Late Miocene Time Research Articles

Solid sediment load history of the Zambezi Delta

We calculate the solid sediment load history of the Zambezi River for the last 120 Ma (i.e. Middle Cretaceous–Recent times). Our starting point is a detailed grid of two-dimensional seismic reflection profiles, calibrated by well-log information. After conversion from two-way travel time to depth, we made simple assumptions about the compaction history in order to construct isochore maps of solid sediment load and yield as a function of geological time. Our results show that solid sediment load has varied by ∼1 order of magnitude over the last 120 Ma. There have been three periods of elevated flux. The first period occurred in Late Cretaceous times (90–65 Ma) and was synchronous with the rapid denudation of southern Africa recognised by, for example, apatite fission track modelling. The second period occurred in Oligocene times (34–24 Ma) during proposed rapid regional uplift of Southern Africa. The youngest phase of elevated flux started in Late Miocene times (10 Ma) and has continued to increase rapidly through to the present day. A large proportion of this increase can be attributed to a doubling of the size of the Zambezi catchment during the Pliocene. At other times, we suggest that load variations can be used to bound the uplift history of the region, which encompasses the catchment. Finally, changes in the shape of the Zambezi Delta through time suggest that the Mozambique current, which sweeps through the Mozambique Channel from northeast to southwest, initiated at the start of the Miocene.

Quantifying the contribution of tectonics vs. differential compaction in the development of domes along the Mid‐Norwegian Atlantic margin

AbstractA sequential restoration based on combined backstripping and unfolding methods affords the opportunity to study the Cenozoic evolution of two low amplitude domes in the Mid‐Norwegian extensional margin, the Helland Hansen Arch and the Vema Dome. The integration of growth strata geometries observed in both flanks of the domes demonstrate that the structures grew by a variable combination of tectonics and differential compaction mechanisms. Sequential restoration shows that the Helland Hansen Arch grew between Early Oligocene and earliest Late Pliocene times (33–1.9 Ma). During the first phase of growth (33–9 Ma), the tectonic compression accounted for a minimum of 27% of the total dome amplitude. During Late Miocene to Pliocene times (9–1.9 Ma), differential compaction was the mechanism for dome growth. During Late Pliocene times, the Helland Hansen Arch grew with the highest rates coinciding with initial deposition of prograding wedges (3.6–1.9 Ma). In contrast, the Vema Dome started to develop in Early Eocene times and grew at a fairly constant rate up to Early Pliocene times at 3.6 Ma. The amplification of the Vema Dome took place through both differential compaction and tectonics between Early Eocene and Late Miocene times (54.8–7 Ma). The tectonic contribution accounted for a minimum of a 37% of the total dome amplitude. During Pleistocene times, the progradation of clastic wedges led to a decrease of the amplitudes of both the Helland Hansen Arch and the Vema Dome. The different timing of tectonic growth for analysed domes and arches suggest that a small and protracted phase of compression affected the Mid‐Norwegian Margin. This agrees with well‐known widespread contractional deformation affecting the Atlantic Margin of the European Plate during the Tertiary.

Bolboforma — an overview

A summary of the present knowledge ofBolboforma is presented in this paper. The genusBolboforma contains a diverse group of marine, mostly single-chambered enigmatic microfossils (phytoplankton, possibly Chrysophyta) which produced calcitic monocrystalline spheroidal tests with or without inner cysts and with various types of ornamentation. The genusBolboforma occurs in the time interval between late Early Eocene to Late Pliocene, at middle and higher latitudes, and thus, has not been recorded in Quaternary to Recent Sediments. The genus is represented globally, but the first and the last occurrence of the genus appear to be spatially diachronous in both hemispheres.Bolboforma started in the southern hemisphere at the Campbell Plateau (SW Pazific) during the Early Eocene approximately 53 Ma ago, and the genus lived there until latest Miocene times (5.3 Ma at the Kerguelen Plateau, Southern Indian Ocean). The first occurrence ofBolboforma in the northern hemisphere is observed in Upper Eocene Sediments (ca. 36.5 Ma) in the Labrador Sea (North Atlantic), and its youngest occurrence is observed in the Hatton-Rockall Basin (North Atlantic) in the Late Pliocene at 2.84 Ma. Well established and common species permit the definition of nineteenBolboforma zones/subzones. Not all of these are observed in both hemispheres. In the southern hemisphere all four Paleogene zones, but only eight Neogene zones are present, in the northern hemisphere only one Paleogene zone, but fourteen Neogene zones have been determined.

