Tectonic Phases Research Articles

2D Sequential Restoration and Basin Evolution of the Wichianburi Sub-basin, Phetchabun Basin, Central Thailand

The Wichianburi Sub-basin is currently the only productive area in the southern part of the Phetchabun Basin, central Thailand. It is structurally dominated by NNW-SSE to NNE-SSW trending normal faults as a result of multistage rifting since the Late Oligocene. Half-graben and full-graben basin geometries can be observed from 2D regional seismic sections. In this study, structural restoration techniques were applied to validate the structural interpretation of the original hardcopy of the 2D seismic sections. Stratigraphic information is compiled from published papers and well reports. Our results revealed that most of the deformation was concentrated during the Late Oligocene. Main depocenters for the syn-rift sediments focused in the basin center along the west-dipping normal faults. These faults cut the prerift section and their orientations were possibly controlled by the Permo-Triassic fabrics that underlie the Phetchabun Basin. By measuring the length of the profiles before and after faulting, the restorations show that the extensions of the Wichianburi Subbasin decrease from 12.30% during the main rift phase (Late Oligocene to Early Miocene) to 2.53% during the second phase of rifting. Rifting only focused in the basin center with the development of NNW-SSE to N-S trending intrarift faults. Since the Middle Miocene, the Wichianburi Subbasin has developed under the tectonic phase of post-rift subsidence with interruption by intrusive activities.

Geomorphological Analysis of the Southwestern Margin of Xanadu, Titan: Insights on Tectonics

AbstractEvidence for tectonic activity on Titan is provided by the presence of eroded mountain ranges. Xanadu is an equatorial region of Titan characterized by a complex topography, even though, overall, it has a lower average elevation compared to its surroundings. We investigated Xanadu's southwestern margin, a part of the region composed of heavily eroded and rugged terrains to the north and east, and of smoother, more uniform terrains to the west and south. The central portions of southwestern Xanadu (SW Xanadu) are characterized by an extensive fluvial network. The presence of such a distinctive feature was the main reason motivating the study of this area, given its potential to provide tectonic indications. Through detailed geomorphological mapping (map scale 1:700,000) on Synthetic Aperture Radar data and analysis of both fluvial drainage patterns and Digital Terrain Models, we identified several putative tectonic structures in this area: normal faulting to the west and east, thrust faulting to the north, and small‐scale strike‐slip faulting in its central parts. Pull‐apart basins are depressions bounded by both dip‐slip faults and by (overlapping and/or bending) segments of a major transcurrent fault, i.e., they are basins generated in transtensional tectonic settings. We propose that central SW Xanadu is a pull‐apart basin, bordered by both normal and thrust faults and formed by transtensional tectonics, which we consider to be the most recent tectonic phase active in this area. This basin is characterized by small‐scale strike‐slip faulting within it, on which a fluvial network has subsequently imposed.

Paleotectonic pre-quoternary deposit formation conditions on the territory of Novgorod region

The following article characterizes the paleotectonic conditions timed to the main Earth development periods. The author has demonstrated the meaning of every tectonic phase during the pre-quoternary deposit formation, which is the basis for Novgorod region massive sedimentary strata layer.

Temporal profiling of uplift rate along an active fault using river long profile in the Kuchchh region, Western India

