锦州-迁安太古宙赞岐岩类片麻岩成因及其动力学意义

详细的野外地质调查和综合研究表明冀东-辽西南部地区太古宙变质基底主要由富钾花岗质岩石组成,由锦州至迁安构成一条NEE向延伸200余千米的富钾花岗质岩石带。这些富钾花岗质岩石主要由似斑状/中粒石英二长闪长质-花岗闪长质-二长花岗质片麻岩和中粒二长花岗岩-正长花岗岩构成。全岩地球化学分析表明这些石英二长闪长质-花岗闪长质-二长花岗质片麻岩具有高FeO~T、MgO、K_2O和Mg~#值的地球化学特征,与全球范围内中-新太古宙赞歧岩类相似。LA-ICP-MS锆石U-Pb同位素定年结果表明这些岩石形成于2546~2543Ma。岩石成因研究表明这些赞歧岩类片麻岩形成于俯冲板片及其拖曳的洋壳沉积物、增生楔物质的熔体和受俯冲流体、熔体交代的地幔楔之间相互作用引发的一系列的岩浆作用。这一多样化的赞岐岩类岩浆作用形成了一条新太古代赞岐岩类带,该赞岐岩类带反映了冀东-辽西南部地区新太古代从NNW向SSE向板片热俯冲的动力学体制。     

Sources and geodynamics of the Late Cenozoic volcanism of Central Mongolia: Evidence from isotope-geochemical studies

In the Late Cenozoic, the volcanism of the South Khangai Volcanic Region (SKhVR) spanned the Khangai Range and its framing. Geochronological, petrochemical, geochemical, and isotope studies were performed for volcanic rocks of this region, which are represented by high-K basic and intermediate rocks of OIB affinity. Initial Sr, Nd, and Pb isotope ratios in the volcanic rocks of the SKhVR are close to those of the volcanic rocks of Pitcairn Island and form trends between PREMA, EMI, and EMII sources.     

Seismic strain in the Altai-Sayan active seismic area and elements of collisional geodynamics

Seismic strain estimated from about 900 earthquake mechanisms in the Altai-Sayan area indicates that the area evolves mainly under N-S compression caused by the India-Eurasia collision. Plastic flow in the mountains of the western and central Altai-Sayan area is controlled by convergence of aseismic rigid blocks, including the Dzungarian microplate, the Minusa basin, the Tuva basin, Uvs Nuur and other basins in the region of Great Lakes in Mongolia. Earthquake rupture follows the existing fault pattern. The pattern of rigid blocks and mountain ranges correlates well with upper mantle thermal heterogeneity as imaged by seismic tomography.Earthquake mechanisms in the presence of plate convergence depend on different factors. Slip geometry depends on focal depth at a given geodynamic regime, and the latter, in terms of the seismic process, is controlled by lateral (W-E) constraint. Reverse-slip earthquakes most often originate at shallow depths in regions of constrained compression, such as the Tien Shan, and strike slip is the dominant mechanism under non-constrained and moderately constrained compression. The direction of slip is governed by the parallel component of convergence and by the fault pattern. In regions of strain shadow, slip occurs mostly on normal planes, and shallow earthquakes have strike-slip mechanisms. The crust in the collisional region is divided into systems of rigid and plastic blocks (rheological structure) and of fault blocks (fault-block structure). The two types of systems coexist and determine the generally similar but specifically different features of local mass transfer.     

