超高压变质岩矿物中的显微构造缺陷:来自TEM和FTIR研究的证据

超高压变质矿物的某些显微构造缺陷可能指示了岩石短暂和快速抬升过程。文中报道了中国大别山双河地区超高压硬玉石英岩矿物显微构造缺陷的透射电镜(TEM)和Fourier变换红外光谱(FTIR)的研究结果。用TEM研究方法,在硬玉石英岩中硬玉包裹体内发现了亚微米级天然蒙钠长石(MA,C2/m)、高钠长石(HA,C)和低钠长石(LA,C)三种多形变体。表明岩石在折返过程经历过高温变质作用(>930℃),以及退变质过程的快速冷却;在石英包裹体内发现了纳米级柯石英和石盐子矿物,提供了柯石英转变为石英以及峰期变质条件下高盐流体存在的证据。"名义上无水矿物"(NAMs)的结构水(OH/H2O)是以缺陷形式赋存于矿物结构中。FTIR分析结果显示硬玉、石榴石、金红石和石英中结构水的平均含量分别为1000×10-6、(900~1600)×10-6、>2000×10-6和<4×10-6,硬玉石英岩全岩含水量为(490~600)×10-6,表明在高压-超高压变质作用过程中,地壳或原岩中的水可以通过这些NAMs携带到地球深部。该类显微构造缺陷可能是大陆碰撞造山带在高应变速率下的局部弱化和深部断层作用的结果。     

花岗岩的成岩时代、地球化学特征和成因青海祁漫塔格地区虎头崖矿床Ⅵ矿带

利用 LA ICP MS 锆石 U Pb 法,测得与成矿有关的青海祁漫塔格地区虎头崖矿床Ⅵ矿带花岗岩的成岩年龄为(233.6±1.8)Ma(MSWD=1.2,n=17)。地球化学特征显示：花岗岩属高钾钙碱性、弱过铝质花岗岩;样品的稀土元素组成以总体右倾,轻、重稀土分异明显和具明显的负铕异常为特征;微量元素具有富集 Rb、Th、U、La、Nd 等大离子亲石元素,亏损 Ba、Sr、Nb、P、Ti 等元素的特点。Sr Nd 同位素组成特征显示,花岗岩的源区可能是富集岩石圈地幔。初步研究认为,虎头崖矿床Ⅵ矿带花岗岩可能形成于中、晚三叠世碰撞后碰撞的构造背景下。     

大别山北部蛇绿岩的地球化学制约

常量元素,微量元素,稀土元素,Ｎｄ同位素及氧同位素地球化学特征表明,太别山北部变质镁铁－超镁铁质岩带中存在变质的蛇绿岩,它主要由变质橄榄岩,辉长岩（－辉绿岩？）和基性熔岩三部分组成,其中,变质的基性熔岩的亏损地幔模式年龄ｔＤＭ／Ｍａ＝１０３６．８～１２９３．８,εＮｄ（ｔ）＝７．２～７．７,表明它可能代表１０００Ｍａ左右形成于中等扩张速率（２ｃｍ／ａｄ左右）洋盆条件下的洋壳残片。     

Elemental characteristics and paleoenvironment reconstruction: a case study of the Triassic lacustrine Zhangjiatan oil shale,southern Ordos Basin,China

Using trace elements to reconstruct paleoenvironment is a current hot topic in geochemistry. Through analytical tests of oil yield, ash yield, calorific value, total sulfur, major elements, trace elements, and X-ray diffraction, the quality, mineral content, occurrence mode of elements, and paleoenvironment of the Zhangjiatan oil shale of the Triassic Yanchang Formation in the southern Ordos Basin were studied. The analyses revealed relatively high oil yield (average 6.63%) and medium quality. The mineral content in the oil shale was mainly clay minerals, quartz, feldspar, and pyrite; an illite–smectite mixed layer comprised the major proportion of clay minerals. Compared with marine oil shale in China, the Zhangjiatan oil shale had higher contents of quartz, feldspar, and clay minerals, and lower calcite content. Silica was mainly in quartz and Fe was associated with organic matter, which is different from marine oil shale. The form of calcium varied. Cluster analyses indicated that Fe, Cu, U, V, Zn, As, Cs, Cd, Mo, Ga, Pb, Co, Ni, Cr, Sc, P, and Mn are associated with organic matter while Ca, Na, Sr, Ba, Si, Zr, K, Al, B, Mg, and Ti are mostly terrigenous. Sr/Cu, Ba/Al, V/(V + Ni), U/Th, AU, and δU of oil shale samples suggest the paleoclimate was warm and humid, paleoproductivity of the lake was relatively high during deposition of the shale—which mainly occurred in fresh water—and the paleo-redox condition was dominated by reducing conditions. Fe/Ti ratios of the oil shale samples suggest clear hydrothermal influence in the eastern portion of the study area and less conspicuous hydrothermal influence in the western portion.     

