Zone Of Accretion Research Articles

Seismic Reflection Imaging Reveals Relict Subduction Zone of the Paleo-Pacific Plate in the Northeastern South China Sea

The South China Sea (SCS) is widely accepted as an active margin that is associated with the subduction of the Paleo-Pacific plate during the Mesozoic. However, the exact location of the subduction or suture zone remains unclear. Understanding the location of the subduction zone is crucial for comprehending the Mesozoic tectonic evolution of the South China Block and the Cenozoic rifting process of the SCS. To clarify the position of the subduction zone and the influences of preexisting structures, we used a multichannel seismic reflection profile to investigate the crustal architecture. The seismic profile reveals a crustal “crocodile” structure that is interpreted as relict subduction in the Chaoshan Depression and a set of south-dipping crust-mantle reflectors related to the initial rifting in the continent–ocean transition (COT) zone. The results indicate that a Mesozoic subduction zone is located at the northeastern margin of the SCS and that preexisting structures (subduction-related structures) facilitated the rifting process. Combined with previous studies on the oceanic plateau collision-accretionary zone of the northern SCS and the Mesozoic accretionary zone in Palawan of the southern SCS, we infer that a section of the suture zone of the Paleo-Pacific plate subduction is preserved at the northeastern SCS margin and that the rifting of the SCS may have initiated at the suture zone.

Geochemistry and zircon U-Pb-Hf isotopes of Paleozoic granitoids along the Solonker suture zone in Inner Mongolia, China: Constraints on bidirectional subduction and closure timing of the Paleo-Asian Ocean

The closure of the Paleo-Asian Ocean resulted in formation of the Central Asian Orogenic Belt (CAOB) accompanied by considerable Phanerozoic juvenile crustal growth. As an international frontier topic, whether the Solonker suture zone is the site of final closure of the Paleo-Asian Ocean and records the terminal evolution of the CAOB in Inner Mongolia is still in controversial. This study presents the geochemistry and zircon U-Pb-Hf isotopes of granitoids along the Solonker suture zone to constrain the subduction and closure processes of the Paleo-Asian Ocean. Granitoids from the Xilinhot area in the northern accretionary zone comprise diorites and granodiorites with LA-ICPMS zircon U-Pb ages of 316 ± 2 Ma, 302 ± 2 Ma, 285 ± 2 Ma and 243 ± 4 Ma, positive εHf(t) values of +2.39 to +13.31 and TDM2 model ages of 481–1191 Ma. The ca. 316–285 Ma granitoids were formed by fractional crystallization of regional coeval calc-alkaline basaltic magma in an arc-related setting and the ca. 243 Ma granitoid was generated mainly from partial melting of dominant basaltic source rocks and minor metagraywackes in the northward subduction-related setting. The granitoids from the Linxi area in the southern accretionary zone include muscovite monzogranites and monzogranites with LA-ICPMS zircon U-Pb ages of 525 ± 6 Ma, 274 ± 2 Ma and 261 ± 4 Ma. The ca. 525 Ma muscovite monzogranites have negative zircon εHf(t) values of −19.36 to −13.61 with TDM2 model ages of 2348–2711 Ma. They were generated from partial melting of Neoarchean to Paleoproterozoic supracrustal materials. The ca. 274–261 Ma monzogranites show negative zircon εHf(t) values ranging from −10.48 to −0.66 with TDM2 model ages of 1335–1942 Ma. They were derived from remelting of Paleoproterozoic to Mesoproterozoic supracrustal materials in the southward subduction zone along the northern active margin of the North China Craton. Combining our results with existing data, we infer that the early Paleozoic southward subduction of the Paleo-Asian Ocean started before ca. 525 Ma, and the northward subduction zone lasted to ca. 243 Ma, which implies the bidirectional subduction of the ocean lasted at least until ca. 243 Ma. Our work suggests that along the Solonker suture zone, the regional amalgamation may have occurred after ca. 243 Ma, which closed the Paleo-Asian Ocean.

