Structure and tectonic history of the foreland basins of southernmost South America

The common elements and differences of the neighboring Austral (Magallanes), Malvinas and South Malvinas (South Falkland) sedimentary basins are described and analyzed. The tectonic history of these basins involves Triassic to Jurassic crustal stretching, an ensuing Early Cretaceous thermal subsidence in the retroarc, followed by a Late Cretaceous–Paleogene compressional phase, and a Neogene to present-day deactivation of the fold–thrust belt dominated by wrench deformation. A concomitant Late Cretaceous onset of the foreland phase in the three basins and an integrated history during the Late Cretaceous–Cenozoic are proposed. The main lower Paleocene–lower Eocene initial foredeep depocenters were bounding the basement domain and are now deformed into the thin-skinned fold–thrust belts. A few extensional depocenters developed in the Austral and Malvinas basins during late Paleocene–early Eocene times due to a temporary extensional regime resulting from an acceleration in the separation rate between South America and Antarctica preceding the initial opening of the Drake Passage. These extensional depocenters were superimposed to the previous distal foredeep depocenter, postdating the initiation of the foredeep phase and the onset of compressional deformation. Another pervasive set of normal faults of Paleocene to Recent age that can be recognized throughout the basins are interpreted to be a consequence of flexural bending of the lithosphere, in agreement with a previous study from South Malvinas basin. Contractional deformation was replaced by transpressive kinematics during the Oligocene due to a major tectonic plate reorganization. Presently, while the South Malvinas basin is dominated by the transpressive uplift of its active margin with minor sediment supply, the westward basins undergo localized development of pull-apart depocenters and transpressional uplift of previous structures. The effective elastic thickness of the lithosphere for different sections of each basin is calculated using a dynamic finite element numerical model that simulates the lithospheric response to advancing tectonic load with active sedimentation.     

The Monte Orfano Conglomerate revisited: stratigraphic constraints on Cenozoic tectonic uplift of the Southern Alps (Lombardy, northern Italy)

The Monte Orfano Conglomerate (MOC), exposed in the foothills of the Southern Alps (northern Italy), is one of the few outcrops of sediments documenting the Cenozoic tectonic evolution of the Alpine retrowedge. Calcareous nannofossil biostratigraphy allowed us to constrain the upper part of the MOC, formerly attributed to the Early-Middle Miocene in the type-locality, to the earliest Miocene (Neogene part of the NN1 nannofossil zone). A likely latest Oligocene age is therefore suggested for the bulk of the underlying conglomerates, whose base is not exposed. Deposition of the MOC can be placed within the post-collisional tectonic uplift of the Alps, documented in the Lake Como area by the Como Conglomerate (CC) at the base of the Gonfolite Lombarda Group, and supports the correlation with Upper Oligocene clastic sediments cropping out further to the East, in the Lake Garda and in the Veneto-Friuli areas (“molassa”). The remarkable difference in petrographic composition between the western (CC) and eastern (MOC) clastics deposited in the Alpine retro-foreland basin highlights the synchronous tectonic activity of two structural domains involving different crustal levels. Whilst the bulk of the CC, that straddles the Oligocene/Miocene boundary, records largely the tectonic exhumation of the Alpine axial chain crystalline complexes, the coeval MOC consists of detritus derived from the superficial crustal section (Triassic to Paleogene sedimentary rocks) of the Alpine retrowedge and constrains the onset of the post-collisional deformation phase of the Southern Alps as not younger than the Late Oligocene.     

