前陆冲断带构造分段特征--以准噶尔盆地西北缘断裂构造带为例

前陆冲断带普遍具有构造分段的特点。横断层、侧断坡与斜断坡常是构造分段的边界 ,它们起着运动方向、变形速率、构造样式与成因机制转换的作用。准噶尔西北缘前陆冲断带是古生代晚期—中生代早期发展起来的大型冲断推覆系统 ,南自车排子 ,北至夏子街、红旗坝的大型断裂带为其冲断前锋断裂。由于形成时间、活动方式与受力条件等出现变化 ,车排子—夏子街断裂带被北西向的横断层分割为构造样式与地质结构截然不同的三段 ,南段为红山嘴—车排子断裂带 ,构成车排子断隆的东部逆冲边界 ;中段为具压扭性质的克拉玛依—百口泉断裂带 ;北段为具冲断推覆性质的乌尔禾—夏子街断裂带。中生代晚期—新生代以来该前陆冲断带被稳定埋藏 ,构造分段是导致含油气性差异的主要原因     

A geophysical view of the Southeastern Brazilian margin at Santos Basin: Insights into rifting evolution

This study investigates the rifting structures of Santos Basin at the Southeastern Brazilian margin, based on an integrated geophysical approach. Our aim is to constrain the crustal basement topography of central and northern Santos basin, the presence of magmatism and the role of inherited structures in space and time through the rifting processes. We present a new high resolution aeromagnetic dataset, which in correlation with gravity anomalies enables us to interpret the tectonic trends and crustal basement structures. We calculated the magnetic basement depth for the central and northern Santos Basin using power spectrum analysis. The obtained depths range between 2 and 9 kms, and are comparable with results from previous works. From our integrated study, three margin domains could be identified, which display distinct rifting structures and are characterized by important lateral variation along the margin. The proximal domain displays trends and magnetic basement blocks NE–SW oriented, i.e., parallel to inherited onshore crustal basement with an inflexion to E–W oriented trends; the necking domain is characterized by oblique magnetic basement highs and lows (E–W and NW–SE) and a structural trend change. The trends and magnetic basement highs are bounded by NW–SE negative anomalies, interpreted as transfer zones. Oceanwards at the distal domain, the lineaments and transfer zones show a progressive structural inflexion to ENE and E–W, sub-parallel to adjacent South Atlantic Fracture Zones. The observed crustal basement architecture and segmentation suggest the reactivation of pre-rift structures at the proximal margin and the obliquity of rifting relative to them. From the proximal domain oceanwards the structural pattern may reflect the passage from a “continental type” domain, where lithospheric inheritance controls the deformation, to a distal margin where this influence diminishes and “new” structural trends are formed. We propose that northern Santos Basin show evidences of an intensely deformed zone, where rift evolved under oblique extension, similar to that observed at transform margin segments.     

Late Mesozoic rift evolution and crustal extension in the central Songliao Basin,northeastern China: constraints from cross-section restoration and implications for lithospheric thinning

The Songliao Basin, the largest oil-producing basin in China, was the centre of late Mesozoic rifting and lithospheric thinning in northeastern China. However, the rifts are still poorly revealed due to a thick cover of subsidence successions. By structural interpretation and sequential restoration of cross-sections based on new 2D seismic data and well data, this study presents the structural style, basin evolution, and horizontal crustal extension of the central Songliao Basin. We have developed a novel method to retrieve the regional extension principal strains. The results enable an assignment of rifting into two episodes. The earlier episode (ca. 157–130 Ma) was dominated by distributed faulting of numerous planar normal faults trending NNE–SSW, NNW–SSE, or near NS, probably reflecting pre-existing basement fabrics; in contrast, the later episode (ca. 130–102 Ma) was controlled by localized extension along several major listric faults. Horizontal crustal extension during rifting is estimated to have been 11–28 km (10.6%–25.5%), with the long-term average rate varying from 0.20 to 0.51 mm yr^–1. Regional horizontal strains show a gradual evolution from biaxial extension at the beginning of rifting to WNW–ESE uniaxial stretching during the later rifting episode. Brittle crustal extension is interpreted to have been associated with vertical strain due to tectonic stretching, which is estimated to have contributed more in thinning the lower crust than the mantle lithosphere. Accordingly, a two-episode dynamic model is proposed to explain rifting in the Songliao Basin. We suggest that the earlier event was dominated by delamination of the thickened continental lithosphere, whereas the later event was probably controlled by regional crustal detachment due to slab subduction and stagnancy of the Izanagi lithospheric plate.     

