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1.
H_s型恩施球粒陨石K-Ar年龄为4503±91Ma,~(40)Ar-~(39)Ar坪年龄为4518±8Ma,总气体年龄为4515±23Ma,等时线年龄为4505±16Ma,年龄的一致性表明该陨石未经受过明显的热扰动,它是我国首次发现的Ar保存年龄高达45亿年以上的陨石。陨石形成早期有过短期的快速冷却。陨石母体在4.66±0.04Ma时破裂。恩施球粒陨石原始捕获(~(40)Ar/~(36)Ar)_t为0.89±0.44,推测4.5Ga前太阳风中~(40)Ar/~(36)Ar近于l。 相似文献
2.
稀有气体及宇宙射线暴露(CRE)年龄是研究月球陨石辐射历史的重要媒介,其能够反演陨石所经历的表土层地质过程。本文收集了月球陨石的所有稀有气体浓度、同位素比值和CRE年龄数据,结合前人研究成果进行了对比分析,结果显示,月球陨石角砾岩和非角砾岩稀有气体分别具有"三峰三谷"式和"两峰"式分配模式,且稀有气体浓度从非角砾岩、角砾岩到表土角砾岩逐渐增高;月球陨石不存在太阳高能粒子组分(SEP),但存在太阳风分馏组分(FSW)的可能;月球陨石具有两个不同的CRE年龄,分别为指代地月转移时间的T_(4π)年龄和陨石在表土层受到宇宙射线辐射累积时间的T_(2π)年龄。表土角砾岩和非表土角砾岩的T_(2π)年龄分别约为400~1000 Ma和28~60 Ma,而月球陨石的T_(4π)年龄为(0.4±0.9)Ma;月球陨石在表土层中的埋深为0~7.5 m,其宇宙射线辐射起始年龄普遍大于T_(2π)年龄。未来月球陨石稀有气体研究有望在宇宙成因稀有气体_(2π)产率模型、月球原生稀有气体和紫外激光原位稀有气体测试方法方面取得进展。 相似文献
3.
我国球粒陨石稀有气体的研究 总被引：5，自引：0，他引：5
对43个球粒陨石进行了稀有气体分析,其中34个为我国球粒陨石,9个为国外球粒陨石。43个球粒陨石包括17个H、15个L、6个LL、3个L/LL、1个EH3及1个CV3-an化学群。给出了43个球粒陨石的宇宙射线暴露年龄及气体保存年龄,在此基础上讨论了二者(T_3/T_(21)与T_4/T_(40))之间的关系,划分出~3He_c和~4He_r同步丟失及~4He_r单独丢失两种类型的球粒陨石。 相似文献
4.
40Ar/39Ar年龄谱是研究陨石冲击事件的重要资料。根据对55块陨石40Ar/39Ar冲击年龄和陨石暴露年龄的分析,发现陨石的冲击年龄与陨石类型之间存在对应关系。据此,将陨石冲击事件划分为九期。其中3900-4000Ma、470-540Ma和小于65Ma是陨石母体的三个重要演化阶段。阶段Ⅰ、Ⅱ和Ⅲ(冲击年龄大于30亿年)主要涉及高钙型无球粒陨石。所有球粒陨石的冲击年龄均小于30亿年。陨石暴露年龄因类型而异,铁陨石最大,石铁陨石次之,石陨石最小。 相似文献
5.
灶神星是太阳系最大的硅酸盐质小行星,它的岩石样品(HED族陨石)是目前太阳系最古老的岩浆岩之一,很有可能记录了类地行星最早期地质流体活动的重要信息。本次工作首次在一块非角砾岩平衡型的Eucrite NWA 11592中发现了较粗长的富铁橄榄石脉。通过对NWA 11592陨石进行详细的岩相学和地球化学特征研究,将NWA 11592陨石划为玄武质非角砾岩型Eucrite,冲击变质程度至少为S4,热变质程度为6型。NWA 11592中富铁橄榄石脉最有可能为含H2O流体沿裂隙的沉淀产物,反应系统应是开放且较为氧化的(fO2达IW+0.9),且应发生在灶神星浅层地壳> 4 km的埋藏深度。含H2O流体渗透作用除更多地发生在灶神星表面或近地表外,还有可能发生在灶神星内部的浅层地壳中。 相似文献
6.