River long profiles are widely used as tectonic event markers. Incision/uplift rate estimations based on the dating of river terrace or exposed scarp sediment give long-term averaged uplift rate values with the limitation of not giving the intermediate phases of highs and lows. On the other hand, GPS based estimates provide only decadal-scale uplift rate estimates. In our study, we adopted the long profile inversion methodology to obtain a temporal profile of uplift rate history (over the Late Pleistocene-Holocene time period) along an active fault (the Kuchchh Mainland Fault) in Kuchchh region, western India, which has experienced several large magnitude earthquakes in recent past. We also used long profiles analysis to quantify the transient response of Kuchchh landscape to uplift activity along the Kuchchh Mainland Fault. Steepness index and chi profiles were estimated to display the spatial variability in landscape disequilibrium. Integral method-based chi profiles were used to obtain the optimum value of basin area exponent of the Stream Power Incision Model (SPIM). Our estimates provide a mean uplift rate value of 1.1–1.4 mm/yr along the Kuchchh Mainland Fault during the Late Pleistocene-Holocene period, which matches with the average uplift rate derived from other independent observations in this region. Further, a chronology of major tectonic phases from the estimated uplift rate time series also corroborates with field-based estimates of major incision events in Kuchchh region. We also tested the robustness and sensitivity of our uplift rate estimates to model parameters. Such data can be complementary to the existing sparsely (both spatially and temporally) distributed uplift rate database, which is imperative to seismic hazard assessment.

Deep structure of the Demerara Plateau: From a volcanic margin to a Transform Marginal Plateau

The Demerara Plateau (offshore Suriname and French Guiana) is located at the junction of the Jurassic Central Atlantic and the Cretaceous Equatorial Atlantic Oceans. The study of its crustal structure is fundamental to understanding its tectonic history, its relationship with the adjacent oceanic domains and to enlightening the formation of Transform Marginal Plateaus (TMPs). This study presents two wide-angle seismic velocity models from the MARGATS cruise seismic experiment, and adjacent composite seismic reflection lines. The plateau itself is characterized by a 30 km thick crust, subdivided into three layers, including a high velocity lower crust (HVLC). The velocities and velocity gradients do not fit values of typical continental crust but could fit with volcanic margin or Large Igneous Province (LIP) type crusts. We propose that the, possibly continental, lower crust is intruded by magmatic material and that the upper crustal layer is likely composed of extrusive volcanic rocks of the same magmatic origin, forming thick seaward dipping reflector sequences tilted to the west. This SDR complex was emplaced during hotspot related volcanic rifting preceding the Jurassic opening of the Central North Atlantic and forming the present-day western margin of the plateau. The internal limit of the SDR complex corresponds to the future limit of the eastern margin. The Demerara Plateau would therefore be an inherited Jurassic volcanic margin boarding the Central Atlantic. This margin was reworked during the Cretaceous at the eastern limit of the Jurassic SDR complex, creating the present-day northern transform margin and the eastern divergent margin along the Equatorial Atlantic. This study also highlights the major contribution of thermal anomalies such as hotspots and superposed tectonic phases in the history of TMPs, which share a great number of characteristics with Demerara.

The lower Miocene flint conglomerate, Jylland, Denmark: a result of the Savian tectonic phase

The early Miocene was an important period for the development of the eastern North Sea. Tectonism in North-West Europe resulted in uplift of the Scandinavian mountains, reactivation of salt structures, inversion of old graben structures and deposition of the most coarse-grained deposits in the Danish pre-Quaternary succession. Some of these deposits were later cemented into conglomerates. The deposits are common in the fluvial parts of the Billund Formation (Aquitanian) and the basal transgressive lag of the late Aquitanian – Burdigalian Klintinghoved Formation capping the Billund Formation. Questions remained as to the age of these deposits and what they infer about tectonic events in the region. This study reviews the geology of the flint-dominated conglomerates and presents the first dates for a sample of these unique deposits. We observe grain sizes up to 5 cm diameter. Palynological analyses place the sample as early Miocene. Some samples from the area have suggested a local source near active salt structures, associated with the uplift of the pre-Neogene sedimentary successions. We suggest that the common occurrences of flint clasts in the lower Miocene succession reveal significant erosion of Upper Cretaceous and Danian chalk, likely associated with the uplift of the Scandinavian lowlands during the Savian tectonic phase, early Miocene.

