Middle Miocene graben development in Crete and its possible relation to large-scale detachment faults in the southern Aegean

The linkage between the development of south-facing Cretan graben and large-scale detachment faulting in the southern Aegean is unknown. Widespread Serravallian deposits in the Ierapetra graben of Crete supply constraints to Middle Miocene graben development in the southern Aegean. The Ierapetra graben, and by inference the Cretan graben in general, were hitherto believed to have formed as a result of sinistral transpression during N–S shortening. We argue that the formation of the Cretan graben is due to N–S extension. The south-dipping, N–S-extending Kritsa normal fault served as the master fault controlling graben development in the Ierapetra graben. The Kritsa normal fault is either an antithetic fault related to the top-N Cretan detachment or a synthetic fault associated with the top-S Ios detachment. The overall geometry and timing relationships lead us to favour a connection with the Ios detachment, which in turn implies a large-scale displacement on the Ios detachment.     

The nappe pile of eastern Crete

In eastern Crete four allochthonous units with different styles of deformation are piled up above the autochthonous Cherty Limestone (“Plattenkalk”). The emplacement of the nappes is discussed. Diapiric uplift of the Cycladic area was accompanied by large-scale gravity sliding in the direction towards the Aegean arc. There is no evidence from geophysical data for the existence of a subduction zone. Therefore, the transport of the eastern Cretan nappes may be better explained by gravity tectonics than by the model of plate tectonics.     

Structural evolution and strike-slip tectonics off north-western Sumatra

Based on new multi-channel seismic data, swath bathymetry, and sediment echosounder data we present a model for the interaction between strike-slip faulting and forearc basin evolution off north-western Sumatra between 2°N and 7°N. We examined seismic sequences and sea floor morphology of the Simeulue- and Aceh forearc basins and the adjacent outer arc high. We found that strike-slip faulting has controlled the forearc basin evolution since the Late Miocene. The Mentawai Fault Zone extends up to the north of Simeulue Island and was most probably connected farther northwards to the Sumatran Fault Zone until the end of the Miocene. Since then, this northern branch jumped westwards, initiating the West Andaman Fault in the Aceh area. The connection to the Mentawai Fault Zone is a left-hand step-over. In this transpressional setting the Tuba Ridge developed. We found a right-lateral strike-slip fault running from the conjunction of the West Andaman Fault and the Tuba Ridge in SSW-direction crossing the outer arc high. As a result, extrusion formed a marginal basin north of Simeulue Island which is tilted eastwards by uplift along a thrust fault in the west. The shift of strike-slip movement in the Aceh segment is accompanied by a relocation of the depocenter of the Aceh Basin to the northwest, forming one major Neogene unconformity. The Simeulue Basin bears two major Neogene unconformities, documenting that differences in subsidence evolution along the northern Sumatran margin are linked to both forearc-evolution related to subduction processes and to deformation along major strike-slip faults.     

中国东部中—新生代大陆构造的形成与演化

20世纪60年代提出的"威尔逊旋回"以关闭洋盆两侧板块的碰撞作为板块运动旋回的终结,然而板块构造学说"登陆"20多年来的实践说明这种认识是不全面的。大陆弥散而宽广的陆内变形说明洋盆闭合两侧板块的碰撞并未终止板内构造作用。古亚洲大陆形成后中国东部中—新生代广泛发育的板内构造变形、岩浆活动、克拉通内盆地的形成都和古亚洲大陆南、北,印度洋和北冰洋洋脊的持续扩张、西太平洋和菲律宾洋壳的俯冲相关。本文拟厘清中国东部中—新生代大陆构造形成与演化的重大事件、构造性质、形成背景及其时空展布:(1)晚海西—印支期古特提斯洋关闭陆块拼合碰撞古亚洲大陆雏形形成;(2)晚侏罗—早白垩世蒙古—鄂霍茨克海闭合,陆-陆碰撞古亚洲大陆形成,挤压逆冲推覆构造在陆内变形中形成高潮,西太平洋伊佐奈岐洋壳板块的斜俯冲叠加了自东而西的影响;(3)早白垩世晚期—古近纪加厚地壳-岩石圈减薄、转型,陆内伸展变形达到高潮,大陆克拉通泛盆地、准平原化;(4)始新世晚期—早中新世(40~23 Ma)太平洋板块运动转向对东亚大陆NWW向的挤压和印度洋脊扩张印—澳板块对古亚洲南部陆-陆碰撞挤压的叠加,形成中国东部新生的构造地貌;(5)中-上新世—早更新世受东亚—西太平洋巨型裂谷系和印度洋中脊扩张的叠加影响,中国东部岩石圈地幔隆升、地壳减薄,陆缘、陆内伸展变形相继形成边缘海、岛弧、裂谷型盆地和剥蚀高原地貌;(6)早更新世晚期(0.9~0.8 Ma)—晚更新世末(0.01 Ma)中国东部大陆构造地貌基本形成。     

