GRV021512和GRV021931:我国新发现的二块南极橄辉无球粒陨石的岩石学特征

取自南极格罗夫山两块橄辉无球粒陨石 ,GRV0 2 15 12陨石具有典型的橄辉陨石结构 ,由 48.3 %的橄榄石、9.4%的易变辉石和3 8.1%的碳质基质组成。而 GRV0 2 2 93 1则表现为碎裂结构 ,少量斑状橄榄石 (19.1% )和易变辉石 (14 .1% )镶嵌于富碳质基质 (66.3 % )中。两块陨石的粗粒橄榄石和易变辉石的核部成分均匀 ,成分落在橄榄石 -易变辉石橄辉无球粒陨石的富铁亚类之中。所有橄榄石颗粒的边缘和裂隙均具有还原环带。在富碳基质中金刚石与石墨共生呈团块和脉状产出 ,本文就两块陨石的岩石和金刚石的成因进行了讨论。GRV021512和GRV021931:…     

Exposure ages and radiogenic ages of ureilite(GRV 024516) and ordinary chondrite(GRV 024517) from Antarctica

The GRV 024516 and GRV 024517 meteorite samples collected from Grove Montains,Antactica are ureilite and H5 ordinary chondrite,respectively.Based on the study of mineralogy-petrology,the cosmic-ray exposure ages and gas retention ages of these two meteorites were determinated and calculated.Their cosmic-ray exposure ages are 33.3 Ma,51.7 Ma,and gas retention ages are 1936.8 Ma and 3720 Ma,respectively.The ureilite contains diamond,graphite and amorphous C,which are mainly carrier of noble gases indicating obviously shock metamorphism effects,which induced 40Ar partial loss.The H5 chondrite indicates thermal metamorphism of parent body,its gas retention age fall the range between 3220 Ma and 4510 Ma of the least shocked H5 chondrites     

我国在南极格罗夫山发现的首块古铜钙长无球粒陨石(GRV 150277)及其外源碎屑研究

HED(Howardite-Eucrite-Diogenite)族陨石及其可能母体灶神星是国际深空探测与小行星研究的热点。其中,经历了复杂撞击混合成岩作用而形成的Howardite(古铜钙长无球粒陨石),是研究灶神星表土层物质组成与演化这一国际前沿领域的主要对象。21世纪以来,中国在南极格罗夫山回收了大量陨石,这为我国行星科学的发展提供了重要的研究标本。我国目前已分类的南极陨石中发现有3块Eucrite陨石,其为研究灶神星岩浆活动提供了重要机遇。本次工作对2016年收集到的南极格罗夫山陨石GRV 150277进行了系统性岩石学与矿物学研究。研究结果表明GRV 150277具有典型的角砾结构,主要由近乎等比例的Diogenite陨石和Eucrite陨石碎屑组成,是我国在南极发现的第一块Howardite陨石。此外,GRV 150277中还可见少量的铁陨石与CM型陨石碎屑,表明灶神星表土层遭受了多种小行星撞击。GRV 150277陨石的发现及其外源碎屑的详细研究,对确定灶神星表土层物质组成与演化历史具有重要的指示意义。     

南极月球陨石MIL05035矿物学、岩石学及演化历史

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。     

南极碳质球粒陨石中两个富尖晶石球粒状难熔包体的岩石学和矿物化学特征

富尖晶石球粒状CAI(富Ca-Al难熔包体)是球粒陨石中一种特殊类型的CAI,在南极格罗夫山碳质球粒陨石GRV020025和GRV021579中共发现两个富尖晶石球粒状CAI———GRV020025-3RI8和GRV021579-3RI5。GRV020025-3RI8具有占统治地位的尖晶石,在球粒的最外边存在严重蚀变的不规则边,钙钛矿主要分布在靠近边的位置。与GRV020025-3RI8比较,GRV021579-3RI5的尖晶石中的钙钛矿消失,深绿辉石出现,薄薄的蚀变层位于尖晶石核和富钙辉石边之间。两个富尖晶石球粒状CAI的尖晶石均具有低含量FeO和ZnO的特征,而且GRV021579-3RI5具有较GRV020025-3RI8更高的TiO2含量。岩石学和矿物化学特征表明,GRV020025-3RI8和GRV021579-3RI5都经历过熔融结晶过程,它们的蚀变均发生在非氧化的含水或无水的环境中。     

Petrology of ureilites from Grove Mountains, Antarctica：Constraints on the origins

