合浦盆地——中国南方扭性盆地模式

位于广西南部的合浦盆地是中、新生代发育的小型沉积盆地，从该区的区域构造特征及大量地震资料揭示的盆地结构构造特征分析认为，合浦盆地的形成和发展始终受到区域性力偶的控制，表现出明显的张扭作用特征，后期（第三纪）受到压扭作用的强烈改造，合浦盆地这一发育特征在相当程度上反映了中国南方众多沉积盆地的共同特点。     

冀中坳陷下第三系构造背斜成因分类

冀中坳陷的下第三系构造背斜主要形成于伸展断陷背景下 ,与正断层系统联系紧密。根据背斜与断层关系 ,基本类型可分为 3种 ,即纵向、横向和复合背斜 ;根据具体构造力学背景 ,这 3种背斜可进一步分为 8类 ,即 :重力滑动型、张扭型、拆离拱张型、逆牵引型、断层线偏转型、侧接型、复杂变换型、复合型。这些背斜是构造演化的产物 ,在一定程度上指示了坳陷内的构造演化规律 ,同时又是形成油气藏的有利圈闭 ,目前已取得显著勘探成效     

Geochemistry of Pliocene/Pleistocene basalts along the Central Anatolian Fault Zone (CAFZ), Turkey

Abstract

Pliocene-Pleistocene volcanism accompanied strike-slip-related transtensional deformation along the K?z?l?rmak fault segment of the Central Anatolian fault zone (CAFZ) in the west of ?ark??la (Sivas-central Turkey). These volcanic rocks are represented by alkali olivine basalts. They can be divided into four different sub-groups on the basis of their Zr, Nb, TiO₂ contents. A primitive mantle-normalized incompatible trace element diagram for four subgroups shows close similarity to typical OIB pattern. Some of the incompatible trace element ratios (Ce/Y, Zr/Nb, La/Ba, La/Nb) are also akin to OIB values. Highly fractionated REE patterns (La/Yb_N=24.7–9.2) with no Eu anomaly are the main features of the alkali basalts and are comparable to alkaline volcanism in continental rift zones. On the basis of Al₂O₃/TiO₂, Nb/Y, Zr/Y Zr/Nb ratios, the geochemical differences among four sub-groups can be explained by variable degrees of partial melting of compositionally similar mantle source. Th/Nb, Th/Y, Nb/Y ratios and the primitive mantle-normalized trace element diagram suggests significant amount of crustal involvement for most of the alkali olivine basalts erupted along the CAFZ. Rupture of the continental lithosphere by strike-slip-related transtensional deformation might have caused decompressional partial melting of the asthenospheric mantle and generating alkali olivine basalts in this region. © 2001 Éditions scientifiques et médicales Elsevier SAS.     

Fault kinematic and Plio-Quaternary paleostress evolution of the Bakırçay Basin,Western Turkey

ABSTRACT

At the end of the Cenozoic, western Turkey was fragmented by intense intra-continental tectonic deformation resulting in the formation of two extensional areas: a transtensional pull-apart basin systems in the northwest, and graben systems in the central and southwest areas. The question of the connection of this Late Cenozoic extensional tectonics to plate kinematics has long been an issue of discussion. This study presents the results of the fault slip data collected in Bak?rçay Basin in the west of Turkey and addresses changes in the direction of extensional stresses over the Plio-Quaternary. Field observations and quantitative analysis show that Bak?rçay Basin is not a simple graben basin that has evolved during a single phase. It started as a graben basin with extensional regime in the Pliocene and was transformed into a pull-apart basin under the influence of transtensional forces during the Quaternary. A chronology of two successive extensional episodes has been established and provides reasoning to constrain the timing and location of subduction-related back-arc tectonics along the Aegean region and collision-related extrusion tectonics in Turkey. The first NW–SE trending extension occurred during the Pliocene extensional phase, characterized by slab rollback and progressive steepening of the northward subduction of the African plate under the Anatolian Plate. Western Turkey has been affected, during the Middle Quaternary, by regional subsidence, and the direction of extension changed to N–S, probably in relation with the propagation of the North Anatolian Fault System. Since the Late Quaternary, NE–SW extension dominates northwest Turkey and results in the formation and development of elongated transtensional basin systems. Counterclockwise rotation of Anatolian block which is bounded to the north by the right-lateral strike-slip North Anatolian Fault System, accompanies to this extensional phase.     