巨鲕的微生物成因:来自重庆石柱地区下寒武统的证据

巨鲕的产出时代多见于新元古代和早三叠世,而寒武纪的巨鲕却鲜见报道。近期,笔者在重庆石柱地区下寒武统天河板组中发现厚约35cm的透镜状巨鲕灰岩。在该层巨鲕灰岩中,巨鲕粒径一般为5～7mm,最大可达9mm,约占岩石组分的55％,与大量强烈重结晶的正常鲕粒伴生。钙质生物壳体较常见,颗粒间见亮晶方解石胶结物。研究区巨鲕最外圈纹层上常见蓝细菌化石,形成发育不完全的突起状“夭折的纹层”;巨鲕内的暗色纹层中亦见杂乱交错的、有一定重结晶的蓝细菌等微生物化石。故推测其为微生物成因形成的,且早寒武世频繁的强风暴背景和蓝细菌等微生物的积极参与是该层巨鲕形成的必备条件。     

A global positioning measurement system for regional geodesy in the caribbean

Low cost, portable receivers using signals from satellites of the Global Positioning System (GPS) will enable precision geodetic observations to be made on a large scale. A number of important geophysical questions relating to plate-motion kinematics and dynamics can be addressed with this measurement capability. We describe a plan to design and validate a GPS-based geodetic system, and to demonstrate its capability in California, Mexico and the Caribbean region. The Caribbean program is a prototype for a number of regional geodetic networks to be globally distributed.

In 1985, efforts will be concentrated on understanding and minimizing error sources. Two dominant sources of error are uncertainties in the orbit ephemeris of the GPS satellites, and uncertainties in the correction for signal delay due to variable tropospheric water vapor. Orbit ephemeris uncertainties can be minimized by performing simultaneous satellite observations with GPS receivers at known (fiducial) points. Water vapor corrections can be made by performing simultaneous line-of-sight measurements of integrated water vapor content with ground-based water vapor radiometers. Specific experiments to validate both concepts are outlined.

Caribbean measurements will begin in late 1985 or early 1986. Key areas of measurement are the northern strike-slip boundary, and the western convergent boundary. Specific measurement plans in both regions are described.     

塔中古生界油田水的成因和混合的证据

塔中地区奥陶纱、志留系和石炭系油田水的主元素、微量元素、＾８７Ｓｒ／＾８６Ｓｒ、δＤ、δ＾１８Ｏ及全岩的＾８７Ｓｒ／＾８６Ｓｒ测试结果表明,油田水相对于海水蒸发曲线,富Ｓｒ＾２＋、Ｃａ＾２＋、ＣＦ而贫Ｋ＾＋、Ｍｇ＾２＋,系水－岩反应改造的产物。远高于海水的＾８７Ｓｒ／＾８６Ｓｒ值表明油田水具有钾长石等矿物溶解的影响。油田水＾８７Ｓｒ／＾８６Ｓｒ－１／Ｓｒ的关系显示具有两种混合趋势,一种是奥陶系油田     

Evidence for variations of mechanical properties in the Friuli seismic area

Tidal strains of the earth were extracted from three horizontal strainmeter records (1979–1986) in the Friuli seismic area by the “filter method”. The areal strain factor, ignoring the tidal loading effects, shows that its time variation is significant: their amplitudes in 1986 are about 50% of those in 1979.

The modifications of mechanical properties, estimated in terms of the local shear and bulk modulus variations, were obtained considering the envelope of the tidal strain signals. The seismic wave velocity determined by the simultaneous inversion of the arrival time data of the local seismometric network displayed comparable changes.

A major change both in the seismic velocities and the elastic parameters started in March 1982, which was about 11 months before an earthquake of magnitude 4.1, the largest event from 1979 to 1986, which occurred within the seismic network on Feb. 10, 1983.     

Late Cenozoic geodynamics and mechanical coupling of crustal and upper mantle deformations in the Mongolia-Siberia mobile area

