Tectonic Data Research Articles

GEOLOGICAL STRUCTURE OF EASTERN SUBPARPATHIANS IN MUNTENIA AS REFLECTED BY THE GRAVITY ANOMALY

Based on a geographical material involving: the Bouguer anomaly map calculated for average densities, three simulations of the regional and local successive anomaly separated by square networks with sides of 1, 2 and 4 km, the structure of the gravity anomaly was analyzed namely: the distribution of the belts of the major gradient, the regional anomaly (morphology of the regional anomaly, separation degree of the regional anomaly, presence of a local anomaly with deep geological sources, gravimetric effects of maximum), the local anomaly (modification of the morphology and the intensity of the terms of the local anomaly, modification of the orientation systems of the great axes of the local terms, variation of the contours of the maximum and minimum zones with the investigation depth), the correction profiles transverse to the major geological structures of the area. The gravimetric elements analyzed allowed the simulations (the structural geological-gravimetric maps regarding the architecture of both of the crystalline basement and of the overlying sedimentary deposits). The tectonic data contained in this map give information about: the structure of the crystalline, the structure of sedimentary deposits, the causal relations between the structure of sedimentary deposits and the structure of the substratum.

Sedimentology and structure of the Paleogene Nummulitic series of Corsica: Reconstruction of the southern termination of the western Alpine foreland basin

AbstractNummulitic Limestones deposits are preserved along the tectonic contact between the Variscan basement and Alpine units of Corsica. These marine carbonates, dated from the Late Palaeocene to the Middle Eocene, were deposited within a foreland flexural basin that is considered to be the southern continuation of the Alpine foreland basin of southeast (SE) France. However, in contrast with the Nummulitic Limestones of SE France, those of Corsica are far less documented. This field‐based study constrains the sedimentology, stratigraphy and structure of the Nummulitic Limestones of Corsica in three localities (Balagne, Corte and Sari‐Solenzara) to identify factors that controlled foreland basin development and to clarify its significance within the early alpine orogen. The microfacies, microfaunal assemblages and siliciclastic fractions are characterised throughout the succession at each locality. The results indicate the existence of an important Variscan basement relief to the west of the basin (West Corsican Massif) that supplied early alluvial fans found at the base of the foreland succession in the northernmost Balagne area. Continuous high clastic input strongly reduced the development and diversity of the overlying Nummulitic Limestones facies and fauna. Further south, limestones in the Corte and Sari‐Solenzara areas are thicker and contain richer fauna. Three depositional models corresponding to the carbonate ramp system are proposed for the Nummulitic Limestones and used to construct paleogeographic maps illustrating the transgressive evolution of the Corsican foreland basin from the Early to the Late Eocene. Based on our results and available regional tectonic data and LT thermochronological data, we propose that the Nummulitic marine transgression took place within a continuous foreland basin encompassing southern Corsica and SE France during the early development of the western alpine arc.

Geomorphological and Neotectonic Structures Studied in the Southern Part of the Moesian Platform in Romania

The Moesian Platform represents a major tectonic unit of the foreland of the Carpathians and Balkans, spanning across the southern part of Romania and the northern part of Bulgaria. Although the Moesian Platform is considered to be a stable tectonic unit, it has played a significant role in the geological history of the region, influencing the development of the surrounding Carpathian and Balkan mountain ranges, making it an area of interest for studying tectonic history, geological structures, and landscape evolution. In the southern part of the Moesian Platform in Romania, delineated to the north and to the east by the steep slopes of the Argeş River valley and to the south by the steep slopes of the Danube River valley, an elevated and W–E promontory-looking geomorphological feature identified by the local inhabitants as “hill” is distinct from the neighbouring flat relief of the Romanian plain. This study is the result of a comprehensive investigation into the geomorphological features and neotectonic structures within this region. An intriguing outcrop displaying a filled fault, cutting and displacing the Quaternary sedimentary formations of the recently named Argeş Promontory, shed light on recent tectonic activities that have influenced the landscape. By integrating field observations, geological, and tectonic data, as well as satellite geodetic data, our results contribute to a better understanding of the study area’s regional geodynamics, emphasizing the significant role of tectonic activity in shaping the present-day landscape.

