Late Triassic initial closure of the Mongol-Okhotsk Ocean in the western segment: Constraints from sedimentological,detrital zircon ages and paleomagnetic evidence

The Mesozoic evolution of the Mongol-Okhotsk Ocean (MOO) has significantly affected the configuration of the modern Asian continent. Although a scissor-like closure of the MOO has long been proposed, when and how the MOO closed are still hotly debated, especially the timing of initial closure of the MOO in its western segment, hindering our understanding of both the evolution of the MOO and tectonics of the northern Asian continent. In order to uncover the timing of initial closure of the MOO, we performed a multidisciplinary study in sedimentology, detrital zircon U-Pb dating and paleomagnetic on the Late Triassic clastic strata from the Tarvagatay Block and the Amuria Block (AMB) on the both sides of the Mongol-Okhotsk Suture. The upper Triassic strata on both sides of the suture were dominated by plant fossil-bearing alluvial-fluvial facies sediments, which unconformably overlain pre-Triassic geological units, indicating a terrestrial setting after the closure of the MOO. Detrital zircon U-Pb dating results revealed consistent age distribution patterns for samples from both sides of the suture with a predominant peak at ∼253–251 Ma and a secondary peak at ∼359–357 Ma, representing two main arc magmatic events during the bidirectional subduction of the MOO in the Late Devonian-Early Carboniferous and Late Permian-Early Triassic. Coeval Late Triassic paleomagnetic poles were obtained from the northern AMB and Tarvagatay Block, revealing a comparable paleolatitude of the AMB (∼31–33°) and Tarvagatay Block (∼32–34°) in the Late Triassic, arguing for that the western segment of the MOO should have closed at the Late Triassic. The compilation of sedimentology, detrital zircon U-Pb dating, magmatic and paleomagnetic evidence provides integrated constraints on the Late Triassic initial closure of the MOO in its western segment.     

The Central Iberian arc, an orocline centered in the Iberian Massif and some implications for the Variscan belt

An arcuate structure, comparable in size with the Ibero-Armorican arc, is delineated by Variscan folds and magnetic anomalies in the Central Iberian Zone of the Iberian Massif. Called the Central Iberian arc, its sense of curvature is opposite to that of the Ibero-Armorican arc, and its core is occupied by the Galicia-Trás-os-Montes Zone of NW Iberia, which includes the Rheic suture. Other zones of the Iberian Massif are bent by the arc, but the Ossa-Morena and South Portuguese zones are not involved. The arc formed during the Late Carboniferous, at final stages of thermal relaxation and collapse, and an origin related with right-lateral ductile transpression at the scale of the Variscan belt is proposed. The Central Iberian arc explains the width of the Central Iberian Zone, clarifies the position of the allochthonous terranes of NW Iberia, and opens new perspectives for correlations with the rest of the Variscan belt, in particular, with the Armorican Massif, whose central zone represents the continuation of the southwest branch of the arc detached by strike-slip tectonics.     

Apparent polar wandering for the Atlantic-bordering continents: Late Carboniferous to Eocene

We present a compilation of reliable paleomagnetic pole positions from five continental plates (North America, Europe, the Iberian Peninsula, Africa, and South America) for ten time intervals ranging from Late Carboniferous to Eocene. Only well-dated results obtained by demagnetization techniques have been used. Paleomagnetic poles are plotted with respect to the paleo-positions of the continents, as reconstructed from correlations of marine magnetic anomalies in the Atlantic Ocean by Pitman and Talwani and from the fit by Bullard et al. The poles from North America, Europe and the younger poles from Africa show a very good grouping for most of the ten intervals considered, and a continuous apparent polar wandering path is obtained. These data have been used to construct paleolatitude maps for most intervals; thus the relative positions of the continents were established from sea-floor spreading data and their absolute positions on the globe were determined from paleomagnetic data. The older data from South America and the other Gondwana continents show a systematic deviation from those of the northern continents for Late Paleozoic and Early Triassic time periods. An explanation is offered in a different continental reconstruction between Laurasia and Gondwanaland before Middle Triassic times.     