胶东东部中生代走滑逆冲构造带的超微构造研究

胶东东部区域上处于秦岭-大别-苏鲁造山带的东端,是中生代的走滑逆冲构造带.进行超微构造研究有利于解决岩石的变形机制问题.应用偏光显微镜和透射电子显微镜方法,进行了胶东东部走滑逆冲构造带显微构造及超微构造研究.研究认为主要走滑逆冲剪切带的石英位错亚构造以线位错为主,并常见位错环、位错弓弯、位错壁、位错列、位错网及亚晶粒等构造型式颗粒等.石英超微位错构造总体反映的是中温或低温塑性变形环境;石岛剪切带、荣成剪切带、牟平剪切带的平均古差异应力值呈现逐渐降低的趋势,跟温度呈反相关的关系.     

Miocene to recent calc-alkalic volcanism in eastern Taiwan: K-Ar ages and petrography

K-Ar radiometric datings are presented for volcanic rocks from the Coastal Range of Taiwan and from Lanhsu and Lütao islands. The samples involved are basalts, andesites and dacites which show the main petrological and geochemical characteristics of island arc magmas. The K-Ar data show that volcanic activity occurred from Early Miocene to Early Pliocene times in the Coastal Range and in Lanhsu Island, and during Pliocene times (ca. 1.3–4.3 Ma) in Lütao Island. The geological significance of Early and Middle Miocene ages is discussed with respect to hydrothermal/metasomatic alterations which have affected most of the samples. A significant increase in incompatible elements (e.g., K and Sr) is shown to have occurred during Pliocene to Recent times, and is exemplified by the compositions of the Lanhsu, and Lütao volcanic rocks. The origin of these chemical variations is related to the magmatic effects of crustal thickening linked to the transition from subduction to collision regimes.     

Brittle tectonics and major dextral strike-slip zone in the Buda karst (Budapest,Hungary)

Three large (kilometric-scale) caves were studied in the Buda hills and the main directions of cave corridors, fault planes and mineralized veins were measured. Different stages of mineralizations are recognised: calcite scaleno-hedrons, baryte, silica, gypsum. New investigations of fluid inclusions in the baryte suggest a crystallization temperature of 50 °C and a freshwater fluid source. Microtectonic analysis allows the reconstruction of the successive tectonic events: (1) a NE-SW extensional phase at the Late Eocene-Early Oligocene limit (phase I), (2) a strike-slip phase with NW-SE compression and NE-SW extension during the Late Oligocene-Early Miocene (phase II), (3) a NW-SE transtensional phase (phase III) and finally (4) a NE-SW extensional phase of Quaternary age (phase IV). The major phase is the strike-slip one, characterized by an important dextral strikeslip zone: the Ferenc-hegy zone.     