A new Moho map of the African continent from seismic, topographic, and tectonic data

We use seismic surveys (853 stations and 79 seismic profiles) to compile a new continental Moho model of the African continent of which 90% is formed by the Precambrian crust. The result reveals considerable Moho depth variations, with values ranging from 14 to 20 km for the Afar Triple Junction and Turkana Lake to 46 km beneath the Rif Mountains, parts of the Ethiopian Plateaus, and the Namaqua-Natal Belt. A localized Moho deepening (∼44 km) is found beneath the western and eastern blocks of the Congo Craton, the central part of Victoria Lake, the Rehoboth Province, the eastern part of the Kaapvaal Craton, and the Irumide Belt. A shallow Moho depth is detected beneath wide areas in North, Central, and East Africa, particularly along the North Africa coast (24–30 km), the Mauritanian Belt (26–30 km), the West and Central African Rift System (30–32 km), the Benue Trough (24–28 km), and beneath the Rwenzori Mountains (26–30 km) and the southern part of Somali Plate (22–26 km). At many locations, a Moho relief is characterized by significant changes across different tectonic provinces; from the Afar Triple Junction, Turkana Depression, and the Somali Plate to the Main Ethiopian Rift, between the Rwenzori region, from the Gabon-Cameroon Shield to the Benue Trough, and from the western border of the West African Craton to the Mauritanian Belt. According to our estimates, an average Moho depth beneath the African continent is 36.1 km. Comparison of our result with selected global, continental, and regional Moho models shows large differences that locally even exceed ±15 km.

Earth’s interior dynamics drive marine fossil diversity cycles of tens of millions of years

The fossil record reveals that biotic diversity has fluctuated quasi-cyclically through geological time. However, the causal mechanisms of biotic diversity cycles remain unexplained. Here, we highlight a common, correlatable 36 ± 1 Myr (million years) cycle in the diversity of marine genera as well as in tectonic, sea-level, and macrostratigraphic data over the past 250 Myr of Earth history. The prominence of the 36 ± 1 Myr cycle in tectonic data favors a common-cause mechanism, wherein geological forcing mechanisms drive patterns in both biological diversity and the preserved rock record. In particular, our results suggest that a 36 ± 1 Myr tectono-eustatically driven sea-level cycle may originate from the interaction between the convecting mantle and subducting slabs, thereby pacing mantle-lithospheric deep-water recycling. The 36 ± 1 Myr tectono-eustatic driver of biodiversity is likely related to cyclic continental inundations, with expanding and contracting ecological niches on shelves and in epeiric seas.

Sediment recycling by continental subduction indicated by B-Hf-Pb-Nd isotopes from Miocene–Quaternary lavas in the northern margin of Tibet

Although it has been argued that sediment recycling plays an important role in the differentiation of the continental crust, boron (B) isotopic data does not support a direct input of subducted sediments into arc magmas. This raises questions about the viability of sediment recycling as a process in the differentiation of continental crust. Here, we report B isotopic data from Miocene–Quaternary lavas derived from different sources in the northern margin of Tibet. These lavas have high B contents and negative δ11B values close to those of continental sediments. Strongly peraluminous rhyolites have the highest B (93 to 1559 ppm) contents with negative δ11B (−9.7 to −17.9) values. Adakitic dacites and trachyandesites exhibit the lowest B (18 to 29 ppm) contents with markedly negative δ11B (−12.0 to −35.7) values whereas olivine leucitites have B (37.2 to 59.3 ppm) contents with negative δ11B (−8.3 to −15.6) values. These lavas also have enriched Hf-Pb-Nd isotopic compositions similar to those of sediments. This data, combined with numerical modelling and geophysical and tectonic data for Cenozoic continental subduction in the northern margin of Tibet, indicates that: (1) the strongly peraluminous rhyolites were generated by partial melting of mica-bearing continental sedimentary rocks subducted to the depth of mid-to-lower crust; (2) adakitic lavas were derived by partial melting of sediment-bearing thickened lower crust underwent dehydration and eclogites-facies metamorphism; and (3) olivine leucitites were generated by partial melting of enriched mantle metasomatized by sediment-bearing eclogite-facies crust-derived melts. Thus, at continental convergent margins, continental subduction is an important mechanism for sediment recycling and the evolution of continental crust.