The sedimentary record of the exhumation of a granitic intrusion into a collisional setting: the lower Gonfolite Group,Southern Alps,Italy

The clastic wedge of the Gonfolite Lombarda Group (GLW) accumulated during Oligocene–Miocene times in the Southern Alps foreland basin, formed on the southern, inner side of the Alpine belt. It represents the depositional counterpart of the exhumation and erosion of the Central Alps metamorphic–magmatic units.Among the Central Alps units, the Tertiary Bergell Intrusion (TBI) is one of the principal sources of pebbles occurring within the GLW. Geochronologic data, both from intrusive pebbles and present-day outcrops of intrusive rocks, document the rapid uplift history of the GLW source area.The lower Gonfolite clastic wedge (Como Conglomerate and Val Grande Sandstone Formations, Oligocene–Early Miocene) has been investigated through the study of sandstone and conglomerate petrology for detecting the effects in the sedimentary record of this collision-related event.The main results are: (i) sandstone petrology of the Como Conglomerate records an evolution from feldspatholithic to feldspathic sandstones; (ii) the related Q/F–F/L ratios suggest an evolution from a mixed plutonic–metamorphic to a mainly plutonic source; (iii) consistently, conglomerate petrology records a progressive increase of plutonic pebbles (from nearly 0–50% of the total), a corresponding decrease of metamorphic clasts (from nearly 80 to nearly 50%) and the disappearance of cover rock fragments. Considering the high relief/short transport setting of the GLW clastic routing system, these values probably resemble the real proportions of such rocks in the Gonfolite catchment area.During the Aquitanian, the return to a metamorphic-rich source is recorded both by sandstones and conglomerates at the top of the Como Conglomerate and in the Val Grande Sandstone. This last signal is interpreted as the result of the reorganisation of the Gonfolite source area, possibly related to the northward shift of the main Alpine divide.     

Syn‐extension leucogranite deformation during convergence in the Eastern Central Alps: example of the Novate intrusion

The Novate intrusion is a Late Alpine leucogranite that intruded the structures related to dextral back‐thrusting along the Periadriatic Fault System in the Eastern Central Alps. The Novate granite was heterogeneously deformed from amphibolite to greenschist facies conditions during cooling of the intrusion. The deformation inside the granite is characterized by strongly localized and anastomosed ductile shear zones surrounding lenses of weakly deformed granite and by late faults formed at the brittle–ductile transition. The fault kinematic analysis of conjugated shear zones suggests that the Novate leucogranite was emplaced at 25 Ma in an extensional regime along the southern tip of the Forcola Fault. A model of extensional jog opening by vertical shearing along the Forcola Fault provided the space for magma accommodation. The Novate granite is the first evidence for orogen‐parallel syn‐extensional leucogranite emplacement during the Oligocene collision in the Alps.     

Lithostratigraphy and planktonic foraminiferal biostratigraphy of the late Eocene-Middle Miocene sequence in the area between Wadi Al Zeitun and Wadi Al Rahib,Al Bardia area,northeast Libya

The present study deals with the lithostratigraphy and planktonic foraminiferal biostratigraphy of the Late Eocene-Middle Miocene sequence in the Al Bardia area, northeast Libya. The lithostratigraphical studies carried out on three stratigraphical surface sections, namely Wade Al Rahib, Wadi Al Hash and Wadi Al Zeitun, led to the recognition of three rock units from base to top: (1) the Al Khowaymat Formation (Late Eocene-Early Oligocene); (2) the Al Faidiyah Formation (Late Oligocene-Early Miocene); and (3) the Al Jaghboub Formation (Early-Middle Miocene). The planktonic foraminiferal biostratigraphical analysis led also to the recognition of nine planktonic foraminiferal zones ranged in age from Late Eocene to Early Miocene with one larger foraminiferal zone of Middle Miocene age. These are, from base to top, as follows: Truncorotaloides rohri Zone (Late-Middle Eocene, Lutetian), Globigerinatheka semiinvoluta and Turborotalia cerroazulensis s.l. Zones (Late Eocene, Priaborian), Cassigerinella chipolensis/Pseudohasitgerina micra Zone (Early Oligocene, Rupelian), Globigerina ciperoensis ciperoensis, Globorotalia kugleri Zones (Late Oligocene, Chattian), Globigerinoides primordius Zone (Early Miocene, Aquitanian), Globigerinoides altiaperturus/Catapsydrax dissimilis and Globigerinoides trilobus Zones (Early Miocene, Burdigalian), and the larger benthonic foraminiferal zone, Borelis melo melo Zone (Middle Miocene, Langhian to Serravallian). The study of planktonic foraminifera proved the existence of a regional unconformity between the Early and Late Oligocene, with the Middle Oligocene deposits being absent (absence of Globigerina ampliapertura and Globorotalia opima opima Zones), and another, smaller unconformity located between the Late Eocene and Early Oligocene, in which the uppermost part of the Late Eocene is missing.     