Devonian-Carboniferous unconformity in Argentina and its relation to the Eo-Hercynian orogeny in southern South America

The Devonian-Carboniferous contact in southern South America, characterized by a sharp unconformity, has been related to the Late Devonian-Early Carboniferous Eo-Hercynian orogeny. The Calingasta-Uspallata basin of western Argentina and the Sauce-Grande basin (Ventana Foldbelt) of eastern Argentina have been selected to characterize this unconformity. The Eo-Hercynian movements were accompanied in western Argentina by igneous activity related to a Late Devonian—Early Carboniferous magmatic arc mainly exposed today along the Andean Cordillera. This magmatic activity is partly reflected also in eastern Argentina (Ventana Foldbelt), where isotopic dates suggest a thermal event also related to the intrusions present to the west in the North Patagonian Massif and Sierras Pampeanas. The scarcity of Lower Carboniferous deposits in the stratigraphic record of southern South America suggests that the Early Carboniferous was a time interval dominated by uplift and erosion followed by widespread subsidence during the Middle and Late Carboniferous. The origin of the Eo-Hercynian orogeny can be linked with the convergence between the Arequipa Massif, and its southern extension, and the South American continent. Its effects are best represented along the Palaeo-Pacific margin, although distant effects are discernible in the cratonic areas of eastern South America. Correspondence to: O. R. López-Gamundí     

Plate tectonics and volcanism in the gibraltar arc

Late Tertiary and Quaternary volcanism of southeastern Spain can be fitted in a platetectonics model, taking into account the post-Paleozoic evolution of the stable and semimobile Iberian areas and the new orogenic belts bordering the Mediterranean between Africa and the Iberian Peninsula.The occurrence and distribution of calc-alkaline and potassic volcanism suggest an oceanic crust sinking downwards from the Iberian plate. This active margin is causally related to the convergence and collision of Iberia and Africa during Late Cretaceous—Early Miocene time span.A pre-collision distensive phase is inferred from the stratigraphie and tectonic record between the Triassic and Late Cretaceous, while since the Late Miocene another distensive phase is related to the actualistic features.     

Palaeoenvironmental significance of Late Permian palaeosols in the South‐Eastern Iberian Ranges,Spain

The Late Permian (Wuchiapingian) Alcotas Formation in the SE Iberian Ranges consists of one red alluvial succession where abundant soil profiles developed. Detailed petrographical and sedimentological studies in seven sections of the Alcotas Formation allow six different types of palaeosols, with distinctive characteristics and different palaeogeographical distribution, to be distinguished throughout the South‐eastern Iberian Basin. These characteristics are, in turn, related to topographic, climatic and tectonic controls. The vertical distribution of the palaeosols is used to differentiate the formation in three parts from bottom to top showing both drastic and gradual vertical upwards palaeoenvironmental changes in the sections. Reconstruction of palaeoenvironmental conditions based on palaeosols provides evidence for understanding the events that occurred during the Late Permian, some few millions of years before the well‐known Permian‐Triassic global crisis.     

Late Devonian-Early Carboniferous peak sulphide mineralization in the Western Hercynides

