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991.
新疆构造运动期序及特征 总被引:6,自引:2,他引:6
新疆地域辽阔,地质构造运动复杂,特征各异。前人曾对新疆构造运动的划分及命名做了大量工作,但多有不一致,有些构造运动的划分或命名依据不足,因此失去了应有的代表性。现根据实际资料,对新疆地质构造运动重新归纳和认识,提出新疆境内构造运动可划分为11期32幕(次),其中前寒武纪6期、古生代2期17幕(次),中新生代3期9幕(次) 相似文献
992.
993.
Preliminary study of crust-upper mantle structure of the Tibetan Plateau by using broadband teleseismic body waveforms 总被引:2,自引:0,他引:2
Lu-Pei Zhu Rong-Sheng Zeng Francis T. Wu Thomas J. Owens George E. Randall 《地震学报(英文版)》1993,6(2):305-316
As part of a joint Sino-U.S. research project to study the deep structure of the Tibetan Plateau, 11 broadband digital seismic
recorders were deployed on the Plateau for one year of passive seismic recording. In this report we use teleseimic P waveforms
to study the seismic velocity structure of crust and upper mantle under three stations by receiver function inversion. The
receiver function is obtained by first rotating two horizontal components of seismic records into radial and tangential components
and then deconvolving the vertical component from them. The receiver function depends only on the structure near the station
because the source and path effects have been removed by the deconvolution. To suppress noise, receiver functions calculated
from events clustered in a small range of back-azimuths and epicentral distances are stacked. Using a matrix formalism describing
the propagation of elastic waves in laterally homogeneous stratified medium, a synthetic receiver function and differential
receiver functions for the parameters in each layer can be calculated to establish a linearized inversion for one-dimensional
velocity structure.
Preliminary results of three stations, Wen-quan, Golmud and Xigatze (Coded as WNDO, TUNL and XIGA), located in central, northern
and southern Plateau are given in this paper. The receiver functions of all three stations show clear P-S converted phases.
The time delays of these converted phases relative to direct P arrivals are: WNDO 7.9s (for NE direction) and 8.3s (for SE
direction), TUNL 8.2s, XIGA 9.0s. Such long time delays indicate the great thickness of crust under the Plateau. The differences
between receiver function of these three station shows the tectonic difference between southern and north-central Plateau.
The waveforms of the receiver functions for WNDO and TUNL are very simple, while the receiver function of XIGA has an additional
midcrustal converted phase. The S wave velocity structures at these three stations are estimated from inversions of the receiver
function. The crustal shear wave velocities at WNDO and TUNL are vertically homogeneous, with value between 3.5–3.6 km/s down
to Moho. This value in the lower crust is lower than the normal value for the lower crust of continents, which is consistent
with the observed strong Sn attenuation in this region. The velocity structure at XIGA shows a velocity discontinuity at depth
of 20 km and high velocity value of 4.0 km/s in the midcrust between 20–30 km depth. Similar results are obtained from a DSS
profile in southern Tibet. The velocity under XIGA decreases below a depth of 30 km, reaching the lowest value of 3.2 km/s
between 50–55 km. depth. This may imply that the Indian crust underthrusts the low part of Tibetan crust in the southern Plateau,
forming a “double crust”. The crustal thickness at each of these sites is: WNDO, 68 km; TUNL, 70 km; XI-GA, 80 km.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, Supp., 581–592, 1992. 相似文献
994.
位于南海北缘的珠江口盆地深水区作为我国海洋油气勘探的重点区域,具有良好的油气勘探前景。本文利用钻井地热测量数据分析了珠江口盆地深水区现今地温场及岩石圈热结构特征,通过古温标反演和拉张盆地模型正演相结合的方法定量揭示了白云凹陷新生代以来的热史,总结了不同地热地质条件对油气生成的影响。研究结果表明:珠江口盆地大地热流分布特征具有北低南高的特点,同时具有“热幔冷壳”的特征。珠江口盆地深水区始新世以来经历了两期拉张过程,第一期(47.8~33.9 Ma)拉张自始新世发生,拉张强度较大,凹陷中心基底热流快速上升至~82 mW/m2;第二期(23~13.8 Ma)拉张发生于中新世,此次拉张在白云凹陷南部更强烈,白云凹陷主体在 13.8 Ma达到最高古基底热流,此后进入热沉降阶段,基底热流值一直缓慢下降。磷灰石裂变径迹、磷灰石(U-Th)/He及锆石(U-Th)/He联合反演给出了最高古地温在13.8 Ma附近达到,后期温度基本稳定。 相似文献
995.
Summary X-ray diffraction studies reveal that most scapolites belong to space groupP4
2
/n. The mean intensity of weak reflections violating body-centered symmetry, reaches a maximum around 37 per cent meionite and extrapolates to zero at the pure end-members. All intermediate scapolites of the marialitemeionite series are pseudobody-centered, and as the composition approaches that of the end-members the structure becomes truly body-centered (I4/m).The weakh+k+l odd reflections are directly related to (1) orderdisorder of Al and Si in the tetrahedral framework and (2) structural distortion from body-centered symmetry.Scapolites may be regarded as a continuous, homogeneous solid solution. The cell dimensions are only approximately linearly related to composition and there is a maximum deviation from linearity, for those scapolites (25% Me 45% Me) whose symmetry departs the most from body-centered symmetry. These phenomena are interpreted in terms of the structural characteristic of the scapolites.