Structures and tectonic evolution of the external zone of Alpine Corsica

This paper presents a structural analysis of the external zone of Alpine Corsica, including the autochthonous domain and overlying external nappes (Santa Lucia and Balagne nappes). Two stages of nappe emplacement are identified occurring prior to and after the deposition of the Eocene sediments which were laid down upon first generation thrust contacts but are imbricated with their composite (continental and ophiolitic) basement by second generation thrusts. Five generations of structures with regional extent have been distinguished. However, the first generation has not been recognized within the visible part of the autochthon domain.Eoalpine first generation structures, restricted to allochthonous units, and Late Eocene to Early Oligocene second generation structures were nearly contemporaneous with the two stages of thrusting. The precise significance of E-W third generation structures is poorly understood. Broadly N-S fourth generation structures resulted from Oligocene compressive tectonics (folding and local backthrusting). Finally, fifth generation structures were generated during a Miocene extensional stage.These results are partly consistent with structural features previously reported in the southern and the northern outcrops of the Schistes lustrés, i.e. the main part of the allochthonous domain. A summary of a regional tectonic evolution is thus proposed for Alpine Corsica from Eoalpine obduction to Miocene extension.     

Clastic sedimentation in the Late Oligocene Southalpine Foredeep: from tectonically controlled melting to tectonically driven erosion

The Villa Olmo Conglomerate (lower member of the Como Conglomerate Formation, Gonfolite Lombarda Group, Southern Alps, Italy) represents the first coarse clastic inputs into the Oligocene Southalpine Foredeep. A number of techniques including sedimentary lithofacies analyses, clast counts on turbidite conglomerate bodies, sandstone petrography through Gazzi–Dickinson point‐count method and XRF analyses, and optical and minero‐chemical analyses on single clasts have been performed, in order to better define the sediment source area and geodynamic conditions which promoted sedimentation in the Southalpine Foredeep at the end of the Oligocene. The Villa Olmo Conglomerate interdigitates with the upper part of the Chiasso Formation, and gradually passes upward into the overlying Como Conglomerate Formation. Provenance analyses (conglomerate clast counts and sandstone petrography) reveal a strong metamorphic provenance signal, likely sourced from eroded Southalpine basement. An increase in igneous plutonic clasts reflects sediment supply from the Southern Steep Belt and a decrease of volcano‐sedimentary Mesozoic cover sequences. Optical and minero‐chemical analyses on volcanic detritus detect the presence of sub‐intrusive to effusive, andesite to rhyolite products, ascribable to the Varese‐Lugano Permian volcanoclastic suite, as well as Oligocene andesite products. Plutonic clasts document the presence of tonalites, granites, and brittle deformed granodiorites (with two micas), being likely sourced from the tonalite tail of the Bergell Pluton and the plutonic units of the Bellinzona‐Dascio Zone. The identification of this provenance suite implies palaeo‐drainage from the region between Varese (Southern Alps) and the Bellinzona‐Dascio Zone (Central Alps). The Villa Olmo Conglomerate is the first depositional record of the onset of tectonically driven erosion in the Alpine belt. We infer that the previous low sediment budget regime (Eocene–Middle Oligocene) was a consequence of a tectonically controlled melting phase, during which tectonic events promoted magmatic production in the middle crust of the Central Alps at rates higher than those of crustal deformation, so inhibiting sediment production. We conclude that changes in the deep structures of the Alpine Orogenic chain have controlled the main geodynamic processes during Oligocene–Neogene times, and have controlled sediment composition and supply into the Southalpine Foredeep. Copyright © 2015 John Wiley & Sons, Ltd.     