A Caribbean and Central America Seismic Hazard Model for Sovereign Parametric Insurance Coverage

ABSTRACTA fully probabilistic seismic hazard model with a single domain and sufficiently accurate resolution level for national analyses has been developed, for the Caribbean and Central America, to support the design of parametric earthquake policies offered by the Caribbean Catastrophe Risk Financing Facility to sovereign countries. This model provides updated earthquake hazard and risk information for 34 countries in the region, allowing to obtain detailed seismic hazard results at any location within the area of analysis. Besides a detailed zonation of subduction and crustal sources, updated seismicity and tectonic data have been utilized. Different seismicity, geometric, and rupture models have been adopted using state-of-the-art methodologies and tools. The main output of this model is a stochastic event-set, which is the hazard representation utilized not only to compute a long-term overview of the seismic hazard in the region but also to probabilistically estimate earthquake modeled losses at a national level that are used as triggers for underpinning parametric earthquake insurance. Although not of direct interest for parametric insurance purposes, this model also yields hazard maps and uniform hazard spectra for different return periods. For the operational purposes of the parametric insurance coverage, a postevent tool was developed to calculate, in near-real time, the ground-motion intensities associated with any earthquake within the region under study. This is done automatically by choosing a rupture plane from the moment tensor solution based on predefined rules while maintaining full consistency with all the assumptions made in the probabilistic seismic hazard analysis. The predicted ground motions in the region and the vulnerability functions developed for the exposed assets are then used to estimate whether the economic losses for each affected country exceed the trigger value stated in the country-specific insurance policy conditions and whether a payout should be issued, which is typically disbursed within 14 days.

Retracing the Africa–Eurasia nascent convergent boundary in the western Mediterranean based on earthquake and GNSS data

In the western Mediterranean, following the intervening continent-continent collision, the subduction of the Tethyan ocean has progressively come to an end or almost in large sectors. Compressional deformation connected with the ongoing Africa–Eurasia convergence has therefore progressively resumed mostly along the southern passive margins of the Mediterranean back-arc basins. The aim of this paper is to trace this nascent boundary and constrain its kinematics through geodetic and seismological data recorded between the Ionian Sea and Gulf of Cadiz, and through pre-existing tectonic data. Based on these data, the nascent plate boundary is drawn, kinematically defined, and compared with the previously identified boundaries in the same region. The nascent boundary is weaving and formed by variably oriented inherited structures. It is characterized by a discrepancy between the general motion of Africa with respect to Eurasia and the local contractional/compressive axes deduced from geodetic and seismic data. The oblique convergence along the nascent boundary matches that recorded in other instances of subduction initiation elsewhere; however, the average convergence rate (∼5mm/yr) in the Mediterranean seems currently too small for such a subduction initiation. Based on the assumption of a future northward tectonic vergence (i.e., Eurasian foreland), the Tyrrhenian, Algerian, and Betic salients, the Oran and Fès recesses, and the Ionian, Trans-Alboran, and Gibraltar transfer zones are identified along the nascent boundary. The latter zones connect salients and recesses through strike-slip displacements. The Algerian offshore hosts a long segment of the boundary characterized by locally increased seismic rate and actual northward vergence that would suggest this area being the first nucleus of subduction initiation in the western Mediterranean, as was previously proposed.

Stagnated eclogitic slab-related shoshonitic series volcanic rocks in West Tianshan, Xinjiang, China: Insights from Li-B-Sr-Nd-Hf-Pb isotope and trace element compositions

