Tectonic Terranes Research Articles

Late Cretaceous High‐Sr/Y Granitic Rocks in the Eastern Tibetan Plateau: Crustal Thickening During Continental Collision

AbstractHigh‐Sr/Y granitic rocks, characterized by intermediate–high SiO2 contents (> 56 wt.%), high La/Yb ratios (> 20), and low Y (< 18 ppm) and Yb (< 1.9 ppm) contents, have drawn much attention from geologists in the past decades. They were originally named adakites and defined as granitic magma in convergent plate margins formed by partial melting of subducted young (< 25 Ma), hot, and hydrated oceanic slab. Recent studies suggest that these rocks can also be formed in a variety of non‐subduction‐related tectonic settings through different petrogenetic processes including partial melting of thickened lower continental crust, providing important constraints on crustal growth and evolution throughout the Earth's history.The Tibetan plateau, generally considered as an archetype of collisional orogen, was formed by the successive accretion of different tectonic terranes to the southern margin of the Eurasia plates since the Early Paleozoic. Geologically, the Tibetan plateau comprises several W–E trending terranes (the Kunlun, North Qiangtang, South Qiangtang, and Lhasa terranes) and northernmost India (the Himalaya region). These terranes have undergone significant crustal thickening during the continental collision events. The crustal thickness of the Tibetan plateau is asymmetric, being thickest under the Lhasa terrane and thinning more gradually towards the north than to the south. From south to north, the crustal thickness increases from ∼50 km in the Himalaya region, to ∼70–80 km under the Lhasa terrane, and decreases to ∼65 km under the North and South Qiangtang terranes and ∼55 km beneath the Kunlun terrane. The present crustal thickness of the Tibetan plateau has generally been attributed to the Cenozoic collision between the Indian and Eurasian plates and the subsequent intracontinental convergences since ∼55 Ma. However, doubts were raised about this interpretion in the past few years. For example, recent studies indicated the crust of the Lhasa terrane had been significantly thickened during ca. 140–130 Ma in response to the subduction of the Neo‐Tethyan Ocean, although the Cretaceous marine strata across the Lhasa terrane demonstrates that it was thin enough to be within the reach of sea level during at least the early Late Cretacous. Whether the South Qiangtang terrane underwent crustal thickening before Cenozoic or not remains an unanswered question.In this study, new zircon U–Pb geochronologic and Hfisotopic, and whole‐rock geochemical data of the Late Cretaceous high‐Sr/Y granitoids from the eastern South Qiangtang terrane are presented. LA–ICP–MS zircon U–Pb dating produced ages (92.0 ± 1.1 Ma, 88.8 ± 0.7 Ma, and 91.5 ± 0.6 Ma) of formation for the Leiwuqi granitoids of the South Qiangtang terrane, Tibetan Plateau, indicating that they were formed during the Late Cretaceous. The granitoids have low A/CNK ratios (0.94–1.06; <1.10) and P2O5 contents (0.02–0.12 wt.%), geochemically similar to I‐type granitoids. They are characterized by high Sr (350–938 ppm, most > 400 ppm), low Y (5.94–9.67 ppm), with high Sr/Y (36–119, most > 40) and (La/Yb)N ratios (67–394). They exhibit negative zircon ∊Hf (t) values (−9.8 to −1.1) and low MgO (0.32–0.69 wt.%), Cr (2.07–12.17 ppm), and Ni (1.10–5.94 ppm) contents. These features suggest that the granitoids probably were derived from partial melting of thickened lower continental crust (> 50 km). The crust of the South Qiangtang terrane (at least its eastern part) may have been significantly thickened before the Late Cretaceous.

Critically stressed fractures: analysis of the Shaikan Field, Kurdistan Region of Iraq

The Shaikan Field is a large producing oil field in the Kurdistan region of Iraq. It consists of multiple fractured reservoirs consisting of limestones, calcareous sandstones and mudstones. The surrounding tectonic terrane is situated in the seismically active Zagros–Taurus orogenic zone, where present-day stresses are high. The regional stresses are found to impose conditions that satisfy failure along reservoir-bound fractures, suggesting that a significant proportion of fractures are likely to be critically stressed. The in situ maximum principal stress magnitudes are estimated using three methods, namely, the tensile and compressive strengths of reservoir rock, and leak-off test (LOT) data. Stress-field orientations are determined from wellbore image log data, which are used to interpret wellbore breakouts and the associated induced tensile fractures. Reservoir pressure has declined since production started and poroelastic responses have been assessed and used to estimate the present-day stress-state and the criticality of those fractures that are most likely to fail or slip. Although a conventional approach has been used the present authors argue that a new approach to stress response with changing pore pressure should be taken. Unlike the previous theory of criticality in which a reduction in pore pressure is considered to lead to a stabilization of the fracture network, the present study suggests that a system may remain critically stressed regardless of pressure decline. Thematic collection: This article is part of the The Geology of Fractured Reservoirs collection available at: https://www.lyellcollection.org/cc/the-geology-of-fractured-reservoirs

