A reinvestigation of thrusting in Portugese Timor

Field relations from a small area in the Maubisse region of Portuguese Timor fail to support the hypothesis of southward overthrusting of Permian rocks (Audley‐Charles, 1965) or the postulate that the Maubisse Formation represents a mid‐Tethys island group (Audley‐Charles et al., 1972).     

Whole-rock geochemistry of the Hili Manu peridotite,East Timor: implications for the origin of Timor ophiolites ∗

The Hili Manu peridotite occupies a key position at the outer limit of continental crust on the north coast of East Timor. Most models for the tectonic evolution of the Outer Banda Arc interpret peridotite bodies on Timor, such as Hili Manu, as fragments of young oceanic lithosphere from the Banda Arc (upper plate). However, recent workers have used major-element geochemistry to argue that the peridotite bodies on Timor were derived from the Australian subcontinental lithosphere. Our major, trace and isotopic geochemical study of the Hili Manu peridotite body supports a supra-subduction origin from either a forearc or backarc position for the Hili Manu peridotite. In particular, the wide range in Nd and Sr isotopic compositions, overlapping that of arc volcanics from the Sunda – Banda Island arc, and highly fractionated Nb/Ta values indicate a supra-subduction setting. As there is no evidence for subduction beneath the rifted Australian continental margin, it is unlikely that the Hili Manu peridotite is Australian subcontinental lithosphere. This result, along with the clear supra-subduction setting of the Ocuzzi peridotite and associated volcanics in West Timor, gives support to the interpretation that the Miocene collision between the Banda Arc and the Australian continental margin has produced widespread ‘Cordilleran’-style ophiolites on Timor.     

The Bouguer gravity field and crustal structure of eastern Timor

The results from a recent North—South gravity traverse across eastern Timor show that the Bouguer gravity field is characterized by a strong, 6 mGal/km, gradient on the north coast. This gradient appears to be a fundamental feature of Timor and of the Outer Banda Arc. Preliminary computer models suggest that, to a first approximation, the gradient is due to a vertical fault at the north coast of Timor separating oceanic crust from continental crust. The fit between the computed and observed gradient can be improved significantly by assuming a northward-dipping lithospheric slab, north of Timor. The model further indicates that the Australian continental crust extends at least as far as the north coast of Timor.     

Deformation and metamorphism of the Aileu Formation,north coast,East Timor and its tectonic significance

The large block of metamorphic rocks along the north coast of East Timor is of special interest as it occurs at the boundary between continental and oceanic crust in an island arc-continent collision zone. A detailed study of the structure and metamorphic history of 400 km² of this formation showed it has a complex history of penetrative deformation but the structure is coherent.Pelites, psammites and limestones interlayered with dolerites and amphibolites have been metamorphosed in a medium pressure environment. They now form a metamorphic province zoned from low greenschist facies in the southwest to upper amphibolite facies in the east. The earliest recognised deformation phase predated the metamorphism and produced a widespread layer—parallel schistosity but no recognisable folds. The second deformation phase post-dated the metamorphic maximum and micropetrological evidence indicates a gradual cooling during this event. This deformation produced tight folds with an axial plane schistosity and transposed the earlier structures. The progressively weaker third and fourth phases developed crenulation cleavages and related folds, under greenschist facies conditions. Open, fifth phase, macroscopic folds were probably synchronous with strike slip faulting parallel to the north coast. Later dip slip faulting juxtaposed the Aileu Formation with Permian and Mesozoic sediments of very low metamorphic grade.Reconnaissance K/Ar radiometric dating using hornblende and biotite showed the prograde metamorphic maximum occurred before 11 Ma ago and implies that the second, and strongest, deformation phase occurred in the late Miocene. This young age establishes the relationship of the deformation events to the collision between Australia and the Inner Banda Arc.The proposed models for the structure of Timor must be modified to fit the deformation history of the Aileu Formation. If Timor is essentially autochthonous, the Aileu Formation was probably deposited in a Palaeozoic graben and the metamorphic maximum may have occurred in the Jurassic. The overthrusting models must be modified in the light of the close correlation in time between penetrative deformation and emplacement of the proposed thrust sheets. The analogy proposed between Timor and ‘normal’ convergent margins is not supported but it may be possible to draw analogies with the Molucca Sea.     

The Sumba enigma: Is Sumba a diapiric fore-arc nappe in process of formation?