This study presents major, trace element and Li-B-Sr–Nd–Pb-Hf isotope compositions of post-collisional (Permian) shoshonitic volcanic rocks (SVRs) from West Tianshan, NW China. Zircon U Pb dating indicates that the West Tianshan SVRs were mainly formed in the late Early Permian (272–279 Ma). They include absarokites, shoshonites and banakites, which have variable SiO 2 (46–63 wt%) and K 2 O (2.12–8.12 wt%) contents. They display enrichment in light rare earth elements (LREE) and depletion in heavy rare earth elements. They are enriched in large ion lithophile elements (e.g., La, Rb and Ba) and depleted in high field strength elements (e.g., Nb, Ta and Ti) with slightly negative to negligible Eu anomalies, pronounced positive Pb anomalies and low Nb/U (9.32 ± 6.54), Ce/Pb (0.14–10.0, average 5.03 ± 3.02), relatively high Nb/Ta (16.74 ± 2.72) and Zr/Hf (39.56 ± 6.06) ratios. They have relatively high Li contents (26.0–93.0 ppm) and B contents (6.19–84.7 ppm), and low but variable δ 7 Li (−4.0‰ to +2.4‰). They are characterized by low ( 87 Sr/ 86 Sr) i (0.7045–0.7068), positive ε Nd (t) values (+0.31 − +5.53), relatively low 206 Pb/ 204 Pb (18.16–18.65), 207 Pb/ 204 Pb (15.51–15.63) and 208 Pb/ 204 Pb (37.97–39.22) and positive ε Hf (t) (+5.4 − +12.5). These features consistently suggest a metasomatized enriched mantle source having affinities with an EM I-like reservoir for the SVRs. Source enrichment was generated dominantly by subducted slab related aqueous fluid and altered oceanic crust (AOC) melts. Dehydration modeling of Li and B isotopes and Li, Y, B, Nb trace element fractionation collectively show that the flat, deeply subducted and stagnated, eclogitic slab suffered progressive dehydration(~5–12%)and was distinctly 7 Li-depleted. Based on these compositional features and model calculations, we suggest that West Tianshan SVRs had an enriched mantle source metasomatised by aqueous fluid and hydrous slab melt, and their parental magmas were derived from variable mixing of spinel and garnet peridotite (60Gt:40Sp − 80Gt:20Sp). Taking into account petrogenetic and regional tectonic data, we suggest that the West Tianshan SVRs developed in an intraplate setting during the late Early Permian. It is most probable that the Early Permian Tarim mantle plume, located in the south side of the study area, promoted Early Permian asthenospheric upwelling that resulted in melting of a fossil subduction-enriched source to produce shoshonitic volcanic rocks in the West Tianshan. • Lower δ7Li and wider range are evidently lighter than most volcanic suites world-wide. • A deeply subducted and stagnated eclogitic slab is one end-member of enriched source. • Parental magmas were from mixing of garnet and spinel peridotite (60/40–80/20). • SVRs formed in post-collision transition from subduction-related to intraplate setting.

Low variability runoff inhibits coupling of climate, tectonics, and topography in the Greater Caucasus

Hypothesized feedbacks between climate and tectonics are mediated by the relationship between topography and long-term erosion rates. While many studies show monotonic relationships between channel steepness and erosion rates, the degree of nonlinearity in this relationship varies by landscape. Mechanistically explaining controls on this relationship in natural settings is critical because highly nonlinear relationships imply low sensitivity between climate and tectonics. To this end, we present a coordinated analysis of cosmogenic 10Be concentrations in river sands paired with topographic, hydroclimatic, and tectonic data for the Greater Caucasus Mountains where topography is invariant along-strike despite large gradients in modern precipitation and convergence rates. We show that spatial patterns in erosion rates largely reflect regional tectonics with little sensitivity to mean precipitation or runoff. The nonlinearity in the erosion rate – steepness relationship may arise from very low runoff variability, which we attribute to the large contribution from snowmelt. Transitioning from rainfall- to snowmelt-driven runoff as mean elevation increases is common to many mid-latitude mountain ranges. The associated decrease in runoff variability may represent important, unrecognized dynamics inhibiting the sensitivity of tectonics to climate more broadly.

Co-Occurrence of HIMU and EM1 Components in a Single Magellan Seamount: Implications for the Formation of West Pacific Seamount Province