Oblique oceanic opening and passive margin irregularity,as inherited in the Zagros fold‐and‐thrust belt

The Zagros fold‐and‐thrust belt of SW Iran represents deformation of the former Arabian passive margin since Permian–Triassic opening of the Neo‐Tethys ocean. The Zagros belt is characterized by a present‐day structural salient‐recess setting inherited from past marginal embayment‐promontory geometry, which was involved in discontinuous ophiolite obduction and diachronous continental collision. We examine outcrop‐scale Mesozoic extensional brittle tectonics, preserved as syn‐depositional normal faults within the folded strata, in terms of stress tensor inversion. The result is then integrated with belt‐scale isopach, seismic and topographical data to delineate the geometry of a major irregularity along the passive margin originating from oblique oceanic opening. The implication of this configuration within the tectonic framework of oceanic closure is discussed.     

Area balancing as a test of models for the deep structure of mountain belts,with specific reference to the Alps

Basic concepts of structural restoration are applied to crustal cross-sections through mountain belts to explore large-scale tectonic models and deep structure. However, restored sections should account for variations in pre-orogenic crustal thicknesses. Crustal balancing approaches are reviewed and applied to two Alpine sections, coinciding with deep seismic experiments: NRP-20 East (Central Alps) and ECORS-CROP (Western Alps). Existing studies assume large (>300 km) orogenic contraction and only moderately thinned pre-orogenic crust. The resulting restored sections contain more crust than is imaged beneath the present-day Alps, the missing crust generally assumed to be subducted. Two kinematic modifications reduce the requirement for subduction: thinning and buoyancy-driven return flow of ultra-high-pressure metamorphic rocks during orogenesis; and pre-orogenic hyperextension. Using large stretching factors for the pre-orogenic crust negates crustal subduction on both Alpine transects. If the lower crust was approximately rigid, restorations of the Central Alps require strongly depth-heterogeneous stretching of upper and lower crust during Mesozoic rifting. Relaxing this requirement allows uniform lithospheric stretching, a corollary consistent with published subsidence estimates. Restorations make implicit statements on the form of pre-orogenic basins and the structure of continental margins incorporated into mountain belts that can in turn provide tests of tectonic models.     

Intracontinental orogenic transition: Insights from structures of the eastern Junggar Basin between the Altay and Tianshan orogens

Detailed subsurface structure of the eastern Junggar Basin is investigated using a large number of high-resolution two-dimensional reflection seismic profiles and well data. Our results reveal thrust faults, some of which are with strike-slip component, and fault-related folds dominating the subsurface structure of the study area. The thrust faults mainly show a divergent pattern towards the west and convergence towards the east. We divide these thrust faults and folds into three structural systems. The north thrust system, located in the north of the study area, is characterized by top-to-the southwest imbricate thrusts initiated from late Paleozoic. The central transpression system, dominating the central study area, mainly consists of thrust faults with visible strike-slip component, active from early Mesozoic until Cretaceous. The South thrust system includes top-to-the southeast thrusts in the southern part of the study area. The existence of these structural systems indicates that the eastern Junggar Basin underwent obvious intracontinental deformation in Mesozoic, probably due to the continuous convergence between the Altay and the Tianshan orogens after the main collision-accretion processes of the Central Asian Orogenic Belt.     

