塔里木盆地构造不整合成因及对油气成藏的影响

本文利用钻井及区域地震资料,对塔里木盆地6个关键构造不整合的结构特征、分布范围开展了详细的研究,确定了不整合面与下伏地层的夹角、遭受剥蚀的方向、剥蚀程度及不整合面的分布,对不整合的成因及其油气成藏作用进行了探讨。加里东中期形成的志留系与上奥陶统构造不整合(T⁰₇)主要为由南向北剥 蚀,向北剥蚀范围可达阿-满坳陷南部;在盆地南部西昆仑、阿尔金早古生代中期造山构造作用下,形成和田古隆起和卡塔克古隆起,塔北隆起仅在西部有活动。加里东晚期形成的上泥盆统-石炭系与中下泥盆统不整合(T⁰₆)主要表现为双向角度不整合特征,盆地受来自南缘和北缘造山带的挤压作用,形成了北、东、南三面连接的周缘环形隆起,塔北隆起构造活动强度及范围大于卡塔克隆起、和田-巴楚隆起。海西期形成的三叠系与二叠系不整合(T⁰₅)主要为由北东向南西的剥蚀,存在两个剥蚀阶地现象,盆地主要遭受来自北东和北部的挤压,在塔北隆起西部形成了高角度不整合。印支运动形成的侏罗系与前侏罗系不整合(T⁶₄)主要存在于盆地的东北部及西南部,塔北和孔雀河地区形成了中等角度单斜型角度不整合,塔东隆起形成了褶皱角度不整合,巴楚隆起成为塔西南坳陷的前缘隆起。燕山期形成的白垩系与前白垩系不整合(T⁰₄)表现为北北东-南南西、北北西-南南东两组方向的抬升剥蚀,盆地西南、东南断隆剥蚀强度大。喜马拉雅早期主要受南北向挤压,形成古近系与前古近系双向的角度不整合(T¹₃),后期巴楚隆起持续抬升剥蚀,大部分缺失白垩系-古近系,盆地受挤压、走滑构造作用明显增强。构 造不整合的形成与区域构造运动及不同时期盆地周缘的造山带形成响应,不同时期构造运动的主要作用范围、强度,不仅控制了构造不整合的结构特征和分布,而且控制着古隆起的发育演化,构造不整合对不整合圈闭油气成藏有控制作用。     

Cambro-Ordovician magmatism in the Delamerian orogeny: Implications for tectonic development of the southern Gondwanan margin

The Delamerian Orogen formed at the final stages of assembly of the Gondwana supercontinent. This system marks the initiation of subduction of the Pacific oceanic lithosphere along a prior rifted and extended passive margin. This paper explores the magmatic consequences following the early Cambrian initiation at the palaeo-Pacific margin in South Australia (SA) and western Victoria. Our data reveal a 50 Ma syn- to post-Delamerian tectono-magmatic history. Sampled from drill core from beneath the eastern Murray Basin cover in eastern SA, boninitic high Mg andesite from drill hole KTH12 and 516.1 ± 2 Ma quartz diorite suggest that first subduction established a volcanic arc within easternmost SA. Pacific-ward trench retreat then resulted in arc migration to reach the Mt Stavely Belt and Stawell Zones in western Victoria by ~510 Ma where boninitic arc magmatism continued until ~490 Ma. In the SA foreland of the Delamerian Orogen, early (522 ± 4 Ma) alkali basalt gave way to intrusion and extrusion of MORB-like tholeiites of back-arc basalt character.Through much of the middle and late Cambrian the SA Delamerian was in the back-arc and under extension but with periodic compression resulting from periodic Pacific-Australian plate coupling beneath the forearc in western Victoria.In SA syn-tectonic I- and S-type granites reflect interaction of MORB-like back-arc magmas and their transported heat with continental-derived sediment of the Kanmantoo Group. The termination of the Delamerian orogeny at ~490 Ma was accompanied by buoyancy-controlled, exhumation and erosion. This was driven by delamination of a mafic, crustal underplate, whose re-melting at 1.5 to 2 GPa and 1050 °C generated the unique 495 ± 1 Ma Kinchina/Monarto adakite. Delamination resulted in lithospheric mantle thinning and local convective overturn allowing upwelling of the asthenosphere to drive the post-kinematic magmatic phase of the Delamerian, yielding voluminous 490 Ma–470 Ma A-type granites.     