ABSTRACT Our general understanding of mantle composition and dynamics mainly comes from the composition of lavas from oceanic intraplate volcanoes. They are generally accepted to originate from deep, relatively stationary mantle plumes. Many groups of seamounts comprising the West Pacific Seamount Province (WPSP), however, do not form long-lived, narrow and continuous chains of volcanoes with clear age progression; thus, their origin does not seem to fit this general model. Here we show a wide compositional spectrum of lavas from the Pako guyot within the Magellan seamount trail (MST), an age-progressive but short-lived volcanic chain in the WPSP. For the first time, both extreme high μ = 238U/204Pb mantle (HIMU)- and enriched mantle 1 (EM1)-like mantle plume components occur in a single seamount in the Pacific Ocean. Based on alteration resistant trace element and Sr–Nd–Pb–Hf isotopic compositions, the Pako lavas fall into three distinct groups. Group 1 has a distinctive HIMU composition with high (206Pb/204Pb)i ratios (20.41–20.94) similar to the Arago (also known as ‘Young Rurutu’ or ‘Atiu’) hotspot composition, suggesting derivation from a HIMU mantle source. Groups 2 and 3 EM1-like lavas comprise the dominant rock type and display the largest Sr–Nd–Pb–Hf isotopic variations that can be best explained by mixing between melts of focal zone (FOZO) and EM1-like mantle components. Additionally, olivine phenocrysts from Group 3 EM1-like lavas have high Ni contents, Fe/Mn and Mn/Zn ratios and low Zn/Fe*10 000 ratios, which can be explained through fractional crystallization of high-pressure partial melts from fertile peridotite. The EM1-like Groups 2 and 3 lavas are compositionally similar to the Rarotonga hotspot composition, suggesting that the MST is possibly an old trace of the Rarotonga hotspot, which is most likely a long-lived hotspot generated above a deep mantle plume. Combined with existing geochemical and tectonic data, we propose that the Magellan seamounts were likely derived from partial melting of a heterogeneous mantle plume containing HIMU, FOZO and EM1-like components. Alternatively, they could have been derived from the Arago and Rarotonga mantle plumes, each having its distinct compositional signature. The occurrence of HIMU- and EM1-like mantle plume components in a single volcano suggests that the superposition of compositionally different hotspot volcanic trails in the South Pacific could have played an important role in the generation of the WPSP.

Petrology of Mt. Kıra continental alkali lavas with arc-like signature, Batman, SE Anatolia, Turkey: Evidence for mafic juvenile lower crust assimilated intraplate basalts in the collision- and mantle flow-driven geodynamic setting of Arabian Foreland

Mineral phase variations and compositions of Early Pliocene (40Ar39Ar ages ranges 5.092 ± 0.030–4.892 ± 0.024 Ma) continental alkali basalts cropped out on Mt. Kıra, NE of Batman Province, SE Anatolia, and located approximately 75 km east of well-known Karacadağ Volcanic Complex (KVC) in Diyarbakır Province, record indications of pre-eruptive assimilation of the lower crust by OIB-like basaltic magmas from Arabian Foreland, which are proved by available data of juvenile lower crustal xenoliths in northern Syria Cenozoic basalts. Diopsitic augites with low Mg#’s (0.65–0.73) in Mt. Kıra basalts depict a compositional prone to clinopyroxenes (Mg#, 0.60–0.76) in Syrian lower crustal xenoliths and coexist with Ca- and Mn-rich fayalitic olivines (Fo63–36), Ca-poor (An72–13) plagioclases, and FeTi oxides. Mt. Kıra lavas, classified as hawaiites, are characterized by the narrow ranges of low SiO2 (46.30–47.68 wt%), Al2O3 (13.74–14.41 wt%), MgO (3.48–4.16 wt%), and high total alkali (Na2O + K2O, 5.26–5.89 wt%), Fe2O3 (13.97–15.38 wt%), TiO2 (3.44–3.61 wt%), CaO (7.20–8.99 wt%), and P2O5 (1.54–1.71 wt%) contents, and with low Cr (< 14 ppm) and Ni (< 20 ppm) values. Except for unusual ZrHf depletion, they exhibit typical arc-like (or crust-like) sharp negative anomalies of NbTa and Ti and possess high concentrations of Y (45–51 ppm), Sc (28–33 ppm), and Heavy REE (e.g., Dy, 9.25–10.73 ppm; Er, 4.74–5.27 ppm; Yb, 3.79–4.44 ppm). Two-component mixing model, and radiogenic 87Sr/86Sr (0·7,044,010–0.705396) and 143Nd/144Nd (0.512676–0.512812) isotopic compositions, which overlap with bulk-silicate earth, for Mt. Kıra basalts, provide evidence for the mafic juvenile lower crustal assimilation by OIB-like basaltic magmas derived from a common enriched mantle source. High Ba/La, Ba/Ta, Ba/Nb, Zr/Nb, and low Nb/La, La/Sm, Nb/Th, La/Yb, and Dy/Yb ratios, which coincide with those of Syrian lower crustal xenoliths, appears as geochemical hallmarks for decoupling of juvenile lower crust assimilated Mt. Kıra, NW Syria and some of KVC basalts from least contaminated ones in Arabian Foreland. The enrichments in Y, Fe, and Ti and depletions in Al and Sr in Mt. Kıra lavas, however, are attributed to post-eruptive chemical weathering processes. Based on petrological and tectonic data, it is proposed that the northern Arabian Foreland Cenozoic volcanism was triggered by the combined effect of both collision- and mantle flow-driven forces with a kinematic linkage. Asthenospheric mantle flow and upwelling, which supply a thermal source, caused the deep mantle processes and interaction between asthenosphere and lithosphere, which was formed the amphibole-bearing garnet lherzolitic (asthenospherized) metasomes (mantle flow-induced metasomatism) at the base of the SCLM accreted from the ductile asthenosphere, prior to partial melting. Partial melting of such re-fertilized metasomes and surrounding wall rock was most likely produced hybrid parental magmas via mixing variable proportions of melt fractions from a garnet lherzolite source with melt fractions from an amphibole-bearing garnet lherzolite source. On the other hand, concurrently running of collision-induced temporarily changing regional stress -compressional or extensional- regimes caused i) the development of surface tectonic structures in a dynamic topography that reactivated the pre-Neogene deep tectonic structures, ii) multiphase rapid uplifts, and iii) prominent deep channeling for the upwelling enriched mantle-derived hybrid magmas to penetrate. The shallow level lower crustal assimilation of this OIB-like hybrid mantle melts, generated the Mt. Kıra, NW Syria, and some of KVC basalts in the Arabian Foreland, during magmas en route to the surface.