The formation and aqueous alteration of CM2 chondrites and their relationship to CO3 chondrites: A fresh isotopic (O, Cd, Cr, Si, Te, Ti, and Zn) perspective from the Winchcombe CM2 fall

AbstractAs part of an integrated consortium study, we have undertaken O, Cd, Cr, Si, Te, Ti, and Zn whole rock isotopic measurements of the Winchcombe CM2 meteorite. δ66Zn values determined for two Winchcombe aliquots are +0.29 ± 0.05‰ (2SD) and +0.45 ± 0.05‰ (2SD). The difference between these analyses likely reflects sample heterogeneity. Zn isotope compositions for Winchcombe show excellent agreement with published CM2 data. δ114Cd for a single Winchcombe aliquot is +0.29 ± 0.04‰ (2SD), which is close to a previous result for Murchison. δ130Te values for three aliquots gave indistinguishable results, with a mean value of +0.62 ± 0.01‰ (2SD) and are essentially identical to published values for CM2s. ε53Cr and ε54Cr for Winchcombe are 0.319 ± 0.029 (2SE) and 0.775 ± 0.067 (2SE), respectively. Based on its Cr isotopic composition, Winchcombe plots close to other CM2 chondrites. ε50Ti and ε46Ti values for Winchcombe are 3.21 ± 0.09 (2SE) and 0.46 ± 0.08 (2SE), respectively, and are in line with recently published data for CM2s. The δ30Si composition of Winchcombe is −0.50 ± 0.06‰ (2SD, n = 11) and is essentially indistinguishable from measurements obtained on other CM2 chondrites. In conformity with petrographic observations, oxygen isotope analyses of both bulk and micromilled fractions from Winchcombe clearly demonstrate that its parent body experienced extensive aqueous alteration. The style of alteration exhibited by Winchcombe is consistent with relatively closed system processes. Analysis of different fractions within Winchcombe broadly support the view that, while different lithologies within an individual CM2 meteorite can be highly variable, each meteorite is characterized by a predominant alteration type. Mixing of different lithologies within a regolith environment to form cataclastic matrix is supported by oxygen isotope analysis of micromilled fractions from Winchcombe. Previously unpublished bulk oxygen isotope data for 12 CM2 chondrites, when combined with published data, define a well‐constrained regression line with a slope of 0.77. Winchcombe analyses define a more limited linear trend at the isotopically heavy, more aqueously altered, end of the slope 0.77 CM2 array. The CM2 slope 0.77 array intersects the oxygen isotope field of CO3 falls, indicating that the unaltered precursor material to the CMs was essentially identical in oxygen isotope composition to the CO3 falls. Our data are consistent with earlier suggestions that the main differences between the CO3s and CM2s reflect differing amounts of water ice that co‐accreted into their respective parent bodies, being high in the case of CM2s and low in the case of CO3s. The small difference in Si isotope compositions between the CM and CO meteorites can be explained by different proportions of matrix versus refractory silicates. CMs and COs may also be indistinguishable with respect to Ti and Cr isotopes; however, further analysis is required to test this possibility. The close relationship between CO3 and CM2 chondrites revealed by our data supports the emerging view that the snow line within protoplanetary disks marks an important zone of planetesimal accretion.

Eastward extension of the Solonker Suture beneath the central Songliao Basin, NE China: Evidence from a deep seismic reflection profile

The Solonker Suture is one of the most important structures in central Asia and marks the location of closure of the Paleo-Asian Ocean and the assemblage of the North China and Siberia cratons during the Late Permian - Early Triassic. The suture is traceable for ∼ 700 km within the Central Asian Orogenic Belt, but its eastward extension beneath the Songliao Basin has not been defined. In this paper, we present a 127.3-km-long N–S deep seismic reflection profile across the central Songliao Basin. The data acquired from five large-size and four medium-size dynamite shots were used to generate a single-fold reflection profile imaging the Moho and the structures of the crust and upper mantle. The southern end of the profile reveals a northward-dipping reflector that extends 80 km into the mantle. This dipping reflector is interpreted as a fossil subduction zone. The new data from this study suggest that the Songliao Terrane may not be a single micro-continent block or orogenic belt but a composite terrane that comprises the North Accretionary Zone, South Accretionary Zone, and northern margin of the North China Craton from north to south. The fossil subduction zone is regarded as part of the NE-trending extension of the Solonker Suture beneath the central Songliao Basin.