Delamerian Glenelg tectonic zone,western Victoria: Geology and metamorphism of stratiform rocks

The Cambro‐Ordovician Glenelg tectonic zone of western Victoria is a distinctive metamorphic‐igneous segment of the Delamerian Orogenic Belt comprising two northwest‐striking regional metamorphic segments of andalusite‐sillimanite type prograding towards an axial granitic batholith. The second of five deformations (D₂) was most significant, producing isoclinal folds, transposition and a pervasive regional foliation (S₂). Southwest of the central batholith, biotite to migmatite zones contain mainly quartzo‐feldspathic rock (turbiditic metagreywacke, quartzo‐feldspathic schist and migmatite), plus less common metaquartzite and calc‐silicate rocks and minor metapelite. Metagabbro, metadolerite and amphibolite typically have the chemistry of mid‐ocean ridge basalts. Serpentinite pods and sheets were tectonically introduced to low‐grade areas. Northeast of the central batholith, quartzo‐feldspathic rock occupies the sillimanite and migmatite zones exclusively, with a regional concentration of pegmatites adjacent to the zone boundary. Gross interleaving of quartzo‐feldspathic schist, migmatite, pegmatite and muscovite‐bearing granitic rock is characteristic. Peak metamorphic conditions of 550 MPa at 640°C leading to migmatite formation were established by D₂ time and accompanied by tonalite‐granodiorite and pegmatite emplacement. Subsequently, the thermal high contracted to the northeast culminating in the more extensive syn‐, post‐D4 to pre‐D5 granitic magmatism.     

Delamerian Orogeny and potential foreland sedimentation: A review of age and stratigraphic constraints

A review of available geochronology and biostratigraphy leads to the conclusion that a considerable thickness of Cambrian sedimentary rocks exposed in the Arrowie and Stansbury Basins, South Australia, was probably deposited in a foreland setting during early phases of the Delamerian Orogeny. In contrast to most previous stratigraphic correlation schemes, we consider that the pre‐tectonic Kanmantoo Group was deposited synchronously with the locally thick upper Hawker Group in essentially en echelon basins during a final phase of extensional sedimentation within the Adelaide ‘Geosyncline’. The base of the locally overlying ‘redbed package’ (base of the Billy Creek and Minlaton Formations) is interpreted as the sedimentological signature of the onset of convergent deformation and associated uplift within the Delamerian Orogen at about 522 Ma. This early ('Kangarooian') phase of the Delamerian Orogeny is interpreted as the progressive development of a coherent sigmoidal fold‐thrust belt within the combined Fleurieu‐Nackara Arcs, with locally developed high‐temperature‐low‐pressure metamorphism and granitoid intrusions dating from about 516 Ma. The ‘redbed package’ is absent from the Fleurieu‐Nackara Arc region and displays isopach, palaeocurrent and facies trends consistent with derivation from this uplifted area or from the associated flexural bulge to the west. From seismic evidence we conclude that thick foreland basin deposits are present beneath Gulf St Vincent. Late phases of the Delamerian Orogeny led to local and relatively mild deformation of the early foreland deposits.     

鄂尔多斯盆地加里东期不整合面类型及分布特征*

加里东期不整合面是早古生代华北板块内一个重要的盆地性质转换界面。鄂尔多斯盆地奥陶系风化壳岩溶型油气藏和二叠系本溪组、太原组铝土质泥岩气藏的发现,促进了地质学家对该地区古生代加里东运动性质的探讨。基于大量的野外露头、钻井和地震资料,对加里东运动形成的不整合面的识别标志、不整合类型及其空间分布、不整合结构和时间变量进行深入解析。研究表明: (1)加里东运动后,鄂尔多斯盆地的古地貌形态大致可分为鄂托克旗—定边一带的高地貌区、神木—靖边—富县以及吴忠地貌过渡区、中东部地势低缓东倾区; (2)奥陶系顶部不整合面相邻地层呈角度各异的接触关系,具有“削截(下)—整一(上)”、“削截(下)—超覆(上)”的结构,整体表现为盆地边缘为具削截和褶皱的高角度不整合、盆缘向盆内过渡地区的低角度不整合及盆内大范围分布的平行不整合; (3)不整合面也是上、下古生界之间形成的主要风化壳界面,长期的沉积间断和风化剥蚀为该区铝土质泥岩发育奠定了环境背景,而铝土岩不仅可作为下古生界风化壳气藏的理想盖层,同时也是陇东勘探新区天然气大规模聚集成藏的有利场所。     