Comprehensive analysis of the parameters characterizing contemporary and neotectonic deformations of the Earth’s crust and upper mantle developed in the Mongolia-Siberia area is presented. The orientation of the axes of horizontal deformation in the geodetic network from the data of GPS geodesy is accepted as an indicator of current deformations at the Earth’s surface. At the level of the middle crust, this is the orientation of the principal axes of the stress-tensors calculated from the mechanisms of earthquake sources. The orientation of the axes of stress-tensors reconstructed on the basis of structural data is accepted as an indicator of Late Cenozoic deformations in the upper crust. Data on seismic anisotropy of the upper mantle derived from published sources on the results of splitting of shear waves from remote earthquakes serve as indicators of deformation in the mantle. It is shown that the direction of extension (minimum compression) in the studied region coincides with the direction of anisotropy of the upper mantle, the median value of which is 310–320° NW. Seismic anisotropy is interpreted as the ordered orientation of olivine crystals induced by strong deformation owing to the flow of mantle matter. The observed mechanical coupling of the crust and upper mantle of the Mongolia-Siberia mobile area shows that the lithospheric mantle participated in the formation of neotectonic structural elements and makes it possible to ascertain the main processes determining the Late Cenozoic tectogenesis in this territory. One of the main mechanisms driving neotectonic and contemporary deformations in the eastern part of the Mongolia-Siberia area is the long-living and large-scale flow of the upper mantle matter from the northwest to the southeast, which induces both the movement of the northern part of the continent as a whole and the divergence of North Eurasia and the Amur Plate with the formation of the Baikal Rift System. In the western part of the region, deformation of the lithosphere is related to collisional compression, while in the central part, it is due to the dynamic interaction of these two large-scale processes.     

Mediterranean Tertiary lamproites derived from multiple source components in postcollisional geodynamics

In the Mediterranean area, lamproitic provinces in Spain, Italy, Serbia and Macedonia have uniform geological, geochemical and petrographic characteristics. Mediterranean lamproites are SiO₂-rich lamproites, characterized by relatively low CaO, Al₂O₃ and Na₂O, and high K₂O/Al₂O₃ and Mg-number. They are enriched in LILE relative to HFSE and in Pb, and show depletion in Ti, Nb and Ta. Mediterranean lamproites show huge regional variation of Sr, Nd and ²⁰⁷Pb/²⁰⁴Pb isotopic values, with ⁸⁷Sr/⁸⁶Sr range of 0.707-0.722, εNd range from −13 to −3, and ²⁰⁷Pb/²⁰⁴Pb range of 15.62-15.79.Lamproitic rocks are derived from melts with three components involved in their origin, characterized by contrasting geochemical features which appear in ²⁰⁶Pb/²⁰⁴Pb, ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd space: (i) a mantle source contaminated by crustal material, giving rise to crust-like trace element patterns and radiogenic isotope systematics, (ii) an extremely depleted mantle characterized by very low whole-rock CaO and Al₂O₃, high-Fo olivine and Cr-rich spinel, which isotopically resembles European peridotitic massifs and lithospheric mantle; (iii) a component originating from the convecting mantle, characterized by unradiogenic ⁸⁷Sr/⁸⁶Sr and radiogenic ¹⁴³Nd/¹⁴⁴Nd and ²⁰⁶Pb/²⁰⁴Pb. These components demand multistage preconditioning of the lamproite-mantle source, involving an episode of extreme depletion, followed by involvement of terrigenous sediments, and finally interaction with melts originating from the convecting mantle, some of which are probably carbonatitic.We use our data on Mediterranean lamproites to characterize the mantle composition under the whole Alpine-Himalaya belt. Lamproites are an integral part of postcollisional volcanism, and are the most extreme melting products from a mantle which is ubiquitously crustally metasomatized. Enriched isotope signatures in Himalayan volcanics can also be explained by the involvement of subducted sediments instead of by proterozoic mantle lithosphere.     

阿拉善变质基底古元古代晚期的构造热事件

阿拉善地块可分为太古宙的叠布斯格杂岩(岩群)、古元古代的巴彦乌拉山杂岩(岩组)和古-中元古代的阿拉善杂岩(岩群)、波罗斯坦庙片麻杂岩和毕级格台片麻杂岩。太古宙的叠布斯格岩群和片麻岩中的锆石记录了1926Ma和1802Ma的变质事件年龄,角闪石记录了1918Ma的变质事件年龄,斜长石记录了1722Ma的冷却年龄。同时,在波罗斯坦庙变形的片麻状杂岩中的锆石记录了1839Ma的岩浆事件年龄。该区古元古代晚期的构造热事件,可初步将划分为2000～1900Ma的早期事件和1850～1800Ma的晚期事件,并在时间和特点上与大青山-集宁-大同一带变质地体中广泛发育古元古代晚期的岩浆-变质事件非常相似,进而表明,华北克拉通西部陆块中的古元古代晚期造山带(孔兹岩带)向西可延伸到阿拉善东部地区。     