Paleostress Analysis from Fractures in Kalosh Anticline, Kurdistan Region, North‒East of Iraq

Fractures analysis carried out throughout traverses across Kalosh anticline. The anticline is located ~30 km south of Sulaimaniyah city, Kurdistan region, NE Iraq. It extends NW‒SE for ~17 km within the high folded zone of the northwestern segment of the Zagros Foreland Fold Thrust Belt. The aim of this work is for unraveling the tectonic history and detecting tectonic episodes responded for the initiation and development of the anticlinal structure. More than 450 fracture planes were classified into sets and systems according to their relations with three mutually perpendicular geometric axes (tectonic axes). Tension sets are ac and bc, the first one formed by extension along fold axis accompanying direct compression perpendicular to fold trend, whereas the second is the product of relaxation that motivated the primary compression. The shear systems are hk0, h0l and 0kl developed successively during direct compression and subsequent relaxation episodes of each tectonic force. Field observations and paleostress analysis indicate that the area was subjected to four stress phases. First is primary compressive tectonic phase in the directions NE‒SW. The second compressive tectonic stress in the direction NW–SE considered as a secondary phase. Third was extension tectonic phase in the direction NE–SW which developed during the final uplift stage of folding is normal to the major fold trend. The fourth is NW–SE extension face considerate as extension stress related to the primary NE‒SW compressive stress.

Stratigraphy and geochronological constraints of the Serra Sul Formation (Carajás Basin, Amazonian Craton, Brazil)

The Carajás Basin, Amazonian Craton, hosts extensive Neoarchean to Paleoproterozoic sedimentary archives, which are still poorly constrained regarding their depositional settings, ages, and type of basin in which they have been deposited. In this study, we performed detailed sedimentological investigations and U-Pb dating of detrital zircon in four drill cores intercepting the recently defined Serra Sul Formation. Our data show that this formation corresponds to various shallow to deep subaqueous environments. Shallow water environments are characterized by local occurrences of microbially-mediated structures, while deep water environments are characterized by polymictic conglomerates resulting from the mixing of materials of different origins during downslope debris flow. Both sedimentary facies and common occurrence of syn-sedimentary deformations attest for recurrent slope instabilities. Geochronological investigations allow to define a maximum depositional age of 2684 ± 10 Ma, that is several tens million years younger than other Neoarchean sedimentary units of the Carajás Basin. Major peaks in age distribution indicate that the Serra Sul Formation derives from local sources that constitute the basement of the Carajás Basin. The infilling of the Carajás Basin by local sources, together with sedimentary facies and depositional environments attesting for slope instabilities, suggest that the Serra Sul Formation was deposited during an active extensional tectonic phase. Such Neoarchean to early Paleoproterozoic tectonic setting compares with those documented in many other cratons worldwide and suggests that it could correspond to the break-up of one of the first documented supercontinent.

Characteristics and generation modeling of some source rocks in the South Eastern offshore Mediterranean area, Egypt

The offshore North Sinai area contains attractive approaches to be investigated by means of hydrocarbon potential. The present work aims at evaluating three source rock units; the Upper Jurassic, the Lower Cretaceous, and the Upper Oligocene that have a varying lithology including limestones, marl, and shales. The evaluation is based on results of TOC, Rock-Eval pyrolysis, and vitrinite reflectance analyses for ditch cuttings from 5 wells. Besides, constructing 1D basin models for several wells took place in the present study to estimate the generation timing. The geochemical results show that the Upper Jurassic contains poor to good organic quantity with poor to good hydrocarbon generating potential of type II/III and type III kerogen. The Lower Cretaceous rocks are poor to very good in terms of organic richness and hydrocarbon generating potential as well and belong to type II/III and minor type III kerogen. Moreover, a poor to good richness was encountered for the Upper Oligocene, with poor to fair hydrocarbon generation potential of kerogen type III. 1D basin modeling results indicate that three main tectonic phases influenced the burial history comprising the Jurassic-Cretaceous rift, the Late Cretaceous-Oligocene uplift associated with the Syrian arc folding, and the Late Miocene rift. These movements affected the thermal maturity in the studied area. The Upper Oligocene source rock is immature to early mature in most of the studied wells, whereas the Lower Cretaceous and Upper Jurassic source rocks were entered the main stage of hydrocarbon generation earlier in the eastern wells than the western wells, related to a variant tectonic impact in the area. The top oil window was reached at depth ranges from 2300 m in Mango-3 well to 4000 m in Hout-1 well, while the base of the oil window is found only in Mango-1 well at 4300 m depth.