Peat mounds of southwest Tasmania: Possible origins

Small mounds of peat rise several metres above the level of the water‐table at Melaleuca Inlet and Louisa Plains on the buttongrass plains in southwest Tasmania. Possible origins of the peat mounds have been explored by pollen analysis and radiocarbon dating of a set of samples taken from a vertical section of one peat mound at Melaleuca. The peat accumulation is entirely of Holocene age although the mound is underlain by sapric peats preserving a cold climate palynoflora of probable Late Pleistocene age. Peats at and near the base of the mound accumulated under a heath sedgeland during the earliest Holocene while after about 7630 a BP the peat‐forming vegetation was shrub‐dominated. The radiocarbon data indicate two main phases of overall peat accumulation, between 7630 and 5340 a BP (Middle Holocene) and between 4450 and 450 a BP (Late Holocene), that were interrupted by a wildfire which burnt into the surface peats. The maintenance of high surface and internal levels of moisture almost certainly was the critical factor behind the low incidence of in situ fires burning into the surface peats on the mound. The perennial influx of groundwater below the mound is a possible origin that fits well with our observations, although the expansion and contraction of soils cannot be discounted as an initiating factor. Enhanced nutrient input from birds may have helped promote growth in the peat‐forming communities. The data do not support the mounds being eroded remnants of a former blanket peat cover or being due to periglacial activity. The peat mounds of southwest Tasmania deserve maximum protection because of their rarity in the Australian landscape and, it seems, elsewhere.     

Tasman Fold Belt System in Tasmania

In western Tasmania Eocambrian and Cambrian rock sequences accumulated in narrow troughs between and within Precambrian regions which became geanticlines. The largest trough is meridional and is flanked by the Tyennan Geanticline to the east and the Rocky Cape Geanticline to the west. Within this trough ultramafic and mafic igneous masses, some of which are dismembered ophiolites, occur below a structurally conformable but erosional surface. This surface is at the base of an early-Middle Cambrian turbidite sequence, which grades upward into a probable correlate of the Owen Conglomerate that ranges into the Ordovician. Fault-bounded areas of Rocky Cape strata occur at the eastern boundary of the sedimentary trough deposits. A considerable pile of mineralized calcalkalic volcanic material, in which granite was emplaced, accumulated between the sedimentary trough deposits and the Tyennan Geanticline. Movements along Cambrian faults near and parallel to the margin of the Tyennan Geanticline caused angular unconformities. Above the unconformities occur volcaniclastic sequences that pass conformably upward into shallow marine and terrestrial Owen Conglomerate, derived from the Tyennan Geanticline.The transgressive Owen Conglomerate and its correlates are followed conformably by shallow marine limestone, of Early to Late Ordovician age. These limestone deposits covered much of western Tasmania and are succeeded conformably by Silurian to Early Devonian beds of shallow-marine quartz sandstone and mudstone.Pre-Middle Devonian rocks of western Tasmania extend to the Tamar Tertiary trough. In the northeast of Tasmania, immediately to the east of the Tamar trough, are sequences of interbedded mudstone and turbidite quartz-wacke of the Mathinna Beds, ranging in age from Early Ordovician to Early Devonian.The Cambrian to Early Devonian rocks of Tasmania are extensively deformed and show flattened parallel folds. In western Tasmania the folds are dated as late-Early to early-Middle Devonian because fragments of the deformed rocks occur in undisturbed Middle Devonian terrestrial cavern fillings. Folds of the northeastern Tasmania Mathinna Beds are probably of the same age. This widespread Devonian deformation is correlated with the Tabberabberan Orogeny of eastern Australia.In western Tasmania the geanticlines of Cambrian times behaved as relatively competent blocks during the Devonian folding, which is of two main phases. In the earlier phase the competent behaviour of the Tyennan Block determined the fold patterns. In the north the dominantly later folds resulted from movement from the northeast. During this later Devonian phase the Tyennan Block yielded in a northwesterly trending narrow zone of folding.In northeast Tasmania the Mathinna Beds exhibit folds which indicate a tectonic transportation opposite in direction to that which resulted in the folds of similar age in western Tasmania.Granitic rocks, dated 375-335 m.y., were emplaced within the folded rocks of Tasmania with usually sharp, discordant contacts. Foliations in the batholiths of northeast Tasmania suggest post-intrusion deformations involving east—west flattening. The late deformations may be related to lateral movements along a fracture zone which brought the Mathinna Beds of northeast Tasmania into juxtaposition with the rocks of contrasting stratigraphical and structural characteristics of western Tasmania.Flat-lying Late Carboniferous and younger deposits rest unconformably on the older rocks.     