Brittle tectonics and major dextral strike-slip zone in the Buda karst (Budapest,Hungary)

Abstract

Three large (kilometric-scale) caves were studied in the Buda hills and the main directions of cave corridors, fault planes and mineralized veins were measured. Different stages of mineralizations are recognised: calcite scaleno- hedrons, baryte, silica, gypsum. New investigations of fluid inclusions in the baryte suggest a crystallization temperature of 50 °C and a freshwater fluid source. Microtectonic analysis allows the reconstruction of the successive tectonic events: (1) a NE-SW extensional phase at the Late Eocene-Early Oligocene limit (phase I), (2) a strike-slip phase with NW-SE compression and NE-SW extension during the Late Oligocene-Early Miocene (phase II), (3) a NW-SE transten- sional phase (phase III) and finally (4) a NE-SW extensional phase of Quaternary age (phase IV). The major phase is the strike-slip one, characterized by an important dextral strike- slip zone: the Ferenc-hegy zone. © Elsevier, Paris     

The eastern Jura: Relations between thin-skinned and basement tectonics,local and regional

The thesis area of Hans Cloos in the eastern Jura straddles the boundary between the Paleogene structures of the Tabular Jura, a part of the southeastern end of the Rhine graben, and the Neogene folds and thrusts of the Folded Jura. A recent reflection seismic survey in the area adjacent to the east provides new information on the subsurface structure and the relation between three superposed tectonic events. The main boundary fault zones of a deep and complexly faulted late Paleozoic trough, trending ENE, were reactivated in the early Tertiary. Faulted flexures and small folds, rooted in the basement and Paleozoic, with an amplitude of usually 100 to 300 m were produced, rather than the normal faults typical for the extensional fields of the Rhine-Bresse graben system in the west and the Bavarian Molasse basin in the east. This suggests their being part of a transform zone between these extensional fields. During Jura décollement in the Neogene these inherited, deeply rooted sub-décollement structures remained passive: their small size is kinematically incompatible with the intense subsequent thrusting and folding of the thin Mesozoic-Tertiary skin. However, thrust ramps were apparently nucleated at the respective southern foot of these Paleogene flexures and folds. The best defined and simplest of these composite structures is the Mandach structure within the Tabular Jura, a south-facing flexure of about 300 m relief, developed in the Paleogene by reactivation of the northern border fault zone of the Paleozoic trough. In the Neogene a north-vergent décollement thrust, which is connected with the regional Jura décollement in the middle Triassic evaporites, was initiated at its site.The southernmost nucleation point at the southern limit of the folded Jura was apparently re-used after intervals of northward spreading of décollement. There is evidence that a similar succession of events took place in the central and western Jura as well. Regionally, the boundary faults of at least some of the Paleozoic troughs were reactivated in the early Tertiary as transform zones linking the Rhein-Bresse-Rhone graben systems, while these early Tertiary tectonics in turn provided important boundary conditions for Jura décollement, which is the result of northward propagation of the Europa-Africa collision zone in the Neogene.

---

Zusammenfassung Das Dissertationsgebiet von Hans Cloos im östlichen Jura liegt im Grenzbezirk zwischen den untertertiären Strukturen des Tafeljuras, einem Teil des Südostens des Rheingrabens, und den neogenen Falten und überschiebungen des Faltenjuras. In jüngster Zeit wurden reflexionsseismische Aufnahmen von ausgezeichneter Qualität im östlich anschlie\enden Gebiet durchgeführt. Sie förderten kritische neue Informationen zutage über die Untergrundstruktur und die Beziehungen zwischen drei aufeinanderfolgenden tektonischen Ereignissen. Das älteste ist dokumentiert in einem mehrere Kilometer tiefen und komplex zerbrochenen und gefalteten spätpaläozoischen Trog, der ungefähr ONO streicht. Seine wichtigsten Randbruchzonen wurden im Untertertiär reaktiviert, und zwar entstanden leicht zerbrochene Flexuren und kleine Falten, die in der Tiefe wurzeln und eine Amplitude von ungefähr 100–300 Meter erreichen. Dieser tektonische Stil steht im Gegensatz zu den gleichaltrigen Dehnungsfeldern sowohl im Westen (Rhein-Bresse Grabensystem) wie auch im Osten (Bruchsysteme des bayrischen Molassebeckens). Daraus möchte man schlie\en, da\ das Untersuchungsgebiet in einer vermittelnden Transformzone liegt. Während der neogenen Jura-Abscherung über den Trias-Evaporiten blieben diese kleinen Strukturen passiv: ihre geringe Grö\e ist kinematisch inkompatibel mit der intensiven Uberschiebungs- und Faltentektonik der abgescherten Sedimenthaut. Anderseits wurden nach der seismischen Evidenz an ihrem jeweiligen Südfu\ überschiebungsrampen nukleiert. Die am besten definierte und einfachste dieser zusammengesetzten Strukturen ist die Mandach-Struktur im Tafeljura, eine nach Süden blickende Flexur von etwa 300 Metern Höhe. Sie entstand im Paläogen durch Reaktivierung der nördlichen Randbruchzone des paläozoischen Troges. Die Datierung als Paläogen gelingt in der östlichen Forsetzung. Im Neogen entwickelte sich an dieser Flexur eine nordvergente überschiebung, die gegen Süden in die allgemeine Abscherung des Juras über den Evaporiten der mittleren Trias übergeht.Der südlichste Nukleationspunkt für überschiebungen am Südfu\ des Juras wurde offenbar wiederholt aktiviert nach Intervallen, in denen sich die Abscherung nach Norden ausbreitete. Er könnte als eine Art »überschiebungsmühle« bezeichnet werden. Es gibt mancherlei Anzeichen für eine ähnliche Reihenfolge der Ereignisse im zentralen und westlichen Jura. Regional gesehen wurden besonders die Randstörungen wenigstens einiger der paläozoischen Tröge im Paläogen reaktiviert, und zwar hauptsächlich als Transformzonen im Rhein-Bresse-Rhone-Graben-System. Anderseits lieferte diese untertertiäre Tektonik wesentliche Randbedingungen für die neogene Jura-Abscherung, die Front der sich gegen Norden ausbreitenden Kollisionszone zwischen Europa und Afrika.