Über schwache Reflexe, welche der Raumzentrierung der Skapolithe widersprechen
Zusammenfassung Röntgenbeugungs-Untersuchungen zeigen, daß die meisten Skapolithe der RaumgruppeP4 2 /n angehören. Die durchschnittliche Intensität der schwachen Reflexe, welche der Raumzentrierung widersprechen, erreicht bei 37% Meionit-Momponente ein Maximum — für die reinen Endglieder nähert sie sich dem Wert Null. Alle intermediären Skapolithe der Marialith-Meionit-Reihe sind pseudo-raumzentriert und mit Annäherung der Zusammensetzung an jene der Endglieder wird die Struktur echt raumzentriert (I4/m)Die schwachenh+k+l ungerade Reflexe stehen (1) mit Ordnung-Unordnung von Al und Si im Tetradergerüst und (2) mit strukturellen Abweichungen von der Raumzentrierung in Beziehung.Die Skapolithe können als kontinuierliche homogene Mischkristallreihe betrachtet werden. Die Zelldimensionen ändern sich nur ungefähr linear mit der Zusammensetzung; die stärkste Abweichung von der Linearität tritt bei jenen Skapolithen (25% Me bis 45% Me) auf, deren Symmetrie am stärksten von der Raumzentrierung abweicht. Diese Phänomene werden aus den strukturellen Eigenheiten der Skapolithe interpretiert.相似文献
996.
997.
The Qingchengzi orefield is a large polymetallic ore concentration area in the Liaodong peninsula,northeastern China,that includes twelve Pb-Zn deposits and five Au-Ag deposits along its periphery.The ore-forming age remains much disputed,which prevents the identification of the relationship between the mineralization and the associated magmatism.In this paper,we quantitatively present the feasibility of making ore mineral ~(40)Ar/~(39)Ar dating and report reliable ~(40)Ar/~(39)Ar ages of lamprophyre groundmass,K-feldspar and sphalerite from the Zhenzigou deposit.Direct and indirect methods are applied to constrain the timing of mineralization,which plays a vital role in discussing the contribution of multistage magmatism to ore formation.The low-potassium sphalerite yielded an inverse isochron age of 232.8±41.5 Ma,which features a relatively large uncertainty.Two lamprophyre groundmasses got reliable inverse isochron ages of 193.2±1.3 Ma and 152.3±1.5 Ma,respectively.K-feldspar yielded a precise inverse isochron age of 134.9±0.9 Ma.These four ages indicate that the mineralization is closely associated with Mesozoic magmatism.Consequently,regarding the cooling age of the earliest Mesozoic Shuangdinggou intrusion(224.2±1.2 Ma)as the initial time of mineralization,we can further constrain the age of the sphalerite to 224–191 Ma.These new and existing geochronological data,combined with the interaction cutting or symbiotic relationship between the lamprophyre veins and ore veins,suggest that the Pb-Zn-Au-Ag mineralization in the Qingchengzi orefield mainly occurred during three periods:the late Triassic(ca.224–193 Ma),the late Jurassic(ca.167–152 Ma)and the early Cretaceous(ca.138–134 Ma).This polymetallic deposits are shown to have been formed during multiple events coinciding with periods of the Mesozoic magmatic activity.In contrast,the Proterozoic magmatism and submarine exhalative and hydrothermal sedimentation in the Liaolaomo paleorift served mainly to transport and concentrate the ore-forming substances at the Liaohe Group with no associated Pb-Zn-Au-Ag mineralization. 相似文献
998.
999.
Simultaneous observations of the 7–9 July 1966 solar particle event by energetic particle detectors on three satellites, IMP-III, OGO-III and Explorer 33 are utilized to show that large spatial gradients are present in the fluxes of 0.5–20 meV protons and 45 keV electrons. The event is divided into three parts: the ordinary diffusive component, the halo, and the core. The core corotates with the interplanetary field, and therefore it and the surrounding halo are interpreted as spatial features which are connected by the interplanetary magnetic field lines to the vicinity of the flare region. Upper limits to the interplanetary transverse diffusion coefficient for 4–20 meV protons at 1 AU are derived from the width of the halo. These are at least two orders of magnitude less than the parallel diffusion coefficient for the same energy particles.It is argued that the observed flux variations cannot be explained by an impulsive point source injection for any physically reasonable diffusion model. Instead, since the interplanetary transverse-diffusion coefficient is small for these low-energy particles, the observed spatial features are interpreted as the projection to 1 AU by the interplanetary field lines of an extensive injection profile at the sun. The geometry of the injection mechanism is discussed and it is suggested that some temporary storage of the flare particles occurs near the sun.Now at NASA, Goddard Space Flight Center, Greenbelt, Md., U.S.A. 相似文献
1000.