Ureilites are a common group of achondrites with a high abundance of carbon. They probably have a genetic relationship with chondrites, hence provide an insight into origin and evolution of terrestrial planets. A new meteorite-rich region, Grove Mountains (GRV), was found by the Chinese Antarctic Research Expedition, with discovery of 9834 meteorites. Of 2433 meteorites classified, 9 ureilites have been identified. In this paper, we report petrography of 6 of these ureilites. Four ureilites contain graphite and exhibit triangle conjunction and common reduced margins of olivine. GRV 052382 probably experienced heavy shock metamorphism followed by fast cooling, as indicated by mosaic texture or fine-grained granular texture of olivine. GRV 022931 was highly reduced of these ureilites, with olivine as isolated grains in abundant carbonaceous matrix. All 9 ureilites are monomict, and are classified into subtype II (with medium FeO content, Fa15-18) and subtype I (with high FeO content, Fa>18) based on compositions of the cores of olivine. The diverse mineral compositions and petrography of these ureilites suggest that they are not paired and reveal a multi-event history of the parent body. Partial melting of the parent body produced carbon-rich magma, followed by crystallization of graphite and silicates. Later, graphite was partially inverted to diamond by shock events. Reburial of the shocked debris experienced various degree of thermal metamorphism. Finally, these rocks were excavated from the parent asteroid and ejected into Earth-cross orbit by another impact event.     

橄辉无球粒陨石的矿物-岩石学特征及其分类

本文主要综述单矿和复矿碎屑橄辉无球粒陨石的矿物-岩石学特征及冲击变质效应,并依据Δ17O,δ13C,mg#[MgO/(MgO+FeO)mol%],稀有气体,辉石丰度及辉石类型讨论橄辉无球粒陨石的分类和成因模式。橄辉无球粒陨石为超基性的岩浆岩,既显示原始无球粒陨石,又显示分异无球粒陨石的一些特征,并认为是来自球粒陨石质母体的部分熔融,大多数典型的橄辉无球粒陨石具单矿碎屑岩的结构,复矿碎屑岩质橄辉无球粒陨石较少,其角砾岩碎片含单矿碎屑岩橄辉无球粒陨石的石屑碎屑及其它物质。橄辉无球粒陨石为原始和分异特征的混合物,其成因模式主要是超基性火成堆积岩或部分熔融的残余。     

西宁陨石的岩石学特征及其类型划分

西宁陨石具有典型的球粒结构,球粒轮廓依稀可辨-模糊,基质重结晶程度中-高等,次生斜长石粒度5-40μm,部分颗粒大于50μm。橄榄石和低钙辉石的化学成分均一：球粒中橄榄石Fa24.7-25.2,平均Fa24.9,相对标准偏差PMD值0.64%;低钙辉石Fs21.3-21.9 En 77.6-78.2 Wo 0.46-0.57,平均Fs21.5,Fs的PMD值0.84%。说明该陨石已达热力学平衡状态,为平衡型普通球粒陨石。根据该陨石结构构造特征、金属含量、矿物化学组成特征和热变质特征（平衡温度为778℃）,西宁陨石被划分为L群普通球粒陨石,岩石类型为5型,但已开始向6型过渡。该陨石的冲击变质程度为S3,风化程度W0。陨石母体形成之后遭受了冲击变质作用和热变质作用,导致原始球粒破碎、脱玻化和基质重结晶。     

格罗夫山普通球粒陨石的磁化率和化学分类方法对比分析

我国经过五次南极格罗夫山科学考察后,从南极格罗夫山地区回收到11452块陨石样品。南极陨石回收后面临着庞大的基础分类工作,需要确定其化学群和岩石类型。由于传统的化学分类方法不仅有损样品,而且样品制备耗时耗力,需要大量的经费和人力支持才能完成陨石的基础分类工作。因而国际上也在探索使用快速、无损的磁化率分类方法来确定陨石的类型。我国陨石基础分类工作得到科技部样品共享平台的资助,在2003年和2006-2008年期间开展了四次陨石分类工作,共确定了2300多块普通球粒陨石的化学群、岩石类型、冲击强度和风化程度。本文在基础分类工作的基础上,探讨这些样品的磁化率分析结果,并给出磁化率分类的适用范围及应用前景。     

Exposure ages and radiogenic ages of ureilite(GRV 024516) and ordinary chondrite(GRV 024517) from Antarctica

The GRV 024516 and GRV 024517 meteorite samples collected from Grove Montains,Antactica are ureilite and H5 ordinary chondrite,respectively.Based on the study of mineralogy-petrology,the cosmic-ray exposure ages and gas retention ages of these two meteorites were determinated and calculated.Their cosmic-ray exposure ages are 33.3 Ma,51.7 Ma,and gas retention ages are 1936.8 Ma and 3720 Ma,respectively.The ureilite contains diamond,graphite and amorphous C,which are mainly carrier of noble gases indicating obviously shock metamorphism effects,which induced 40Ar partial loss.The H5 chondrite indicates thermal metamorphism of parent body,its gas retention age fall the range between 3220 Ma and 4510 Ma of the least shocked H5 chondrites