NWA 8545 是一块玄武质无球粒陨石,它与碳质陨石(CC)NWA 011 成对.CC 被认为是来自于外太阳系的一类物质,由于同位素异常,它们区别于来自内太阳系的非碳质陨石(NC).NWA 011 及其成对陨石作为CC中稀有的玄武质无球粒陨石,其记录的岩浆过程可以被用来研究外太阳系早期行星母体的岩浆活动.本文利用扫描电镜、电子探针和激光剥蚀电感耦合等离子质谱仪(LA-ICP-MS)对NWA 8545 中的辉石、斜长石和陨磷钙钠石进行岩相学以及原位主微量元素的分析,并根据矿物模式丰度计算全岩稀土元素含量.电子探针结果显示NWA 8545 与 HED族陨石Eucrite(钙长辉长无球粒陨石)具有相似的主量元素特征,同时其岩相学与5 型Eucrite类似.激光微量数据表明辉石、斜长石和陨磷钙钠石的稀土元素配分都表现出略微的Ce异常,但其辉石的Ba、Sr等元素并未出现明显的富集现象,即该陨石受地球风化作用影响不明显.利用辉石和斜长石的稀土元素含量,计算平衡熔体的成分,显示其平衡熔体的成分都与全岩的成分比较接近,可以认为两者是在封闭的体系下接近同时结晶.结合变质过程和母体岩浆的成分,本文认为NWA 8545 是由其母体岩浆在经历分离结晶过程后喷发到母体行星表面冷却形成的. 相似文献
7.
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。 相似文献
8.
撞击作用发生在太阳系形成和演化的所有阶段,是最基本的地质过程之一.陨石可以从微观尺度记录下这些重要的过程.在所有陨石族群中,L 群普通球粒陨石保留了最完备的冲击变质记录,对撞击发生的时间、冲击过程中的物理条件提供了重要制约.矿物学证据表明,在太阳系形成 100 Ma 内,L 群陨石母体可能发生一次撞击裂解事件,并在随后重组.4. 48 Ga左右,原始小行星带经历大范围的撞击作用,这一事件也记录于L群普通球粒陨石中,可能是由月球大撞击事件溅射的大量碎屑进入到原始主小行星带引起.约800 Ma,包括L群陨石母体在内的内太阳系部分天体经历了同时期撞击事件,可能由这一时期裂解的大质量小行星产生的溅射物引发.L群陨石母体在～465 Ma发生撞击裂解,这一事件在 L 群陨石中保留了丰富的矿物学、年代学记录,并在地球全球奥陶纪地层发现相关信息.综合与该事件相关的所有L群陨石冲击变质特征,本文认为该裂解事件是由一颗大直径(18～22 km)石陨石质小行星,以较低速率(5～6 km/s)撞击导致.同位素年代学数据表明,L 群普通球粒陨石母体很可能未受到晚期大撞击事件的影响,这难以用L群陨石母体过小予以解释.可能的原因有:① L群普通球粒陨石母体在原始主小行星带分布非常有限,导致其受到晚期大撞击事件影响的概率不高;② 晚期大撞击事件对原始主小行星带的影响可能并没有之前估计的那么严重,一个持续时间更长但更加温和的撞击模型更加符合现阶段的观察. 相似文献
9.