Dating the Tethyan Ocean in the Western Alps with radiolarite pebbles from synorogenic Oligocene molasse basins (southeast France)

For the first time in the Western Alps, radiolarite pebbles collected from Tertiary foreland molasse conglomerates are treated for microfossil extraction and dated. Among forty pebbles collected in the field, seven of them released diagnostic radiolarian assemblages ranging in age from Late Bajocian?CEarly Callovian to Middle Oxfordian?CEarly Tithonian. These ages overlap previous biochronological data obtained from in situ localities of the Schistes Lustrés Piemont zone of the French-Italian Alps and triple the number of diagnostic radiolarite samples known so far in this segment of the chain. The diagnostic pebbles are characterized by low grade metamorphism, showing that some eroded thrust-sheets from the oldest parts of the ocean escaped any tectonic burial during the Alpine convergence. Mixing of low and high-grade radiolarites, mafics and ultramafics pebbles implies that various ocean-derived units were exposed. This tectonic scenario involves tight refolding and severe uplift of the Eocene subduction wedge in the Early Oligocene.     

Deformation history of the ophiolite sequence from the Balagne Nappe,northern Corsica: insights in the tectonic evolution of Alpine Corsica

In Alpine Corsica, the Jurassic ophiolites represent remnants of oceanic lithosphere belonging to the Ligure‐Piemontese Basin located between the Europe/Corsica and Adria continental margins. In the Balagne area, a Jurassic ophiolitic sequence topped by a Late Jurassic–Late Cretaceous sedimentary cover crops out at the top of the nappe pile. The whole ophiolitic succession is affected by polyphase deformation developed under very low‐grade orogenic metamorphic conditions. The original palaeogeographic location and the emplacement mechanisms for the Balagne ophiolites are still a matter of debate and different interpretations for its history have been proposed. The deformation features of the Balagne ophiolites are outlined in order to provide constraints on their history in the framework of the geodynamic evolution of Alpine Corsica. The deformation history reconstructed for the Balagne Nappe includes five different deformation phases, from D1 to D5. The D1 phase was connected with the latest Cretaceous/Palaeocene accretion into the accretionary wedge related to an east‐dipping subduction zone followed by a Late Eocene D2 phase related to emplacement onto the Europe/Corsica continental margin. The subsequent D3 phase was characterized by sinistral strike‐slip faults and related deformations of Late Eocene–Early Oligocene age. The D4 and D5 phases were developed during the Early Oligocene–Late Miocene extensional processes connected with the collapse of the Alpine belt. Copyright © 2003 John Wiley & Sons, Ltd.     

Evolution of the European Cenozoic Rift System: interaction of the Alpine and Pyrenean orogens with their foreland lithosphere