The anomalous updomed morphological expression of Sumba island, its enigmatic lack of strong Neogene deformation and the northward morphological indentation of southern Sumbawa and Flores require explanation.The stratigraphy of Sumba may be correlated with the Cretaceous to Miocene part of the Timor allochthon. The sedimentary and eruptive rock succession in Sumba shows remarkable similarities with the allochthonous Palelo, Wiluba and Cablac deposits of Timor. In both islands the Cretaceous parts of these sequences are regarded as characteristic of fore-arc deposits built on thin continental crust.The Timor nappe is interpreted as a 5 km thick tectonic flake of the Banda fore-arc thrust onto the Australian continental margin in the mid-Pliocene collision. The postulated Sumba nappe has not yet been thrust onto the Australian margin which, in the Sumba region, has not yet converged as close to the arc as in the Timor area. The postulated Sumba nappe is interpreted as a diapiric elongated dome of the Sunda fore-arc that is being squeezed by the converging margin of Australia against the volcanic islands of Sumbawa and Flores.The absence of indications on the seismic reflection profiles for the presence of the thrust fault of the Sumba nappe may perhaps be explained by the thrusts being nearly horizontal within flat-lying strata.The Savu thrust is correlated with the probably older (pre-Late Pliocene) Wetar Suture as a major southward dipping lithospheric rupture. East of 124°E, this suture does not seem to have moved much since the mid-Pliocene collision that emplaced the nappes on Timor. However, microearthquake data suggest some activity is continuing.     

西天山造山带的构造变形特征研究

西天山造山带由伊犁中天山北缘－北天山推覆走滑系统、伊犁中天山南缘－南天山推覆走滑系统和两者之间的伊犁地块组成。伊犁中天山北缘－北天山推覆走滑系统包括北天山推覆构造带、伊犁中天山北缘逆冲带和中天山北缘断裂带。伊犁中天山南缘－南天山推覆系统包括中天山南缘逆冲带、南天山北坡增生楔推覆席、南天山北坡早古生代被动陆缘推覆席、南天山南坡晚古生代洋壳－火山弧－复理石复合推覆席、中天山南缘断裂带和南天山南坡断裂带。区域构造和变形构造的研究表明西天山推覆构造主要奠定于早二叠世早期，走滑运动发生于晚二叠世－早三叠世。中新生代，沿古生代构造有进一步的推覆和走滑运动发生     

Palaeomagnetic reconnaissance result from the maubisse formation,east timorand its tectonic implication

A preliminary palaeomagnetic investigation of the supposedly allochthonous Permian Maubisse Formation in East Timor yielded a mean direction of magnetization of decl. = 140E, incl. = +45 and α₉₅ = 13°. This direction is indistinguishable from that of the autochthonous Permian Cribas Formation reported earlier. The apparent agreement between the palaec magnetism of the two Formations is interpreted to imply that both are autochthonous and have been part of the Australian continental margin since the Permianand does not support the supposed Asian origin for the Maubisse Formation.     

The Structure and Stratigraphy of the Western External Sierras of the Pyrenees,Northern Spain

The External Sierras of the southern Pyrenees represent the frontal thrust complex of a south Pyrenean thrust sheet which was active from the late Eocene to early Miocene. Triassic, Cretaceous and Eocene limestones, sandstones and mudstones involved in this thrusting can be divided into eight mappable units. Mapping and the construction of serial sections across the Western External Sierras show that the amount of southward translation of the thrust sheet increases eastwards from the thrust tip. There is an increased slip of at least 5km along 30km of the External Sierras. Structures show a progressive development from a “primitive” form in the west to a more complex thrust and fold geometry in the east. The general pattern is one of thrust and fold development in response to compression from the north. Backthrusting has occurred on the forward side of the frontal thrust complex. These backthrusts cut up section towards the north and form triangle zones where they intersect thrusts which cut up sections towards the south. The latest thrust movements deformed early Miocene fanglomerates and were out-of-sequence reactivations of earlier thrusts.     

Tectonic collision processes after plate rupture

Rupture of a continental plate subducted below a forearc produces a fold and thrust mountain belt with fast overthrusting of nappes. Post-rupture plate unflexing leading to reflexure provides a mechanism for foreland basin formation. Application to the Australia-Banda Arc collision accounts for the origin of the Timor Trough, its imbrication and contemporaneous extension in outer arc, as well as reversal of subduction direction after the emplacement of nappes.     