Modes and geometry of crustal-scale detachment folding in hot orogens—Insights from physical modeling

Detachment folding can be defined as the displacement and buckling of a competent layer above a rheologically weak horizon during tectonic shortening, frequently addressed in the context of salt tectonics. More recent studies have focused on influence of detachments in large-scale lithospheric deformation where the detachment horizon is represented by partially molten lower crust.This study addresses the geometric, kinematic and dynamic behavior of crustal-scale detachment folds using heated paraffin wax as an analogue for partially molten lower crust. Various thermal and shortening rate scenarios were tested in order to characterize deformation patterns within hot orogens in general, and to find an appropriate range of temperature gradients and shortening rates for the detachment folding regime. Five different regimes of lower crustal deformation were identified: 1. Homogeneous thickening or bulging, 2. Short-wavelength folding, 3. Development of diapir-shape folds or ductile faults, 4. Detachment folding and 5. Formation of lower crustal finger-like protrusions.Models are compared to various natural prototypes worldwide, in particular a series of metamorphic domes in the Central Asian Orogenic Belt (CAOB). Detailed analysis of the kinematic-dynamic evolution of the detachment folding scenario revealed an asymmetrical evolution of the folds associated with rotation of the limbs, as well as flexural flow of the lower weak mushy crust around the molten core. Pressure gradients in the fold cores saturated by melt controlled the sequential injections and outflows of partially/molten material between folds’ cores and the melt source layer at the base of the system. This resulted in accumulation of melt in the foreland of the accretionary zone, with higher melt absorption potential for newly developed folds. These observations may have significant implications for the development of pseudo-symmetrical metamorphic domes in the CAOB.

A transient apical extracellular matrix relays cytoskeletal patterns to shape permanent acellular ridges on the surface of adult C. elegans.

Epithelial cells secrete apical extracellular matrices to form protruding structures such as denticles, ridges, scales, or teeth. The mechanisms that shape these structures remain poorly understood. Here, we show how the actin cytoskeleton and a provisional matrix work together to sculpt acellular longitudinal alae ridges in the cuticle of adult C. elegans. Transient assembly of longitudinal actomyosin filaments in the underlying lateral epidermis accompanies deposition of the provisional matrix at the earliest stages of alae formation. Actin is required to pattern the provisional matrix into longitudinal bands that are initially offset from the pattern of longitudinal actin filaments. These bands appear ultrastructurally as alternating regions of adhesion and separation within laminated provisional matrix layers. The provisional matrix is required to establish these demarcated zones of adhesion and separation, which ultimately give rise to alae ridges and their intervening valleys, respectively. Provisional matrix proteins shape the alae ridges and valleys but are not present within the final structure. We propose a morphogenetic mechanism wherein cortical actin patterns are relayed to the laminated provisional matrix to set up distinct zones of matrix layer separation and accretion that shape a permanent and acellular matrix structure.

Assessment of shoreline change and its relation with Mangrove vegetation: A case study over North Konkan region of Raigad, Maharashtra, India

Vulnerability of SLR varies from place to place with 20th century observing greatest threat to it. Mangroves along the shore are the one to first sustain this impact of SLR. In the present study, an attempt has been made to understand the relation between shoreline changes with mangrove habitat through remote sensing data and geospatial technique. Shoreline change rate has been calculated for the years 2000, 2012 and 2019, in Digital Shoreline Analysis System by End Point Rate. Change analysis indicates that in last 20 years erosion dominated the study area with an average rate of -0.02m/yr. During 2000 to 2012, relatively higher erosional rates (-0.35m/yr) were observed. While from 2012 to 2019 accretion process dominated this area with a rate of 0.43m/yr. Sonakothakar, Mothe Bhal and Dadar with denudation, have observed landward progradation of mangroves whereas, at Aware, a zone of accretion exhibited a seaward progradation of mangroves. A direct relation with the shoreline change has been observed with mangrove habitat. Mangroves are consider as salt feeder and so spatial changes in their colony is ought to be frequent in the present context of climate change and SLR. This type of integrated study will help to understand active process over the shore and help to conserve mangrove habitat. Such regional scale studies should be carried out before implementing any coastal conservation projects.

