized in a large number at the edge of the ordinary pyroxene, and a small amount of heterocrystalline or elongate on the side of the calcium feldspar; The early crystallized ordinary pyroxene precipitated with volatile pyroxene, and olivine crystallized at the edge of pyroxene and plagioclase, then ilmenite and meteorite precipitated, and quartz was filled with cracks along the first crystalline minerals such as olivine and calcium feldspar. The strong impact metamorphism made the plagioclase transform into meltmorillonite almost entirely, and most of the quartz changed into silica glass, with a series of surface deformation, the impact melting vein developed, and the impact metamorphism degree was at least S5. This study provides important evidence for magmatic evolution and impact metamorphism on the moon.
【作者单位】： 桂林理工大学 广西隐伏金属矿产勘查重点实验室;桂林理工大学地球科学学院;
【基金】：国家自然科学基金项目(41173077) 广西隐伏金属矿产勘查重点实验室主任基金项目(13-A-01-02)联合资助
【分类号】：P185.83;P588.145
[Abstract]:The MIL05035 rock type of lunar meteorite belongs to ordinary pyroxene low titanium basalt with long structure of coarse grain and no breccia. The main minerals are pyroxene (60.2%), plagioclase (27.3%) and olivine (6.05%), secondary minerals are quartz (4.36%), ilmenite (1.25%) and meteorite (0.84%), and contain a very small amount of Ti,Fe rich spinel and apatite. The post-eutectic three-phase aggregates composed of calcium-ferroxene iron olivine quartz are widely developed. The pyroxene particles have obvious chemical composition inhomogeneity and exsolution tablets, the core is relatively poor in iron, calcium and magnesium (Fs30.2-60.8Wo14.2-35.0), and the edge part is rich in iron, calcium and magnesium (Fs47.5-64.9Wo22.8-44.3). The feldspar plagioclase has a weak composition ring with relatively alkali rich metal elements (Ab9.3-12.3,Or0.31-1.03) in the edge and Ab7.6-10.6,Or0.12-0.36 in the nucleus, which contains the residual plagioclase from the unmelted petrifaction. Olivine has two types of occurrences: coarse olivine (Fa95.5-96.6) and fine olivine (Fa88.9-93.5) in post-syntectic crystal. Most of the vein-like quartz is converted to silica glass, and the nuclear quartz has a wide Raman spectrum characteristic peak (448~502cm-1), which indicates that the quartz has undergone impact metamorphism and retrograde metamorphism. Block quartz distributes between coarse olivine grains or olivine contact boundary with plagioclase and pyroxene and forms filling structure with plagioclase while wormlike quartz distributes in fine post-grain eutectic. The inheritance of pyroxene composition, the continuity of structure, and the impact darkening of optical characteristics in the edge of the coarse pyroxene and the post eutectic. Evidence of the correlation with the structure of the impact melting pulse and the cleavage of the development of coarse-grained pyroxene in the post-eutectic, It is considered that the post-eutectic may be due to the decomposition and formation of ferroxene due to the retrograde metamorphism of impingement pressure release and temperature reduction. According to the observation of rock mineral structure, the composition analysis and MELTS simulation indicate that the magmatic evolution process of the meteorite parent rock may be as follows: the mother magma first produces a very small amount of titaniferrite after lowering the temperature, and then the ordinary pyroxene and calcium feldspar crystallize successively; With the decrease of temperature, the poor calcium iron ordinary pyroxene, the iron calcium iron pyroxene and the iron ordinary pyroxene crystallized in a large number at the edge of the ordinary pyroxene, and a small amount of heterocrystalline or elongate on the side of the calcium feldspar; The early crystallized ordinary pyroxene precipitated with volatile pyroxene, and olivine crystallized at the edge of pyroxene and plagioclase, then ilmenite and meteorite precipitated, and quartz was filled with cracks along the first crystalline minerals such as olivine and calcium feldspar. The strong impact metamorphism made the plagioclase transform into meltmorillonite almost entirely, and most of the quartz changed into silica glass, with a series of surface deformation, the impact melting vein developed, and the impact metamorphism degree was at least S5. This study provides important evidence for magmatic evolution and impact metamorphism on the moon.
【作者单位】： 桂林理工大学 广西隐伏金属矿产勘查重点实验室;桂林理工大学地球科学学院;
【基金】：国家自然科学基金项目(41173077) 广西隐伏金属矿产勘查重点实验室主任基金项目(13-A-01-02)联合资助
【分类号】：P185.83;P588.145
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