CENOZOIC FAULTING ALONG THE SOUTHEASTERN EDGE OF THE TIBETAN PLATEAU IN THE YANYUAN AREA AND ITS TECTONIC IMPLICATIONS

CENOZOIC FAULTING ALONG THE SOUTHEASTERN EDGE OF THE TIBETAN PLATEAU IN THE YANYUAN AREA AND ITS TECTONIC IMPLICATIONS     

Thermal history of Australian passive margin cover sequences accreted to Timor during Late Neogene arc–continent collision,Indonesia

Paleotemperature indicators and apatite fission track analysis of Australian continental margin cover sequences accreted to the active Banda arc–continent collision indicate little to no heating during rapid late Neogene uplift and exhumation. Thermal maturation patterns of vitrinite reflectance, conodont alteration and illite crystallinity show that peak paleotemperatures (PPT) increase with stratigraphic and structural burial. The highest PPT is found in the northern hinterland of the accretionary wedge, which was beneath progressively thicker parts of the upper plate towards the north. Major discontinuities in the pattern of PPT are associated with the position of major thrust ramps such as those forming the Ramelau/Kekneno Arch (RKA). PPT for Upper Triassic to Neogene strata south of the RKA are 60–80°C, which are similar to, and in many cases lower than, correlative and age equivalent units drilled on the NW Australian Shelf. Permian to Lower Triassic sedimentary strata thrust over younger units within and north of the RKA have PPT of 100–220°C. Thrust sheets accreted beneath the upper plate have PPT approximately 90°C higher than those frontally accreted. Metamorphism of the northernmost units of these sequences yield PPT of >300°C. Thrust stacking yields an inverted thermal profile of PPT decreasing discontinuously downward and to the south (towards the foreland). The timing of PPT is constrained by apatite fission track ages from mostly Triassic continental margin cover sequences. Ages of Upper Triassic units are primarily coeval with deposition and show little evidence of thermal annealing, whereas those of Lower Triassic units are almost completely annealed and range from 1.8±0.5–19.2±9.7 Ma. The clustering of apatite fission track ages into two distinct groups indicates that the upper boundary of the partial annealing zone has remained for some time at a Triassic stratigraphic interval in the slope and rise of the NW Australian continental margin. The position of this zone on the present shelf is higher in the stratigraphic column due to the greater thickness of post-breakup shelf facies units. Thrust stacking of rise, slope and shelf units produces an inverted vertical profile of increasing apatite fission track age with depth. Lack of any long confined track lengths in apatite from all of the units requires rapid and recent exhumation of the thrust stack, which is coincident with rapid phases of Pliocene–Pleistocene exhumation documented throughout Timor. These data preclude pre-Late Miocene tectonic burial or pre-Pliocene exhumation of the NW Australian continental margin.     

南秦岭东段下寒武统黑色岩系钒矿成矿地质背景浅析

南秦岭下寒武统黑色岩系形成于扬子地块北部被动陆缘裂谷裂陷盆地中,以发育巨厚的硅质岩、碳硅质岩、泥质岩夹碳酸盐岩、重晶石矿层为特征.沿控盆同生断裂运移的含钒的含矿热液被泥质岩吸附,构成矿源层,印支-燕山期自北向南顺层滑脱逆冲推覆,基底与盖层之间滑脱逆冲推覆韧性剪切带使得矿源层成矿元素活化迁移聚集成矿.牛山、凤凰山、平利基底隆起周缘是寻找钒矿的最有利区段.     

Localized ductile thrusting north of the Variscan Front,Ross Island,southwest Ireland

Two thrusts occur on Ross Island: the Head of Ross Thrust and the more southerly Ross Island Thrust. These lie to the north of the Killarney–Mallow Fault (KMF), the boundary frequently interpreted as the Variscan Front. The Ross Island Thrust, exposed in outcrop and in seven borehole cores, has emplaced dark blue–grey limestones of the Courceyan Ballysteen Formation over pale grey–brown Rockfield Limestone Formation of Chadian–Holkerian age. These lithologies at Ross Island exhibit a continuum of deformation at both the micro‐ and macro‐scale, beginning with the generation of a spaced cleavage, formed during layer parallel shortening, that was subsequently rotated into parallelism with fold axial planes. Extensional microstructures are predominant in thin section and are associated with attenuation of the fold limb. Calcite veins are also attenuated and lie parallel to a mylonitic fabric close to the thrust plane. Lithological boundaries, the prominent pressure solution cleavage and the southerly dipping limb of an asymmetrical antiform are all parallel and form a composite planar anisotropy. This has controlled the location of the ductile Ross Island Thrust, which formed during the attenuation and shearing of a common fold limb. Ductile thrusts within the limestones at Ross Island contrast with the reactivation of basin‐margin extensional faults further to the south along the major KMF. The Ross Island Thrust is considered to result from deformation ahead of the major northerly propagating Variscan décollement thrust and does not necessitate a continuous décollement structure north of the KMF. Mineralization at Ross Island exhibits remobilization associated with the formation of a pressure‐solution cleavage and probably pre‐dates thrusting. Copyright © 2003 John Wiley & Sons, Ltd.     