Oblique transpression in the western thrust front of the Colombian Eastern Cordillera

New kinematic data reveal that the main faults of the western foothills of the Colombian Eastern Cordillera are a series of left-lateral to oblique thrusts that are offset by steeply dipping, northwest-trending, left-lateral, strike-slip faults. Kinematic data were collected from the main structures that dominate the 350-km length of the western foothills of the Eastern Cordillera, north of Bogota (La Salina–Bituima, Cambrás, Dos Hermanos–Alto del Trigo, and Bucaramanga faults). These data indicate that transpression is responsible for the Cenozoic formation of the folds and thrusts that deform the Mesozoic and Cenozoic sedimentary sequences of the Middle Magdalena Valley. Kinematic and structural data suggest that the La Salina–Bituima fault changed from a reverse fault to a fault with a left-lateral, strike-slip sense of displacement during middle to late Miocene times. As it propagated, a transpressive zone was generated in the western foothills of the Eastern Cordillera, with the development of arcuate, oblique-reverse secondary faults on the leading edge of the Magdalena basin (e.g. Cambrás, Dos Hermanos). This development implies that during the Neogene (?), the tectonics of the western foothills were dominated by nonplanar deformation with shortening accompanied by significant left-lateral, strike-slip displacements. These new data indicate that the oblique convergence vector imposed by convergence among the Nazca, Caribbean, and South American plates is not fully partitioned in space but instead must be distributed in a diffuse zone of transpressional deformation along the western margin of the Eastern Cordillera and its associated foreland basin.

Aksaray and Ecemis Faults—Diapiric Salt Relationships: Relevance to the Hydrocarbon Exploration in the Tuz Golu (Salt Lake) Basin, Central Anatolia, Turkey

Due to activitiy of the Aksaray and Ecemis Faults, volcanic intrusion and westward movement of the Anatolian plate, diapiric salt structures were occurred in the Tuz Golu (Salt Lake) basin in central Anatolia, Turkey. With the collisions of the Arabian and Anatolian plates during the late Cretaceous and Miocene times, prominent ophiolitic obduction occurred in the Pontides and Taurides along the North Anatolian Fault (NAF) and East Anatolian Fault (EAF). The NAF and EAF intersect each other in the Karliova region, in eastern Turkey. At this point, due to the northward movement of the Arabian plate in SE Turkey, the Anatolian plate shifted toward the west and south along the fault zones. The same geological tectonic model is proposed at the intersection point of the Aksaray Fault (AF) and Ecemis Fault (EF) in central Anatolia. The westward movement of the Anatolian plate between these two faults resulted in the formation of the diapiric salt structures, volcanic intrusions and overpressure zones in the study area. Paleogeological reconstructions of the Tuz Golu basin indicate that the salient positive structures in the basin were formed during late Eocene-Oligocene times. These structures, like the Yeniceoba-Bezirci and Karapinar-Kochisar trends, are oriented in a NW-SE or N-S directions between the Kirsehir and Sivrihisar-Bozdag massifs. The subsidence rate and Paleogeographic evolutions in the basin show that the southeastern sector of the Tuz Golu basin remained shallower relative to the central and northwestern regions. Based on the paleostructural, subsidence and geothermal reconstructions, it has been concluded that the oil generation and migration zones and geothermal trends are oriented in a NW-SE direction in the Tuz Golu basin.

Evolution of the sedimentary system beneath the deep Pacific inflow off eastern New Zealand

