克拉玛依侏罗纪橄榄玄武岩中菱铁矿的成因

克拉玛依市西盆山交界处发育体罗纪杏仁玄武岩-橄榄玄武岩-含菱铁矿橄榄玄武岩组合,主要由橄榄石、单斜辉石、斜长石(中长石—拉长石为主)、钛铁矿、玄武玻璃及少量磷灰石组成,含菱铁矿橄榄玄武岩中存在原生菱铁矿(≈10%)和少量碱性长石。橄榄石及单斜辉石的Mg~#为≈70,单斜辉石属于富Ti普通辉石。含菱铁矿橄榄玄武岩中的菱铁矿常常包裹浑圆状斜长石,且与斜长石呈锯齿状接触。本文提供的岩相学观察表明,菱铁矿与玄武玻璃、斜长石、单斜辉石和钛铁矿呈明显的共生关系。在有些情况下观察到玄武玻璃与菱铁矿充填在斜长石格架的现象。含菱铁矿橄榄玄武岩玻璃中FeO含量最高至29.2%,CaO含量<1.5%,即熔体具有富Fe贫Ca的特点。早结晶的碳酸盐矿物是以菱铁矿为主的菱铁矿-白云石固溶体(另含少量菱锰矿)。斜长石大量结晶促使熔体不断亏损CaO,并导致较晚结晶的碳酸盐矿物向菱铁矿端元演化。菱铁矿发育有明显的成分梯变带(FeO和CaO含量表现出突变)。玄武玻璃的Mg~#普遍较低且变化范围大,橄榄玄武岩中玻璃的Mg~#值最高为64,含菱铁矿橄榄玄武岩中玻璃的Mg~#值最低至≈23。依据地质温压计,克拉玛依侏罗纪玄武岩浆的形成温度为1300℃～1340℃,压力为3.0～4.0GPa。基于本文的研究,我们认为克拉玛依侏罗纪含菱铁矿橄榄玄武岩岩浆由含CO_2,橄榄岩在软流圈中经极低程度部分熔融形成,该岩浆在快速上升过程中通过结晶分异作用形成了菱铁矿。     

Mesozoic extension in the Basque–Cantabrian basin (N Spain): Contributions from AMS and brittle mesostructures

In this work we analyse and check the results of anisotropy of magnetic susceptibility (AMS) by means of a comparison with palaeostress orientations obtained from the analysis of brittle mesostructures in the Cabuérniga Cretaceous basin, located in the western end of the Basque–Cantabrian basin, North Spain. The AMS data refer to 23 sites including Triassic red beds, Jurassic and Lower Cretaceous limestones, sandstones and shales. These deposits are weakly deformed, and represent the syn-rift sequence linked to basins formed during the Mesozoic and later inverted during the Pyrenean compression. The observed magnetic fabrics are typical of early stages of deformation, and show oblate, triaxial and prolate magnetic ellipsoids. The magnetic fabric seems to be related to a tectonic overprint of an original, compaction, sedimentary fabric. Most sites display a NE–SW magnetic lineation that is interpreted to represent the stretching direction of the Early Cretaceous extensional stage of the basin, without recording of the Tertiary compressional events, except for sites with compression-related cleavage.Brittle mesostructures include normal faults, calcite and quartz tension gashes and joints, related to the extensional stage. The results obtained from joints and tension gashes show a dominant N–S to NE–SW, and secondary NW–SE, extension direction. Paleostresses obtained from fault analysis (Right Dihedra and stress inversion methods) indicate NW–SE to E–W, and N–S extension direction. The results obtained from brittle mesostructures show a complex pattern resulting from the superposition of several tectonic processes during the Mesozoic, linked to the tectonic activity related to the opening of the Bay of Biscay during the Early Cretaceous. This work shows the potential in using AMS analysis in inverted basins to unravel its previous extensional history when the magnetic fabric is not expected to be modified by subsequent deformational events. Brittle mesostructure analysis seems to be more sensitive to far-field stress conditions and record longer time spans, whereas AMS records deformation on the near distance, during shorter intervals of time.     

豫西小秦岭地区太华杂岩中花岗质片麻岩的元素地球化学及其构造意义

豫西小秦岭地区太华杂岩中花岗质片麻岩为古老侵入岩,主要由黑云斜长片麻岩、黑云钾长片麻岩和黑云二长片麻岩等类型岩石组成,具有ＴＴＧ岩系的组成特征,元素地球化学特征反映其形成于类似现代板块碰撞带的构造环境．     

浙西上奥陶统于潜组Spirodesmos遗迹化石组合的环境意义

在概述了浙江西部上奥陶统于潜组的沉积学特征,并进而描述了发现的14个遗迹化石属基础上,从4个方面对Spirodesmos为代表的遗迹组合进行了环境分析:(1)14个遗迹属中仅3个属为穿相型分子,其余占遗迹总属2/3以上的遗迹化石均为典型的深水型分子,它们都是Nereites遗迹相的主要成员,因此该遗迹组合可归属于深海Nereites遗迹相中;(2)大部分遗迹化石呈复杂规则弯曲的形态,这种形态的遗迹化石是深海环境的遗迹化石标志;(3)14个遗迹属均为觅食迹和牧食迹,它们的行为习性,尤其是牧食迹主要分布于深海环境;(4)多数遗迹属的水深分布均在200m以下。由此可认为Spirodesmos遗迹组合是半深海-深海环境的产物。     

Characteristics of the Variation of Cross Fault Short-Baseline and Short-Range Leveling in Western Yunnan Earthquake Test Site Before Lijiang M_S7.0 Earthquake

Results of analysis of variation of cross fault short-baseline and short-range leveling in Western Yunnan Earthquake Test Site (WYETS), results show that among five observation stations of cross fault short-baseline and short-range leveling in WYETS before the Lijiang MS7.0 Earthquake occurred in February 1996 only Yongsheng observation station (epicentral distance 82 km) located at Chenghai fault shows great variation about one year before the earthquake. And the nearest observation station, Lijiang (epicentral distance 42 km); presents great coseismic variation, but does not show obvious anomalous variation before the earthquake. There are no significant variations related to the earthquake at the other three observation stations. Two methods are used in analysis of the observed data and some valuable results have been obtained.     