---

Résumé Le terrain de thèse de Hans Cloos dans le Jura oriental se situe dans la zone limite entre les structures paléogènes du Jura tabulaire, partie de la terminaison sud-est du fossé rhénan, et les plis et charriages néogènes du Jura plissé. Récemment, des relevés de sismique-réflexion d'excellente qualité ont été effectués dans la région située immédiatement à l'Est. Ils ont fourni de nouvelles informations sur la structure du sous-sol et sur les relations entre trois évéments tectoniques successifs. Le premier de ceux-ci concerne un bassin d'âge paléozoÏque supérieur, profond de plusieurs kilomètres, de direction générale Est-Nord-Est, faillé et plissé de manière complexe. Ses zones faillées les plus importantes ont été réactivées au Tertiaire inférieur, avec formation de flexures et de petits plis d'une amplitude de 100 à 300 m environ, légèrement faillés et enracinés dans le socle. Ce style tectonique s'oppose à celui des champs d'extension de mÊme âge qui sont situés soit à l'Ouest (fossés Rhin-Bresse), soit à l'Est (champs de failles du bassin molassique bavarois). On peut déduie de là que le domaine en question se situe probablement dans une zone intermédiaire à failles transformantes. Pendant le décollement néogène le long des évaporites du Trias, ces petites structures sont restées passives: du point de vue cinématique, leurs faibles dimensions sont incompatibles avec la déformation intense par charriages et par plis de la couverture décollée. D'autre part, selon les données sismiques, des rampes de chevauchement ont pris naissance au pied méridional de ces flexures. Parmi ces structures composées, la mieux défine et la plus simple est celle de Mandach dans le Jura tabulaire: c'est une flexure à regard sud d'une hauteur d'environ 300 m. Elle s'est formée au Paléogène (y inclus l'Aquitanien) par réactivation de la marge faillée septentrionale du bassin paléozoÏque. Plus à l'Est, cette réactivation se révèle d'âge »pré-molasse marine supérieure« (Burdigalien). A l'endroit de cette flexure, il s'est développé pendant le Néogène un petit chevauchement de vergence nord qui passe vers le Sud au décollement général du Jura sur les évaporites du Trias moyen.Le point le plus méridional aù des chevauchements ont été engendrés au pied sud du Jura a été réactivé plusieurs fois, après des intervalles marqués par l'expansion du décollement vers le Nord (»moulin à chevauchements«). Il existe plusieurs indications d'une succession semblable d'événements dans le Jura central et occidental. Du point de vue régional les failles bordières de plusieurs bassins paléozoÏques ont été réactivées au Paléogène, surtout dans les zones transformantes du système des fossés Rhin-Bresse-RhÔne. D'autre part cette tectonique paléogène a fourni des conditions marginales dont le rÔle fut important lors du décollement néogène, qui a constitué le front septentrional de la collision entre l'Europe et l'Afrique.