燕辽裂陷槽中元古界不整合面的性质

燕辽裂陷槽中元古代沉积层序中出现多个沉积间断和不整合面。本次研究对其中的5个不整合面进行野外考察,分析其地质特征并进行地层对比,最后判断其性质。大红峪组底部、高于庄组底部和杨庄组底部的不整合面是沉积属性,其中大红峪组底部不整合面是海侵超覆沉积的结果,高于庄组底部和杨庄组底部的不整合面由海平面升降变化所引起;铁岭组顶部和下马岭组顶部不整合面是构造属性,系大规模的抬升运动所造成。     

Remarkable Cave,Tasmania

At Remarkable Cave, southern Tasmania, Triasssic sedimentary rocks are intruded by Jurassic dolerite to form a sheet-like body of unknown thickness to the east of and below Remarkable Cave. The sedimentary rocks near sea-level at Remarkable Cave show deformation and flow structures, and are composed of recrystallised predominantly quartz and feldspar with some darker alteration minerals and zeolite in the more massive parts of the recrystallised rock. The deformation was caused by the intrusion of dolerite. At the top of the sheet-like body to the east of Remarkable Cave there is rheomorphic veining into the dolerite following joint fractures. The dolerite is locally transgressive. In Remarkable Cave, dolerite must occur just below the floor of the cave to heat the sedimentary rocks to much higher temperatures than typical contact aureoles in the area, supporting a local feeder geometry, or compositional control.     

Syntectonic unconformities of the Alto Cardener,Spanish Pyrenees: a genetic interpretation

The age of three syntectonic unconformities belonging to the Upper Eocene—Middle Oligocene is discussed. The structural characteristics of the conglomerates in the Catalonian south Pyrenees are described with special attention to mechanisms of tectonics and sedimentation and to the lateral relationships between conformity, progressive unconformity (or cumulative wedge system) and angular unconformity. The older unconformities have been tectonically deformed. A new genetic model is proposed to explain offlaponlap mechanisms of each folding phase and the development of angular and progressive unconformities.     

The lithospheric transition between the Delamerian and Lachlan orogens in western Victoria: new insights from 3D magnetotelluric imaging

The magnetotelluric (MT) method was used to image the crust and upper mantle beneath the Delamerian and Lachlan orogens in western Victoria, Australia. During the Cambrian time period, this region changed from being the extended passive margin of Proterozoic Australia into an Andean-style convergent margin that progressively began to accrete younger oceanic terranes. Several broadband MT transects, which were collected in stages along coincident deep (full crust imaging) seismic reflection lines, have now been combined to create a continuous 500 km east–west transect over the Delamerian–Lachlan transition region in the Stawell Zone. We present the electrical resistivity structure of the lithosphere using both 3D and 2D inversion methods. Additionally, 1D inversions of long-period AusLAMP (Australian Lithospheric Architecture Magnetotelluric Project) MT data on a 55 km regionally spaced grid were used to provide starting constraints for the 3D inversion of the 2D profile. The Delamerian to Lachlan Orogen transition region coincides with the Mortlake Discontinuity, which marks an isotopic discontinuity in Cenozoic basalts, with higher strontium isotope enrichment ratios in the Lachlan Orogen relative to the Delamerian Orogen. Phase tensor ellipses of the MT data reveal a distinct change in electrical resistivity structure near the location of the Mortlake Discontinuity, and results of 3D and 2D inversions along the MT profile image a more conductive lower crust and upper mantle beneath the Lachlan Orogen than the Delamerian Orogen. Increased conductivity is commonly ascribed to mantle enrichment and thus supports the notion that the isotope enrichment of the Cenozoic basalts at least partially reflects an enriched mantle source rather than crustal contamination. Fault slivers of the lower crust from the more conductive Lachlan region expose Cambrian boninites and island arc andesites indicative of subduction, a process that can enrich the mantle isotopically, and also electrically, by introducing carbon (graphite) and water (hydrogen).     