Results from Ocean Drilling Program sites 1121–1124 show the Eastern New Zealand Oceanic Sedimentary System (ENZOSS) evolved in response to: (1) the inception of the circum-Antarctic circulation, (2) orbital and non-orbital regulation of the global thermohaline flow, and (3) development of the New Zealand plate boundary. ENZOSS began in the early Oligocene following opening of the Tasmanian gateway and inception of the ancestral Antarctic Circumpolar Current (ACC) and SW Pacific Deep Western Boundary Current (DWBC). Widespread erosion, marked by the Marshall Paraconformity, was followed by extensive drift formation in the late Oligocene–early Miocene. Alternating nannofossil chalk and nannofossil-rich mud deposited in response to 41-kyr orbital regulation of the abyssal circulation, with the mudstones representing times of increased inflow of corrosive southern-source waters. Drift deposition at the deepest sites was interrupted by bouts of erosion coincident with Mi1–5 isotopic events signifying expansions of the East Antarctic Ice Sheet and enhanced bottom water formation. By late Miocene times, the basic ENZOSS was established. South of Bounty Trough, the energetic ACC instigated an erosional/low depositional regime. To the north, where the DWBC prevailed, orbitally regulated drift deposition continued. Increased convergence at the New Zealand plate boundary enhanced the terrigenous supply, but little of this sediment reached the deep ENZOSS as the three main sediment conduits – Solander, Bounty and Hikurangi channels – had not fully developed. The Plio–Pleistocene heralded a change from a carbonate- to terrigenous-dominant supply caused by interception of the DWBC by the three channels (∼1.6 Ma for Bounty and Hikurangi, time of Solander interception unknown). The Solander and Bounty fans, and Hikurangi Fan-drift systems formed, and drifts downstream of those systems, received terrigenous detritus. Supply increased with accelerating uplift along the plate boundary, but delivery to the DWBC was regulated by eustatic fluctuations of sea level. Times of maximum supply to all three channels was during glacial lowstands whereas the supply either ceased (Bounty, Solander), or reduced (Hikurangi) in highstands. In glacial times, sediment was entrained by a DWBC invigorated by an increased input of Antarctic bottom water. The ACC also accelerated under strengthened glacial winds. Thus, glacials were times of optimum sediment supply to ENZOSS depocentres where depositional rates were 2–3 times more than interglacial rates.

Stable isotopic studies of palaeosol sediment from Upper Siwalik of Himachal Himalaya: evidence for high monsoonal intensity during late Miocene?

Palaeosols from sedimentary section exposed 2800 m at Haripur–Kolar on Somb River in Himachal Himalaya were studied for stable isotopes of carbon, oxygen, and hydrogen along with Sr isotopic ratios. Stable isotopic studies of middle and upper Siwalik sections from Pakistan and Nepal region have been used for inferring the palaeoclimate of the region during Early and Late Miocene time. The aim of our work was to extend this type of study to Himachal Himalaya, India. Carbon isotopes in palaeosol carbonate nodule and associated organic matter indicate an abrupt transient of C 3 vegetation dominance around 4 Ma. This transient disrupted the general trend of C 4 ecological dominance observed from about 8 to 4 Ma in this region of Asian subcontinent. We attribute this observation with the higher monsoonal intensity, which also is supported by different archives from the region ( G. bulloides abundance from DSDP core from the Arabian Sea and grass pollens abundances on land). We propose that greater moisture availability around 4 Ma due to higher monsoonal activity caused an abrupt transient of C 3 dominance in this region. The proposition is further supported by our data on δ 18O of carbonates and δ D of clay, showing depletion around 4 Ma. Observed high 87Sr/ 86Sr ratios in carbonates around the same time period suggest increased weathering and, in turn, higher rainfall activity.

Cenozoic tectonics of the China continental margin: insights from Taiwan

Abstract The continental margin to the east and south of China comprises an active margin in the East China Sea, a collision mountain belt in Taiwan, and a passive margin in the South China Sea. These three segments were generally regarded as separate tectonic entities and their interrelations have long been the subject of debate. Here we synthesize available information to outline the tectonic and geological background of the China margin, examine the link between Taiwan and the neighbouring China margins, and thereby establish a Cenozoic evolutionary model. The China margin is floored with a pre-Cenozoic continental basement covered with an up to 10-km-thick pile of Cenozoic sedimentary strata. The continental basement has been invariably stretched and moulded into a series of northeast-trending horsts and grabens. Except in the Okinawa Trough of the East China Sea, the Cenozoic sedimentary cover typically exhibits a two-tier tectonostratigraphic structure, with narrow Palaeogene rift basins draped by a blanket-like Neogene-Quaternary sequence. The two-tier structure prevails in the entire inner part of the China margin, including the Taiwan Strait off western Taiwan. In the outer China margin, however, the two-tier structure persists only in the South China Sea, and is in stark contrast with the collisional orogen of Taiwan and the Ryukyu arc of the East China Sea. By untangling the contractional deformation of the northern Taiwan mountain belt, it has been possible to reconstruct a precollisional tectonostratigraphic section with a distinctive two-tier structure shown by a Palaeogene half-graben covered with a Miocene drape sequence. When put together with Palaeogene rift basins of the Taiwan Strait, it becomes clear that the precollisional continental margin of Taiwan resembles that of the South China Sea, characterized by two lines of Palaeogene rift basins. Hence before the collision started in Late Miocene times, Taiwan was part of the passive South China margin that extended northward to the southern Ryukyu area. Ever since the end of the Cretaceous, the China continental margin has been dominated by extensional tectonics, regardless of the presence or absence of subduction zones. In the Early Cenozoic, extensive crustal attenuation resulted in region-wide subsidence and formation of rift basins. Extension in the South China Sea culminated in Late Oligocene times, when part of the outer margin was drifted away by the opening ocean basin. In the East China Sea, the margin remained intact and became separated from the South China Sea margin by a transform fault. From the Miocene onwards, the South China Sea margin has been passively subsiding, sporadically punctuated with basaltic volcanism. In the East China Sea margin, the Okinawa Trough has opened and the Ryukyu volcanic arc thrived. The NE edge of the South China Sea margin was deformed as the Taiwan orogen.