---

, . , , , . , . , ENE, , . , , , 100–300 . - - -, - . , . : . , , . , . . 300 , . . . , . , , , . , . , , . : - . , , . . , .

     

Australian palaeomagnetism and the Phanerozoic plate tectonics of eastern Gondwanaland

All palaeomagnetic investigations from the Phanerozoic of Australia are summarized and critically reviewed. Some smaller studies have been combined to produce more viable palaeomagnetic poles all of which are only considered if standard cleaning procedures were used. Analysis of the resulting data shows that during the Early Palaeozoic the pole paths for northern and central Australia are similar confirming the regions were a single unit during that time. However, these paths and the one derived from a limited region of southeast Australia approach each other from opposite directions and appear to converge during the Devonian. This observation is consistent with interpretations of the geology of the Tasman Orogenic Zone in terms of plate-tectonic models and with palaeomagnetic data from the Gondwanic continents. The presence of possible ancient plate margins bounding the region, from which most palaeomagnetic results from southeast Australia are derived, confirms that this region only became welded to the main Australian plate in Devonian times. Data for the Mesozoic of southeast Australia continue to be incompatible both with the generally accepted Australia—Antarctica relationship and with all other Gondwanic results. There appears to be no geological evidence in support of the large-scale relative motion inferred by the data and they remain a puzzling inconsistency. Cenozoic results, however, are entirely compatible with the northward motion of Australia away from Antarctica as inferred from sea-floor spreading. Comparisons with results from India suggest that the drift history of India prior to 75 m.y. ago involved movement from a location adjacent to Antarctica. It is proposed that the Wharton Basin was occupied by a northerly extension of Peninsular India which lay adjacent to western Australia. This larger Indian subcontinent broke away from both Antarctica and Australia about 140 m.y. ago.     

Facies and palaeogeographic evidence for the Miocene evolution of the Isparta Angle in its regional eastern Mediterranean context

We summarise facies evidence for four Miocene Basins (Lycian, Aksu, Köprü and Manavgat) within the Isparta Angle. Facies patterns are plotted on six palaegeographic maps restored to their pre-late Miocene setting. These maps are used to help infer the various controls on deposition. Facies trends and structural features suggest that the individual basins were kinematically linked within the overall African–Eurasia convergence zone. The Miocene Basins represent a classic example of how related basins may develop within an evolving orogen subject to variable controls through time. The dominant control was tectonic although autocyclic sedimentary processes (e.g., reef growth), and both relative and eustatic sea-level change played a significant role.From the palaeogeographic reconstructions and the tectonic context of the Isparta Angle, we infer that during the early Miocene, the westerly Lycian basin and the neighbouring Aksu basin experienced flexural subsidence related to southeastward thrusting of the Lycian Nappes. More distal effects of the forebulge may have caused uplift around the Aksu and Köprü basins initiating N–S half-grabens bounded by master faults on the eastern side of each basin. Later, the eastern basins of the Isparta Angle were influenced by regional northward subduction and inferred slab retreat within a remnant of the Southern Neotethys located within the Mediterranean Sea at the intersection of the south Aegean and Cyprus arcs.     