NWA 11288 是一块2015 年发现的玄武岩质辉玻无球粒陨石,具有典型的次辉绿结构,主要由辉石(面积比68. 6%)和熔长石(面积比28. 1%)组成,含少量磷酸盐(面积比 1. 35%)、不透明矿物(面积比 1. 45%)和二氧化硅等副矿物.通过扫描电子显微镜、电子探针和拉曼光谱等实验分析方法,对NWA 11288 进行了岩相学、矿物学及冲击变质作用研究.基于辉石核部的Ti/Al 比值,推测其结晶压力为 930 MPa,结晶深度约为50 km,接近火星壳幔边界.NWA 11288 经历过强烈的冲击变质作用,其中长石全部熔长石化,发育冲击熔脉及熔融囊并出现重结晶的辉石和柯石英.柯石英具有一种前人未报道的新产状:以柯石英-石英-二氧化硅玻璃三相集合体共生,柯石英和石英主要分布在集合体的边部,包裹着核部的二氧化硅玻璃,指示柯石英是在卸压阶段从熔体中结晶形成,且在后续的卸压阶段部分柯石英转变为石英.此外,熔融囊中可见自形的斯石英形态的二氧化硅玻璃;粒间区域可见具有斯石英/赛石英典型特征的二氧化硅颗粒.这些冲击变质特征说明NWA 11288 经历的峰值温度至少为1600℃,峰值压力或可高达15～20 GPa.通过对比NWA 11288 和NWA 8657/8656 的岩石结构、矿物化学成分以及冲击变质特征,本文认为NWA 11288 很可能是NWA 8657/8656 的成对陨石. 相似文献
10.
钙长辉长无球粒陨石(Eucrite)是 Howardite-Eucrite-Diogenite(HED)族陨石的重要成员,也是研究灶神星壳演化历史的重要对象.本文研究了多个玄武质Eucrite样品中主要的SiO2相——普通石英和鳞石英的成因,进而讨论其对Eucrite陨石热演化的启示.研究对象包括不同冲击程度样品,以探讨陨击过程对SiO2同质多象转变的影响.冲击程度较弱的包括未角砾化样品NWA 3162 、NWA 6594 和Igdi,冲击程度较强的为单碎屑角砾岩Millbillillie、Camel Donga和NWA 1654.研究结果显示,不同样品中的普通石英和鳞石英各自均具有相似的岩相学和化学成分,但不同冲击程度样品中普通石英产状存在系统差异.结合Eucrite热变质历史,本研究认为普通石英并非来自共生鳞石英的相变,而是形成于更早期高温 SiO2相的转变.Eucrite 中广泛存在的鳞石英则很可能是普通石英在后期撞击事件中发生部分熔融快速结晶形成.Eucrite中普通石英和鳞石英可能经历的主要形成过程如下:① 岩浆喷发形成高温SiO2 (方石英和/或鳞石英);② 随后长期热变质中高温 SiO2转变形成普通石英,并因体积缩小发育孔洞结构;③ 后期冲击作用再加热,导致普通石英部分熔融形成鳞石英,在高冲击程度的样品中还普遍发育普通石英的羽状裂理.本研究在Eucrite中观察到的普通石英和鳞石英分别形成于不同阶段热事件.大多数Eucrite中存在普通石英和鳞石英共生,表明Eucrite在热变质后普遍受到热扰动,内部微区受热不均一性明显.上述普通石英和鳞石英成因的厘定,为微区或单碎屑矿物同位素年代学定年样品的选择以及年代学结果的地质解释提供了依据. 相似文献
11.
Statistical evaluation of 3056 δ13C measurements in carbonate rocks and fossils shows that they record a 2‰ 13C depletion from the late Proterozoic to the early Paleozoic, a 2.5‰ enrichment to the Permian, and a 1.5‰ depletion to the Cenozoic. These variations, not controlled primarily by facies or alteration phenomena, correlate negatively with the δ34S sulfate secular trend, as confirmed by collation of 1083 δ34S measurements. The correlation suggests that the biologically mediated redox fluxes of the C and S cycles have been approximately balanced through this long span of geological time, generally levelling available oxygen. Such a redox system is consistent with the controlling mechanism proposed by Garrels and Perry (1974). Consequently, the sedimentary reservoirs of Corganic as well as Sbacteriological'have varied through geological time. 相似文献
12.