A GIS Approach Using Morphometric Data Analysis for the Identification of Subsurface Recent Tectonic Activity. Case Study in Quaternary Outcrops—North West of Tunisia

The combination of structural and lithological data with morphometric indicators in a GIS environment constitutes a methodological approach with high added value to identify neotectonic deformations, in particular in the Quaternary outcrops where faults are generally masked by thick recent sediments. This approach, based on the crossing of multisource data, is used in this work to understand the mechanisms that generate landscape forms in the Quaternary outcrop of Oued Lahmar, which belongs to the northwest of Tunisia. In fact, the databases of various morphometric indicators, extracted from the hydrographic network, have been generated using remote sensing data and open sources applications. This database has been enriched by lithological and tectonic data extracted from the regional geological map, to understand the results of the morphometric analysis. The results obtained provide valuable information on the identification of subsurface activity in Oued Lahmar and large vicinity areas with heterogeneous geomorphic and structural characteristics. Indeed, this study revealed the existence of an E-W subsurface tectonic control covered by the Quaternary sedimentary series not indicated on the geological map of the region. This tectonic direction, which follows most of the magmatic outcrop edge in the region, may allow the intrusion of magma and the rejuvenation of ancient deep faults.

Original

The geology and tectonics of an area play a very important role in the development of geomorphic features and drainage of a region. The Rangit River Basin is a part of Sikkim-Darjeeling Himalaya that contains very significant geological and tectonic characteristics. The basin has mainly three rock groups that are Central Crystalline Complex, the Daling group and the Gondwana group. The spectacular feature of this basin is Rangit Window, where the underlying Gondwana rock group is exposed from overlaying Daling group. Rangit basin exhibits both folded and fault structures which are indeed unique. A detailed study of litho-tectonic setup as well as to identify geomorphic features of this basin geological maps from of Geological Survey of India and topographical maps from Survey of India along with tectonic maps and secondary data have been used. This study is an attempt to show the relation between litho-tectonic setup and drainage development. The river basin is the product of morphotectonics and morphoclimatic mechanisms. Evidence of the faulting, folding, thrusting, fractures and cracks as a witnessed on-field point to the influence of neo-tectonism episodes have been noticed in the study area. Some micro landform features have also been identified after extensive fieldwork in the study area. The present study is an attempt to understand the significant role of rock structure in drainage development in the study area.