The evolution of the European Cenozoic Rift System (ECRIS) and the Alpine orogen is discussed on the base of a set of palaeotectonic maps and two retro-deformed lithospheric transects which extend across the Western and Central Alps and the Massif Central and the Rhenish Massif, respectively.During the Paleocene, compressional stresses exerted on continental Europe by the evolving Alps and Pyrenees caused lithospheric buckling and basin inversion up to 1700 km to the north of the Alpine and Pyrenean deformation fronts. This deformation was accompanied by the injection of melilite dykes, reflecting a plume-related increase in the temperature of the asthenosphere beneath the European foreland. At the Paleocene–Eocene transition, compressional stresses relaxed in the Alpine foreland, whereas collisional interaction of the Pyrenees with their foreland persisted. In the Alps, major Eocene north-directed lithospheric shortening was followed by mid-Eocene slab- and thrust-loaded subsidence of the Dauphinois and Helvetic shelves. During the late Eocene, north-directed compressional intraplate stresses originating in the Alpine and Pyrenean collision zones built up and activated ECRIS.At the Eocene–Oligocene transition, the subducted Central Alpine slab was detached, whereas the West-Alpine slab remained attached to the lithosphere. Subsequently, the Alpine orogenic wedge converged northwestward with its foreland. The Oligocene main rifting phase of ECRIS was controlled by north-directed compressional stresses originating in the Pyrenean and Alpine collision zones.Following early Miocene termination of crustal shortening in the Pyrenees and opening of the oceanic Provençal Basin, the evolution of ECRIS was exclusively controlled by west- and northwest-directed compressional stresses emanating from the Alps during imbrication of their external massifs. Whereas the grabens of the Massif Central and the Rhône Valley became inactive during the early Miocene, the Rhine Rift System remained active until the present. Lithospheric folding controlled mid-Miocene and Pliocene uplift of the Vosges-Black Forest Arch. Progressive uplift of the Rhenish Massif and Massif Central is mainly attributed to plume-related thermal thinning of the mantle-lithosphere.ECRIS evolved by passive rifting in response to the build-up of Pyrenean and Alpine collision-related compressional intraplate stresses. Mantle-plume-type upwelling of the asthenosphere caused thermal weakening of the foreland lithosphere, rendering it prone to deformation.     

Stages in the Magura Basin: a case study of the Polish sector (Western Carpathians)

The Magura Basin domain developed in its initial stage as a Jurassic-Early Cretaceous rifted passive margin that faced the eastern parts of the oceanic Alpine Tethys. In the pre- and syn-orogenic evolution of the Magura Basin the following prominent periods can be distinguished: Middle Jurassic-Early Cretaceous syn-rift opening of basins (1) followed by Early Cretaceous post-rift thermal subsidence (2), latest Cretaceous–Paleocene syn-collisional inversion (3), Late Paleocene to Middle Eocene flexural subsidence (4) and Late Eocene - Early Miocene synorogenic closing of the basin (5). The driving forces of tectonic subsidence of the basin were syn-rift and thermal post-rift processes, as well as tectonic loads related to the emplacement of accretionary wedge. This process was initiated at the end of the Paleocene at the Pieniny Klippen Belt (PKB)/Magura Basin boundary and was completed during Late Oligocene in the northern part of the Magura Basin. During Early Miocene the Magura Basin was finally folded, thrusted and uplifted as the Magura Nappe.     

Uppermost Cretaceous–Lower Tertiary Ulukışla Basin,south-central Turkey: sedimentary evolution of part of a unified basin complex within an evolving Neotethyan suture zone

The Ulukışla Basin, the southerly and best exposed of the Lower Tertiary Central Anatolian Basins, sheds light on one of the outstanding problems of the tectonic assembly of suture zones: how large deep-water basins can form within a zone of regional plate convergence. The oldest Ulukışla Basin sediments, of Maastrichtian age, transgressively overlie mélange and ophiolitic rocks that were emplaced southwards onto the Tauride microcontinent during the latest Cretaceous time. The Niğde-Kirşehir Massif forming the northern basin margin probably represents another rifted continental fragment that was surrounded by oceanic crust during Mesozoic time. The stratigraphic succession of the Ulukışla Basin begins with the deposition of shallow-marine carbonates of Maastrichtian–Early Palaeocene age, then passes upwards into slope-facies carbonates, with localised sedimentary breccias and channelised units, followed by deep-water clastic turbidites of Middle Palaeocene–Early Eocene age. This was followed by the extrusion of c. 2000 m of basic volcanic rocks during Early to Mid Eocene time. After volcanism ended, coral-bearing neritic carbonates and nummulitic shelf sediments accumulated along the northern and southern margins of the basin, respectively. Deposition of the Ulukışla Basin ended with gypsum deposits including turbidites, debris flows, and sabkhas, followed by a regional Oligocene unconformity.The Ulukışla Basin is interpreted as the result of extension (or transtension) coupled with subsidence and basic volcanism. After post-volcanic subsidence, the basin was terminated by regional convergence, culminating in thrusting and folding in Late Eocene time. Comparisons of the Ulukışla Basin with the adjacent central Anatolian basins (e.g. Tuzgölü, Sivas and Şarkişla) support the view that these basins formed parts of a regional transtensional (to extensional) basin system. In our preferred hypothesis, the Ulukışla Basin developed during an intermediate stage of continental collision, after steady-state subduction of oceanic crust had more or less ended (“soft collision”), but before the opposing Tauride and Eurasian continental units forcefully collided (“hard collision”). Late Eocene forceful collision terminated the basinal evolution and initiated uplift of the Taurus Mountains.     