Auger electron spectroscopy has been used to study K-feldspar that has been reacted with both aqueous 10% HF and a 50% mixture of a 10% HF/0.1 N H2SO4 solution. In the feldspar/HF system, the resulting feldspar surface was shown to have been fluorinated; depth profiling, using argon ion sputtering, showed the fluorination to have occurred substantially into the mineral bulk. In the feldspar/ system, the resulting surface contained both fluorine and sulfur. The fluorination had again penetrated into the bulk, but the sulfur could be removed with mild argon ion sputtering. The signal ratio was much lower on the feldspar surface treated with the 10% HF/0.1 N H2SO4 solution than the feldspar surface treated with the weaker 10% HF acid solution. 相似文献
13.
Marc Javoy Jacqueline Marette Françoise Pineau 《Geochimica et cosmochimica acta》1973,37(9):2017-2019
Partial fluorination experiments developed on a 26 mg sample of Luna 16 fines show a big 18O enrichment in the first oxygen evolved similar to those observed by Epstein and Taylor on Apollo samples and probably related to the high solar wind content of this sample. 相似文献
14.
15.
The δC13 value for sedimentary organic carbon in four estuaries of the Gulf of Mexico increases with radial distance from the river mouth. Mass balance calculations indicate that terrestrial organic carbon is limited to sediments within a relatively short distance from the river mouth. This distance is a function of the discharge rate of the river. For the Mississippi River, terrestrial organic carbon is limited to sediments within 69 km of the mouth of Pass à Loutre and 61 km of South Pass. These data indicate that the low δC13 (< ?22%.) values reported for Pleistocene sediments in the Gulf of Mexico may be the result of factors in addition to the postulated large influx of terrestrial organic carbon. 相似文献
16.
Results of an Ar age spectrum obtained on a sample of the Kirin chondrite (K-5-13) show a similar character to previous published analyses of Kirin samples K-1 and K-2. The K-5-13 age spectrum shows clear evidence of having been substantially outgassed during a presumed collisional event about 0.5 Ga, ago, in good agreement with the estimate obtained from K-2, The differing amounts of 40Ar loss registered by K-2 and K-5-13 during the 0.5 Ga event of about 60 and 50%, respectively, allows calculation of their vertical separation in the parent body at about 10cm. 相似文献
17.
A modified Redlich-Kwong equation of state is used to calculate the solubility of CO2 in methane at various temperatures and pressures. From the solubility of CO2 in CH4 at the triple point and at final melting (Th < Tfm), and the molar volume of solid CO2, the volume of solid at the triple point, and the molar volume of the inclusion can be calculated using a mass balance. The pressure at the melting point is calculated from the equation of state.The algorithm predicts composition, molar volume, pressure at final melting and the isochor pressure (for a given temperature of trapping) for CO2-CH4 fluid inclusions for the case Th < Tfm, given Th, Tfm and experimental data on Ph and dco2 (solid) at Th. 相似文献
18.
The oxygen isotopic compositions of over 100 Archean clastic metasedimentary, felsic metavolcanic and gneissic rocks from selected areas within the Superior Province have been determined. δ18O values of low grade, immature clastic metasediments range from 8.0 to 13.3%. and hence are somewhat depleted in 18O relative to other clastic metasediments. The lower 18O content is attributed to the large proportion of unaltered rock fragments in the Archean metasediments. Felsic metavolcanics have a similar range of δ18O values (7.3 to 13.0%..δ18O values for the middle amphibolite facies Pakwash paragneiss (8.8–11.7%.) are higher than those determined for the amphibolite to granulite facies Twilight paragneiss (7.3–9.2%.). Archean orthogneisses such as the Clay Lake gneiss (7.0–9.0%.), the Cedar Lake gneiss (7.4–8.7%.) and the Footprint gneiss (5.9-8.8%.) have δ18O values similar to those of the Twilight paragneiss. Therefore, at least at metamorphic grades higher than middle amphibolite facies, Archean metasedimentary gneisses may have δ18O values that are indistinguishable from those of Archean orthogneisses, and hence are no longer isotopically recognizable as metasedimentary rocks. 相似文献
19.