冀东马兰峪背斜南翼与西部倾伏端盖层变形特征及其构造意义

燕山中部冀东遵化、迁西、青龙一带以太古宇深变质结晶岩系为核部的东西向构造形迹长期以来被认为是一个复式背斜构造,近年来又有学者提出它是一个中生代变质核杂岩。这2种不同认识涉及到华北克拉通北部中生代区域大地构造演化和稳定克拉通内部大型基底结晶岩系的剥露机制问题。对马兰峪背斜南翼和西部倾伏端盖层岩系开展的详细构造研究表明,变形总体表现为连续的褶皱变形及伴生的逆冲构造;构造样式表现为基底卷入式的厚皮构造与盖层内部软弱岩系控制的薄皮构造共存的特征;变形机制表现为顺层挤压导致的纵弯弯曲和相关的断裂构造;近南北向的缩短率介于16%～27%之间。盖层岩系中未发现变质核杂岩构造模型所预期的系列高角度正断层。基底与盖层不整合面接触带尽管在后期构造变形过程中曾经发生过局部的差异性滑动,但并不是造成大规模构造剥蚀和地壳柱切失的剥离断层。因此,冀东马兰峪背斜不是中生代的变质核杂岩,而是水平挤压背景下基底结晶岩系与盖层共同卷入纵弯褶皱变形的厚皮式褶皱构造。     

Passive and active margin history of the northern Tatricum (Western Carpathians,Slovakia)

The Tatricum, an upper crustal thrust sheet of the Central Western Carpathians, comprises pre-Alpine crystalline basement and a Late Paleozoic-Mesozoic sedimentary cover. The sedimentary record indicates gradual subsidence during the Triassic, Early Jurassic initial rifting, a Jurassic-Early Cretaceous extensional tectonic regime with episodic rifting events and thermal subsidence periods, and Middle Cretaceous overall flexural subsidence in front of the orogenic wedge prograding from the hinterland. Passive rifting led to the separation of the Central Carpathian realm from the North European Platform. A passive margin, rimmed by peripheral half-graben, was formed along the northern Tatric edge, facing the Vahic (South Penninic) oceanic domain. The passive versus active margin inversion occurred during the Senonian, when the Vahic ocean began to be consumed southwards below the Tatricum. It is argued that passive to active margin conversion is an integral part of the general shortening polarity of the Western Carpathians during the Mesozoic that lacks features of an independent Wilson cycle. An attempt is presented to explain all the crustal deformation by one principal driving force - the south-eastward slab pull generated by the subduction of the Meliatic (Triassic-Jurassic Tethys) oceanic lithosphere followed by the subcrustal subduction of the continental mantle lithosphere.     

Salt décollement and rift inheritance controls on crustal deformation in orogens

We investigate the factors that control the shortening distribution and its evolution through time in orogenic belts using numerical models. We present self‐consistent high‐resolution numerical models that simulate the inversion of a rift to generate an upper crustal antiformal stack, a wide outer pro‐wedge fold‐and‐thrust belt, characterised by a two‐phase evolution with early symmetric inversion followed by formation of an asymmetric doubly‐vergent orogen. We show that a weak viscous salt décollement promotes gravitational collapse of the cover. When combined with efficient erosion of the orogenic core and sedimentation in adjacent forelands, it ensures the thick‐skinned pro‐wedge taper remains subcritical, promoting formation of an upper crustal antiformal stack. Rift inheritance promotes a two‐phase shortening distribution evolution regardless of the shallow structure and other factors. Comparison to the Pyrenees strongly suggests that this combination of factors led to a very similar evolution and structural style.     

Crustal structure of the southern Dabie ultrahigh-pressure orogen and Yangtze foreland from deep seismic reflection profiling

A new 140‐km‐long seismic reflection profile provides a high‐resolution crustal‐scale image of the southern Dabieshan high‐pressure (HP) metamorphic belt and the Yangtze foreland fold‐and‐thrust belt. The seismic image of the stacked section shows that the southern Dabieshan metamorphic terrane and Yangtze foreland belt are separated by a large north‐dipping fault. In the foreland the upper crust is dominated by a series of folds and thrusts formed during the collisional stage in the mid‐Triassic; it was reworked by crustal extension resulting in the formation of a late Jurassic and Cretaceous red‐bed basin. The southern Dabieshan profile shows stacked crustal slabs developed along the margin of the collisional orogenic belt. The Moho reflectors at 10–11 s (～30–33 km) are seismically prominent and segmented by a number of south‐verging thrusts that were probably developed by foreland‐directed thrusting of the deeply subducted continental crust during exhumation. The seismic reflection profile suggests that structures related to the Triassic–Jurassic subduction and exhumation of the Yangtze plate are preserved despite the severe crustal extension superimposed during the late Mesozoic and Cenozoic.     