西准噶尔走滑断裂系元素分布特征及其成矿意义

我国新疆西北部西准噶尔走滑断裂构造体系(简称"西准系")是中亚造山带巴尔喀什马蹄形构造的向东延伸部分,由于中生代成吉思-准噶尔断裂的右行走滑断裂作用而被分成了两个部分。西准系是一个多米诺式的走滑断裂构造体系,主要由达拉布特断裂、玛依勒断裂、巴尔鲁克断裂等三条NE走向的左行走滑断裂及其夹在它们之间的地块所组成,可能是晚古生代与走滑断裂相关的陆条弯曲(褶皱)作用的产物。同时,西准噶尔地区也是重要的晚古生代成矿带,产出有一些大型和超大型的金属矿床,包括包古图斑岩铜矿、哈图金矿、萨尔托海铬铁矿和杨庄铍矿床等。本文分析了西准系走滑断裂构造与元素分布之间的关系。结果显示,西准噶尔成矿带元素与地球化学块体以及铜、金、钼、铬铁矿等矿床的分布,均受晚古生代西准系的形成与演化过程的控制。其中,庙尔沟、红山岩体与金地球化学块体之间的反对称分布特征,说明了花岗岩类侵入体和金元素在达拉布特断裂左行走滑过程中发生了重要的物质调整与迁移作用。庙尔沟岩体的逆时针旋转运动,造成了环状断裂与裂隙系统,以及与之相对应的Cu、Pb等元素风火轮式的分布形式。走滑断裂作用与岩体旋转运动的共同结果,导致了金元素沿断裂和裂隙的迁移与成矿,使得西准地区金矿床在断裂和裂隙中的发育。断裂构造体系与元素地球化学异常之间的关系,可以用来有效指导西准地区未来矿产资源的勘查。     

Upper mantle beneath Kamchatka: The depth model and its relation to tectonics

The comparative analysis of geological-geophysical data on the deep structure of the Kamchatka Peninsula and the seismic tomography model of the upper mantle revealed the coordinated spatial structure of the regional lithosphere with outlining beneath eastern Kamchatka and the boundaries, thickness, and distribution area of the asthenolith, which was first defined under its central part. Low-velocity bodies connected with the velocity structure of the focal layer and its seismicity patterns are established under recent volcanic belts. It is shown that subordination of the upper mantle structure to fault tectonics is a dominant feature at some of its levels. The system of NW-trending faults in the Petropavlovsk-Kamchatskii area, which is likely responsible for significant horizontal displacements in the upper mantle, is most contrasting. It is assumed that defined asthenolith heterogeneities continue under the Sredinnyi (Median) Range.     

The 2005 Heidelberg and Speyer earthquakes and their relationship to active tectonics in the central Upper Rhine Graben

We determine the source parameters of three minor earthquakes in the Upper Rhine Graben (URG), a Cenozoic rift, using waveforms from permanent and temporary seismological stations. Two shallow thrust-faulting events (M _L = 2.4 and 1.5) occurred on the rift shoulder just south of Heidelberg in March 2005. They indicate a possible movement along the sediment–crystalline interface due to tectonic loading from the near-by Odenwald. In February 2005, an earthquake with a normal-faulting mechanism occurred north of Speyer. This event (M _L = 2.8) had an unusual depth of about 22 km and a similar deep normal-faulting event occurred there in 1972 (M _L = 3.2). Other lower crustal events without fault plane solutions are known from 1981 and 1983. At such a depth, inside the lower crust, ductile behaviour instead of brittle faulting is commonly assumed and used for geodynamic modelling. Based on the newly available fault plane solutions we can confirm the brittle, extensional regime in the upper and lower crust in the central to northern URG indicated in earlier studies.     

The Okahandja Lineament and its significance for Damaran tectonics in Namibia

The Okahandja Lineament is considered to represent the southern margin of a magmatic arc produced by the northerly subduction of the Damran Ocean between 750 and 520 Ma ago. Sediments of the Orogen and granitoid intrusives produced by subduction and crustal melting, underwent shear deformation between 675 and 575 Ma in a low angle zone of sinistral sense shear.The Okahandja Lineament represents a zone of differential movement between the Central and Southern Zones of the Orogen during this simple shear deformation. Both overriding and overriden plates were deformed at about 550 and 520 Ma. Production of open S.E. verging structures on the northern plate was accompanied by more intense thrust and fold nappe production on the southern margin of the Damaran Orogen. During this last deformation event, the Central magmatic Zone was downfolded under the southern zone. This fold is the present expression of the Okahandja Lineament. Two tectonic models are proposed for the structures identified within the Central and Southern Zones of the Orogen, combined with evidence from the northern coastal arm of the Orogen.