The Late Devonian-Early Carboniferous (Dinantian) within the Western Hercynides is marked by the formation of volcanic-hosted massive sulphide deposits: Chessy and Chizeuil in the Brévenne and Somme successions of the French Massif Central; Bodennec and La Porte-aux-Moines in the Châteaulin Basin of the French Armorican Massif; Rio Tinto, Neves-Corvo, Tharsis, etc., in the Volcano-Sedimentary formation of the Iberian Pyrite Belt; and Ketara, Draa Sfar and Hajar in the Jebilet-Guemassa district of the Moroccan Southern Meseta. Although these deposits show a slightly diachronous emplacement in response to a progressive migration of the metalliferous event from Late Devonian in France to Dinantian in Morocco, it is nevertheless possible to define an overall metalliferous ‘‘peak” around 350 Ma. The mineralization of the Armorican, Iberian and Moroccan sectors took place in epicontinental domains of the outer zone of the Hercynian belt, whereas that of the northeastern Massif Central occurred within the inner zone of the belt. This difference is registered by variations both in the geochemical characteristics of the ores (Sn in the outer zone and Mo-Ni in the inner zone) and in their lead isotopic signatures (clear mantle participation exclusively in the inner zone). In many cases the ores appear to be closely related to the felsic member of a bimodal magmatic association, although the massive sulphide deposits in the outer zone are more commonly associated with sedimentary rocks whereas those in the inner zone are hosted by felsic volcanic rocks. Another feature that should be noted is that the host sequences of the massive sulphide deposits commonly seem to be underlain by chaotic formations (notably with olistoliths) reflecting the beginning of Hercynian orogenic activity in the outer zone. It can be concluded that the peak mineralization took place within tensional domains developed during a period of plate convergence, and that it occurred around 350 Ma after a major period of Devonian compression but before the Carboniferous continental closure.     

南天山：晚古生代还是三叠纪碰撞造山带？

伊犁-哈萨克斯坦板块和塔里木-卡拉库姆板块之间的南天山造山带是‘中亚型造山带’的典型代表之一，经历了复杂的构造演化与地壳增生过程。传统上，它被视为华力西期褶皱带或晚古生代碰撞造山带。但近年来，部分学者提出它可能为三叠纪碰撞造山带。本文在综述南天山造山带的蛇绿岩、高压变质岩、花岗岩类等方面研究成果的基础上，讨论了其碰撞造山的时限。我国境内南天山西段碰撞造山可能开始于早石炭世（345Ma），结束于晚石炭世末（300Ma左右）。二叠纪时期，南天山至整个中亚地区进入后碰撞演化阶段。现有资料证实南天山为一晚古生代碰撞造山带，并非一三叠纪碰撞造山带。     

中国东北地区蛇绿岩

我国东北地区位于中亚造山带的东段,经历了复杂的增生造山过程,其所属微陆块的基底属性及拼贴位置、洋-陆转换一直是地学界研究的热点。根据近年来的研究进展,我们将东北地区微陆块划分为额尔古纳地块、兴安增生地体、松嫩-锡林浩特地块和佳木斯地块。同时综述了东北地区蛇绿岩/蛇绿混杂岩带的时空分布、年代学及地球化学的新资料,讨论了其构造背景及俯冲-增生过程。东北地区增生造山不仅涉及古亚洲洋和古太平洋,还可能与泛大洋有关,包括早奥陶世-晚三叠世古亚洲洋主洋盆及古亚洲洋分支——新元古代-晚寒武世新林-喜桂图洋、早寒武世-晚石炭世嫩江洋、新元古代-晚志留世黑龙江洋和晚二叠世-中侏罗世牡丹江洋的演化。早石炭世末-晚石炭世初,东北地区古亚洲洋分支洋盆全部闭合,所有微陆块完成聚合形成统一的东北陆块群。晚二叠世-早三叠世时期,古亚洲洋主洋盆沿索伦-西拉木伦-长春-延吉缝合带自西向东从早到晚以剪刀式最终闭合,完成东北陆块群与华北板块的拼接。晚三叠世-早侏罗世时期古太平洋板块俯冲启动,东北地区进入古太平洋俯冲增生构造体系。     

Post Late Paleozoic tectonism in the southern Catalan Coastal Ranges (NE Spain), assessed by apatite fission track analysis