Polyphasic tectonic history of the N70° DASA Graben (northern, Niger)

Located in northern Niger, the N70° DASA graben is a trough discovered recently in the Tim Mersoï basin. In this study, a tectonic history of the DASA graben was presented based on the combined use of satellite imagery, field observations and measures, available literature and borehole data. These data were used to analyse the sedimentary facies and the tectonic deformations in the DASA graben, and derive their relative chronology. For this purpose, uplift and rift deformations and their interactions with sedimentation were characterized. Overall, the analyses suggest that the DASA graben was affected from the Carboniferous to the Cretaceous by three major tectonic phases: the first phase was an uplifting stage with extension during the Carboniferous to Permian; the second phase was a rifting stage. The mean extension was ~ N160° and dominantly produced ENE-WSW trending normal faults; and the third phase was a postrift stage. It was characterized by a ~ N130° compression. The structural and sedimentological features defined the DASA graben as a particular type of syn-sedimentary basin evolving from a transpressive tectonic regime during the period ranging from Carboniferous to Permian to an extensive tectonic regime during the period ranging from Triassic to Lower Cretaceous. Thus, the second period marked by an extensional regime would probably be related to the initial stage of the opening of the Atlantic Ocean. After this rifting period, the DASA graben was affected by a compressional phase related to the collision between Africa and Europe.

Permian post-collisional basic magmatism from Corsica to the Southeastern Alps

Post-Variscan Early Permian magmatism is widespread from Corsica to the Eastern Alps. After the formation of the Variscan orogenic belt between Laurussia and Gondwana, felsic and mafic bodies were emplaced during an extensional tectonic phase. This study focuses on a mafic dyke swarm that intruded in the region of Ajaccio (Corsica, France) and on a gabbroic intrusive complex outcropping in the Eastern Alps (Bressanone/Brixen, South Tyrol, Italy) both of which were emplaced during this extensional event. New U-Pb data from zircon show that both of these intrusions were emplaced at ca. 282 Ma. Most Ajaccio dykes display a calc-alkaline affinity and are characterized by enrichment of LILE (Large Ion Lithophile Elements) and LREE over HREE (Light and Heavy Rare Earth Elements) and HFSE (Nb, Ta, Hf, Zr; High Field Strength Elements). Two dykes show tholeiitic affinity and are characterized by marked LREE and Th-U depletion and by minor negative Nb-Ta anomalies on multi-element diagrams, which is typical for within-plate basalts. Bressanone/Brixen gabbros display similar geochemical features to the Ajaccio calc-alkaline samples with LREE enrichment over MREE (Medium Rare Earth Elements) and HREE, and HFSE depletion. Such characteristics are also confirmed by trace element data obtained by LA-ICP-MS on clinopyroxene and plagioclase crystals.The calc-alkaline to tholeiitic dykes are characterized by enriched to depleted Sr-Nd-Pb isotopic compositions, respectively. Some Ajaccio dykes and the Bressanone/Brixen gabbros are clearly affected by crustal contamination. However, the combination of trace element and isotopic variations suggests that mantle source heterogeneities were also involved. Isotopic compositions of the Ajaccio dykes reveal the presence of two distinct mantle source signatures: an enriched mantle (EM) component, which dominates the composition of the calc-alkaline-like suite, while a DMM (Depleted MORB Mantle) component dominates the source of the tholeiitic suite. The EM mantle source likely formed during Variscan subduction, however the composition of the tholeiitic suite requires a source composed dominantly of depleted mantle, with a minor contribution from both the subducting slab and supra-subduction mantle wedge. The mantle source of the tholeiitic magmas possibly originated from greater depths (compared to the calc-alkaline-like suite) during the post-orogenic extensional phase potentially due to break-off and/or roll-back of the Variscan slab or mantle flow from the front or margins of the subducted slab.Notably, coeval Permian mafic intrusive bodies from throughout Corsica (Bocca di Tenda, Porto, Pila Canale) and from the Australpine and Southalpine Alps intruded at a similar time and have geochemical features that are very similar to the Ajaccio dyke swarm and Brixen gabbro. This indicates that a widespread Permian magmatic province developed in a post-orogenic extensional tectonic setting at the margin of the former Variscan belt. During the Middle-Late Triassic magmatism with similar enriched geochemical signatures occurred in the Southern Alps, Dinarides, Australpoine domains and at the end of the Triassic over central Pangea (Central Atlantic Magmatic Province). This would highlight the importance that the Variscan orogeny had in the development of a more fertile mantle.