Transcurrent continental tectonics model for the Ossa-Morena Zone Neoproterozoic–Paleozoic evolution,SW Iberian Massif,Portugal

The Ossa-Morena Zone (SW Iberian Massif) was affected by continuous orogen-parallel transcurrent continental tectonics from the Neoproterozoic to the Carboniferous times, involving transtension (TT) and transpression (TP) processes that co-existed together, occurred separately in neighbouring regions by the means of strain partitioning or even worked diachronically. A first stage of transpression TP1 took place during the Late Neoproterozoic–Lower Cambrian as a result of Cadomian arc-continent collisional processes. Structures generated by transtension TT1 from Cambrian to Lower Devonian were related to strong lithosphere stretching responsible for the development of basins controlled by major detachments, tilting, rifting and important tectono–thermal diachronic processes. Denudation phenomena and inhibition of sedimentation related with thermal uplift (asthenosphere upwelling) and consequent subsidence caused by isostatic equilibrium, involving generalized transgressions, were processes responsible for major unconformities. The Variscan TP2-TT2 episodes that followed diachronically TP1-TT1, by maintaining the orogen-parallel transport direction, were concomitant with syntectonic deposition of continental basins in the OMZ and foreland basins in the SPZ. TT2 local transtension and tectonic exhumation of deep crustal rocks along major shear zones, favoured the opening of tectonic troughs filled up by sediments and volcanism. TP2 shortening have generated fold axes parallel to the orogen-strike and composite dissymmetric flower structures.     

Morpho-tectonic analysis of the Azores Volcanic Plateau from a new bathymetric compilation of the area

The existing studies of the Azores triple junction, although based on specific geological or geophysical data, largely rely upon morphological considerations. However, there is no systematic bathymetric coverage of this area, and the quality of the available bathymetric charts does not allow consistent morpho-structural analysis.In this work we present a new bathymetric grid elaborated with all the available data sources in an area comprised between 24° W to 32° W and 36° N to 41° N. The basic data set corresponds to the merge of NGDC data with new swath profiles. This new map, included as an Appendix, combined with other results from seismology and neotectonics, is the basis for the study of the morpho-structural pattern of the Azores area, the present day stress field and its implications on the current view of the Azores geodynamics.As a major result, we conclude that the Azores region is controlled by two sets of conjugated faults with 120° and 150° strikes that establish the framework for the onset of volcanism, expressing as linear volcanic ridges or as point source volcanism. This interaction develops what can be considered as the morphological signature of the Azores Spreading axis segmentation. We argue that the Azores domain, presently in a broad transtensional regime, is acting simultaneously as a ultra slow spreading centre and as a transfer zone between the MAR and the dextral Gloria Fault, as it accommodates the differential shear movement between the Eurasian and African plates.     

赣中宁都北部地区新构造活动初探

江西省中部宁都北部地区断裂构造发育,ETM453合成图像线形影像主要有北东向、北北东向和北西向,少量近东西向,线性构造具明显的新构造运动踪迹,地质证据有断层的走滑、地震、温泉和水系被错断等。其中,斜贯研究区中部的桃山断裂构造为一向南东下滑的右行张扭性断层,具捩断层性质,其挽近时期明显的构造运动造成桃山构造上盘距构造面不远的地带,特别是桃山构造的北东端如打鼓寨岩体北东部及外围,侵蚀作用较弱,保矿条件较好,具有较大的找矿潜力。     

Arc-parallel extension in preparation of the rotation of southwest Japan: Tectonostratigraphy and structures of the Lower Miocene Ichishi Group