On the tectonic origin of Iberian topography

The present-day topography of the Iberian peninsula can be considered as the result of the Mesozoic–Cenozoic tectonic evolution of the Iberian plate (including rifting and basin formation during the Mesozoic and compression and mountain building processes at the borders and inner part of the plate, during the Tertiary, followed by Neogene rifting on the Mediterranean side) and surface processes acting during the Quaternary. The northern-central part of Iberia (corresponding to the geological units of the Duero Basin, the Iberian Chain, and the Central System) shows a mean elevation close to one thousand meters above sea level in average, some hundreds of meters higher than the southern half of the Iberian plate. This elevated area corresponds to (i) the top of sedimentation in Tertiary terrestrial endorheic sedimentary basins (Paleogene and Neogene) and (ii) planation surfaces developed on Paleozoic and Mesozoic rocks of the mountain chains surrounding the Tertiary sedimentary basins. Both types of surfaces can be found in continuity along the margins of some of the Tertiary basins. The Bouguer anomaly map of the Iberian peninsula indicates negative anomalies related to thickening of the continental crust. Correlations of elevation to crustal thickness and elevation to Bouguer anomalies indicate that the different landscape units within the Iberian plate can be ascribed to different patterns: (1) The negative Bouguer anomaly in the Iberian plate shows a rough correlation with elevation, the most important gravity anomalies being linked to the Iberian Chain. (2) Most part of the so-called Iberian Meseta is linked to intermediate-elevation areas with crustal thickening; this pattern can be applied to the two main intraplate mountain chains (Iberian Chain and Central System) (3) The main mountain chains (Pyrenees and Betics) show a direct correlation between crustal thickness and elevation, with higher elevation/crustal thickness ratio for the Central System vs. the Betics and the Pyrenees. Other features of the Iberian topography, namely the longitudinal profile of the main rivers in the Iberian peninsula and the distribution of present-day endorheic areas, are consistent with the Tertiary tectonic evolution and the change from an endorheic to an exorheic regime during the Late Neogene and the Quaternary. Some of the problems involving the timing and development of the Iberian Meseta can be analysed considering the youngest reference level, constituted by the shallow marine Upper Cretaceous limestones, that indicates strong differences induced by (i) the overall Tertiary and recent compression in the Iberian plate, responsible for differences in elevation of the reference level of more than 6 km between the mountain chains and the endorheic basins and (ii) the effect of Neogene extension in the Mediterranean margin, responsible for lowering several thousands of meters toward the East and uplift of rift shoulders. A part of the recent uplift within the Iberian plate can be attributed of isostatic uplift in zones of crustal thickening.     

A crustal thrust system in an intracratonic tectonic environment

An intracratonic thrust belt, developed during the early Carboniferous in central Australia, deformed the Amadeus Basin and its basement, the Arunta Block. This belt is characterized by a marked structural asymmetry (vergence) and by the deposition of a thick molasse basin on the foreland. A review of existing field data shows that décollement tectonics produced folding, thrusting, faulting and back-faulting of the sedimentary sequence. Thin-skinned tectonics extend into the basement to produce recumbent folds and têtes plongeantes of nappe structures rooted in steeply dipping mylonite zones of greenschist to amphibolite grade. Minimum horizontal shortening displacements are 50–100 km resulting in a 50–70% contraction of the upper part of the basement. The structures and shortening are best explained by a crustal duplex, characterized by a crustal-scale thrust system, i.e. a sole thrust and imbricate faults, responsible for an isostatic bending of the underthrust slab. The observed Bouguer anomaly profiles support this crustal model. The dynamic evolution of this thrust belt on the scale of the crust is of thin-skin type.     