We report the first apatite fission-track thermochronologic data for 17 samples from the southern Catalan Coastal Ranges of NE Spain. Thermal histories of Carboniferous metasediments, Late Hercynian intrusions and Lower-Triassic Buntsandstein sediments from three tectonic blocks, Miramar, Prades and Priorat, are derived and interpreted within the geodynamic framework and tectonic evolution of the region. The apatite fission-track ages range from 198±24 to 38±5 Ma and mean fission-track lengths are all <13.3 μm. Samples throughout the study area underwent total track annealing during the Late Hercynian magmatic episode, followed by fast cooling prior to the deposition of Lower Triassic sediments. The Lower Triassic sediments and basement rocks underwent a temperature increase during a first Mesozoic rift phase in Middle Triassic–Early Jurassic times resulting in the complete or near complete annealing of the fission-tracks. During a second Mesozoic rifting stage, in Late Jurassic to Early Cretaceous time, differential tectonic block activity is observed in the three studied tectonic blocks. Subsequently, during Late Cretaceous a long-period of thermal stability, detected in all samples, is related to the post-rift episode. The onset of fast cooling registered in the apatite fission track system during Paleogene times is related to the Pyrenean orogeny. Compressional forces associated with the ongoing southern migration of the convergence forces at the Iberian plate boundaries caused unroofing of about 2–3 km of material of the Prades and northwestern flank of the Priorat block. Extensional collapse in Late Oligocene–Miocene related to the Western Mediterranean rifting triggered the denudation of about 2 km of material from the southeastern flank of the Miramar, Prades and Priorat blocks.     

The missing Rheic Ocean magmatic arcs: Provenance analysis of Late Paleozoic sedimentary clastic rocks of SW Iberia

Early Carboniferous turbiditic sedimentary rocks in synorogenic basins located on both sides of the Rheic suture in SW Iberia were studied for provenance analysis. An enigmatic feature of this suture, which resulted from closure of the Rheic Ocean with the amalgamation of Pangea in the Late Carboniferous, is that there are no recognizable mid- to Late Devonian subduction-related magmatic rocks, which should have been generated during the process of subduction, on either side of it. U–Pb LA–ICP-MS geochronology of detrital zircons from Early Carboniferous turbidites in the vicinity of the Rheic suture in SW Iberia, where it separates the Ossa–Morena Zone (with Gondwana continental basement) to the north from the South Portuguese Zone (with unknown/Meguma? continental basement) to the south, reveals the abundance of mid- to Late Devonian (51–81%) and Early Carboniferous (13–25%) ages. The Cabrela and Mértola turbidites of the Ossa–Morena and South Portuguese zones, respectively, are largely devoid of older zircons, differing from the age spectra of detrital zircons in the oldest (Late Devonian) strata in the underlying South Portuguese Zone, which contain abundant Cambrian and Neoproterozoic ages. Mid- to Late Devonian zircons in the Cabrela Formation (age cluster at c. 391 Ma, Eifelian–Givetian transition) and Mértola Formation (age clusters at c. 369 Ma and at c. 387 Ma, Famennian and Givetian respectively) are attributable to a source terrane made up of magmatic rocks with a simple geological history lacking both multiple tectonic events and older continental basement. The terrane capable of sourcing sediments dispersed on both sides of the suture is interpreted to have been completely removed by erosion in SW Iberia. Given that closure of the Rheic Ocean required subduction of its oceanic lithosphere and the absence of significant arc magmatism on either side of the Rheic suture, we suggest: 1) the source of the zircons in the SW Iberia basins was a short-lived Rheic ocean magmatic arc, and 2) given the lack of older zircons in the SW Iberia basins, this short-lived arc was probably developed in an intra-oceanic environment.     

滇西藏东三江地区主要地块碰撞拼合的古地磁分析

利用古地磁数据，结合与构造活动有关的沉积记录以及古生物地理信息，对华南、思茅、保山、缅泰、印支、拉萨和喜马拉雅地块进行了古纬度和纬度运移量的对比研究，以确定云南西部三江地区主要地块的碰撞拼合历史。结果表明：(1)思茅地块可能源于华南地块；(2)保山和缅泰地块在晚石炭世至晚二叠世发生快速北移；(3)保山与华南地块于晚二叠世碰撞之后，和缅泰地块、华南地块以及印支地块继续向北漂移，直到晚三叠世；(4)保山与华南地块间的古特提斯洋可能于早志留世张开，晚二叠世闭合。     

First Triassic palaeomagnetic constraints from Junggar (NW China) and their implications for the Mesozoic tectonics in Central Asia