Tectonic terranes underlying the present-day Caribbean plate: their tectonic origin, sedimentary thickness, subsidence histories and regional controls on hydrocarbon resources

Abstract Thick sedimentary cover (≤16 km), vintage seismic and disparate crustal terranes have hindered understanding of the basement underlying the Caribbean plate. The plate formed by Early Cretaceous to Miocene amalgamation of four crustal types: the Caribbean Large Igneous Province oceanic plateau; the Chortis continental block; the related Great Arc of the Caribbean and Siuna/Mesquito Composite Oceanic Terranes island arc blocks; and the Colombian and Venezuelan basin oceanic crust. We characterize each terrane through interpretation of surface geology, 62 000-line-km of 2D seismic reflection data, 366 seismic refraction stations, 47 wells, 74 basement samples, 2D forward modelling, magnetic and gravity anomaly grids, and integration of previous studies. Basins overlying island arc crust are small, fault-bounded and deep, while on continental crust, they are broader and shallower. Strongly flexed oceanic and oceanic plateau crust along amagmatic subduction zones on the southern and northeastern edges of the Caribbean plate produce the largest and deepest sediment-filled basins. Areas of proven hydrocarbon source rocks and mapped seeps are associated with continental and island arc terranes in the western Caribbean plate, while organically-rich, but immature, Late Cretaceous source rocks occur across the more elevated areas of the central and eastern Caribbean plate interior.

Stress-strain analysis and its tectonic implications for the Fatima suture zone, western Arabian Shield, Saudi Arabia

The Fatima suture zone (FSZ) consists of highly thrusted and folded mafic, ultramafic and volcanic-sedimentary rocks and is bounded by granitic rocks. This study addresses the kinematics and deformation types of the FSZ using brittle and ductile tectonic fabrics for paleostress and paleostrain constructions, modes of fault initiation and reactivation and establishment of the Neoproterozoic tectonic sequence. The results show that the study area is characterized by five tectonic events that differ in time, location, and regime. The first tectonic event (D1) preceded FSZ development and was followed by two tectonic events (D2 and D3) that significantly affected rock deformations and were related mainly to FSZ formation. Progressive changes from transpressional to transtensional regimes are attributed to the divergent movements that occurred between the subducted Asir and Jiddah tectonic terranes on either side of the FSZ. Post-FSZ tectonic events (D4 and DT) occurred during the late development stage of the Arabian Shield and were not strong enough to develop prominent deformations. During tectonic deformation in the FSZ and its environs, faults initially developed with orientations and slip types compatible with the prevailing stress parameters. The superposed tectonic regimes inherited new faults and reactivated pre-existing faults. The formation of new slips on the reactivated fault planes depended on the stress parameters and fault strikes without changing their initial orientations. The slip types and orientations of the new faults reflected the stress regime. The rotation of fault planes during ductile deformation inside the FSZ has been proven, whereas brittle deformation at its shoulders has occurred without fault rotation.

MANTLE TERRANES OF THE SIBERIAN CRATON: THEIR INTERACTION WITH PLUME MELTS BASED ON THERMOBAROMETRY AND GEOCHEMISTRY OF MANTLE XENOCRYSTS