Development of an Oblique Subduction Zone—Tectonic Evolution of the Tethys Suture Zone in Southeast Turkey

The Southeast Anatolian orogen, part of the Mediterranean-Himalayan orogenic belt, may be divided into three approximately E-W-trending zones. From south to north, they are the Arabian platform, an imbricated zone, and a nappe zone. The eastern part of the Arabian platform includes a lower Paleozoic to lower Miocene sedimentary sequence and ophiolitic rocks that were obducted on the platform during Late Cretaceous time. Also, in the eastern part of the nappe zone consisting of lower and upper nappe packages, three major Paleocene-Oligocene deformational phases occurred, related to late-early Paleocene-early Eocene, late Lutetian, and late Oligocene nappe emplacements. These amalgamated nappes collided with the Arabian plate and were welded onto it at the latest stage of the orogenic evolution during late early Miocene time. The imbricated zone consists of units that were compressed and sandwiched between the nappes and the Arabian platform. In the nappe and imbricated zones, various island-arc volcanics and associated units developed related to the northward subduction of Neotethys during the Late Cretaceous to the late Oligocene. The ages of volcanic units decrease from west to east. This reflects oblique subduction of the ocean floor; its remnant presently underlies the northerly nappes.

The Misis–Andırın Complex: a Mid-Tertiary melange related to late-stage subduction of the Southern Neotethys in S Turkey

The Mid-Tertiary (Mid-Eocene to earliest Miocene) Misis–Andırın Complex documents tectonic-sedimentary processes affecting the northerly, active margin of the South Tethys (Neotethys) in the easternmost Mediterranean region. Each of three orogenic segments, Misis (in the SW), Andırın (central) and Engizek (in the NE) represent parts of an originally continuous active continental margin. A structurally lower Volcanic-Sedimentary Unit includes Late Cretaceous arc-related extrusives and their Lower Tertiary pelagic cover. This unit is interpreted as an Early Tertiary remnant of the Mesozoic South Tethys. The overlying melange unit is dominated by tectonically brecciated blocks (>100 m across) of Mesozoic neritic limestone that were derived from the Tauride carbonate platform to the north, together with accreted ophiolitic material. The melange matrix comprises polymict debris flows, high- to low-density turbidites and minor hemipelagic sediments.The Misis–Andırın Complex is interpreted as an accretionary prism related to the latest stages of northward subduction of the South Tethys and diachronous continental collision of the Tauride (Eurasian) and Arabian (African) plates during Mid-Eocene to earliest Miocene time. Slivers of Upper Cretaceous oceanic crust and its Early Tertiary pelagic cover were accreted, while blocks of Mesozoic platform carbonates slid from the overriding plate. Tectonic mixing and sedimentary recycling took place within a trench. Subduction culminated in large-scale collapse of the overriding (northern) margin and foundering of vast blocks of neritic carbonate into the trench. A possible cause was rapid roll back of dense downgoing Mesozoic oceanic crust, such that the accretionary wedge taper was extended leading to gravity collapse. Melange formation was terminated by underthrusting of the Arabian plate from the south during earliest Miocene time.Collision was diachronous. In the east (Engizek Range and SE Anatolia) collision generated a Lower Miocene flexural basin infilled with turbidites and a flexural bulge to the south. Miocene turbiditic sediments also covered the former accretionary prism. Further west (Misis Range) the easternmost Mediterranean remained in a pre-collisional setting with northward underthrusting (incipient subduction) along the Cyprus arc. The Lower Miocene basins to the north (Misis and Adana) indicate an extensional (to transtensional) setting. The NE–SW linking segment (Andırın) probably originated as a Mesozoic palaeogeographic offset of the Tauride margin. This was reactivated by strike-slip (and transtension) during Later Tertiary diachronous collision. Related to on-going plate convergence the former accretionary wedge (upper plate) was thrust over the Lower Miocene turbiditic basins in Mid–Late Miocene time. The Plio-Quaternary was dominated by left-lateral strike-slip along the East Anatolian transform fault and also along fault strands cutting the Misis–Andırın Complex.