青海省风火山地区砂岩铜矿成矿时代的裂变径迹热年代学证据

风火山盆地古近纪和新近纪沉积包括下部连续沉积的早始新世—早渐新世风火山群和早渐新世雅西措群,以及不整合其上的早中新世五道梁群。风火山地区的砂岩铜矿全部产于风火山群1岩组的灰(绿)色砂岩层中。采自风火山群1岩组含矿层和非含矿层中的3个磷灰石样品,分别获得了(22.5±2.3)Ma、(33.1±6.0)Ma和(28.0±3.6)Ma的裂变径迹年龄数据。其中33.1～28.0 Ma代表了该地区砂岩铜矿的成矿年龄.22.5 Ma则代表了成矿后构造热事件的年龄。风火山砂岩铜矿的成矿年龄处在其上覆的雅西措群沉积年龄范围内.显示砂岩铜矿是盆地早期沉积物压实脱水流体的产物。     

Heat flow and geodynamics in the Tyrrhenian Sea

The present heat flow in the southern Tyrrhenian Sea appears as a transient thermal wave that has migrated eastward in time. The higher heat flow in the south‐eastern side of the basin confirms the suggestion of an eastward‐migrating rift. Punctuation of the Tyrrhenian backarc extension in lithospheric boudins is accompanied by a concentrated increase in heat flow generated by asthenospheric intrusions and related magmatism progressively moving eastward. The migration of the asthenosphere in the same direction could explain these phenomena.     

广西云开地区新华铅锌(银)矿床白云母Ar-Ar年代学及其成矿动力学背景

新华铅锌(银)矿床位于钦杭成矿带南端云开地区的六万大山隆起区,是以铅锌为主的含银热液脉型多金属矿床。矿体赋存在含堇青石黑云母花岗岩中,主要呈脉状和透镜状产出。文章利用激光阶段加热技术对与矿化密切共生的白云母进行Ar-Ar年龄测定。结果表明,新华铅锌(银)多金属矿床的~(40)Ar/~(39)Ar坪年龄为(165.3±1.6)Ma(MSWD=0.38),反等时线年龄为(165.2±1.6)Ma(MSWD=0.42),等时线年龄和坪年龄一致,代表了白云母的冷却年龄和矿床的形成年龄,表明该矿床的形成与云开地区燕山早期的岩浆活动有关,这与区域成矿事件相吻合。结合前人对华南地区地球动力学背景的研究成果,初步认为新华铅锌(银)矿床形成于中-晚侏罗世碰撞板块边缘再次活化,岩石圈伸展的构造背景。     

Evolution of Alpine eclogites in the Eastern Alps: Implications for Alpine geodynamics

In the Eastern Alps Alpine eclogites are generally associated with rocks of continental lithosphere, while eclogites that are associated with oceanic assemblages are restricted to minor exposures. Such eclogites are exposed both in the Penninic unit of the Tauern Window and in the Austroalpine nappe complex. (1) In the central southern part of the Tauern Window (Eclogite Zone) eclogites and associated high pressure metasediments of a distal continental margin are intercalated between Penninic basement units. A mylonitic eclogitic foliation and stretching lineation are contemporaneous to the high pressure metamorphism and are related to the subduction of distal Penninic continental margin sequences. Continuous subduction of cool lithosphere resulted in blueschist facies overprint of the whole Penninic nappe pile. (2) Within the Middle-AustroAlpine Koralm/Saualm region most eclogites are eclogitic mylonites documenting plastic deformation of omphacite and garnet. The meso- and macroscale structures indicate an overall extensional regime possibly related to a large-scale SE-directed ductile low-angle normal shear zone. The eclogites are associated with migmatite-like structures and are intruded by pegmatites. This indicates decreasing pressure, but isothermal or even increasing temperature conditions during exhumation.These relationships argue for the subduction of Penninic continental lithosphere in the foot-wall of the Austroalpine unit at the time of exhumation of the Koralm/Saualm eclogites. Formation of the Austroalpine eclogites is explained by subduction of continental lithosphere, and subsequent, rapid exhumation in an upper plate tectonic position within an extensional regime.     