Cenozoic exhumation history at the core of the Andes at 31.5°S revealed by apatite fission track thermochronology

The Andes at ~31°-32°S lie above the Chilean-Pampean flat slab zone (~27–33°S), where several morphostructural units developed resulting in a large orogenic width. The core of the Andes is composed of the La Ramada fold-and-thrust belt in Principal Cordillera and the basement blocks of Frontal Cordillera. While rock uplift of these blocks has been broadly constrained to the middle Miocene based on structural and provenance studies, thermochronologic approaches with the potential to directly constrain the timing and amount of exhumation have not been exploited until recently. Apatite fission track data from a ~1 km vertical profile collected within the Carboniferous Pico Los Sapos Batholith in the High Andes at 31.5°S places some constraints on the thermal evolution of the region since the Paleocene. The age-elevation profile combined with inverse thermal modeling and previous AHe thermochronology, indicates an episodic cooling/exhumation history. Rocks cooled rapidly in the early Cenozoic (ca. 65-55 Ma), followed by a period of relative thermal and tectonic stability when residence in an apatite partial annealing zone (PAZ) from at least ~52 Ma to ca.15 Ma, followed by final rapid cooling beginning ca. 15 Ma. We interpret early Cenozoic and middle Miocene rapid cooling events as to be related to erosional exhumation during Andean contractional phases, associated with thrust activity along the Mondaquita Fault. The age-elevation profile is partially duplicated, with upper samples being offset ~500 m due to back-thrusting since the late Miocene. The preservation of part of an exhumed PAZ indicates 3–5 km of exhumation since the onset of rapid cooling/exhumation at ~15 Ma. Although evidence for an early Cenozoic compressional phase in the High Andes at this latitude is scarce, the occurrence of a regional K-T (~65 Ma) unconformity supports our results. The Eocene Inca phase, registered north of 30°S, on the other hand, is not shown in our thermochronological data, suggesting that this tectonic phase did not affect the core of the Andes south of this latitude. Independent geological evidence both from the hinterland (structural, geochemical and thermochronological analyses) and foreland (provenance studies) corroborate our findings of a middle Miocene deformational event in the core of the Andes at 31.5°S.

New insights on the Neogene tectonic evolution of the Aksu Basin (SE Turkey) from the Anisotropy of Magnetic Susceptibility (AMS) and paleostress data