Tectonic denudation of a Late Cretaceous–Tertiary collisional belt: regionally symmetric cooling patterns and their relation to extensional faults in the Anatolide belt of western Turkey

Thermochronological data reveal that the Late Cretaceous–Tertiary nappe pile of the Anatolide belt of western Turkey displays a two-stage cooling history. Three crustal segments differing in structure and cooling history have been identified. The Central Menderes metamorphic core complex represents an ‘inner’ axial segment of the Anatolide belt and exposes the lowest structural levels of the nappe pile, whereas the two ‘outer’ submassifs, the Gördes submassif to the north and the Çine submassif to the south, represent higher levels of the nappe pile. A regionally significant phase of cooling in the Late Oligocene and Early Miocene affected the outer two submassifs and the upper structural levels of the Central Menderes metamorphic core complex. In the northern part of the Gördes submassif, cooling was related to top-to-the-NNE movement on the Simav detachment, as the apatite fission-track ages show a northward-younging trend in the direction of movement on this detachment. In the Çine submassif, relatively rapid cooling in Late Oligocene and Early Miocene times may have been related to top-to-the-S extensional reactivation of the basal thrust of the overlying Lycian nappes. The second phase of cooling in the Anatolide belt is related to Pliocene to Recent extension resulting in the formation of the Central Menderes metamorphic core complex in the inner part of the Anatolide belt. Core-complex development caused the formation of supra-detachment graben, which document the ongoing separation of the Central Menderes metamorphic core complex from the outer submassifs.

Kinematic evidence for Late Mesozoic–Miocene emplacement of the Lycian Allochthon over the Western Anatolide Belt, SW Turkey

AbstractRecent controversies relating to the transport directions of the Lycian Allochthon and the kinematic relationships of this to the underlying Menderes Massif are addressed by looking at the structural record preserved at the main tectonic boundaries within the Lycian Allochthon. Rocks today within the Lycian Thrust Sheets were deposited as a north‐facing Late Palaeozoic– Mesozoic rift/passive margin succession that formed in a northern Neotethys Ocean separating the Menderes–Tauride block and Eurasia. The allochthon was emplaced onto the southern continental margin in stages from latest Cretaceous to Late Miocene times. Throughout the Lycian Allochthon early kinematic fabrics indicate that the allochthon was emplaced, and successively transported, from northwest to southeast. Mylonites at the contact between the Lycian Allochthon and the underlying Menderes Massif exhibit top‐to‐the‐east non‐coaxial flow. The major tectonic boundaries within the allochthon preserve various kinematic indicators showing top‐to‐the‐southeast transport.An intra‐platform basin (Tavas/Bozdağ unit), represented by structurally low Mesozoic–Palaeogene successions, probably originated as a rift basin between the Menderes Massif to the north and the Bey Dağları carbonate platform to the south. However, there is no structural evidence that the Lycian Thrust Sheets or the Lycian Peridotite Thrust Sheet were rooted in this basin. Copyright © 2003 John Wiley & Sons, Ltd.

Late Cenozoic tectonics and stratigraphy of northwestern Anatolia: the effects of the North Anatolian Fault to the region

In northwest Anatolia, there is a mosaic of different morpho-tectonic fragments within the western part of the right-lateral strike-slip North Anatolian Fault (NAF) Zone. These were developed from compressional and extensional tectonic regimes during the paleo- and neo-tectonic periods of Turkish orogenic history. A NE-SW-trending left-lateral strike-slip fault system (Adapazari-Karasu Fault) extends through the northern part of the Sakarya River Valley and began to develop within a N–S compressional tectonic regime which involved all of northern Anatolia during Middle Eocene to early Middle Miocene times. Since the end of Middle Miocene times, this fault system forms a border between a compressional tectonic regime in the eastern area eastwards from the northern part of the Sakarya River Valley, and an extensional tectonic regime in the Marmara region to the west. The extension caused the development of basins and ridges, and the incursions of the Mediterranean Sea into the site of the future Sea of Marmara since Late Miocene times. Following the initiation in late Middle Miocene times and the eastward propagation of extension along the western part of the NAF, a block (North Anatolian Block) began to form in the northern Anatolia region since the end of Pliocene times. The Adapazari-Karasu Fault constitutes the western boundary of this block which is bounded by the NAF in the south, the Northeast Anatolian Fault in the east, and the South Black Sea Thrust Fault in the north. The northeastward movement of the North Anatolian Block caused the formation of a marine connection between the Black Sea and the Aegean/Mediterranean Sea during the Pleistocene.