We have studied variations in the structure and composition of minerals from the pipes of the Yakutian kimberlite province (YKP) in different mantle terranes of the Siberian craton. The study was based on an extensive database, including the microprobe analysis datasets consolidated by IGM, IG, IEC and IGDNM SB RAS and ALROSA and geochemical analysis of minerals performed by LA‐ICP‐MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry). The reconstruction shows layering under the tubes, including 6–7 slab that were probably formed due to subduction; the slabs are separated by pyroxenitic, eclogitic and metasomatic layers and dunite lenses. Transects and mantle profiles across kimberlite fields are constructed. Within the limits of the revealed tectonic terranes, we assume a collage of microplates formed in the early – middle Archean. Extended submeridional structures of the tectonic terranes are not always confirmed at the mantle level. Beneath the Anabar and Aldan shields, the mantle sections show more coarse layers and 3–4 large horizons of dunites with garnet and pyroxene nests separated by ilmenite‐ phlogopite metasomatites and pyroxenites. Terranes representing the suture zones between the protocratons (e.g. Khapchan) are often saturated with eclogites and pyroxenites that may occur as leghthy ascending bodies of magmatic eclogites penetrating through the mantle lithosphere structure (ML). A nearly ubiquitous pyroxenite layer at the level of 3.5–4.5 GPa formed probably in the early Archean with a high heat flux during melting of eclogites and was subsequently traced by plume melts. Within the early Archean protocratons – granite‐greenstone terranes (Tungus, Markha, Berekta, and Sharyzhalgai, ~3.8–3.0 Gyr [ Gladkochub et al., 2019 ], the mantle lithosphere is less depleted and largely metasomatized. The ML structure of the Daldyn and Magan granulite‐orthogneiss terranes is layered with folding revealed in the north‐to‐south sections from the Udachnaya pipe to the Krasnopresnenskaya pipe, which is less pronounced in the latitudinal direction. From the Daldyn field to the Alakit field, there is an increase in the degree of metasomatism, and higher alkalinity of pyroxenes and larger amounts of phlogopite are noted. The most productive Aikhal and Yubileinaya pipes are confined to a dunite core, which is accompanied by a change in the specialization of high‐charge elements Ta‐Nb to Zr‐Hf. Within the limits of the Magan terrane, the thin‐layer structure of the middle and upper parts of the craton keel is replaced with a sharply depleted productive horizon at its base. The mantle of the granite‐greenstone Markha terrrein comprises eclogite (often pelitic) horizons, which suggests subduction of the continental lithosphere or sediments. In the central and northern parts of the Siberian craton, most structures in the mantle are sinking to the west at small angles. The geochemistry features of garnets and pyroxenes from various mantle terranes are considered in detail.

The southern São Francisco Craton puzzle: Insights from aerogeophysical and geological data

Accretionary orogens are considered as the result of the major crust production process, and terranes are accreted material representing distinctive assemblages regarding age and evolution. Scientific advances in the last years show that the southernmost São Francisco Craton includes Archean, Paleoproterozoic and Neoproterozoic areas. We used aerogeophysical data and field geology to understand the extension of individual pieces of this tectonic puzzle. We described five magnetometric lineaments. A–, B– and C–lineaments are related to dyke swarms of different ages. D– and E–lineaments represent regional-scale tectonic structures. In a tectonic perspective, we have identified the following terranes: (i) the Archean São Tiago crust (2.67 Ga), which is part of the São Francisco proto-craton; two Siderian juvenile arcs, represented by the (ii) Cassiterita (2.47 Ga) and the (iii) Resende Costa/Lagoa Dourada (2.36–2.35 Ga) orthogneisses; and two Rhyacian arcs, the (iv) juvenile Serrinha (2.22–2.20 Ga) and the continental Ritápolis (2.19–2.10 Ga) arcs. Tectonic terranes and five magnetic subdomains were identified on the basis of (i) association of shear zones/faults with quartz veins in the field; (ii) low– and high–intensity magnetic anomalies; (iii) sharp contrast in Euler solution intensities; and (iv) high–contrast in radioelement contents in the gammaspectrometric maps. Processing of aerogeophysical data permitted us to propose a new scenario on the evolution of the southern São Francisco Craton, and in particular of the Mineiro belt. The integration between aerogeophysical, new and compiled geologic information, provides a robust model for the understanding of individual tectonic pieces of the studied area.

A new crustal thickness model for mainland China derived from EIGEN-6C4 gravity data

In this study, we present a new crustal thickness model of mainland China created from the inversion of EIGEN-6C4 global gravity model. We took advantage of a high-resolution gravimetric data and the regularized inversion, based on the Gauss-Newton formulation of Bott’s equation to resolve the Moho topography. The inversion process uses tesseroids to account for the earth curvature. Moho depth modeling for such a massive landmass cannot ignore the earth’s curvature. The Bouguer effect, terrain effect, and gravity effect due to sediments were also corrected and calculated in a spherical approximation. The resulting crustal thickness model was validated with 2992 seismological data points and compared with continental-scale crustal thickness models for mainland China. The final crustal thickness model shows a minimum value of ∼26 km in Eastern China to a thick crust of over 75 km under the Tibetan Plateau. Nevertheless, the results also show a considerable difference in unconstrained areas of the Tibetan plateau with a crustal thickness of ∼20 km and ∼6 km in sedimentary areas. The tectonic terranes show similar depth estimates for all the continental scale models of mainland China, but the lateral variation differs considerably. The results also expose two East-West fold belt trends on the Tibetan Plateau, a 44 km thick crust between Western and Eastern China, and a 37 km NNE trend line, which separates the stable eastern cratonic blocks from the thinned crustal blocks. Overall, our high-resolution model yields an improved representation of crustal features over previously gravity crustal thickness models of mainland China.