浙赣皖交界区新元古代火山-沉积岩系的比较——有关火山作用同期异相的探讨

本文综合野外地质、同位素年代学和岩石地球化学资料,对浙赣皖交界区,即江南造山带东段发育的众多新元古代火山—沉积岩系进行了对比研究。从岩石组合及其大地构造含义和火山作用同期异相的观点加以认识.揭示它们的内在联系,为该区地层单元的清理和归并提供依据。     

New seismic images of the crust in the central Trans-Hudson Orogen of Saskatchewan

A reprocessing program to enhance the correlation between the surface geology and the seismic data has been completed for seismic line 9 (eastern 100 km) and line 10 in the central region of the Trans-Hudson Orogen of Saskatchewan, Canada. The new seismic images through lateral continuity of reflectivity provide sufficient detail to resolve the discrepancy between the low-dipping, layer-parallel and dextral-reverse nature of the Sturgeon-Weir shear zone (line 9) observed in the field and its steeply dipping (apparent) normal displacement character interpreted on the basis of the initial processing. Furthermore, the new interpretation provides a strong confirmation of the role of Pelican Thrust as a major detachment zone — the main `sole thrust' — along which juvenile allochthons have been carried across the Archaean microcontinental block. The images are also refined enough to suggest: (a) a boundary within the Pelican Thrust between its internal and external suites; (b) a possible boundary separating a lower (older?) Archaean basement from its upper (younger?) counterpart; and (c) sub-Moho events (M2) which reveal possible involvement of the upper mantle in the collisional tectonic process in addition to the well defined Moho (M1) which probably represents the youngest of the post-collisional detachments.     

Prograde high- to ultrahigh-pressure metamorphism and exhumation of oceanic sediments at Lago di Cignana, Zermatt-Saas Zone, western Alps

Pelagic metasediments and MORB-type metabasalts of the former Tethyan oceanic crust at Cignana, Valtournanche, Italy, experienced UHP metamorphism and subsequent exhumation during the Early to Late Tertiary. Maximum PT conditions attained during UHP metamorphism were 600–630 °C, 2.7–2.9 GPa, which resulted in the formation of coesite-glaucophane-eclogites in the basaltic layer and of garnet-dolomite-aragonite-lawsonite-coesite-phengite-bearing calc-schists and garnet-phengite-coesite-schists with variable amounts of epidote, talc, dolomite, Na-pyroxene and Na-amphibole in the overlying metasediments. During subduction the rocks followed a prograde HP/UHP path which in correspondance with the Jurassic age of the Tethyan crust reflects the thermal influence of relatively old and cold lithosphere and of low to moderate shear heating. Inflections on the prograde metamorphic path may correspond to thermal effects that arise from a decrease in shear heating due to brittle-plastic transition in the quartz-aragonite-dominated rocks, induced convection in the asthenospheric mantle wedge and/or heat consumption by endothermic reactions over a restricted PT segment during subduction. After detachment from the downgoing slab some 50–70 Ma before present, the Cignana crustal slice was first exhumed to ca. 60 km and concomitantly cooled to ca. 550 °C, tracing back the UHP/HP prograde path displaced by 50–80 °C to higher temperatures. Exhumation at this stage is likely to have occurred in the Benioff zone, while the subduction of cool lithosphere was going on. Subsequently, the rocks were near-isothermally exhumed to ca. 30 km, followed by concomitant decompression and cooling to surface conditions (at < 500 °C, < 1 GPa). During this last stage the UHPM slice arrived at its present tectonic position with respect to the overlying greenschist-facies Combin zone. In contrast to the well-preserved HP/UHPM record of the coesite-glaucophane eclogites, the HP/UHP assemblages of the metasediments have been largely obliterated during exhumation. Relics from which the metamorphic evolution of the rocks during prograde HP metamorphism and the UHP stage can be retrieved are restricted to rigid low-diffusion minerals like garnet, dolomite, tourmaline and apatite.     

红河断裂北段土壤中断层气含量变化特征

介绍了作者在滇西地震预报实验场区进行的土壤中断层气研究结果．沿红河断裂带断层气组分Ｈ２,ＣＯ２,Ｈｇ和Ｒｎ含量很高．沿该断裂洱源测线断层气Ｈ２,ＣＯ２和Ｒｎ含量最低,向南Ｈ２,ＣＯ２含量逐渐升高,其中以定西岭测线的Ｈ２,ＣＯ２含量最高．表明在该段断裂活动强烈,而洱源一带断裂活动较弱．     

1996年包头西6.4级地震震兆特征的特殊性

１９９６年包头西６．４级地震是一次十分重要的地震,又是一个非常特殊的地震。集二十多年对强震前主要震兆特征和地震活动图像演化的认识,无论在６．４级地震前看到的,还是震后震例总结的,种种震兆异常基本集中在临河地区,而不是包头地区。