Flexural subsidence by 29 Ma on the NE edge of Tibet from the magnetostratigraphy of Linxia Basin, China

This study provides a detailed magnetostratigraphic record of subsidence in the Linxia Basin, documenting a 27 Myr long sedimentary record from the northeastern edge of the Tibetan Plateau. Deposition in the Linxia Basin began at ∼29 Ma and continued nearly uninterruptedly until ∼1.7 Ma. Increasing rates of subsidence between 29 and 6 Ma in the Linxia Basin suggest deposition in the foredeep portion of a flexural basin and constrain the timing of shortening in the northeastern margin of the plateau to Late Oligocene–Late Miocene time. By Late Miocene–Early Pliocene time, a decrease in subsidence rates in the Linxia Basin associated with thrust faulting and a ∼10° clockwise rotation in the basin indicates that the deformation front of the Tibetan plateau had propagated into the currently deforming region northeast of the plateau.

Intraplate mountain building in response to continent–continent collision—the Ancestral Rocky Mountains (North America) and inferences drawn from the Tien Shan (Central Asia)

The intraplate Ancestral Rocky Mountains of western North America extend from British Columbia, Canada, to Chihuahua, Mexico, and formed during Early Carboniferous through Early Permian time in response to continent–continent collision of Laurentia with Gondwana—the conjoined masses of Africa and South America, including Yucatán and Florida. Uplifts and flanking basins also formed within the Laurentian Midcontinent. On the Gondwanan continent, well inboard from the marginal fold belts, a counterpart structural array developed during the same period. Intraplate deformation began when full collisional plate coupling had been achieved along the continental margin; the intervening ocean had been closed and subduction had ceased—that is, the distinction between upper versus lower plates became moot. Ancestral Rockies deformation was not accompanied by volcanism. Basement shear zones that formed during Mesoproterozoic rifting of Laurentia were reactivated and exerted significant control on the locations, orientations, and modes of displacement on late Paleozoic faults. Ancestral Rocky Mountain uplifts extend as far south as Chihuahua and west Texas (28° to 33°N, 102° to 109°W) and include the Florida-Moyotes, Placer de Guadalupe–Carrizalillo, Ojinaga–Tascotal and Hueco Mountain blocks, as well as the Diablo and Central Basin Platforms. All are cored with Laurentian Proterozoic crystalline basement rocks and host correlative Paleozoic stratigraphic successions. Pre-late Paleozoic deformational, thermal, and metamorphic histories are similar as well. Southern Ancestral Rocky Mountain structures terminate along a line that trends approximately N 40°E (present coordinates), a common orientation for Mesoproterozoic extensional structures throughout southern to central North America. Continuing Tien Shan intraplate deformation (Central Asia) has created an analogous array of uplifts and basins in response to the collision of India with Eurasia, beginning in late Miocene time when full coupling of the colliding plates had occurred. As in the Laurentia–Gondwana case, structures of similar magnitude and spacing to those in Eurasia have developed in the Indian plate. Within the present orogen two ancient suture zones have been reactivated—the early Paleozoic Terskey zone and the late Paleozoic Turkestan suture between the Siberian and East Gondwanan cratons. Inverted Proterozoic to early Paleozoic rift structures and passive-margin deposits are exposed north of the Terskey zone. In the Alay and Tarim complexes, Vendian to mid-Carboniferous passive-margin strata and the subjacent Proterozoic crystalline basement have been uplifted. Data on Tien Shan uplifts, basins, structural arrays, and deformation rates guide paleotectonic interpretations of ancient intraplate mountain belts. Similarly, exhumed deep crustal shear zones in the Ancestral Rockies offer insight into partitioning and reorientation of strain during contemporary intraplate deformation.