六合地区新元古代-新生代下地壳的成分与形成机制:来自麻粒岩包体的证据

六合地区地处扬子克拉通的西缘,前人对该地区下地壳的成分与形成机制尚无系统认识。本文通过研究新生代幔源侵入岩中所携带的深源捕虏体为认识该地区下地壳的成分和形成机制提供了直接证据。该捕虏体为高级正变质岩(麻粒岩相),岩性分别为石榴石透辉岩、石榴石角闪透辉岩、石榴石角闪岩。三者全岩Si O2=43.85%~50.82%,MgO=6.83%~14.77%,Mg#=0.50~0.64,Cr=87.1×10~(-6)~616×10~(-6),Ni=19.7×10~(-6)~143×10~(-6),皆属于低镁石榴石堆晶岩。通过石榴石-单斜辉石Mg-Fe交换地质温度计计算得知石榴石角闪岩的形成温度721~774℃,形成深度为45~47km,石榴石角闪透辉岩和石榴石透辉岩的形成温度803~829℃,形成深度为48~51km,说明三者皆形成于下地壳。捕虏体锆石多为变质锆石,锆石U-Pb年龄分别为259±9Ma和773±23Ma。捕虏体的全岩Sm-Nd等时线年龄分别为251±4Ma和809±64Ma。259Ma的锆石εHf(t)=-5.69~10.3,773Ma的锆石εHf(t)=5.87~17.7。年代学数据和锆石Hf同位素数据表明六合地区下地壳受到新元古代和晚二叠世岩浆底侵作用,同时发生变质作用。新元古代捕虏体富集大离子亲石元素(LILE),如Rb、Ba、Sr。高度亏损高场强元素(HFSE),如Nb、Ta、Ti。εNd(t)=4.36~5.28。表明在新元古代时期,六合地区的地壳受到俯冲弧岩浆底侵,经过批式熔融计算得知底侵岩浆源自地幔石榴石-尖晶石橄榄岩10%~30%部分熔融。晚二叠世捕虏体富集大离子亲石元素(LILE),如Rb、Ba、Sr。轻度亏损高场强元素(HFSE),如Nb、Ta、Ti。εNd(t)=-5.68~2.33。表明在晚二叠世时期,六合地区的地壳受到地幔柱-岩石圈地幔相互作用产生的岩浆底侵,经过批式熔融计算得知底侵岩浆由地幔石榴石-尖晶石橄榄岩10%~20%部分熔融而成。综上所述,在新元古代板块俯冲和晚二叠世地幔柱的分别作用下,六合地区的地壳受到地幔物质的加入形成镁铁质的新生下地壳。     