Northwestern China belts result from the Palaeozoic collage of Central Asia and the subsequent reactivations due to far-field effects of the Mesozoic Tibetan and the Cenozoic Himalayan collisions. Triassic is a crucial period to understand and decipher the tectonics related to these two episodes. About 250 oriented palaeomagnetic cores from 43 sites were collected from six sections of Upper Permian to Late Triassic sandstone, in South and West Junggar, Northwestern China. Thermomagnetic, IRM and hysteresis measurements reveal magnetite as the main carrier of the magnetic remanence with minor hematite and maghemite. Stepwise thermal demagnetisation has generally isolated two components. The low temperature component, up to 300–350 °C, displays a direction consistent with the present-day geomagnetic field. The locality-mean directions related to the high temperature component (above 350 °C) were also calculated. Two out of six sections display intense viscous magnetisation and the occurrence of maghemite reveals a possible Cenozoic chemical remagnetisation for these two localities. For the other four localities, we assume that the magnetisation is primary because: (1) AMS measurements reveal a primary fabric, (2) there are local occurrences of antipodal polarities, and (3) palaeolatitudes of tilt-corrected poles are compatible with previous studies. The consistency between the Early Triassic poles of West and South Junggar indicates that Junggar evolved as a rigid block only since Early Mesozoic. The comparison of the Late Palaeozoic and the Early Mesozoic poles of Junggar and those of Siberia and Tarim shows major rotations between the Late Permian and the Late Jurassic–Early Cretaceous. These periods of discrete rotations are characterized by strike-slip faulting in Tianshan and Altai and they may correlate with the major episodes of coarse-grained detrital sedimentation and uplift of the range. Especially, the counter-clockwise rotations of Junggar relative to Tarim and Siberia, which occurred between the Early and the Late Triassic and between the Late Triassic and the Late Jurassic, are accommodated by transpressive tectonics in the Tianshan and the Altai belts. This reactivation is a far-field effect of Tibetan blocks diachronous collisions. Therefore, these first Triassic palaeomagnetic results from Junggar infer that post-Carboniferous rotations were due to the combined effect of the post-orogenic transcurrent movement and the Mesozoic oblique reactivation.     

The Bentong–Raub Suture Zone

It is proposed that the Bentong–Raub Suture Zone represents a segment of the main Devonian to Middle Triassic Palaeo-Tethys ocean, and forms the boundary between the Gondwana-derived Sibumasu and Indochina terranes. Palaeo-Tethyan oceanic ribbon-bedded cherts preserved in the suture zone range in age from Middle Devonian to Middle Permian, and mélange includes chert and limestone clasts that range in age from Lower Carboniferous to Lower Permian. This indicates that the Palaeo-Tethys opened in the Devonian, when Indochina and other Chinese blocks separated from Gondwana, and closed in the Late Triassic (Peninsular Malaysia segment). The suture zone is the result of northwards subduction of the Palaeo-Tethys ocean beneath Indochina in the Late Palaeozoic and the Triassic collision of the Sibumasu terrane with, and the underthrusting of, Indochina. Tectonostratigraphic, palaeobiogeographic and palaeomagnetic data indicate that the Sibumasu Terrane separated from Gondwana in the late Sakmarian, and then drifted rapidly northwards during the Permian–Triassic. During the Permian subduction phase, the East Malaya volcano-plutonic arc, with I-Type granitoids and intermediate to acidic volcanism, was developed on the margin of Indochina. The main structural discontinuity in Peninsular Malaysia occurs between Palaeozoic and Triassic rocks, and orogenic deformation appears to have been initiated in the Upper Permian to Lower Triassic, when Sibumasu began to collide with Indochina. During the Early to Middle Triassic, A-Type subduction and crustal thickening generated the Main Range syn- to post-orogenic granites, which were emplaced in the Late Triassic–Early Jurassic. A foredeep basin developed on the depressed margin of Sibumasu in front of the uplifted accretionary complex in which the Semanggol “Formation” rocks accumulated. The suture zone is covered by a latest Triassic, Jurassic and Cretaceous, mainly continental, red bed overlap sequence.     