Quaternary uplift vs tectonic loading: a case study from the Lucanian Apennine, southern Italy

Uplift rates have been calculated for a large sector of the Lucanian Apennine (“axial zone” of the southern Apennines, Italy), using both geomorphological observations (elevation values, ages and arrangement of depositional and erosional landsurfaces and other morpho-tectonic indicators) and stratigraphical and structural data (sea-level-related facies, fault kinematics and offset estimations). These data have been compared with those derived from clay mineralogy of Mesozoic pelagic successions ( Lagonegro units), outcropping in the same sector of the chain, which gave information on tectonic loading. The values of the Quaternary uplift rates of the southern Apennines axial zone vary from a minimum of 0.2 mm/ yr to a maximum of about 1.2 mm/ yr . Intermediate values (0.5– 0.7 mm/ yr ) have been calculated for the other studied areas. Using geomorphological features and late Pliocene to Pleistocene successions involved in the genesis of erosional and depositional landsurfaces, the same rates ( ∼0.6 mm/ yr ) have been obtained for a large time span (about 2 Ma ) in the Melandro basin and adjacent Maddalena Mts. Therefore, during the last 2 Ma , the total uplift amount of the axial zone of the Lucanian Apennine is about 1.2– 1.3 km , with local peaks of 1.5 km . On the other hand, the Mesozoic pelagic units experienced a tectonic loading of 4– 5 km , as estimated by means of illite crystallinity (in the range 0.6– 1.1 Δ°2θ ), percentage of illitic layers in illite/smectite mixed layers (60–90%) and white mica polytypes (in the range of 10–35%). The Quaternary uplift and the related erosion rates of the southern Apennines are unquestionably due to strike-slip faulting and, above all, due to extensional tectonics coupled with thermal/isostatic regional raising. The gap of several kilometres derived from the comparison between uplift rates and tectonic loading values may be explained only by different exhumation modalities starting from late Miocene time.

Palaeomagnetic evidence for the Gondwanian origin of the Taurides and rotation of the Isparta Angle, southern Turkey

AbstractThe Taurides, the southernmost of the three major tectonic domains that constitute present‐day Turkey, were emplaced following consumption of the Tethyan Ocean in Late Mesozoic to mid‐Tertiary times. They are generally assigned an origin at the northern perimeter of Gondwana. To refine palaeogeographic control we have investigated the palaeomagnetism of a range of Jurassic rocks. Forty‐nine samples of Upper Jurassic limestones preserve a dual polarity remanence (D/I=303/−9°, α95=6°) interpreted as a primary magnetization acquired close to the equator and rotated during emplacement of the Taurides. Result from mid‐Jurassic dolerites confirm a low palaeolatitude for the Tauride Platform during Jurassic times at the Afro–Arabian sector of Gondwana. Approximately 4000 km of Tethyan closure subsequently occurred between Late Jurassic and Eocene times. Although related Upper Jurassic limestones and Liassic redbeds preserve a sporadic record of similar remanence, the dominant signature in these latter rocks is an overprint of probable mid‐Miocene age, probably acquired during a single polarity chron and imparted by migration of a fluid front during nappe loading. This is now rotated consistently anticlockwise by c. 30° and conforms to results of previous studies recording bulk Neogene rotation of the Isparta region following Lycian nappe emplacement. The regional distribution of this overprint implies that the Isparta Angle (IA) has been subject to only small additional closure (<10°) since Late Miocene time. A smaller amount (c. 6°) of clockwise rotation within the IA since Early Pliocene times is associated with an ongoing extensional regime and reflects an expanding curvature of the Tauride arc produced by southwestward extrusion of the Anatolian collage as a result of continuing northward motion of Afro–Arabia. Copyright © 2002 John Wiley & Sons, Ltd.

Post-collisional sediment budget history of the Alps: tectonic versus climatic control

Based on the sediment budget of the Eastern, Swiss and Western Alps since the Oligocene the regional tectonic evolution has been identified as the dominant factor. It is superimposed on the influence of both regional and global climate change and global sea-level change. During late Pliocene and Pleistocene times, climate became the dominant factor because of cyclic glaciations. The early post-collisional history of the Alps is characterized by a doubling of sediment discharge rates around the Rupelian/Chattian boundary. This increase is attributed to isostatic re-adjustment either after large-scale thermal reorganization of the lithosphere related to slab break-off, or to crustal thickening as continental crust became subducted. From Middle Oligocene to Late Miocene times, the overall trend of sediment discharge rates in the entire Alps was modified only during relatively short-lived phases. These are characterized by an increase in Aquitanian (ca. 23–21 Ma) and late Burdigalian times (ca. 18–16.4 Ma), and a decrease in early to middle Burdigalian (21–19 Ma) and Langhian to Serravalian times (16.4–12 Ma). An important, still ongoing period of uplift, reflected by rapidly increasing sediment discharge rates, started in latest Miocene times in the Swiss and Western Alps and affected the Eastern Alps some 2 million years later. The reason for this uplift is not clear, but deep-seated lithospheric processes appear to be likely.