How global are the Jurassic–Cretaceous unconformities?

The reality of the global‐scale sedimentation breaks remains controversial. A compilation of data on the Jurassic–Cretaceous unconformities in a number of regions with different tectonic settings and character of sedimentation, where new or updated stratigraphic frameworks are established, permits their correlation. Unconformities from three large reference regions, including North America, the Gulf of Mexico, and Western Europe, were also considered. The unconformities, which encompass the Jurassic‐Cretaceous, the Lower–Upper Cretaceous and the Cretaceous–Palaeogene transitions are of global extent. Other remarkable unconformities traced within many regions at the base of the Jurassic and at the Santonian–Campanian transition are not known from reference regions. A correlation of the Jurassic–Cretaceous global‐scale sedimentation breaks and eustatic curves is quite uncertain. Therefore, definition of global sequences will not be possible until eustatic changes are clarified. Activity of mantle plumes is among the likely causes of the documented unconformities.     

鄂尔多斯盆地加里东期不整合面类型及分布特征*

加里东期不整合面是早古生代华北板块内一个重要的盆地性质转换界面。鄂尔多斯盆地奥陶系风化壳岩溶型油气藏和二叠系本溪组、太原组铝土质泥岩气藏的发现,促进了地质学家对该地区古生代加里东运动性质的探讨。基于大量的野外露头、钻井和地震资料,对加里东运动形成的不整合面的识别标志、不整合类型及其空间分布、不整合结构和时间变量进行深入解析。研究表明: (1)加里东运动后,鄂尔多斯盆地的古地貌形态大致可分为鄂托克旗—定边一带的高地貌区、神木—靖边—富县以及吴忠地貌过渡区、中东部地势低缓东倾区; (2)奥陶系顶部不整合面相邻地层呈角度各异的接触关系,具有“削截(下)—整一(上)”、“削截(下)—超覆(上)”的结构,整体表现为盆地边缘为具削截和褶皱的高角度不整合、盆缘向盆内过渡地区的低角度不整合及盆内大范围分布的平行不整合; (3)不整合面也是上、下古生界之间形成的主要风化壳界面,长期的沉积间断和风化剥蚀为该区铝土质泥岩发育奠定了环境背景,而铝土岩不仅可作为下古生界风化壳气藏的理想盖层,同时也是陇东勘探新区天然气大规模聚集成藏的有利场所。     

The Cambrian metamorphic history of Tasmania: The Metapelites

The metamorphic complexes of Tasmania formed during the Cambrian (ca 510 Ma) as a result of rapid compression in a subduction zone setting followed by rapid exhumation, which brought various fault-bounded metamorphic complexes back to the surface in less than 5 Ma. The two highest grade complexes, the Franklin Metamorphic Complex, and the Port Davey Metamorphic Complex, experienced initial growth of metamorphic garnets at ～560°C, ～0.56 GPa. However, their subsequent metamorphic histories diverge, with the FMC displaying a marked increase in pressure (to 1.4 GPa at peak P/T), while the PDMC shows only a slight increase in pressure (to ～0.7 GPa). Both complexes show only a minor increase in temperature (～100°C) between initial garnet growth and peak metamorphic conditions. Rapid exhumation of these complexes can be accounted for by a slab-breakoff model. However, the difference in peak pressure between these complexes requires either continued subduction of the FMC while the PDMC had already begun its return towards the surface or that the subduction zone geometry resulted in significantly different pressures occurring contemporaneously within portions of the channel, which are not far removed from one another.     