The junction between the Aegean and Cyprus arc in the southern Turkey forms a triangular-shaped morphological structure so-called Isparta Angle (IA). In Neogene time, the inner part of the Isparta Angle became overlain by sedimentary basins including Manavgat, Köprüçay and Aksu, characterized by marine clastics and carbonates.Aksu Basin, one of these marine basins, provides geological records about the Neogene crustal deformation and stress field in the Eastern Mediterranean region. Therefore, we kinematically assess if and when tectonic stress fields affected the Aksu basin in early Miocene to recent times. For this purpose, Anisotropy of Magnetic Susceptibility (AMS) data (AMS) of cored samples and fault-slip data from the brittle mesoscopic faults were collected. The ~490 oriented samples for Anisotropy of Magnetic Susceptibility measurements were analyzed and two different maximum magnetic lineation's directions are recognized; 1) N–S magnetic lineation in Pliocene and 2) from N–S to NW-SE magnetic lineation in the Miocene. The results inferred from more than 1000 fault-slip data collected from 83 different sites combined with AMS results demonstrate that the Aksu Basin developed under four different tectonic phases; 1) ~E-W extensional phase (related to basin formation), 2) ~N–S compressional (Lycian) phase, 3) ~(N)E-(S)W compressional (Aksu) phase and 4) N–S extensional (Recent) phase.

Permo–Triassic sedimentary fills and tectonic phases off Mid Norway: seismic investigation of the Trøndelag Platform

Permo–Triassic sedimentary fills and tectonic phases off Mid Norway: seismic investigation of the Trøndelag Platform

Bedrock and detrital zircon thermochronology to unravel exhumation histories of accreted tectonic blocks: An example from the Western Colombian Andes

The Northern Andes are the result of multiple tectonic phases, which include extensional and compressional volcanic arcs, strike-slip fragmentation, and accretion of exotic terranes. The alternations of these tectonic settings have overprinted and fragmented the geological record, which has hindered precise paleogeographic and tectonic reconstructions. In the western segment of the Colombian Andes, the oceanic-cored Western Cordillera (WC) and the continental Central Cordillera (CC) are separated by the Romeral Fault Zone (RFZ). This segment of the Andes preserves the record of Cretaceous back-arc extension, the onset of compression, and the accretion of the Caribbean plateau during the Late Cretaceous-Paleocene. To refine the tectonic evolution of the Western Colombian Andes, this study documents new detrital zircon fission-track (ZFT) data from the Meso-Cenozoic sedimentary cover in the CC, the RFZ, and the WC; new ZFT and zircon helium (ZHe) bedrock data from the CC and the RFZ; and new U–Pb detrital data from the Miocene sedimentary cover of the RFZ. Within the RFZ, we obtained bedrock ZFT ages of 239.0 ± 11.0 Ma and 111.1 ± 4.3 Ma, and detrital ZFT data from the Abejorral Formation are interpreted as the result of post-magmatic cooling and Cretaceous rifting. Late Cretaceous to Eocene ZFT and ZHe ages (~61–50 Ma) in the CC and detrital ZFT data in the WC record exhumation and deformation of the CC during and after the collision of the Caribbean plateau with the continental margin. Finally, detrital U–Pb and ZFT data from the Amagá Formation record the formation of a Miocene intermountain basin. This study reconstructs the basin geometries and the deformation patterns before, during, and after the collision of the Caribbean plateau with the South American margin. We highlight that in accretionary orogens, in which prolonged deformation and erosion have removed the sedimentary cover, the quantification of differential basement exhumation is key to reconstruct thick-skin deformation and to define major tectonic boundaries.

Senonian platform-to-slope evolution in the tectonically-influenced Syrian Arc sedimentary belt: Beni Suef Basin, Egypt