Tertiary evolution of the central Menderes Massif based on structural investigations of metamorphics and sedimentary cover rocks between Salihli and Kiraz (western Turkey)

Augen gneisses, mica schists, and marbles of the Menderes Massif and its sedimentary cover rocks are exposed south of the Gediz graben. The augen gneisses form the structurally lowest part of the studied lithological sequence, and are overlain by a schist complex. The structurally highest part is formed by a series of marbles. The ages of this lithological sequence range from Precambrian to Early Paleocene. Furthermore, this sequence records the tectonic evolution since the Precambrian. The sedimentary cover of the Menderes Massif consists of two groups of sediments from Early Miocene to Quaternary. The lower group, the Alayehir group, consists of Early- to mid-Miocene-aged fluvial and limnic sediments which form the lower and the upper parts, respectively. The Alayehir group is overlain by mainly fluvial sediments of the Gediz group. Both the Alayehir and the Gediz groups are separated by an angular unconformity. Six deformational phases could be distinguished within the metamorphic rocks of the Menderes Massif and its Tertiary cover. The structures which were interpreted to belong to deformational events predating the Paleocene are summarized as deformational phase D1. D1 structures were nearly completely overprinted by the subsequent deformation events. The second deformational phase D2 occurred between Early Eocene and Early Oligocene. D2 occurred contemporaneously with a Barrovian-type regional metamorphism. The third deformational phase D3 is characterized by folding of the axial planes which formed at the end of Early Oligocene. The deformational event D4 occurred during the Late Oligocene and is related to an extensional period. The deposition of the sedimentary rocks which belong to the Tertiary cover of the Menderes Massif that started in the Early Miocene was interrupted by a compressional phase (D5) during the Late Miocene. Sediments which were deposited since the Early Pliocene record structures which were related to a young extensional phase (D6). This extensional phase has continued to the Present.     

青藏高原东缘古近纪粗碎屑岩沉积学及其构造意义

青藏高原东缘古近纪盆地的填图和沉积学研究表明,在青藏高原东缘区域性走滑-挤压构造背景下形成的古近纪盆地内广泛发育厚层—巨厚层状的紫红色粗碎屑岩系。其沉积特征指示为一种近源快速堆积的泥石流和辫状河道沉积体,形成于干旱炎热气候条件下的典型陆内冲积扇环境。盆地充填序列、粗碎屑岩层序、动植物化石和盆地内岩浆岩~(40)Ar-~(39)Ar年代学等综合研究结果表明,古近纪盆地内粗碎屑岩大约形成于38～29 Ma。该时期与青藏高原东缘北段(横断山地区)古近纪盆地的形成和南段(兰坪—思茅地区)大盆地的裂解时间基本一致,这很可能预示着青藏高原在晚始新世—早渐新世期间曾发生过整体的快速构造隆升。     

Non-marine sedimentation associated with Oligocene-Recent exhumation and uplift of the Central Taurus Mountains,S Turkey