D. E. Kelsey R. W. White T. J. B. Holland R. Powell 《Journal of Metamorphic Geology》2004,22(6):559-578
Sapphirine, coexisting with quartz, is an indicator mineral for ultrahigh‐temperature metamorphism in aluminous rock compositions. Here a new activity‐composition model for sapphirine is combined with the internally consistent thermodynamic dataset used by THERMOCALC, for calculations primarily in K2O‐FeO‐MgO‐Al2O3‐SiO2‐H2O (KFMASH). A discrepancy between published experimentally derived FMAS grids and our calculations is understood with reference to H2O. Published FMAS grids effectively represent constant aH2O sections, thereby limiting their detailed use for the interpretation of mineral reaction textures in compositions with differing H2O. For the calculated KFMASH univariant reaction grid, sapphirine + quartz assemblages occur at P–T in excess of 6–7 kbar and 1005 °C. Sapphirine compositions and composition ranges are consistent with natural examples. However, as many univariant equilibria are typically not ‘seen’ by a specific bulk composition, the univariant reaction grid may reveal little about the detailed topology of multi‐variant equilibria, and therefore is of limited use for interpreting the P–T evolution of mineral assemblages and reaction sequences. Calculated pseudosections, which quantify bulk composition and multi‐variant equilibria, predict experimentally determined KFMASH mineral assemblages with consistent topology, and also indicate that sapphirine stabilizes at increasingly higher pressure and temperature as XMg increases. Although coexisting sapphirine and quartz can occur in relatively iron‐rich rocks if the bulk chemistry is sufficiently aluminous, the P–T window of stability shrinks with decreasing XMg. An array of mineral assemblages and mineral reaction sequences from natural sapphirine + quartz and other rocks from Enderby Land, Antarctica, are reproducible with calculated pseudosections. That consistent phase diagram calculations involving sapphirine can be performed allows for a more thorough assessment of the metamorphic evolution of high‐temperature granulite facies terranes than was previously possible. The establishment of a a‐x model for sapphirine provides the basis for expansion to larger, more geologically realistic chemical systems (e.g. involving Fe3+). 相似文献
20.
Silica‐undersaturated, sapphirine‐bearing granulites occur in a large number of localities worldwide. Such rocks have historically been under‐utilized for estimating P–T evolution histories because of limited experimental work, and a consequent poor understanding of the topology and P–T location of silica‐undersaturated mineral equilibria. Here, a calculated P–T projection for sapphirine‐bearing, silica‐undersaturated metapelitic rock compositions is constructed using THERMOCALC for the FeO‐MgO‐Al2O3‐SiO2 (FMAS) and KFMASH (+K2O + H2O) chemical systems, allowing quantitative analysis of silica‐undersaturated mineral assemblages. This study builds on that for KFMASH sapphirine + quartz equilibria [Kelsey et al. (2004) Journal of Metamorphic Geology, vol. 22, pp. 559–578]. FMAS equilibria are significantly displaced in P–T space from silicate melt‐bearing KFMASH equilibria. The large number of univariant silica‐undersaturated KFMASH equilibria result in a P–T projection that is topologically more complex than could be established on the basis of experiments and/or natural assemblages. Coexisting sapphirine and silicate melt (with or without corundum) occur down to c. 900 °C in KFMASH, some 100 °C lower than in silica‐saturated compositions, and from pressures of c.≤1 to ≥12 kbar. Mineral compositions and composition ranges for the calculated phases are consistent with natural examples. Bulk silica has a significant effect on the stability of sapphirine‐bearing assemblages at a given P–T, resulting in a wide variety of possible granulite facies assemblages in silica‐undersaturated metapelites. Calculated pseudosections are able to reproduce many naturally occurring silica‐undersaturated assemblages, either within a single assemblage field or as the product of a P–T trajectory crossing several fields. With an understanding of the importance of bulk composition on sapphirine stability and textural development, silica‐undersaturated assemblages may be utilized in a quantitative manner in the detailed metamorphic investigation of high‐grade terranes. 相似文献