Opening of the Japan Sea back arc basin was accompanied by extensional tectonics in the drifting southwest Japan arc. Various trends of Early Miocene grabens in the arc suggest multi-directional rifting, which necessarily involved strike-slip components of some of basin-margin faults. However, such components are not well understood. In this work we conducted a field survey in the Early Miocene Ichishi basin on the northern side of the Median Tectonic Line, central southwest Japan. We found that the basin was a compound of grabens that were formed along normal and sinistral strike-slip faults, the latter of which had northeast–southwest trends. The block faulting in this phase produced basement highs between sub-basins, which were filled with the lower part of the Ichishi Group. We found a low-angle angular unconformity at a middle horizon in the group, with which we define the upper and lower part of the group. The upper part onlapped both the basement highs and the lower part. It means that the transtensional basin formation ceased sometime between 18 and 17.5 Ma in the Ichishi area. The Ichishi basin turned subsequently into a sag basin subsided due to normal faulting probably along the Nunobiki-sanchi-toen fault zone. The transtension and the basin sag were driven by ENE–WSW extensional stress. This arc-parallel extension produced grabens various areas including Ichishi in the Early Miocene. The extensional deformation was eventually localized to the deep rift along the Fossa Magna to make the lithosphere under southwest Japan decoupled from that under northeast Japan. The decoupling allowed the rapid rotation of southwest Japan from ~17.5 Ma. The cluster of those grabens around the Ise bay probably determined the southeastern margin of the Kinki triangle.     

Esk Trough—Yarraman Block contact,an unconformity: Its nature and implications for regional tectonics

Detailed field study in southeast Queensland has resulted in the interpretation of an unconformity at the base of the Esk Trough sequence at its contact with the Yarraman Block (Maronghi Creek beds and associated intrusions). Previously this contact had been considered to be faulted. The nature of the unconformity is very variable with the Esk Formation resting on freshly eroded surfaces, on mature palaeosols and on an immature palaeosol. Immediately above the unconformity, the Esk Formation variably comprises scree breccia, fluvial conglomerate and arenite, and alluvial fan conglomerate and arenite. North‐northwest‐south‐southeast‐striking faults are associated with the unconformity. Where the unconformity parallels these faults, it retains a relatively constant character, but where it is cut by these faults, it shows greater variability, a relationship interpreted to result from contemporaneous tectonism. The Glen Howden Fault extends into structurally disturbed areas previously described as ‘fractured anticlines’ and ‘complex anticlines’, which are here interpreted as flower structures and associated features. The south‐southeast extension of the Glen Howden Fault strikes obliquely across the Esk Trough to finally pass into the South Moreton Anticline previously interpreted as a positive flower structure, and resolves structural and stratigraphic observations that previously appeared anomalous. Inferred strike‐slip movement in the Esk Trough resulted from Early to Middle Triassic north‐northwest‐south‐southeast oblique transtension followed by Late Triassic transpression, and similar tectonism probably affected adjacent portions of the Yarraman Block.     

The sequence of geological events and the dynamics of the Milky Way galaxy

Present‐day galactic data permit the construction of a galactic model in which the galactic gravitational field is described by a gravitational function rather than the Newtonian gravitational “constant” G. The concept of this empirical gravitational function, which is based on galactic orbital velocity data, envisages G as a function of time and space. In this model the interaction of this gravitational function, which has rotational symmetry in the galactic plane, and the slightly elliptical galactic orbit of the solar system results in a systematic variation of G. This interaction specifies a simple galactic time‐scale which can be conveniently compared with events of the geological time‐scale. For reasons of galactic evolution and modifying effects due to suspected changes of mass distributions in the universe with the passage of time, which are classed here under the Dirac‐Jordan Effect, such a comparison is initially restricted to the past 1#fr1/4> cosmic years, or 350 million years. The problems in extending such a comparison to 8 cosmic years are discussed, and such an extension seems promising, but it is hampered by the paucity of geological and geophysical data from the lower Palaeozoic and the Precambrian and the present uncertainties in regard to galactic evolution.

“Worldwide” statistical maxima and minima of the following geological criteria disclose an episodic correlation with the variation of G and the rates of change of G during the past 350 million years, as specified by this galactic model. It is possible to interpret this correlation in terms of accepted geological principles and concepts in most cases. The following geological phenomena are considered in this comparison of the galactic and geological time‐scales for the past 350 million years.

Period boundaries of the stratigraphic system