Cambrian paleomagnetism in the Bateni Ridge: evolution of the Kuznetsk Alatau island arc (southern Siberia)

We present paleomagnetic data on the Cambrian volcanosedimentary complexes of the Bateni Ridge, which correspond to the evolution of the Kuznetsk Alatau island arc. The paleomagnetic poles which served as the basis for the apparent polar-wander path (APWP) were determined. The paleomagnetic data were compared with those on the Cambrian poles for other fragments of the Kuznetsk Alatau island arc.For example, the APWP of the Bateni fragment corresponds to that of the Kiya (Martaiga) fragment of the eastern slope of the Kuznetsk Alatau. The distribution of the paleomagnetic poles suggests that the relative drift of the Kuznetsk Alatau arc fragments and the entire island arc system resulted from large-amplitude strike-slips. In the Cambrian, this paleoarc moved from ～10° N to ～10° S and rotated more than 50° clockwise. In the paleomagnetic record, its accretion is reflected in the coincidence of the Late Cambrian–Early Ordovician poles on the eastern slope of the Kuznetsk Alatau with one another and the coeval poles for the Siberian craton. This coincidence also suggests that the general structure of the present Kuznetsk Alatàu formed as early as the Early Caledonian. Nevertheless, the differences in the position of the poles on the western and eastern slopes of the Kuznetsk Alatau suggest that strike-slip activity along the Kuznetsk–Altai deep fault (the major one in the region) continued in the Late Paleozoic and, probably, in the Mesozoic.     

Simultaneous horst-basin formation and magmatism during Late Variscan transtension: evidence from 40Ar/39Ar and 207Pb/206Pb geochronology in the Ruhla Crystalline Complex

40 Ar/³⁹Ar–mica and ²⁰⁷Pb/²⁰⁶Pb–zircon dates are presented and combined with existing P–T data and the sedimentary record. These data indicate that the RCC was faulted into three segments which underwent different exhumation histories during the Late Carboniferous/Early Permian. The eastern segment shows ⁴⁰Ar/³⁹Ar–biotite data of336 ±4 and 323±3 Ma. Furthermore, it is intruded by the Thuringian Hauptgranite dated at 337±4 Ma by the ²⁰⁷Pb/²⁰⁶Pb single zircon method. At approximately 300 Ma rocks of the eastern segment were finally exposed and, subsequently, subsided as part of the Oberhof pull-apart basin, filled by Late Carboniferous/Early Permian molasse sediments and volcanic rocks (296–285 Ma; Goll 1996). A similar Late Carboniferous evolution is inferred for the western segment, since it is also overlain by Upper Carboniferous volcanic rocks. In contrast to the eastern and western segments, distinctly younger intrusion and cooling ages were recorded for the central segment of the RCC (⁴⁰Ar/³⁹Ar muscovite: 311±3 Ma; ⁴⁰Ar/³⁹Ar biotite: 293–288±3 Ma) that was intruded by the Trusetal Granite, the Ruhla Granite and Brotterode Diorite (²⁰⁷Pb/²⁰⁶Pb single zircon: 298±2, 295±3, 289±4 Ma, respectively). These young data are unique in the MGCR and testify that plutonic activity and cooling of basement rocks took place simultaneously with basin formation and volcanism in the eastern and western segments. Overlying Upper Permian (Zechstein) and Triassic sediments indicate final exposure of the central segment by approximately 260 Ma, as a part of the Ruhla-Schleusingen Horst. Combination of these results with P–T data from the contact aureole of the Trusetal granite indicate that the central segment was unroofed by at least 8.5 km during the Late Carboniferous. The Late Carboniferous/Early Permian horst-basin formation, documented in the RCC, is due to dextral transtensional movements along the NW-trending Franconian fault system. It may have been enhanced by mantle upwelling widespread in Central Europe during the Early Permian that also caused intensive magmatism in the Thuringian Forest region. Received: 2 February 1999 / Accepted: 15 November 1999     