IBM型洋内弧的形成机制:以祁秦增生杂岩带为例

岛弧的形成和演化对于理解板块构造和大陆生长有重要意义.祁连山-西秦岭一带发育两条不同类型的弧岩浆岩带,其北侧为北祁连增生杂岩带,由蛇绿岩、高压变质岩和大陆型弧岩浆岩带组成,形成时代为520~440 Ma.岩浆岩以中酸性火山岩-侵入岩为主,部分地区发育典型双峰式火山岩.南侧为祁秦增生杂岩带,由寒武纪蛇绿岩（525~490 Ma）和奥陶纪IBM型洋内弧岩浆岩（470~440 Ma）组成,蛇绿岩以拉脊山-永靖洋底高原型蛇绿岩为代表,蛇绿岩的上部熔岩部分由夏威夷型苦橄岩、板内碱性玄武岩和板内拉斑玄武岩组成,为大洋板块内部地幔柱活动产物.洋内弧岩浆岩以高镁玄武岩、玄武安山岩、高铝安山岩、玻安岩为主,局部发育赞岐岩.祁秦增生杂岩带的蛇绿岩和弧火山岩组合很好地说明洋底高原与海沟碰撞和俯冲带阻塞是造成俯冲带起始和新的洋内弧形成和发展主要因素.      

东秦岭地区“刘岭群”的重新划分

东秦岭地区原划为泥盆系的“刘岭群”被一条大型韧性推覆剪切带分为南北两个岩系,北部岩系为一套中浅变质的以杂砂岩为主,夹火山熔岩、火山碎屑岩和含陆缘砂碳酸盐岩的沉积-火山建造,其中紧闭、倒转、平卧褶皱和逆冲断层极为发育,沉积学特征及物源分析显示其为早古生代末-晚古生代初华北板块南缘活动大陆边缘沉积;南部岩系为一套由浅变质的粉砂岩、泥质岩、石英砂岩和碳酸盐岩组成的巨厚陆源碎屑沉积,发育东西向陡倾劈理及开阔对称褶皱组成的复式褶皱,沉积学特征和物源分析表明其为晚古生代初期扬子板块北缘沉积。“刘岭群”两岩系的岩性组合、沉积学特征、变质作用、构造变形期次、生物化石特征及形成的大地构造环境等方面的差异足以划分为不同的岩群,“刘岭群”应予解体。     

Phanerozoic history of Western Australia related to continental drift

From north to south, the sedimentary basins of Western Australia change from broad platforms of wholly marine strata that span the entire Phanerozoic (Bonaparte Gulf and Canning Basins) through the intermediate Carnarvon Basin to rifts of nonmarine Permian and Mesozoic strata (Perth Basin). These contrasts in age, facies, and structure reflect different positions of the basins in Gondwanaland: the Bonaparte Gulf and Canning Basins have lain at the continental margin facing an open ocean during the entire Phanerozoic, whereas the Perth Basin lay in the interior of Gondwanaland until India and Australia moved apart in the Cretaceous.

The Eucla Basin came about by events connected with the dispersal of Antarctica and Australia in the Eocene. The northwest part of the Australian Block (Timor and the Timor Sea) was deformed in the Miocene when Australia collided with southeast Asia.     