中国东南部晚中生代-新生代玄武岩与壳幔作用

中国东南部的火山活动在早中生代时期仅有很小规模,晚中生代最早的、较大规模的岩浆活动始于中侏罗世早期,至早白垩世是火山岩浆活动的鼎盛期,在近100个Ma的时间内形成了大面积分布的晚中生代火山-侵入岩,而在新生代则以面积较小的玄武岩浆喷出活动为主,局限分布于沿海一带。以晚中生代湘南、赣南和闽西南的近EW向火山岩带和浙、闽沿海地区的近NNE向火山岩带,以及新生代近NNE向火山岩带为研究对象,对这些火山岩的地球化学特征对比研究,结合时空分布,讨论了它们的起源及其与壳幔相互作用的关系,以及它们形成的构造环境,其结果显示,EW向晚中生代火山岩带（180～170Ma）的西段玄武岩独立产出,且明显属碱性系列;而中段和东段玄武岩和流纹岩伴生,其中的玄武岩均为亚碱性系列的拉斑玄武岩。它们形成于板内拉张构造环境,是中国东南部特提斯构造域向太平洋构造域转换、晚中生代大规模岩浆作用的序幕。研究表明,该火山岩带自西向东表现出不同程度的壳幔相互作用,玄武岩在成岩过程中有少量陆壳组分加入。NNE向晚中生代火山岩带（130～90Ma）主要为流纹质岩石,安山岩和玄武岩很少。即使是双峰式火山岩也以酸性岩为主,玄武岩仅占全部火山岩体积的30％以下。其中的玄武岩主要属钙碱性系列,少数属拉斑系列。它们形成于火山弧构造环境,是中国东南部受太平洋构造域影响发生大规模火山岩浆作用的主旋律。其中玄武岩岩浆成分受到了较高程度的陆壳物质混染,同时代的中性火山岩是由底侵的玄武岩岩浆和陆壳物质来源的酸性岩浆发生岩浆混合作用而形成的,反映了强烈的壳幔相互作用。NNE向新生代火山岩带,分布在浙闽沿海,以碱性系列玄武岩为主,均含幔源包体,并受NNE向大陆边缘断裂构造的控制。它们形成于板内裂谷环境,是中国东南沿海由晚中生代火山弧构造环境转换为新生代板内裂谷环境的标志,起源于软流圈地幔,并有EMII岩石圈地幔的混合组分,但基本没有受到陆壳物质的混染。     

海拉尔盆地早白垩世早期挤压变形事件的厘定及其构造意义

中生代发生在东北亚地区的蒙古-鄂霍次克造山作用一直是国内外地学界十分关注的大地构造事件.综合利用油气勘探新获取的地震反射、钻井、测井等资料,在海拉尔盆地贝尔凹陷早白垩世断陷层序之下识别出一套卷入强烈挤压变形的构造层.构造解析表明它主要由一条北东东向的逆掩断层及其相关的冲断-褶皱变形系统构成.地层岩性特征和碎屑锆石U-Pb测年结果显示,这是一套沉积于晚侏罗世末期的陆相湖盆碎屑岩建造,区域上应归属上侏罗统塔木兰沟组;结合上覆早白垩世断陷盆地的发育和邻区同期变质核杂岩体隆升剥露时代,提出海拉尔盆地这期冲断-褶皱变形事件发生在早白垩世早期(ca. 145~133 Ma),是晚中生代蒙古-鄂霍次克洋闭合后进入强烈陆内造山作用的构造变形记录.      

盆山地壳横向变化对挤压构造变形的影响——来自砂箱模拟实验的启示

前陆克拉通与造山带增生楔在地壳结构、力学性质等方面有明显的差异。挤压作用使盆山地壳横向变化通过构造变形表现出来。本文设计了具有深浅两个滑脱层"克拉通"与不同能干性的"造山楔"接触砂箱模型,通过模拟实验分析了盆山地壳横向差异变化对挤压构造变形的影响。实验结果表明,端部的挤压收缩位移由刚性的"克拉通"推挤相对软弱的"造山楔"使之形成挤压"冲起构造",而"造山楔"发生收缩变形的同时也斜向推挤刚性的"克拉通",并通过克拉通内部的滑脱层将收缩应变向克拉通内部传递。受不同深度滑脱层发育的影响,"克拉通"发育分层不协调收缩变形。在挤压作用下,随着"造山楔"与"克拉通"地壳在横向上能干性差异的增加,"造山楔"收缩形成的"冲起构造"幅度减小,而向"克拉通"侧向(斜向)挤压形成的"反冲构造"幅度增加,"造山楔"通过深层滑脱层向"克拉通"传递收缩应变的调节能力减弱,通过浅层滑脱层向"克拉通"传递收缩应变的调节能力增强。"造山楔"由深层过渡至浅层形成强变形带,由"克拉通"边缘至内部形成的深层冲断褶皱与浅层褶皱冲断组合过渡为深层褶皱与浅层的褶皱冲断组合,"克拉通"边缘的冲断带由深层的前展式楔状逆冲叠瓦扇构造向"克拉通"内部的浅层褶皱组合过渡。实验结果为理解中国西北部复杂山前冲断带构造的形成机制具有启示作用。     