3-D constrained inversion of gravimetric data to map the tectonic terranes of southeastern Laurentia using simulated annealing

Inversion of gravity anomaly data can be an effective tool in reconstructing the geologic history of a region by segregating tectonic terranes with different physical properties. Recent advances in computational capabilities coupled with lithospheric-scale seismic experiments provide the opportunity to conduct 3D regional-scale, constrained inversions of gravity data using global optimization algorithms. Here, a method for inverting gravity anomaly data by combining a finite-element method based forward calculation with a simulated annealing algorithm is introduced. The method is applied to the southeastern Laurentia region, which is comprised of an amalgamation of crustal blocks spanning a tectonic history of over 1.5 Ga. The method better defines the gross crustal density distribution of the region, and proves to be efficient in spatially discriminating between the different tectonic terranes. The tectonic terranes fall within four distinct groups, based on the average crustal density, each of which seem to have undergone a distinct geologic history.

Review on the Tectonic Terranes Associated with Metallogenic Zones in Southeast Asia

The paper presents an overview of the relationships between the interior structures of tectonic terranes and the distribution of tectonic-metallogenic zones in Southeast Asia. Episodic tectonic activities occurred in this archipelagic area, generating metallogenic belts in multi-terranes. Since the Late Paleozoic, opening and closure of the Paleotethys and Neotethys led to multiple suture zones between different blocks, mainly between the Indochina terrane, the Nambung terrane, the Sibumasu terrane and the West Myanmar terrane. During the Mesozoic to Cenozoic, the formation of accreted terranes and their related islands was caused by subduction and collision processes between the Pacific and Australian plates toward the Eurasian Continent, forming Sundaland and its affiliated islands, the Philippines and its subsidiary islands, the Papua New Guinea terrane and its related islands and the Sunda epicontinental arc system. Within the margin of terranes resulted in the structural transfer zones, their secondary tectonic units can be divided into island arc belts, back-arc basins, suture zones, marginal fold belts and orogenic belts. The metallogenic assemblages are mainly distributed within these structural zones of the terranes. According to the relationship between these tectonic units and the distribution of mineral resources, the tectonic-metallogenic belts can be divided into 24 metallogenic belts in Southeast Asia. They are characterized by a diversity and frequency of metallogenic material combination which is likely to reflect the complexity of the material distribution during mineralization processes, mostly by the structural transformation during the dissociation-convergence process between multiple terranes. Therefore, the formation of ore deposits was not only restricted by the evolution (opening and closure) of Paleo-and Neotethys, but may also be controlled by the interaction of the terranes with different tectonic attributes which provided multiple sources of metallogenic material.

Thermal properties of the crust and the lithosphere\u2013asthenosphere boundary in the area of Poland from the heat flow variability and seismic data

High-resolution 3D seismic P-wave velocity model of Poland (Grad et al., Tectonophysics 666:188–210, 2016) and corrected for paleoclimate heat flow map (Majorowicz and Wybraniec, Int J Earth Sci 100(4):881–887, 2011) gridded to a common mesh are used together with four independent thermal models of the crust and upper mantle to calculate heat flow variation with depth and geotherms. Heat flow at Moho depth are calculated and mapped and both confirm large variability with an elevated mantle heat flow (circa 30–40 mW/m2) in the Paleozoic Platform which is some 10–20 mW/m2 higher than Moho heat flow in the north-eastern and south-eastern Poland which belong to a variety of tectonic terranes (the oldest Precambrian Craton, younger Cadomian, Trans-European Suture Zone, Carpathians). Temperatures calculated for the crust show consistent pattern: higher temperatures beneath the Paleozoic Platform and lower temperatures beneath the Precambrian and Cadomian units. At 10 km depth this difference is about 150 °C, about 300 °C at 20 km depth, and about 400 °C at 50–60 km. Assuming the calculated isotherm 580 °C as Curie temperature the magnetic crust thickness was determined as 5–10 km only beneath the Polish Basin, circa 20 km in Carpathians, circa 30 km in Sudetes, and 35–40 km beneath the Precambrian and Cadomian units. Such a thick magnetic crust results from a great depth of Curie temperature, thick crystalline crust, and thin sediments. Mantle heat flow variability is mainly correlating with measured surface heat flow and influences geotherms. Calculated thermal LAB depth follows patterns of heat flow and Moho heat flow variability through Poland with thinnest lithosphere in the high surface heat flow and high mantle heat flow areas. Comparison of this thermal LAB depth estimates with seismic data based LAB depth shows general coincidences when Precambrian Craton vs Paleozoic Platform are considered along the P4 seismic experiment data model (circa 190 km depth vs some 90 km depth, respectively). However, significant differences exist in many areas and especially for the SE Poland when compared with map for the whole of Poland compiled from other seismic reported data.