---

Zusammenfassung Das Okahandja-Lineament wird als der Südrand eines magmatischen Bogens (Wurzelzone eines Inselbogens) verstanden, der auf die nordwÄrts gerichtete Subduktion des Damara Ozeans von 750 bis 520 Ma zurückgeführt wird. Die Sedimente des Orogens und die granitoiden Intrusiva, die durch Subduktion und daraus folgender Aufschmelzung der Kruste entstanden, erlitten mehrfache linksgerichtete Scherdeformation entlang einer flachliegenden Zone zwischen 675 und 575 Ma.Das Okahandja-Lineament stellt eine Zone von Teilbewegungen dar für die einfachen Scherdeformationen zwischen der zentralen und der südlichen Zone des Orogens. Die hangende und die liegende Platte wurden zwischen ca. 550 und 520 Ma deformiert. In der nördlichen Platte wurden offene SE-vergente Strukturen gebildet, wÄhrend gleichzeitig am südlichen Rand des Damara-Orogens durch die grö\ere Beanspruchung Falten-Decken entstanden. Dabei wurde die zentrale magmatische Zone unter die südliche Zone gebogen. Diese Falte ist das heutige Erscheinungsbild des Okahandja Lineaments.Zwei tektonische Modelle werden dargelegt, um die erkannten Strukturen in der zentralen und südlichen Zone des Orogens unter Verwendung der Evidenz vom nördlichen Küstenarm des Orogens zu erklÄren.

---

Résumé Le linéament de Okahandja est considéré comme la marge bordant au sud un «arc magmatique» résultant de la subduction vers le nord de l'Océan damaranique durant l'intervalle 750-520 M. a. - Les sédiments de l'orogène et les intrusions granitoÏdes produites par la subduction et par la fusion de la croûte subirent, entre 675 et 575 M. a., de nobreuses déformations cisaillantes, sénestres, le long d'une zone faiblement inclinée.Le linéament de Okahandja représente, pour les déformations cisaillantes simples une zone de déplacements partiels entre la zone centrale et la zone méridionale de l'orogène. Les deux plaques, celle du toit et celle du mur, de ce chevauchement furent déformées entre approximativement 550 et 520 M. a. Ces structures ouvertes, déversées vers le nord, se formèrent dans la plaque septentrionale, pendant que des nappes en plis naissaient simultanément, sous l'influence d'une forte so sollicitation, dans la marge méridionale de l'orogène damaranique, ce qui entraÎna le ploiement de la zone magmatique centrale sous la zone méridionale. Ce pli est la forme sous laquelle apparaÎt aujourd'hui le linéament de Okahandja.Deux modèles tectoniques sont proposés pour expliqeur les structures ainsi reconnues dans les zones centrale et méridionale de l'orogène, sur la base du fait d'un bras le long de la cÔte septentrionale de l'orogène.

---

Okahandja , - -, 750-520 , . , , , , — , , 675 575 . Okahandja , . , 550 520 . , , . . . , .

     

Ophiolite emplacement by strike-slip tectonics between the Pontide Zone and the Sakarya Zone in northwestern Anatolia, Turkey

Northwestern Anatolia contains three main tectonic units: (a) the Pontide Zone in the north which consists mainly of the Gstanbul-Zonguldak Unit in the west and the BallLda<-Küre Unit in the east; (b) the Sakarya Zone (or Continent) in the south, which is juxtaposed against the Pontide Zone due to the closure of Paleo-Tethys prior to Late Jurassic time; and (c) the Armutlu-OvacLk Zone which appears to represent a tectonic mixture of both zones. These three major tectonic zones are presently bounded by the two branches of the North Anatolian Transform Fault. The two tectonic contacts follow older tectonic lineaments (the Western Pontide Fault) which formed during the development of the Armutlu-OvacLk Zone. Since the earliest Cretaceous, an overall extensional regime dominated the region. A transpressional tectonic regime of Coniacian/Santonian to Campanian age caused the welding of the Gstanbul-Zonguldak Unit to the Sakarya Zone by an oblique collision. In the Late Campanian, a transtensional tectonic regime developed, forming a new basin within the amalgamated tectonic mosaic. The different tectonic regimes in the region were caused by activity of the Western Pontide Fault. Most of the ophiolites within the Armutlu-OvacLk Zone belong to the Paleo-Tethyan and/or pre-Ordovician ophiolitic core of the Gstanbul-Zonguldak Unit. The Late Cretaceous ophiolites in the eastern parts of the Armutlu-OvacLk Zone were transported from Neo-Tethyan ophiolites farther east by left-lateral strike-slip faults along the Western Pontide Fault. There is insufficient evidence to indicate the presence of an ocean (Intra-Pontide Ocean) between the Gstanbul-Zonguldak Unit and the Sakarya Zone during Late Cretaceous time.     