Three related basins in southern Turkey, the Ecemiş Basin, the Karsanti Basin and the Aktoprak Basin, document the Neogene-Recent regional exhumation and surface uplift history of the Central Taurus Mountains. The regional tectonic framework was established by a Late Eocene phase of compressional deformation that ended Tethys-related marine deposition. During the Oligocene–Early Miocene non-marine sedimentation was dominantly from braided rivers flowing from the nascent Taurus Mountains and from the Niğde metamorphic massif further north. During this period erosion more or less kept pace with exhumation and the topography remained subdued, allowing a marine incursion (probably eustatically controlled) into the Karsanti Basin in the east during Early Oligocene time. Regional exhumation was possibly controlled by thermal uplift of an actively extending area located behind the subducting S-Neotethys in the Eastern Mediterranean Sea. During exhumation, largely ophiolitic rocks were eroded, revealing the deformed Mesozoic Tauride carbonate platform beneath. The area was affected by a short-lived pulse of compressional deformation/transpression, probably in Mid-Miocene time, but extensional exhumation then resumed, as indicated by the presence of metamorphic-derived clasts from the adjacent Niğde Massif. Late Miocene deposition was dominated by large inward-draining lakes, consistent with regional evidence of a humid climate during this time. Strong surface uplift took place during Plio-Quaternary time. Drainage to the Mediterranean became established, allowing river valleys to incise deeply into the flanks of the Taurus Mountains. Palaeo-valleys were successively infilled with coarse alluvial sediments. This deposition was influenced by NE–SW trending extensional faults. In addition, the sedimentary evolution of the area was strongly influenced by the NNE–SSW trending Ecemiş Fault Zone, which has experienced ca. 60 km of left-lateral strike-slip since the Late Eocene. An important pulse of normal faulting/transtension in latest Miocene–early Pliocene time generated large fault scarps. These acted as sources for large Plio-Quaternary alluvial fans, which prograded across active strike-slip faults. The morphology of these fans was influenced by a combination of Quaternary climatic change, axial-fluvial downcutting and active strike-slip tectonics. In general, the Plio-Quaternary regional uplift of the Taurus Mountains may relate to underplating of material derived from the African plate during progressive collision with the Anatolian (Eurasian) plate in the vicinity of the easternmost Mediterranean Sea.     

Stratigraphic responses to a major tectonic event in a foreland basin: the Ecuadorian Oriente Basin from Eocene to Oligocene times

The Eocene to Oligocene sediments of the Ecuadorian Oriente Basin record two kinds of second-order stratigraphic response to the tectonic evolution. Lower Eocene shows evidences of local scale syntectonic deposits. This tectonic activity can be related to right lateral convergent movements inverting pre-cretaceous extensional structures. Upper Eocene and Oligocene sediments are integrated as the expression of an isostatic rebound characterizing a basin scale syntectonic deposition. This response is evidenced by a reciprocal architecture of the depositional sequences identified in the sedimentary formations. These data have allowed us to propose a new geodynamic model for the Paleogene evolution of the Oriente Basin.     

Cenozoic magmatism in Kalimantan and its related geodynamic evolution

The NE–SW Tertiary magmatic belt of central Kalimantan is related to two separate periods of subduction; during the Eocene–Oligocene and Late Oligocene–Miocene. The younger magmatic belt is superimposed upon the earlier belt. This magmatic belt is characterized chiefly by Late Oligocene–Miocene volcanic products, among which limited exposures of the Eocene volcanics have also been mapped by previous investigators. This calc-alkaline magmatic belt has become known as the ‘gold belt’ of Central West Kalimantan on account of a number of discoveries of Neogene epithermal gold mineralization. This mineralization is found in central to proximal volcanic settings and occurred at relatively shallow depths. The earliest known subduction-related magmatism took place in the Eocene–Early Oligocene with the emplacement of calc-alkaline silicic pyroclastics, followed by a period of continental collision. Subsequent subduction-related magmatism continued from Late Oligocene–Pleistocene, during which time the magma evolved from calc-alkaline to potassic calc-alkaline. Plio-Pleistocene magmatism resulted in the formation of basalt flows. The present available K–Ar ages of the Cenozoic volcanics range from 51 to 1 Ma.     