Petrogenesis of early cretaceous andesite dykes in the Sulu orogenic belt, eastern China

This study presents data of in-situ mineral major and trace element chemistry, whole-rock major and trace element and Sr–Nd isotope geochemistry, as well as zircon U–Pb dating and Lu–Hf isotope studies of andesite dykes from the Sulu orogenic belt of eastern China to evaluate their petrogenesis and thus to provide insights into crust–mantle interactions in a tectonic terrane that underwent continental subduction and was then overprinted by oceanic subduction. The andesites mainly comprise plagioclase, hornblende, clinopyroxene and magnetite as phenocrysts that are embedded in a groundmass of fine-grained quartz and K-feldspar, with minor amounts of biotite, magnetite, titanite, apatite and zircon. They possess intermediate concentrations of SiO2 (54.97–62.24 wt.%), Na2O + K2O (6.35–7.24 wt.%) and MgO (3.37–7.12 wt.%) with high Mg# values [Mg# = 100 × Mg/(Mg + Fe2+) molar] of 54–64, and are characterized by arc-like trace element patterns that are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE) but depleted in high field strength elements (HFSE). The hornblende and clinopyroxene phenocrysts exhibit enrichment in Th and U but an obvious depletion of HFSE. The andesites have high initial 87Sr/86Sr ratios of 0.7073–0.7086 and negative ɛNd(t) values of −15.7 to −14.4 for whole-rock, and newly crystallized magmatic zircons show negative ɛHf(t) values of −27.0 to −17.6. U–Pb dating on syn-magmatic zircons yields consistent ages of 124 ± 2 to 116 ± 1 Ma, indicating eruption of the andesitic lavas during the Early Cretaceous. Inherited zircons are present and yield Neoproterozoic, Paleoproterozoic and Archean U–Pb ages. Taking into account all these geochemical and geochronological data, and the compositional features of contemporaneously formed mafic–andesitic igneous rocks from the Sulu belt and the adjacent continental crust of the North China Craton, we propose that the andesites crystallized from primary andesitic magmas derived from partial melting of enriched metasomatites in the subcontinental lithospheric mantle. The enriched metasomatites are inferred to be formed by a two-step process: firstly by crust–mantle interactions during the Triassic collisional orogeny and secondly by a subsequent modification by fluids/melts that mainly derive from seafloor sediments during subduction of the paleo-Pacific plate in eastern Asia. Slab rollback of the subducted paleo-Pacific slab and concomitant asthenosphere upwelling are an appropriate geodynamic mechanism for the generation of extensive arc-like magmatism during the Early Cretaceous in the Sulu belt.

Reappraisal of the kinematic history of Nugrus shear zone using PALSAR and microstructural data: implications for the tectonic evolution of the Eastern Desert tectonic terrane, northern Nubian Shield

Nugrus shear zone (NSZ) is a NW-trending semiductile-semibrittle high-strain zone exhibiting obvious sinistral sense of shear. It is regarded by some workers to represent the boundary between the Central Eastern Desert (CED) and South Eastern Desert (SED) of Egypt. A variety of Neoproterozoic lithologies are remarkably affected by the NSZ, encompassing high-grade gneisses, metavolcanics and metavolcaniclastics, gneissose granite, and ophiolitic melange. Visual interpretation and automated lineament extraction have been applied on the local sigma-filtered level 1.5 PALSAR data. Results of directional filtering and line algorithm techniques support the dominance of NW and NE structural trends in the study area. Microstructural and finite strain analyses have been done for the oriented samples of gneisses, metavolcanics, metavolcaniclastics, and gneissose granite using CSS, Fabric 8, and EllipseFit software. The Rf/ϕ and Fry methods demonstrate that the strain ratios of the collected samples are closely compatible and consistent. The core of Hafafit culmination gave 1.5 strain ratio with top-to-the-NW sense of shear, whereas the two rims show 1.7 strain ratio with top-to-the-NE sense of shear. Samples collected along the flanks of Wadi Nugrus show the two types of shear but the NW is dominant with 1.8 strain ratio and sinistral sense of shear, whereas those collected from Wadi Abu Rashid and Wadi Sikiat display 1.4 strain ratio with dextral sense of movement. Finite strain results along with field relations and observations prove that the NSZ and environs experienced a prolonged tectonic history involving at least three deformations (Dl, D2, and D3). D1 phase involves NE-SW shortening and is documented by large-scale NW-trending, NE-dipping, imbricate thrust sheets with NE plunging stretching lineation. D2 was a transpressional phase (660–645 Ma), coeval with the Najd Shear System (NSS), and expressed by the NW- to NNW-trending, steeply dipping, strike-slip shear zones with frequent subvertical foliation and subhorizontal lineation. Exhumation of gneissic domes in Hafafit area was related to this phase. The D3 phase (645–540 Ma) was responsible for the formation of NE-oriented shear with dextral sense of movement. Whether the NW and NE shears are conjugate pairs or not will be a matter of much discussion.