The Granada ignimbrite: A compound pyroclastic unit and its relationship with Upper Miocene caldera volcanism in the northern Puna

The Granada ignimbrite, an Upper Miocene volcanic unit from the northern Puna, previously has been interpreted as an extensive ignimbrite (>2300 km²) associated with eruptions from the Vilama caldera (trap-door event). On the basis of new data, we revise its correlation and redefine the unit as a compound, high aspect ratio ignimbrite, erupted at approximately 9.8 Ma. Calculated volumes (100 km³) are only moderate in comparison with other large volume (>1000 km³) ignimbrites that erupted approximately 2–6 m.y. later in the region (e.g. Vilama, Panizos, Atana). Six new volcanic units are recognized from sequences previously correlated with Granada (only one sourced from the same center). Consequently, the area ascribed to the Granada ignimbrite is substantially reduced (630 km²), and links to the Vilama caldera are not supported. Transport directions suggest the volcanic source for the Granada ignimbrite corresponds to vents buried under younger (7.9–5 Ma) volcanic rocks of the Abra Granada volcanic complex. Episodes of caldera collapse at some stage of eruption are likely, though their nature and timing cannot be defined from available data. The eruption of the Granada ignimbrite marks the onset of a phase of large volume (caldera-sourced) volcanism in the northern Puna.     

走滑断层研究进展及启示

自走滑断层概念提出之后,走滑断层在地质科学研究上的重要性逐渐体现出来,并在几何学、运动学、动力学及其构造意义等方面取得了重要的认识,使得走滑断层的研究得到快速的发展,但其分类及其成因机制分析还存在一定的局限性。在走滑断层相关文献调研的基础上,文章对走滑断层原理、概念和相关术语发展历程进行了归纳总结,同时也对走滑断层的位移特征、识别标志、力学性质、走滑派生或伴生构造、走滑盆地特征、走滑断层分类及走滑断层实例等研究成果进行了系统性研究分析。在此基础上,结合走滑断层的力学机制,提出走滑断层新分类方式,并运用新的分类方式进一步对美国西海岸圣安德列斯断层、新西兰的阿尔卑斯断层和中国著名的郯庐断裂带以及阿尔金断裂带等典型断层进行简要分析。      

Neogene magmatism and its possible causal relationship with hydrocarbon generation in SW Colombia

The Cretaceous oil-bearing source and reservoir sedimentary succession in the Putumayo Basin, SW Colombia, was intruded by gabbroic dykes and sills. The petrological and geochemical character of the magmatic rocks shows calc-alkaline tendency, pointing to a subduction-related magmatic event. K/Ar dating of amphibole indicates a Late Miocene to Pliocene age (6.1 ± 0.7 Ma) for the igneous episode in the basin. Therefore, we assume the intrusions to be part of the Andean magmatism of the Northern Volcanic Zone (NVZ). The age of the intrusions has significant tectonic and economic implications because it coincides with two regional events: (1) the late Miocene/Pliocene Andean orogenic uplift of most of the sub-Andean regions in Peru, Ecuador and Colombia and (2) a pulse of hydrocarbon generation and expulsion that has reached the gas window. High La/Yb, K/Nb and La/Nb ratios, and the obtained Sr–Nd–Pb isotopic compositions suggest the involvement of subducted sediments and/or the assimilation of oceanic crust of the subducting slab. We discuss the possibility that magma chamber(s) west of the basin, below the Cordillera, did increase the heat flow in the basin causing generation and expulsion of hydrocarbons and CO₂.