龙门山断裂带印支期左旋走滑运动及其大地构造成因

位于青藏高原东缘的龙门山构造呈北东—南西向将松潘—甘孜褶皱带和华南地块分割开。前者主要是由一套巨厚的三叠纪复理石沉积组成 ,分布在古特提斯海的东缘。后者由前寒武纪基底和上覆的古生代和中生代沉积盖层组成。位于汶川—茂汶断裂以东的前龙门山存在一系列倾向北西的逆掩断层 ,它们将许多由元古宙和古生代岩层组成的断片向南东置于四川盆地的中生代红层之上 ,构成典型的薄皮构造。许多研究由此断定松潘—甘孜褶皱带和四川盆地之间在中生代发生过大规模的北西—南东向挤压。然而 ,汶川—茂汶断裂西侧的松潘—甘孜褶皱带内部的挤压构造线大多是垂直于而不是平形于龙门山断裂带 ,这表明当时的挤压应力不是北西—南东向而是北东—南西向。近年来在龙门山构造带内发现 ,在三叠纪时龙门山断裂带在发生推覆的同时还经历过大规模的北东—南西向的左旋走滑运动 ,协调走滑运动的主要构造为汶川—茂汶断裂。走滑运动的成因与松潘—甘孜褶皱带北东—南西向缩短有关。汶川—茂汶断裂的左旋走滑在龙门山的北东端被古特提斯海沿勉略俯冲带的消减和发生在大巴山的古生代 /中生代岩层的褶皱和冲断作用所吸收 ,在龙门山的南西端被古特提斯海沿甘孜—理塘俯冲带的消减和松潘—甘孜三叠纪复理石的褶皱和冲断作用所吸?     

Convergence in a thermally softened thick crust: Variscan intracontinental tectonics in Iberian plate rocks

The subduction phase in the development of the Variscan Orogen in SW Europe was followed by an extended period of ‘intracontinental’ tectonics. The progressive temperature rise in the hinterland during plate convergence was accompanied by widespread partial melting in the lower crust and the nucleation of kilometric buckle folds and crustal‐scale shear zones in the stronger upper crust. Thermal mechanical weakening in the core of the orogen was contemporaneous with shortening and thickening in the foreland fold‐and‐thrust belt. We evaluate lithospheric strength profiles in the hinterland and foreland based on the metamorphic and structural record for three tectonic stages. We find that lower crustal strength varied in space as well as in time during orogenesis. Strength contrasts between the foreland and the hot hinterland during convergence may have led to the additional indentation of the foreland into the hinterland of the Ibero‐Armorican Arc.     

The North Tyrrhenian–Northern Apennines post-collisional system: constraints for a geodynamic model

The North Tyrrhenian–Northern Apennines post-collisional system (NTAS) has been analysed on the basis of marine reflection profiles and bibliographic sources with the aim of providing an up-to-date geotectonic and evolutive framework consistent with structural data. The continental rifting began to affect the most internal (western) side of the system in the middle (?)-upper Miocene, while the most external (eastern) zones were touched by rifting only in Pleistocene times. The birth and development of extensive, asymmetric basins took place with a progressive speeding up of rifting towards the external sectors. A diachronous, regionally extended and eastward rejuvenating unconformity, recognizable within the Neogene–Quaternary basins, marks the passage from the syn-rift to the post-rift tectonic regime. While the first is everywhere dominated by extension, the second one produces vertical movements. Reflection terminations related to this unconformity are interpreted in terms of vertical tectonic component. Three zones that experienced different post-rift vertical movements are thus recognized in the NTAS: subsidence in the North Tyrrhenian deep water region; tectonic stability or alternation of moderate subsidence and uplift in the continental shelf and western Tuscany, strong uplift in eastern Tuscany. The updated structural data demonstrate that the NTAS upper crust is crosscut by both Tyrrhenian-dipping and Apennine-dipping low-angle detachment planes, above which the upper crustal blocks rotated and experienced extensional transport along two opposite directions: to the west and to the east, respectively. The coexistence of opposite-dipping crustal surfaces bears two fundamental implications for the NTAS geodynamics. First it stresses the importance of the anti-Apennine transfer faults, since they separate crustal blocks of opposite extension polarity. Secondly, it testifies that the extension tectonics not only re-utilized former crustal thrust planes, but also gave origin to new significant E- and NE-dipping detachment planes. Plan and crossview geometries of faults, together with considerations on the role of the metamorphic core complexes, point to an interpretation of the NTAS structure that is more consistent with the ‘anastomosing shear’ model rather than the 'simple shear' or the ‘delamination’ ones.     