新疆蛇绿岩带的分布、特征及研究新进展

新疆位于亚洲大陆的北部,构造上跨越了古亚洲和特提斯两大构造域,现今主要由中新生代盆地和其间的古生代造山带组成。古生代造山带主要由陆缘岩系和岩浆岩组成,其中夹有洋壳残片和前寒武结晶基底的碎块;洋壳残片从北向南大致分布12条,其中出露较集中的约30多处。这些蛇绿岩,以塔里木盆地为界,北部主要为古亚洲洋的洋壳残片,南部主要为特提斯洋的洋壳残片。在介绍其基本特征的同时,本文侧重报道了近年来新疆区域地质调查的一些成果。     

Ocean trench blocked and obliterated by Banda forearc collision with Australian proximal continental slope

The bathymetry and abrupt changes in earthquake seismicity around the eastern end of the Java Trench suggest it is now blocked south–east of Sumba by the Australian, Jurassic-rifted, continental margin forming the largely submarine Roti–Savu Ridge. Plate reconstructions have demonstrated that from at least 45 Ma the Java Trench continued far to the east of Sumba. From about 12 Ma the eastern part of the Java Trench (called Banda Trench) continued as the active plate boundary, located between what was to become Timor Island, then part of the Australian proximal continental slope, and the Banda Volcanic Arc. This Banda Trench began to be obliterated by continental margin-arc collision between about 3.5 and 2 Ma.The present position of the defunct Banda Trench can be located by use of plate reconstructions, earthquake seismology, deep reflection seismology, DSDP 262 results and geological mapping as being buried under the para-autochthon below the foothills of southern Timor. Locating the former trench guides the location of the apparently missing large southern part of the Banda forearc that was carried over the Australian continental margin during the final stage of the period of subduction of that continental margin that lasted from about 12 Ma to about 3.5 Ma.Tectonic collision is defined and distinguished from subduction and rollback. Collision in the southern part of the Banda Arc was initiated when the overriding forearc basement of the upper plate reached the proximal part of the Australian continental slope of the lower plate, and subduction stopped. Collision is characterised by fold and thrust deformation associated with the development of structurally high decollements. This collision deformed the basement and cover of the forearc accretionary prism of the upper plate with part of the unsubducted Australian cover rock sequences from the lower plate. Together with parts of the forearc basement they now form the exposed Banda orogen. The conversion of the northern flank of the Timor Trough from being the distal part of the Banda forearc accretionary prism, carried over the Australian continental margin, into a foreland basin was initiated by the cessation of subduction and simultaneous onset of collisional tectonics.This reinterpretation of the locked eastern end of the Java Trench proposes that, from its termination south of Sumba to at least as far east as Timor, and probably far beyond, the Java-Banda Trench and forearc overrode the subducting Australian proximal continental slope, locally to within 60 km of the shelf break. Part of the proximal forearc's accretionary prism together with part of the proximal continental slope cover sequence were detached and thrust northwards over the Java-Banda Trench and forearc by up to 80 km along the southwards dipping Savu Thrust and Wetar Suture. These reinterpretations explain the present absence of any discernible subduction ocean trench in the southern Banda Arc and the narrowness of the forearc, reduced to 30 km at Atauro, north of East Timor.     

滇桂交界区印支期前陆褶皱冲断带

最近发现的蛇绿岩指示中、越交界区发育一条古特提斯的地缝合线,分开了越北地块和华南次大陆。滇桂交界处的印支期前陆褶皱冲断带为古特提斯造山带提供了进一步的证据。本文讨论了冲断-推覆构造的特征,提出该地的古特提斯洋具复杂的大陆边缘,沿北西走向段先发生碰撞,之后沿北东东向段发生碰撞,北西向断裂则发生右行的走滑(或右行斜冲)活动。冲断作用是向北或北东扩展的,仰冲的增生杂岩可能掩埋了大部分磨拉石沉积,造成了磨拉石不发育的假象。     

Palaeoproterozoic arc magmatism and collision in Liaodong Peninsula (north-east China)

In the north‐eastern part of the North China Block, a mafic magmatic belt consisting of mafic–ultramafic rocks and marine sedimentary rocks crops out between the northern Archean Anshan Block and a southern Palaeoproterozoic Block. ⁴⁰Ar/³⁹Ar amphibole ages around 1.9 Ga from gabbros, and trace element analyses of gabbros, pyroxenite and shale show that these rocks formed along a Palaeoproterozoic active continental margin. The mafic magmatic belt is interpreted as an arc developed above a south‐directed subduction zone, which was subsequently overthrust to the north upon the Anshan Archean Block. This study provides a new example agreeing with increasing evidence supporting plate mobility and thrust tectonics during the Palaeoproterozoic. These new insights must be considered with regard to the formation of the North China Block by magmatic accretion and tectonic collision.