The Beni Suef Basin is a rift basin that was formed in the Early Cretaceous in response to the break-up of the Gondwana. The infill consists of a thick Mesozoic–Paleogene succession deposited during two main tectonic phases; the Early Cretaceous syn-rift phase and the Late Cretaceous post-rift phase. The post-rift phase was subsequently subjected to an intense compressional tectonic regime related to late Cretaceous Syrian arc tectonics. Within the basin-fill succession, the Senonian deposits, which are composed of carbonates and mixed siliciclastic/carbonate rocks of the “B” and “A” members of the Abu Roash Formation, was formed as a marine platform developed under fluctuated shelfal conditions. These deposits were overlain by chalk of the Khoman Formation that is interpreted to have formed in an outer shelf–middle slope setting. The Senonian succession is subdivided into two 3rd order depositional sequences (Latest Turonian–Early Coniacian SQ-1 and Coniacian–Santonian SQ-2) and one 2nd order depositional sequence (Campanian–Maastrichtian SQ-3). The depositional history of the Senonian in the Beni Suef Basin is interpreted to have been controlled by variable sedimentation accompanied by progradation and retrogradation of carbonate platform between inner and outer shelf environments during the Coniacian–Santonian, and between inner shelf and upper slope environments during the Campanian–Maastrichtian to the end of Senonian. The changes in depositional environments and relative sea-level fluctuations were a factor of the variations in accommodation and sedimentation likely controlled primarily by the Syrian Arc tectonic pulses, which may also have affected basin development and that of the surrounding areas over the northern Western Desert of Egypt particularly during Senonian.

Structural control and Sn-Ta-Nb mineralization potential of pegmatitic bodies in Numbi, South Kivu Eastern D.R Congo

The Numbi pegmatites of South Kivu Province (D.R.C) in the Kibaran belt which intruded the Mesoproterozoic Formation (1.6-0.9 Ga) was investigated to elucidate the structural imprints and geochemical characteristics related to the pegmatitic rocks associated with Sn - Nb - Ta mineralization, source(s) of the mineralisation, processes responsible for its formation and the economic viability of Tin-Niobium-Tantalum mineralisation. The structural features include: the pegmatitic veins with orientation from N150°E to N160°E characterized with direction and dip values averages of N84°E/13°SSE for horizontal veins and N138°E/73°WSW for subvertical veins. From the different stresses, the pegmatite and quartz veins occurred during the same tectonic phase. The characteristic high SiO2, Al2O3, Fe2O3 and Na2O, indicates peraluminous and S-type pegmatite, ferroan and medium to high K, characteristics of a collisional tectonic environment. The pegmatite showed an enrichment of Rb (114.70 – 1000 ppm), Ta (27.50 – 370.90 ppm), Cs (28.90 – 682.80 ppm), Sn (238 – 2451 ppm) and Nb (31.80 – 139.20 ppm) trace element, consistent with indices for mineralisation. The La/Yb vs. La and Sm/Yb vs. La/Sm diagrams established magmatic compositional heterogeneities and/or mixing in the lava suits that formed the pegmatites. Variation plots of Ta vs Ga, Ta vs Cs, Ta vs Cs + Rb and Ta vs K/Cs showed consistent trend of mineralization using their position relative to the Beus and Gordiyenkos line. These ratios - K/Ba, K/Rb, Ba/Rb, Rb/Sr and geochemical models- Y vs. Nb, (Y+Nb) vs. Rb, Zr vs. Ta/Zr, B (=Fe+Mg+Ti) vs A(=Al-(K+Na+2Ca), R1(=4Si+11(Na+K)-2(Fe+Ti)) vs R2(=6Ca+2Mg+Al) with observed tectonic markers like lineation/foliation, joints and veins suggests a structurally controlled mineralisation. The Numbi pegmatites are of partial melting of lithospheric mantle sources, relatively rich in Sn, Ta and Nb of economic value that are structurally controlled.

Sedimentology of Jurassic pelagic carbonate platforms in the Ankara region (Central Anatolia-Turkey)