淮北夹沟—桃山集地区推覆构造研究

本区存在大型中生代推覆构造,所有震旦纪—古生代的沉积岩层都卷入了褶皱和断裂,构造推覆发生在较高构造部位,属脆性变形域,以台阶状逆断层和断层相关褶皱为特征。区内存在若干推覆构造,每个岩片均可分为上盘、下盘和滑动层系三部分,共查明8个滑动岩系。是一种发生在早中生代的盖层推覆,无根褶皱,也是徐宿地区最重要的控煤构造。最后对推覆构造的地球动力学机制进行了讨论。     

ON THE AGE OF METAMORPHISM IN THE JAPANESE ISLANDS

The Sivas Basin extends over a major crustal structure underlying the contact zone between the Tauride and Pontide belts. The Kirsehir block, a continental crustal element lying between the main belts, introduces a subordinate suture in front of the Pontides—the Inner Tauride suture. The junction of the two main sutures occurs between Hafikand Imranli. Four structural zones have been considered. The northern basement of the basin, which includes both the Kirsehir continental crust and thrust sheets of ophiolite and pelagic sediments, forms an imbricate stack with an Eocene cover. The Eocene cover shows two distinct sequences: marine neritic and continental basalts overlying the Kirsehir basement, and deltaic and basinal deposits lying to the southeast. Southward tectonic stacking of the entire pile has occurred repeatedly since Oligocene time. The Sivas Basin proper is separated from the Kirsehir basement by the Kizilirmak Basin. This new structural unit consists of nearly undeformed, middle Miocene sandstones and conglomerates and a Pliocene lacustrine limestone.

The Sivas Basin proper corresponds to a fold-and-thrust belt involving an Oligocene deltaic plain with intervening large-scale evaporitic stages and subsequent lower Miocene shallow-marine deposits. Three distinct tectonic domains are considered—(1) an eastern A domain, characterized by a hinterland of deep imbricate and rare northward thrusts; (2) a transitional B domain, corresponding to a series of lateral thrust branches propagating to the southwest; this domain later was deformed by the (3) C domain, displaying a foreland-dip type of stacking. The Caldag-Tecer-Gurlevik ridge forms a structural entity of topographic highs along the southern margin of the Sivas fold-and-thrust belt. Three Eocene-cored anticlinoria arranged along an E-W relay zone fold a passive-roof composite allochthon including ophiolitic elements together with Upper Cretaceous to Eocene limestone and conglomerate. The sole of this allochthon consists of Oligocene gypsum. The Kangal Basin, a large syncline cored by Pliocene continental deposits, corresponds to the southernmost unit. The boundary with the Caldag-Tercer-Gurlevik ridge is partially concealed by a lower Miocene continental basin, overlain by a N-vergent thrust of a lower Mesozoic limestone of the Taurus platform. If the southeastward propagation of thrusting in the Sivas thrust belt and related northward thrusts at a variety of scales is considered to represent the main thrust over the undeformed Kizilirmak basin, a comparison with modern analog structural features and analog models yields a coherent interpretation of this basin in terms of its forearc-prism evolution. At a larger scale, the Sivas Basin should be considered as a piggyback basin developed along the northward-rotated rear of the Tauride wedge and the synchronous southward thrusting of the Kirsehir-Pontide wedge. At least in early Miocene time, the Inner Tauride and Erzincan sutures corresponded to a single intracontinental thrust zone along which part of the displacement of the southern front of the Tauride has been progressively transferred.