A formation mechanism for hematite-rich spherules on Mars

Gray crystalline hematite on Mars has been detected in three regions, Sinus Meridiani, Aram Chaos, and Valles Marineris, first by the Thermal Emission Spectrometer (TES) onboard the Mars Global Surveyor (MGS) orbiter, and then confirmed by other instruments. The hematite-rich spherules were also detected by the Mars Exploration Rover (MER) Opportunity at Meridiani Planum (Sinus Meridiani). Formation mechanisms of the hematite-rich spherules have been discussed widely since then. Here, we argue for an alternative formation mechanism, that is, the spherules originally formed at Valles Marineris due to the interaction of volcanic deposits and acidic hydrothermal fluids, and then were transported to and deposited at Meridiani Planum and Aram Chaos as alluvial/fluvial sedimentary deposits with other materials such as sulfates and rock fragments during the wash-out flows from Valles Marineris to Meridiani Planum and Aram Chaos. Diagenesis of the hematite-rich spherules may have also been a possible mechanism following sediment transport and emplacement. The hypothesis is consistent with available relevant information to date and provides an insight into the understanding of Martian surficial processes.     

酸性岩浆不混溶演化路径探索——来自福建省政和县一个“超级实验室”的野外证据

一个多世纪以来经历过几代人的不懈努力,尤其是近年来岩浆不混溶作用在业界得到重视,使其理论研究和实践运用都达到了前所未有的高度。笔者在中国东南沿海火山岩中首次发现大规模酸性岩浆不混溶现象,通过详细的岩相学研究揭示,大约温度在900～650℃之间、剧烈的过冷度变化条件下岩浆发生不混溶两液相,一相为富硅的球粒相,另一相为富铁的基体相。不混溶球粒相发展,最初可能由大黏度富桥氧的硅氧四面体-络阴离子团聚集成核,成核后形成珠滴状液滴,液滴聚集成塑性小球,小球碰撞合并奠定球粒个体,球粒个体先后经历过三个世代的反复交叠生长而定型。在浮力和岩浆上侵的综合作用下,无数个球粒个体与熔浆分离、上浮、云集成规模宏大的富硅球粒相,即球粒流纹斑岩地质体,富铁基体相下沉形成英安岩地质体。地球化学特征表明,球粒相富集主元素SiO₂、K₂O、Na₂O和微量元素Sr、Ba;基体相富集主元素Al₂O₃、TiO₂、MgO、TFe₂O₃和微量元素Rb、Cs...     

A Study of Mesoproterozoic Iron Cosmic Micro-spherules from 1.8 Ga and 1.6 Ga Old Strata in the Ming Tombs District, Beijing

Numerous iron cosmic micro-spherules have been discovered from Mesoproterozoic strata including the Changzhougou Formation(1.8 Ga) and the Dahongyu Formation(1.6 Ga) of the Ming Tombs district,Beijing.There are 1 to 30 grains of cosmic spherules per 2 kg of a sandstone sample taken from the bottom of a coarse sandstone bed of the Changzhougou Formation and 56 grains per 3.69 kg of a rock sample from silicified carbonate rocks of the Dahongyu Formation.The surface textures of cosmic spherules analyzed by means of the secondary electron imagery are identical with those reported from references either domestic or abroad.So far the geo-ages of 1.8 Ga and 1.6 Ga of cosmic spherules from the Changzhougou and Dahongyu formations might be older than those reported in the world.Table 1 gives the electron probe analysis data of cosmic spherules for 30 spherule grains and 44 testing points as follows(%):FeO,80-95;Cr_2O_3;0-9.56;NiO,0-0.78;CoO,0-0.46; indicating that the Cr_2O_3 content is higher and FeO content lower in the Changzhougou Formation than in the Dahongyu Formation.The helium isotopic data of cosmic spherules as well as their host rocks vary greatly between the Changzhougou and the Dahongyu formations as shown in Table 2.The data of cosmic spherules of the Changzhougou Formation vs the Dahongyu Formation are 57.5/1.23 in ~3He/~4He(10~(-8));and 55.54/809.60 in ~4He(10~(-6)cm~3STP/g);those of coarse sandstone of the Changzhougou Formation vs silicified carbonate of the Dahongyu Formation are 3.39/2.59 in ~3He/~4He(10~(-8)) and 4.56/2.34 in ~3He(10~(-6)cm~3STP/g).The ratio of analytic data of helium isotopes are different for cosmic spherules and their host rocks;for example,the ~3He/~4He(10~(-8)) values are 16.96 and 0.48,and the ~4He (10~(-6)cm~3STP/g) are 12.18 and 345.98 for the Changzhougou and Dahongyu formations respectively.It was reported that the world's oldest micrometeorites had been found in the Meso-Proterozoic Satakunta Formation,Finland.However,the cosmic spherules from the Meso-Proterozoic Changzhougou and Dahongyu formations are 200 to 400 Ma older than those from the Satakunta Formation.Besides,one carbonaceous chondrite grain was discovered for the first time as the earliest remain formed in the solar nebula from the Dahongyu Formation.     

青海锡铁山铅锌矿床中发现的宇宙尘及其初步研究

本文对发现于锡铁山铅锌矿床中的磁性小球的化学成分、粒度、硬度、形貌、吸收系数、结构和构造进行了分析研究。结果表明,该磁性小球与前人所报道的其他地区的宇宙尘类似。根据它们的化学成分特征(表2、3、4、5)、方铁矿和磁铁矿构成的外壳和α-Fe内核,初步确定其为下古生代宇宙尘。     

深海沉积物中硅质小球的稀土元素丰度特征

近年来对宇宙尘的研究已成为宇宙化学和天文地质学界中的一个很活跃的领域。作者利用中子活化法测定了从深海沉积物中挑选出的硅质和玻璃质小球中的微量元素的含量。结果表明,这些硅质和玻璃质小球主要属地外来的物质。     

白垩-第三纪界线样品异常铱的赋存状态及其地质意义

通过对地质样品中铱的赋存状态研究及对残渣相中微粒的透射电镜分析,得出:在K-T界线样品中铱主要存在于残渣相中,不利于地球化学过程富集铱;铱在残渣相的富集与有机不溶物的存在没有必然联系;白垩-第三纪的生物绝灭事件中有火山活动参与;K-T界线事件的触发物为地外物质撞击。最后提出了K-T界线样品异常铱来源于地外物质撞击和火山喷发的混合模型。     

白垩-第三纪界线样品异常铱的赋存状态及其地质意义

 通过对地质样品中铱的赋存状态研究及对残渣相中微粒的透射电镜分析,得出:在K-T界线样品中铱主要存在于残渣相中,不利于地球化学过程富集铱;铱在残渣相的富集与有机不溶物的存在没有必然联系;白垩-第三纪的生物绝灭事件中有火山活动参与;K-T界线事件的触发物为地外物质撞击。最后提出了K-T界线样品异常铱来源于地外物质撞击和火山喷发的混合模型。