Controls of Deep-Seated Faults and Folds on Hydrocarbon Fluid Migration and Accumulation in Sedimentary Basins: A Case Study from the Northwestern Sichuan Basin, China

Deep-seated faults and folds of foreland basin systems have become important exploration targets in the recent years because they are crucial in controlling fluid migration and hydrocarbon accumulation. In this study, we analyzed the characteristics and formation history of these structures in the northwestern Sichuan Basin using recently acquired two-dimensional (2D) and three-dimensional (3D) seismic data. The seismic interpretation revealed that the thrust sheets, tectonic wedges, and foredeep were well developed in the northwestern Sichuan Basin from the mountain to the basin. Forward thrusts, fault-bend folds, and wedges are the main types of structures in the thrust sheets and tectonic wedges. The deep-seated faults and folds were easily recognized in the high-resolution 3D seismic data. The imbricate thrust faults that merged into detachment layers of the Lower Cambrian are the main types of structures in the foredeep, and they show a prominent strike-slip influence in the horizontal direction. The formation of these structures in the foredeep in the northwestern Sichuan Basin mainly endured two stages of thrusting, including those during the Middle-to-Late Triassic and Cenozoic. Based on the tectonic evolution and seismic data, we infer that these deep-seated faults and folds in the foredeep may have formed earlier than the northern Longmen Shan fold-and-thrust belts and they may have been initially active in the late of Early Triassic and reactive during the Cenozoic. Furthermore, evaporites in the Lower and Middle Triassic were crucial in forming these structures. The petroleum exploration data suggested that the deep-seated faults can facilitate hydrocarbon accumulation. The thrust faults in the foredeep were more likely to act as migration pathways for fluids instead of sealing barriers along the horizontal direction. The interconnected reservoirs of deep-seated folds possess a great potential to allow large-scale hydrocarbon accumulation. Our study provides a good example for evaluating the hydrocarbon exploration potential in the deeply buried area in the sedimentary basin.

SEISMICITY of the KOPETDAG REGION in 2015

In 2015, the seismicity of the Kopetdag region was monitored by the network of 32 seismic stations, including 28 digital and 4 analogue stations. The re-equipment of stationary analogue stations of Turkmenistan with digital GEOSIG equipment, which began in 2013, was continued in 2015 – 6 GEOSIG stations were added to 9 stations of this type, and the analogue equipment at the re-equipped stations was stopped. In 2015, the seismic activity A10 in the Kopetdag region was close to the background level for the period 1992–2014, while the number of weak events significantly exceeded the level of the previous year. The seismic activation along the boundaries of the crustal blocks in the north of the Iranian plate, which began in 2012, continued by the October 12, 2015 earthquake with KR=12.7, Mw=5.2. This strongest earthquake in the territory of Turkmenistan in 2015, named the Kenekesir earthquake by the name of the nearest settlement, accompanied by numerous aftershocks – more than 35000 events with KR=3–11 were located during 80 days after the mainshock within 30 km radius. The aftershock series lasted 186 days and ended in 2016. According to the complex of instrumental seismological and tectonic data, oblique-slip with equal normal and strike-slip components occurred in the source of the mainshock. The rupture plane had a southwestern strike and dipped to the northwest. The maximum ("Bath’s") aftershock occurred on November 16 with KR=11.1. Judging by its remoteness from the mainshock in space and time, and the difference in the type of movement in the source (upthrust), it was caused by stress relaxation in the environment.

Biotectonics of Sulawesi: Principles, methodology, and area relationships.

Biotectonics is an approach to historical biogeography based on the analysis of independently derived biological and tectonic data, which we demonstrate using the island of Sulawesi as an example. We describe the tectonic development of Sulawesi and discuss the relationship between tectonic models and phylogenetic hypotheses. We outline the problem of interpreting areagrams based on single phylogenies and stress the importance of combining all available data into a general areagram. We analysed the distributions of Sulawesi area of endemism endemics (AEEs) using 30 published phylogenies, which were converted into paralogy-free taxon-area cladograms using the programme LisBeth (Zarageta-Bagalis et al. 2012) from which Adams consensus trees were constructed using PAUP (Swofford 2002). The results of our analyses show that the relationship between the areas of endemism is congruent with the terrane history of the island. A further 79 phylogenies of Sulawesi species with extralimital distributions were analysed to determine area relationships of Sulawesi within the broader Indo-Pacific region. We demonstrate the utility of data partitioning when dealing with areas that are geologically and biologically composite by showing that analysing Asian and Australasian elements of the Sulawesi biota separately produced general areagrams that avoid artifice and are interpretable in the light of current tectonic models.