Identificação de Sítios Geológicos para Gestão Prioritária: Propostas para a Geoconservação no Domínio Ceará Central, Nordeste do Brasil

Quantitative assessment of geological sites has been demonstrated as a consistent tool in order to delineate geoconservation strategies, especially for large areas with scarce resources. The working area is located in a vulnerable region in north-eastern Brazil characterised by low socioeconomic conditions. This area comprises an assemblage of 52 geological sites (geosites and geodiversity sites) representing the geodynamic evolution of the Ceara Central Domain, one of the oldest tectonic terranes in Brazil. In this perspective, this work aimed to identify priority sites for geoconservation actions. All geological sites were evaluated by a quantitative assessment concerning the scientific value, the degradation risk, the educational and touristic potential uses and the protection priorities. The assessments were performed by the method available on the GEOSSIT platform developed by Brazilian Geological Survey. Results indicate geological sites with high scientific value, predominance of geosites with moderate degradation risk and medium values for educational and touristic potential uses. Three sorted lists were defined considering only geological sites with high scientific value (geosites) and relevant potential uses. At the end, four priority areas were delineated for a detailed geoconservation plan in the centre-north portion of Ceara Central Domain.

Middle Permian–early Triassic magmatism in the Western Pontides, NW Turkey: Geodynamic significance for the evolution of the Paleo-Tethys

Permian-Triassic magmatic rocks are widely exposed in different tectonic terranes and continental blocks in the Aegean region. This study is focussed on the İstanbul Zone and the Istranca (Strandja) Massif, which are located in the Western Pontides of NW Turkey. The Kırklareli and the Tepecik plutons intruded into the metamorphic basement rocks of the Istranca Massif, and the Sancaktepe pluton is emplaced into the İstanbul Paleozoic sedimentary sequences. We present new geochemical data for these plutons, in order to interpret their petrogenesis and time of emplacement and use this information for geodynamic interpretation. The zircon U–Pb crystallization ages are 268.3 ± 2.1 Ma for the Kırklareli pluton, 249.4 ± 1.5 Ma for the Tepecik pluton and 257.3 ± 1.5 Ma and 253.7 ± 1.75 Ma for the the Sancaktepe pluton. They are high-K, calc-alkaline to shoshonitic granitoids with aluminum saturation index (ASI) values between 0.9 and 1.3, which define them as peraluminous and slightly metaluminous. 87Sr/86Sr(i) values for the studied plutons range between 0.701123 and 0.707704. 143Nd/144Nd(i) ratios calculated for crystallization ages are between 0.512052 and 0.512431, and εNd(i) values vary from −4.71 to 2.22. TDM model ages range between 0.83 and 1.41 Ga. These plutons are enriched in LILEs and LREE and depleted in HFSEs with negative Eu anomalies, indicating that the melts were derived from mafic crustal sources. Our new data suggest that the Kırklareli pluton was generated in a subduction-related magmatic arc, and the highly fractionated Sancaktepe and Tepecik plutons were formed in a back-arc setting in response to the northward subduction of the Paleo-Tethys Ocean during the Mid Permian–Early Triassic.

First Paleomagnetic Constraints on the Latitudinal Displacement of the West Burma Block

Cenozoic collision between India and Eurasia produced the Himalayan-Tibetan orogen, which is commonly considered as the archetypical orogen for continent-continent collision systems. However, there is still no consensus on the amount and mechanism of post-collisional convergence, as well as on the roles of the numerous tectonic terranes comprising the orogen (Jagoutz et al. 2015, 2016; Replumaz et al. 2013, Royden et al. 2008, van Hins-bergen et al. 2011). The West Burma block exhibits a unique geodynamic evolution within this system, influenced by oblique subduction of the Indian plate and significant strike-slip motions along the dextral Sagaing Fault. Furthermore, it is at a key location for paleoenvi-ronmental reconstructions (Cai et al. 2016, Licht et al. 2013). Despite this, robust paleo-magnetic data from the West Burma block is largely absent.Here we report new paleomagnetic, petrological and U-Pb age data to constrain the latitudinal displacement of West Burma. To this end, 45 sites were drilled in the intrusives, extrusives and sediments of the Wuntho arc, Myanmar. Paleomagnetic results were obtained at 30 sites. In addition, 135 paleomagnetic results were obtained from a Late-Eocene mono-clinic sedimentary section in the Chindwin basin, Myanmar.Wuntho arc U-Pb ages cluster in the range 110–90 Ma, indicating a Late-Cretaceous age. Paleomagnetic results from this area show declination values of around 50°–100°, im-plying clockwise rotation of the overall arc dispersed by local-block rotations related to faulting, and inclination values close to zero, corresponding to near-equatorial paleolatitude. Tilt corrections are not available for sites in intrusive rocks. However, the sampling is dis-tributed over a large area (1000 km2) and the results are found inconsistent with regional tilt-ing of the arc. The occurrence of remagnetization after tilting of the country rocks in several sites by the intrusive batholith also support the clockwise rotations and the low paleolati-tude. In the Late-Eocene sediments, normal and reverse polarity magnetizations, alongside the occurrence of numerous ~10 cm thick siderite-rich layers with stable magnetizations, in-dicate a primary detrital or a very early diagenetic origin for the acquisition of the magneti-zation. The sediments constrain a low inclination after tilt correction, which is coherent with the inferred near-equatorial position from the older Wuntho arc rocks. Based on these re-sults, we suggest that accretion of the West Burma block occurred at near-equatorial lati-tude, and that it subsequently underwent significant clockwise rotation and northward translation during the Cenozoic.