Retrogressive fabric development during exhumation of the Voltri Massif (Ligurian Alps,Italy): arguments for an extensional origin and implications for the Alps–Apennines linkage

Geological mapping coupled with structural investigations carried out in the Voltri Massif (eastern Ligurian Alps, Italy) provide new data for the interpretation of the tectonic context controlling main fabric development during exhumation of its high-pressure core. The Voltri Massif is here interpreted as a c. 30 km-long eclogite-bearing, asymmetric dome formed by the progressive verticalisation of the regional, second-phase mylonitic foliation developed during retrogressive greenschist metamorphic conditions. In this light, the exhumation history is driven by a ductile-to-brittle extensional process, operating through low-angle, top-to-the-W multiple detachment systems. A Late Eocene–Early Oligocene age for this extensional episode is proposed on the basis of structural correlations, stratigraphic and radiometric constraints. In this scenario, the Voltri Massif is interpreted as an extensional domain developed to accommodate the Late Eocene–Early Oligocene arching of the Western Alps–Northern Apennines orogenic system.     

Post-Variscan sedimentary record of the SW margin of the Bohemian massif: a review

The late-Palaeozoic to Cenozoic stratigraphic and structural record of the southwestern margin of the Bohemian massif and its extension beneath the southward adjacent Molasse basin shows that it is controlled by a system of basement-involving faults which came into evidence during Stephanian– Autunian times and which were subsequently repeatedly reactivated. Thick Permo-Carboniferous clastics accumulated in fault-bounded transtensional basins aligned with the southwestern Bohemian border zone (SWBBZ). Following late-Autunian deformation of these basins, the SWBBZ was overstepped by late-Permian to Late Jurassic platform sediments, reflecting tectonic stability. During the Early Cretaceous the SWBBZ was strongly reactivated, causing disruption and erosion of its Mesozoic sedimentary cover. Sedimentation resumed in the area of the SWBBZ during late Early and Late Cretaceous with clastic influx from the Bohemian massif reflecting gradually increasing tectonic activity along the SWBBZ. During the Late Senonian and Paleocene transpressional deformations resulted in upthrusting of major basement blocks. In the Molasse basin such structures are sealed by transgressive Late Eocene marine strata. Mio-Pliocene uplift of the Bohemian massif, involving mild reactivation of the SWBBZ, is related to the development of the volcano-tectonic Eger zone. The structural configuration of the SWBBZ is largely the result of Late Senonian–Paleocene compressional intraplate tectonics which play a major role in the structural framework of the northern Alpine and Carpathian foreland.     

西宁和贵德盆地新生代沉积物重矿物变化对构造活动的响应

位于青藏高原东北缘的西宁、贵德盆地的新生代沉积序列较完整的记录了盆地周围物源区构造变形过程。重矿物是碎屑物质的重要组成部分,是最直观、有效揭示源区母岩、构造-沉积过程的重要手段。通过重矿物的系统分析,结合沉积-构造变形,揭示出始新世-上新世末西宁-贵得盆地及其源区经历了几个构造活动阶段:古新世-始新世早期的隆升阶段、始新世中期-渐新世晚期的构造稳定阶段、渐新世末-中新世初的构造隆升阶段、中中新世构造稳定阶段和晚中新世以来的强烈隆升阶段。并结合特征矿物（绿泥石）及古水流分析,推断古近纪西宁-贵德盆地是东昆仑山前一个统一盆地。中新世早期青藏高原的扩张导致了拉脊山开始隆起,使原型盆地解体;约8.5 Ma以来拉脊山强烈隆升,两侧盆地逐渐转变为山间盆地。这为正确理解青藏高原东北缘盆山格局的形成和演化提供了重要依据。