Implication of 40Ar/39Ar–petrochronology in the Buracão orogenic gold deposit for tectonic and low-temperature evolution of the northern Brasília Fold Belt, Brazil

The 40Ar/39Ar ages (muscovite and biotite) and P-T estimations presented here allow us to reconstruct the Pressure–Temperature–time (P–T–t) path from the metamorphic peak to the generation of the orogenic Au (As, Bi, Ag) mineralization in the Buracão area. The application of software-based pseudosections for bulk phyllite composition allows us to better recognize three main stages in the P-T-t path. Rocks from the study area evolved from (i) syn-D1a greenschist metamorphic peak (T = 480–550 °C and P < 4.0 kbar) attained at ca. 538–530 Ma during the W-E shortening related to local D1 deformational stage, which is regionally reported in the external domain of the northern Brasilia Fold Belt. These younger ages, compared to those of mafic and felsic granulites from the northernmost internal domain west of the study area (ca. 610–570 Ma), indicate that the metamorphic peak in the external domain was attained after the internal domain. The (ii) syn-D1b barren type I quartz vein formation (T = 510–260 °C and P < 4.0 kbar) at ca. 531–525 Ma; and (iii) syn-D2a ore-bearing type II quartz vein formation and gold mineralization (T = 345–285 °C and P = 2.7–1.6 kbar) at ca. 522–515 Ma suggest that low temperature may represent cooling P-T conditions of the peripheral supracrustal cover. Moreover, the diachronicity between the local metamorphic peak and the gold mineralization (22 M.y.) is consistent with the structural relationship between gold veins and post-metamorphic peak D2a high deformation zones, which may have acted as fluid corridors through the metasedimentary pile. These features are coherent with the time span observed in several orogenic gold deposits worldwide, especially those associated with high-angle transpressive shear zones developed in the late stages of orogeny. The combination of the Ar–Ar petrochronology with previous published fluid reconstruction and tectonic data suggests metal-rich fluid percolated along regional shear zones through the Traíras Formation under post-metamorphic peak conditions. This regional tectonic and chronology might be useful for geodynamical reconstruction and as a prospection guide in poorly studied orogenic gold of the area.

Reconstructing the Late Pleistocene – Anthropocene interaction between the neotectonic and archaeological landscape evolution in the Apennines (La Sassa cave, Italy)

Caves are one of the most conservative environments on Earth, where archaeological, anthropological, climatic and tectonic data can be well-preserved. Here, we present the results of a multidisciplinary method that allowed us to recognize, for the first time in this area, the interaction between Late Pleistocene to Anthropocene neotectonic and archaeological evolutionary stages of a cave of the Apennines (La Sassa cave), that encompass also its surroundings (Volsci Range and Pontina Plain). Both structural and 3D survey highlighted a step-wise shape of the cave due to normal fault steps that allowed the localized formation of concretions also enveloping archaeological layers. Sixteen 14C ages on fauna and human bones and thousands of archaeological finds provided chronological constraints of faulting in the Late Pleistocene and possibly also after the Middle Bronze Age. In the frame of a region that was not previously recognized as tectonically active, the structural evidence is relevant for understanding the speleogenesis of the cave from the Late Pleistocene and its human occupation. Burial and ritual activities in the cave from the Copper Age to the Middle Bronze Age have been recognized with implications on possible settlement pattern schemes with the La Sassa cave as a “persistent place” in the prehistoric human landscape. The analyses of the ceramic style in a regional framework also suggests the presence of a cultural boundary near La Sassa, which becomes highly osmotic just after the beginning of the Middle Bronze Age. The La Sassa findings provide as well implications for the seismic hazard assessment in a region inhabited by about 0.4 million people.

Fractured carbonate aquifers of Sibillini Mts. (Central Italy)

ABSTRACT The aim of the present map is to illustrate a detailed pre-earthquake hydrogeological conceptual model of the Sibillini Mts. This area was struck by a prolonged seismic sequence of up to Mw 6.5 in 2016. Geological, tectonic, and hydrogeological data were collected from the literature before 2016, subsequently standardized and re-interpretated with the aim of presenting a hydrogeological map (1:50,000 scale) of the Sibillini Mts. carbonate system (Central Italy). The map is supported by 11 hydrogeological both cross and longitudinal sections, which show the underground spatial relationship between aquifers, aquicludes, and tectonic elements. This Map provides a model of comparison for the new hydrogeological conditions emerging from the post-seismic research.