The Jurassic–Lower Cretaceous successions cropping out in three different parts of Central Anatolia (Turkey) were deposited in local basins developed under tectonic influence from the Hettangian to the Oxfordian. Pelagic carbonate platforms (PCPs) were formed in the region during two separate phases in which synsedimentary faulting was active in the basins. Prior to the first tectonic phase, fluvial and tidal sediments, Hettangian-Sinemurian in age, were deposited unconformably on the low-grade metamorphic substrate of the Karakaya Complex (Upper Triassic), with Sinemurian crinoidal limestones above. At the end of the Sinemurian, the PCPs were developed as a result of fragmentation of shallow-marine platforms by normal faults. Across hanging-wall basins and footwall-blocks, the PCP facies: pelagic/hemipelagic nodular and marly Ammonitico Rosso facies, brachiopod-bearing limestone facies with hardgrounds, red fossiliferous mudstone, and calcareous Ammonitico Rosso facies containing blocks, were deposited with marked lateral thickness variations. The platform, which gradually became shallower in relation to the clastic sediments (180 m thick) filling the basin, was fragmented again at the end of the Bathonian. The opening of fractures in the platform is documented by neptunian dykes developed within the clastic facies, filled with Callovian ammonite-bearing mudstone. During the Callovian–Oxfordian, widespread ammonite-bearing red marl draped the clastic facies, although nodular pelagic and oolitic/ammonite limestones are locally present. Moreover, Oxfordian pelagic oolitic facies rest unconformably on Upper Triassic sandstone (Karakaya complex), which is locally intercalated between the metamorphics and the Jurassic cover, wherever these had been unroofed at the footwall of Jurassic normal faults. As a result of the tectonic activity during the Callovian–Oxfordian time, the Ankara region totally became a PCP in the Oxfordian. Condensed, nodular, pelagic oolitic–ammonitic limestones were deposited across the major uplifted blocks in an open-marine environment, previously called the Ankara seamount. These facies constitute an important key level in the Ankara region. Laterally continuous deep-marine sediments overlying the Late Oxfordian–Early Cretaceous PCP deposits indicate the rapid foundering of this sector.

3D Extension at Plate Boundaries Accommodated by Interacting Fault Systems

Complex patterns of normal faults with multiple orientations and/or highly curved shapes have been traditionally explained by successive tectonic phases of 2-dimensional deformation. Alternatively, multiple fault sets have been proposed to develop simultaneously and in orthorhombic symmetry during a single phase of 3-dimensional deformation. We use analogue models of normal faults to demonstrate that, without the influence of pre-existing structures, 3D extension is preferentially accommodated by the alternate, rather than simultaneous, development of faults with different trends. By means of stress-driven interactions, 3D deformation can be partitioned into coupled systems of normal faults, which display geometries commonly observed in tectonic settings affected by interacting plate boundaries. Under radial extension, deformation is accommodated by major curvilinear grabens coupled with minor perpendicular faults, resulting in the triple junctions of grabens observed in Afar. On the other hand, the alternate development of perpendicular faults accommodates synchronous bi-directional and mutually perpendicular extension, giving the same fault pattern observed in the Barents Sea rift-shear margin.

Late Cretaceous-Cenozoic exhumation of Northwestern Guangxi (China) and tectonic implications: Evidence from apatite fission track dating

The study of the Late Cretaceous-Cenozoic uplift and tectonic evolution of the Northwestern Guangxi area in the Youjiang Basin is relevant for understanding the origin and preservation of hydrothermal deposits with ore-hosting potential. Apatite fission-track dating and time-temperature thermal history modelling were performed using six rock samples from the study area. The ages were found to range from 14 to 81 Ma, and in particular, three distinct time intervals could be defined using the apatite fission-track ages: 81–77 Ma, 58–35 Ma, and 17–14 Ma, each corresponding to a specific tectonic-thermal event. The 81–77 Ma event indicates the age of early magmatic activity in northwestern Guangxi. The earliest Himalayan tectonic phase could be attributed to the subduction–collision of the Indo-Asian plate at 58–35 Ma, followed by a second phase of rapid wedging of the Indian plate during the 17–14 Ma interval. We surmise that some hydrothermal deposits, including medium-temperature Cu, Pb, Zn deposits and high-temperature W, Sn, Mo, Bi deposits such as polymetallic Cu–Fe–Mo, and Cu–Mo–(Pb–Zn) porphyry types and skarn types, may be locally present below the low-temperature Carlin-type gold deposits, or at variable depths in northwestern Guangxi. And sand gold deposits may be a relevant prospecting target.