Tectonic controls on groundwater geochemistry in Hormozgan Province, Southern Iran

Hormozgan Province with arid climate is an important source of energy resources for Iran. This study investigates the results of hydrogeochemical investigation and its tectonic control in Hormozgan Province, Southern Iran. The chemical analysis of 158 groundwater samples was evaluated to determine the hydrogeochemical processes and ion concentration background in the region. Several NW-SE trending and NE-dipping basement reverse faults have intersected the area and have divided it into four tectonic terranes. Huge extension of Hormuz Formation in Zagros Foredeep tectonic terrane has increased the cations, Cl and SO4 concentration in groundwaters. HCO3 concentration in Sanandaj-Sirjan Zone and High Zagros is the result of silicate weathering or carbonates. Eighty-three percent of samples have negative CAI values in High Zagros, Sanandaj-Sirjan Zone, and eastern Zagros Fold Thrust Belt. The dominant hydrochemical facies of groundwater are Na-Mg-Ca-Cl (25.3% of samples) and Na-Mg-Cl (20.9% of samples). They are confined to the west of Main Zagros Reverse Fault and east of High Zagros Fault, respectively. The salt content of the groundwater indicates samples with very high salinity—as a result of Hormuz Formation—are mainly limited to the west of High Zagros Fault while samples with high to medium salinity are mainly limited to the east of this fault. Eastward increment of rock weathering is controlled with thrust faults activity of the area and southwestward migration of deformation front. Westward increment of evaporites is compatible with Hormuz Formation/salt dome density through the area.

The 2017 Jiuzhaigou Earthquake: A Complicated Event Occurred in a Young Fault System

AbstractThe Minshan Uplift Zone (MUZ) is located at the eastern margin of the Tibetan Plateau, which is the junction of three tectonic terranes. The observed discrepancy between a high uplifting and low shortening rate over the MUZ is attributed to the intrusion of a viscous lower crust. In the last 50 years, several significant earthquakes occurred at the boundaries of the MUZ, that is, the Huya and Mingjiang faults. On 8 August 2017, the Jiuzhaigou earthquake (Mw 6.5) occurred on the northern extension of the Huya fault. We adopt a joint inversion of the interferometric synthetic aperture radar and teleseismic body wave data to investigate the rupture process of this event. The obtained slip model is dominated by left‐lateral strike slips on a subvertical fault presenting significant shallow slip deficit. The rupture initiation is composed of both thrust and strike‐slip mechanisms producing a non‐double‐couple solution. We also resolve a secondary fault branch forming an obtuse angle with the main fault plane at its northern end. These phenomena indicate that the northern Huya fault is a young (less mature) fault system. Focal mechanisms of the regional earthquakes demonstrate that the northern and southern Huya faults present different combinations of strike‐slip and reversed motion. We attribute such discrepancy to the lateral extension of the viscous lower crust, which appears to extrude to the east beyond the northern Huya fault, in comparison with that confined under the MUZ near the southern Huya fault. This conceptual model is also supported by geomorphological and magnetotelluric observations.

Finite Strain Analysis of the Wadi Fatima Shear Zone in Western Arabia, Saudi Arabia