Geochemistry and geochronology of the Rathjen Gneiss: Implications for the early tectonic evolution of the Delamerian Orogen

The Rathjen Gneiss is the oldest and structurally most complex of the granitic intrusives in the southern Adelaide Fold‐Thrust Belt and therefore provides an important constraint on the timing of the Delamerian Orogen. Zircons in the Rathjen Gneiss show a complex growth history, reflecting inheritance, magmatic crystallisation and metamorphism. Both single zircon evaporation (‘Kober’ technique) and SHRIMP analysis yield best estimates of igneous crystallisation of 514 ± 5 Ma, substantially older than other known felsic intrusive ages in the southern Adelaide Fold‐Thrust Belt. This age places an older limit on the start of the Delamerian metamorphism and is compatible with known stratigraphic constraints suggesting the Early Cambrian Kanmantoo Group was deposited, buried and heated in less than 20 million years. High‐U overgrowths on zircons were formed during subsequent metamorphism and yield a ²⁰⁶Pb/²³⁸U age of 503 ± 7 Ma. The Delamerian Orogeny lasted no more than 35 million years. The emplacement of the Rathjen Gneiss as a pre‐ or early syntectonic granite is emphasised by its geochemical characteristics, which show affiliations with within‐plate or anorogenic granites. In contrast, younger syntectonic granites in the southern Adelaide Fold‐Thrust Belt have geochemical characteristics more typical of granites in convergent orogens. The Early Ordovician post‐tectonic granites then mark a return to anorogenic compositions. The sensitivity of granite chemistry to changes in tectonic processes is remarkable and clearly reflects changes in the contribution of crust and mantle sources.     

Geomorphology of the mountains in NE Tasmania

Book reviewed in this article:
Caine Nel 1983: The Mountains of Northeastern Tasmania. A Study of Alpine Geomorphology     

江汉盆地当阳向斜区主要不整合面剥蚀厚度

本文利用磷灰石裂变径迹、(U-Th Sm)/He及镜质体反射率Ro％等古温标方法综合分析了江汉盆地当阳向斜区主要不整合面剥蚀厚度.结果表明:发育于古近纪末期不整合面T1界面累积剥蚀厚度超过1000m,且局部正反转区域如谢家湾断褶带等则遭受更大规模的剥蚀,剥蚀厚度可能超过2000m,而发育于晚侏罗世一早白垩世的不整合面T11界面累积剥蚀厚度超过4000m,且主要是晚侏罗世早白垩世构造事件的结果,表明该期剥蚀量明显大于古近纪末T1界面剥蚀量;晚三叠世—侏罗纪期间,当阳地区发育前陆坳陷带,侏罗纪堆积体具有明显东厚西薄的楔形体特征,位于盆地东部的前渊区沉积厚度可超过5000m;包括现今三叠系和侏罗系出露区以及江陵凹陷局部断隆区在内的前白垩系在侏罗纪前陆坳陷带发育时期达到最大埋深和最高古温度,其Ro％主要是该期获得的;晚白垩世—古近纪发育的断陷盆地范围可能远比现今残留盆地分布广,江陵凹陷上白垩统—古近系厚度超过9000m,其中古近系可能超过7000m,而在河溶凹陷谢家湾断褶带古近系厚度可超过3300m.     

A cave in Dolerite at Wayatinah,Tasmania

A cave (60 ft. x 30 ft. x 17 ft.) occurs within Jurassic dolerite 600 ft. from the surface. It was formed by zeolitization of a zone in the dolerite followed by solution of the secondary minerals to leave a cavity.     

Lithological stratification in supraglacial sediments: an example from western Tasmania, Australia

Pebble counts of the lithology of glacial sediments in the King Valley show that the content of distantly derived erratics of many sections decreases upwards in near surface sediments. Two factors that contribute to this lithological stratification are dilution of the erratic content of surface sediments by locally derived rocks and lithological stratification of debris within the Pleistocene King Glacier. The common diluting mechanism appears to have been slope detritus derived from the valley sides and small hills that crop out on the valley floor. Lithological stratification of debris in the King Glacier resulted from the altitude of the equilibrium line of the King Glacier relative to the position and altitude of the rock source areas and the thermal regime at the ice-bed interface. The Jurassic dolerite and Permian sediments that crop out above the equilibrium line altitude were transported in subglacial and englacial positions. In contrast, below the equilibrium line sediments that accumulated and were transported in a supraglacial position contained no erratic lithologies. When deposited, the supraglacial sediments formed a siliceous, non-erratic cover over sediments that were transported in subglacial and englacial positions. The model of the mode of sediment transport in the King Valley may have application to areas of alpine glaciation where the distribution of some rock types is restricted to areas above the equilibrium lines of glaciers.