Structure and Cenozoic kinematics of the Eastern Cordillera, southern Bolivia (21°S)

The Eastern Cordillera is a main morphotectonic unit of the central Andes. In southern Bolivia it is predominantly composed of Ordovician sedimentary rocks as thick as 10 km. Revision of the Ordovician stratigraphy and new structural fieldwork resulted in detailed balanced cross sections, improved estimates of crustal shortening, and a new kinematic model for the Eastern Cordillera. New estimates of total shortening in the Eastern Cordillera are up to 95 km (41–44%), higher than previous estimates and sufficient to thicken the Andean crust to its present state between the eastern foreland and the magmatic arc. After initial Tertiary uplift at ∼58 Ma, first thrusts developed in the middle Eocene to early Oligocene (?40–?30 Ma), exhuming the central part of the Eastern Cordillera. Tectonic shortening culminated in late Oligocene and early Miocene time (25–20 Ma) when west facing thrust systems developed in the central and western part of the Eastern Cordillera. Thrusting terminated in the western part by the end of the early Miocene, and middle Miocene tectonic activity was restricted to minor strike‐slip faulting. In the central part, thrusting remained active until the late Miocene. By ∼10 Ma, shortening in the Eastern Cordillera essentially ceased. Kinematic fault analyses indicate clockwise rotation of the shortening direction, from NNE‐SSW or NE‐SW in Eocene‐early Oligocene time over E‐W to WNW‐ESE or even NW‐SE in late Oligocene to middle Miocene time. Nevertheless, WNW‐ESE directed shortening and subvertical extension predominate. Sinistral oblique motion on many thrusts probably reflects plan view flexural slip in the clockwise rotating southern limb of the Bolivian orocline. It is proposed that space problems in the oroclinal hinge slowed the rotation there and caused decoupling of the still rotating south limb along NE trending transfer zones.

Dating the exhumation of a metamorphic dome: geological evidence for pre-Eocene unroofing of the Nigde Massif (Central Anatolia, Turkey)

The timing of exhumation of metamorphic rocks and granitoids of the Nigde metamorphic dome, at the southern tip of the Central Anatolian Crystalline Complex, is a matter of debate. According to some authors, the metamorphic rocks are overlain nonconformably by a sedimentary sequence of late Maastrichtian to Late Palaeocene age. In contrast, other authors recently argued that the Nigde dome represents an extensional core complex of Oligocene–Early Miocene age, finally unroofed during late Miocene times. On the one hand, the results of our study contradict the latter interpretation. A sedimentary sequence of earliest Eocene to early Middle Eocene age nonconformably overlies the high-grade rocks of the Nigde dome on its southeastern flank. Pebbles from the metamorphic rocks are ubiquitous in the conglomerates of this sequence. As a result, the Nigde metamorphic rocks must have reached the surface before Eocene times, or at the very beginning of the Eocene at the latest. The Uckapili granite, whose crystallization age has been inferred to be Early Miocene, has intruded the metamorphic complex during exhumation. The granite is also found as pebbles within the conglomerates of the Eocene sedimentary sequence and, thus, is actually older than the Eocene. Apatite fission track dates of 12–11 Ma across the Nigde dome do not indicate that the metamorphic rocks were still on their way to the surface at that time; instead, they must reflect a later event, which is most probably heating during late Neogene magmatism. Lastly, there is no ductile-then-brittle extensional detachment in the two areas where it has been invoked, that is, on the western and southern flanks of the dome. An extensional detachment nevertheless exists at the top of the Nigde dome, best documented in its northern part, where the detachment fault superposes a superficial unit made up of massive ophiolitic rocks onto the high-grade metamorphic sequence. Field evidence indicates that this detachment developed before Eocene times. On the other hand, our observations do not confirm the nonconformity of the sedimentary sequence dated as late Maastrichtian–Late Palaeocene onto the Nigde high-grade rocks. Field relations show either a tectonic contact between the two, or the direct nonconformity of the Eocene sediments onto the metamorphic rocks. The lack of coarse clasts originating from the Nigde high-grade rocks within the Maastrichtian–Palaeocene sequence further suggests that the metamorphic dome did not reach the surface before Late Palaeocene times. These results compare well with available data from the northwestern part of the Central Anatolian Crystalline Complex, suggesting that exhumation has been broadly synchronous on the scale of the massif, as a result of an episode of high magnitude extension that affected the region in Campanian to Palaeocene times.