Neoproterozoic rocks, Oligocene to Neogene sediments and Tertiary Red Sea rift-related volcanics (Harrat) are three dominant major groups exposed in the Jeddah tectonic terrane in Western Arabia. The basement complex comprises amphibolites, schists, and older and younger granites unconformably overlain by a post-amalgamation volcanosedimentary sequence (Fatima Group) exhibiting post-accretionary thrusting and thrust-related structures. The older granites and/or the amphibolites and schists display mylonitization and shearing in some outcrops, and the observed kinematic indicators indicate dextral monoclinic symmetry along the impressive Wadi Fatima Shear Zone. Finite strain analysis of the mylonitized lithologies is used to interpret the deformation history of the Wadi Fatima Shear Zone. The measured finite strain data demonstrate that the amphibolites, schists, and older granites are mildly to moderately deformed, where XZ (axial ratios in XZ direction) vary from 2.76 to 4.22 and from 2.04 to 3.90 for the Rf/φ and Fry method respectively. The shortening axes (Z) have subvertical attitude and are associated with subhorizontal foliation. The data show oblate strain ellipsoids in the different rocks in the studied area and indication bulk flattening strain. We assume that the different rock types have similar deformation behavior. In the deformed granite, the strain data are identical in magnitude with those obtained in the Fatima Group volcanosedimentary sequence. Finite strain accumulated without any significant volume change contemporaneously with syn-accretionary transpressive structures. It is concluded that a simple-shear deformation with constant-volume plane strain exists, where displacement is strictly parallel to the shear plane. Furthermore, the contacts between various lithological units in the Wadi Fatima Shear Zone were formed under brittle to semi-ductile deformation conditions.

Metamorphic zoning and behaviour of an underthrusting continental plate

AbstractLower continental plates of collision zones are normally inaccessible and their properties inferred by geophysical surveying. By contrast, the eastern margin of the deeply eroded 1‐billion‐year‐old Sveconorwegian Orogen in Scandinavia exposes an underthrusting lower continental plate that records the metamorphic evolution and behaviour during collisional orogeny. A 200 km wide structurally coherent belt of the mid‐ to upper levels of the underthrusting lower plate, composed of Proterozoic igneous protoliths, exposes the gradual transition from unmetamorphosed to high‐P granulite facies. Metamorphic assemblages in Fe–Ti‐rich metagabbro in a continuous ~120 km wide transect across the lower continental plate define a regional metamorphic zoning by eight zones. Significant metamorphic recrystallization is first recorded at conditions of lower to middle amphibolite facies (550–600°C), progressing successively towards the contact with the upper plate to high‐P granulite facies at ~850°C and 10–11 kbar, the latter corresponding to ~40 km depth. An eclogite‐bearing tectonic terrane, detached from the leading edge of the underthrusting plate and extruded back along the interface with the overlying crust, occurs just beneath the lithotectonic contact of the overriding plate. The gradual metamorphic transition demonstrates that, with the exception of the eclogite‐bearing terrane, the underthrusting plate remained essentially structurally coherent despite highly ductile deformation and partial melting. The metamorphic rocks record that, by and large, the underthrusting plate underwent short‐lived metamorphic recrystallization and deformation that started first at an advanced stage of collision, at c. 980–970 Ma; this is in contrast to the eclogite‐bearing terrane which records more protracted metamorphic recrystallization both through prograde metamorphism and decompression. The investigated section is the first described in situ exposure of a coherent underthrusting lower continental plate, and defines a metamorphic field gradient at higher temperatures and P/T than the classical Barrovian style. The exposed section provides potential for increasing understanding of the thermal evolution, rheology, petrophysical properties and distribution of volatiles in an elsewhere inaccessible part of Earth's collisional systems. The data demonstrate that the underthrusting lower continental plate differs in metamorphic character from other parts of orogenic systems in that the crust is relatively dry, competent and responds by significant metamorphic recrystallization first at elevated temperatures (middle amphibolite facies) and that metamorphic recrystallization is largely coupled to deformation that facilitates the entry of hydrous fluids into the crust.

Phylogenetic Affinities of Indian Apple Snails: An Insight into the Tibetan Tectonic Terranes

Gastropods belong to a hyper-diverse clade of molluscs and encompass limpets, slugs and snails. Interestingly, gastropods have effectively colonized land, freshwaters and marine habitats. However, the relationships among and within its constituent taxa remained in flux for decades due to delimitation in their morphological and anatomical features and hence molecular approach has taken a lead. An understanding into the history of Tibetan tectonic terranes is attempted in this article to derive through the phylogeny of Pila. In our study, we have re-evaluated the relationships within Ampullariidae by collecting the species of Pila globosa and Pila virens (India) and analyzed them comparing with 18S rDNA sequences from public domain. Obtained sequences are evaluated through Maximum Likelihood method in MEGA v 5 which clearly established a single cluster for the three individual taxons namely P. globosa with high bootstrap support. Pila virens showed a paraphyletic cluster with Pila ovata. A low bootstrap value of a few species of Pila possibly inferred rapid speciation among them. The novel observation in the present study is that P. virens forming a secondary cluster with the species from Vietnam namely Pila polita, Pila conica and Pila ampullacea has authenticated that the south India and Vietnam are in the same latitude namely 9–20°N, supporting the paleomagnetic data which unravelled that India collided with Asia around 57 mya in the Coenozoic era, whereas ampullariids must have been in co-existence since the Cambrian Period indicating their long evolutionary affinity and zoo-geographical relationship.