北祁连山东段银硐粱早古生代高镁埃达克岩：地球动力学及成矿意义

银硐粱早古生代花岗闪长岩分布在北祁连造山带东段屈吴山地区,侵入于原阴沟群和前寒武纪变质岩系中.它与米家山、扁强沟、清凹山以及南华山花岗岩类共同构成长约220千米的构造-花岗岩带,沿NW-NWW向展布.地球化学研究结果表明,银硐粱花岗闪长岩具有典型的高镁埃达克岩的地球化学特征,它们具有富Na贫K,SiO2＞56%,Al2O3＞15%,Na2O＞4.0%(4.51%～4.92%),K2O(1.96～2.77%),Na2O/K2 O=1.63～2.40,属钙碱性侵入岩;高Sr(599～691×10-6),低Y(6.3～8.1×10-6),Sr/Y＞40(81～94),Y/Yb＞10(Yb＜1.9×10-6),La/Yb＞20(22～45)以及相对于典型的埃达克岩,具有更高的Mg#(58～64,平均59)和相容元素Ni(31～38×10-6)和Cr(35～43×10-6)含量;富集轻稀土元素(LREE),亏损重稀土元素(HREE),(La/Yb)N＞10(16～32),轻微负Eu异常(Eu/Eu·平均为0.94),∑REE(85～112)×10-6;微量元素蛛网图显示,岩石富集大离子亲石元素(Rb、Ba、Sr),Nb-Ta和Ti负异常,相对于Ce和Nd,Sr为正异常.由于银硐粱高镁埃达克岩是俯冲洋壳部分熔融的产物,因此,它的存在表明,老虎山弧后洋盆在早古生代早期发生了向北的俯冲作用.银硐粱Cu-Au成矿作用与高镁埃达克岩关系密切,表明在北祁连构造带东段寻找与埃达克岩有关的Cu-Au矿床是一个新的找矿思路.     

Ophiolitic radiolarites of the Crimea and their significance for geodynamics of Mesotethys

In southern Crimea, at the southeastern foot of the Demerdzhi Mountain, at the base of conglomerates, aged from the Callovian to the Kimmeridgian, there were revealed pebbles of radiolarian cherts, from which using hydrofluoric acid, Triassic radiolarians of fine and satisfactory preservation were identified. Among them were Podobursa primitiva Tekin, Picapora robusta Kozur et Mostler, Spinotriassocampe carnica Kozur et Mostler, etc., by which the age of Crimean radiolarites was dated as Triassic (Ladinian-Early Norian).     

Structure of the sedimentary cover of the Pugachevo mud volcano area in Sakhalin: Evidence from geophysical modeling

The geological-geophysical data on the Pugachevo mud volcano group located in the zone of the submeridional Central Sakhalin Fault (CSF) are analyzed. The results of the density and geothermal modeling along two orthogonal profiles passing through the central part of the Pugachevo area are examined. It is found that the Late Cretaceous sequence of this fault-related area contains a subvertical narrow anomalous deconsolidation cone-shaped zone widening from 1 km on the surface to 4 km at its base (at the depths more than 6 km). The density of the deconsolidation blocks is 2.20–2.22 g/cm³, whereas that of the adjacent blocks reaches around 2.4–2.5 g/cm³. The largest deconsolidation block is located in the Lower Cretaceous Ai Formation, where a vast reservoir zone with mainly hydrocarbon gas (HC) is inferred at depths of more than 4400 m with temperatures of more than 140°C. The modeling results showed that the main reservoir of gases periodically ejected from the Pugachevo mud volcano is localized in the Ai Formation sequence in the tectonically weakened zone of the CSF at depths of 4.5–5.6 km. The overlying sequences contain smaller intermediate reservoirs. The Pugachevo area is promising for economic hydrocarbon reservoirs.     

Formation conditions of thermal springs in the Barguzin-Baikal area: Evidence from trace element and isotopic composition

Based on the relations between the chemical properties of elements, the formation conditions of thermal springs, and the geologic structure of the area, the main factors controlling the geochemistry of local fissure-vein waters were determined. Our results suggest that the most important factors are the temperature gradient and intensity of water exchange, which exert a fluctuating influence on the chemical composition of waters from different parts of the area. The chemical composition of hydrothermal waters provides insight into the geologic evolution of the region and conditions of water-rock interaction. It was shown that hydrochemical parameters can be used to refine the temperature of water heating, to rank springs by the duration of water-rock interaction, to establish the relative age and depth of faults that served as pathways for thermal water discharge, and to determine the geochemical conditions of water migration. The data reported in this paper demonstrate that fault-related mineralization formed during intense volcanic activity at the early stage of Baikal rift development affected the chemical composition of thermal springs.