青藏高原羌D2井海相烃源岩评价和油源对比

南羌塘坳陷D2井中侏罗统曲布组海相碳酸盐岩大部分为差—好烃源岩级别,少部分为非烃源岩级别,有机质母质类型以Ⅱ型为主,热演化处于成熟—高成熟阶段。油源对比分析表明,羌D2井曲布组白云岩和含沥青角砾岩中油质沥青来自该组地层灰岩烃源岩,具自生自储性质。同时,中侏罗统雀莫错组灰黑色泥页岩作为烃源层也存在提供油源的可能性。     

西藏申扎永珠乡晚石炭世和早二叠世的腕足动物化石

申扎地区石炭二叠系发育良好,化石丰富。本文描述的化石采自上下两个层位,下部化石少,以石燕贝类为主, 其组合特征反映了石炭纪腕足类的特点与改则县玛米雪山地区上石炭统所产相似;上部化石丰富,以石燕贝类的Spiriferella和Syrin-gothyris的出现为特征,共生还有长身贝类的Chonetinella,Echinauris,Tylo-pecta等。这个化石组合与西藏其他地区相同时代的化石组合不同。特别是Syringothy-ris在下二叠统的发现具有重要意义。     

塔里木盆地吐木休克构造带断裂构造分析

吐木休克断裂位于塔里木盆地西部,是一条大型基底卷入型断裂构造带,构成塔里木盆地次级构造单元阿瓦提凹陷和巴楚断隆的分界。根据系统的地震资料解释,可以将吐木休克断裂分为西段、中段和东段3部分,各段构造特征有所差异。西段,为单一的基底卷入型高角度逆冲断层,倾向巴楚断隆; 中段,除倾向巴楚断隆的主冲断层外,倾向相反的反冲断层越来越清晰,楔状冲断构造的轮廓逐渐显现出来。同时,在断层上盘还发育第四纪正断层; 东段,倾向巴楚断隆的主冲断层,向上断至中寒武统,未断开中寒武统以上的地层,其冲断位移量完全为倾向阿瓦提凹陷的反冲断层所吸收,形成典型的楔状冲断构造。根据地震资料解释,认为吐木休克断裂带主要存在两期断裂构造:深部高角度基底卷入型逆冲断裂带和其上叠加的浅部正断层。前者形成于库车组沉积前,在库车组沉积期间持续活动,并在新近纪晚期定型; 后者是本次研究首次发现的,形成于第四纪早中期,仅发育在吐木休克断裂带的中部。     

空气中氡浓度的预测

氡是一种放射性惰性气体,它与肺癌的关系已引起人们的高度重视,世界上许多国家都开展了环境氡的研究工作;氡的母体元素铀、镭在地质环境中的分布与空气中的氡浓度水平有密切关系,通过研究地质环境中铀、镭的分布资料,就能快速定性地评价空气中氡浓度水平.     

Early Neoproterozoic granulite facies metamorphism of mafic dykes from the Vestfold Block,east Antarctica

Proterozoic mafic dykes from the southwestern Vestfold Block experienced heterogeneous granulite facies metamorphism, characterized by spotted or fractured garnet‐bearing aggregates in garnet‐absent groundmass. The garnet‐absent groundmass typically preserves an ophitic texture composed of lathy plagioclase, intergranular clinopyroxene and Fe–Ti oxides. Garnet‐bearing domains consist mainly of a metamorphic assemblage of garnet, clinopyroxene, orthopyroxene, hornblende, biotite, plagioclase, K‐feldspar, quartz and Fe–Ti oxides. Chemical compositions and textural relationships suggest that these metamorphic minerals reached local equilibrium in the centre of the garnet‐bearing domains. Pseudosection calculations in the model system NCFMASHTO (Na₂O–CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–Fe₂O₃) yield P–T estimates of 820–870 °C and 8.4–9.7 kbar. Ion microprobe U–Pb zircon dating reveals that the NW‐ and N‐trending mafic dykes were emplaced at 1764 ± 25 and 1232 ± 12 Ma, respectively, whereas their metamorphic ages cluster between 957 ± 7 and 938 ± 9 Ma. The identification of granulite facies mineral inclusions in metamorphic zircon domains is also consistent with early Neoproterozoic metamorphism. Therefore, the southwestern margin of the Vestfold Block is inferred to have been buried to depths of ~30–35 km beneath the Rayner orogen during the late stage of the late Mesoproterozoic/early Neoproterozoic collision between the Indian craton and east Antarctica (i.e. the Lambert Terrane or the Ruker craton including the Lambert Terrane). The lack of penetrative deformation and intensive fluid–rock interaction in the rigid Vestfold Block prevented the nucleation and growth of garnet and resulted in the heterogeneous granulite facies metamorphism of the mafic dykes.     

桂林岩溶洼地和洞穴发生、发展的构造控制剖析

通过对桂林地质构造和岩溶建造的研究,并对岩溶洼地、洞穴发育特征进行分析,认为它们在发生、发展上具有成生的内在联系,从而反映在时空方面具有特定的关系。 这些关系集中表现在岩溶洼地、洞穴是岩溶水沿断裂、裂隙溶蚀、侵蚀扩大、改造、堆积、再改造的结果。其规律性主要反映在方向性、等距性、继承性、成层性及形态关系等几个方面。 实践表明,研究岩溶发育规律,要对构造控制因素进行分析,必须从构造形迹鉴别入手,分析其成生联系、体系归属,了解地质构造的发生。发展阶段和序次,并以此和岩溶岩系(建造)为依据,联系成岩环境(特征)和水文地质条件进行综合分析,才能客观反映构造的控制规律。