川西松潘-甘孜弧前盆地的形成及演化

地处柴南缘昆中蛇绿杂岩带与羌塘地块北缘可可西里—金沙江古缝合线之间的松潘—甘孜褶皱带(包括东昆仑构造带)，其主体应属古特提斯洋晚石炭世一晚三叠世时期向其北侧的柴达木古陆南缘俯冲过程中在活动陆缘弧—沟间隙之间增生形成的一个大型弧前构造带。具有由弧前盆地沉积楔和基底增生杂岩构成的双重结构特点，其形成与冈瓦纳大陆北缘若尔盖“三角”地块的楔入及俯冲带向南迁移有关。大致经历了晚石炭世一早三叠世狭窄弧前盆地和中晚三叠世宽阔弧前盆地两个主要演化阶段。     

Tectonic relationships of Southwest Iberia with the allochthons of Northwest Iberia and the Moroccan Variscides

The Iberian Massif poses a problem of relationships between its northwestern and southern parts. Suture terranes (ophiolites and high-pressure rocks) crop out in NW Iberia but only as allochthonous units, unconnected from their root zone. Sutures cropping out in SW Iberia are discussed in order to relate them to the unknown root of the NW Iberia allochthons. On the other hand, the Moroccan Variscides are very briefly presented with a view to propose their correlation with the Iberian zones. Particularly important is the transition from the Variscides to the Paleoproterozoic basement in Morocco, which is a key argument for palaeogeographic reconstructions.     

大兴安岭中段晚石炭世-早二叠世砂岩碎屑锆石LA-ICP-MS U-Pb年龄及地质意义

位于中亚造山带东段的中国东北地区由众多微地块拼合而成,但各地块间的拼贴时间、位置和演化过程一直是地学界争议的关键科学问题.针对大兴安岭中段蘑菇气地区晚石炭世-早二叠世宝力高庙组砂岩开展了详细的岩相学、碎屑锆石LA-ICP-MS U-Pb年代学研究,分析了砂岩母岩区大地构造背景,进而约束兴安地块与松辽地块的汇聚过程.研究结果表明,砂岩具有成分成熟度低、近源快速沉积特点,碎屑骨架成分显示了火成岩区物源供给.锆石颗粒CL图像、Th/U值及REE特征均指示了锆石为岩浆成因.测试样品中锆石U-Pb年龄主要集中在282~360 Ma（n=134）,峰值年龄约为290 Ma、305 Ma、325 Ma和350 Ma.结合区域内前人的研究成果,暗示了其物源可能来自蘑菇气-嫩江-黑河一线的晚古生代俯冲-同碰撞期岩浆弧;样品中最年轻的锆石U-Pb年龄分别为282±4 Ma（样品15MG10）和287±4 Ma（样品15MG11）,可以限定砂岩的沉积下限为早二叠世.对比索伦-蘑菇气地区晚石炭世-早三叠世砂岩的碎屑锆石年龄组成,发现兴安地块内晚石炭世-早二叠世碎屑组分与松辽地块内中二叠世-早三叠世碎屑组分基本相同,说明兴安地块与松辽地块已于晚石炭世前沿贺根山-黑河缝合带完成拼合.      

The opening of the Bay of Biscay - a review

The anticlockwise rotation of the Iberian Peninsula away from south Brittany during the Mesozoic has been demonstrated from palaeomagnetic data. Marine magnetic, seismic and gravity surveys have indicated that there is oceanic crust in the Bay of Biscay. Initial rifting began in the Triassic but the major part of the rotation of the Iberian Peninsula occurred during the Late Cretaceous. Two mechanisms for the opening of the Bay of Biscay have been proposed, firstly a simple anticlockwise rotation of the Iberian plate and secondly, a 350 km sinistral displacement of the Iberian plate along transform faults about a pole of rotation near Paris. Geological data, partly new, favours the first mechanism but with a pole of rotation approximately 100 km east of the west end of the Pyrenees rather than in the southeast corner of the Bay of Biscay. Geophysical data indicates a further small rotation of the Iberian Peninsula during the Late Eocene which resulted in the formation of the Pyrenees.