Reconstructed ocean plate stratigraphy sequences from the Permian subduction-accretionary complex in the Qinghai-Tibet Plateau

The Permian Tethys subduction-accretionary complex (SAC) in the Qinghai-Tibet Plateau (QTP) is distributed in six geotectonic provinces, which are known as the Zongwulong-Ganjia, the Western Kunlun, the Eastern Kunlun, the Ganzi-Litang, the Xijinwulan-Jinshajiang-Ailaoshan and the Longmucuo-Shuanghu-Nujiang from north to south. The SAC is a set of mélange generated by subduction of oceanic crust at trenches, which consists of relics from mid-ocean ridge, abyssal plains, oceanic island-seamounts, intra-oceanic arcs and trench turbidites. In this paper, we apply the ocean plate stratigraphy (OPS) theory to reconstruct the OPS sequence of the Permian SAC in the QTP. We divided the Permian SAC in the QTP into two types, i.e., convergent zone and accretionary zone according to their tectonic environments. Six relics from mid-ocean ridge, five relics from abyssal plain, five relics from seamount, two relics from intra-oceanic arc, two relics from fore-arc trench, and seven relics from continental fore-arc trench were recognized and then the OPS sequences from different tectonic environments were reconstructed. The spatial-temporal distributions and evolution of ocean basins during the Permian represented by six SACs are discussed.

Cretaceous Tethyan subduction in SE Borneo: Geochronological and geochemical constraints from the igneous rocks in the Meratus Complex

• The igneous rocks in the Meratus Complex mainly formed at ∼115–140 Ma. • The Cretaceous Meratus mafic rocks originated from the slab-related wedge mantle. • The Cretaceous granitoids represent the product of wedge-originated juvenile crust. • Meratus Complex has a NW-Australian affinity and formed in an fore-arc setting. • The Meratus Neotethyan Ocean subducted beneath the Argo fragment until ∼100 Ma. SE Borneo lies at the junction of the Pacific and Tethyan realms. The Mesozoic geological record of the region is dominated by convergent plate margin activity, although the geological details and its broader role in the SE Asia evolution are poorly documented. This paper presents geochronological, whole-rock elemental and Sr-Nd-Pb isotopic data on the igneous rocks from the Meratus Complex in SE Borneo. The Meratus ophiolite might form at the Late Jurassic-Early Cretaceous (∼150–115 Ma), and the spatially-associated Haruyan Volcanics, Belawayan granitoids and their equivalents generated in the Early Cretaceous (∼140–107 Ma). The Haruyan and Pitap formations and their equivalents are dominated by Early Cretaceous (∼140–115 Ma) volcanic rocks and late Early Cretaceous (∼115–100 Ma) siliciclastic rocks, respectively. The mafic-intermediate igneous rocks in the Meratus Complex are characterized by MgO = 2.04–13.20 wt%, TiO 2 = 0.48–1.51 wt%, Nb/La = 0.09–0.42, ε Nd (t) = +4.6–+7.7, ( 206 Pb/ 204 Pb) i = 18.15–18.61, ( 207 Pb/ 204 Pb) i = 15.41–15.63 and ( 208 Pb/ 204 Pb) i = 38.03–38.63, and originated from the slab-related mantle wedge. The granitoids share similar elemental ratios and Sr-Nd-Pb isotopic compositions with the coeval mafic rocks, with Nb/La = 0.20–0.30, ε Nd (t) = +4.8–+6.0, Δ8/4 = 26.2–38.8 and Δ 7/4 = 5.0–7.7, representing the products of the wedge-originated juvenile crust. Synthesis of all data reveals a NW-Australian affinity for SE Borneo. The Early Cretaceous fore-arc tectonic setting extends southerly into the Bantimala (SW Sulawesi) and Luk Ulo (Central Java), constituting a united Early Cretaceous Central Indonesian accretionary zone. The Meratus Ocean subducted beneath the Argo fragment since ∼140 Ma and likely assembled with the Sundaland margin at ∼100 Ma in response to the Neotethyan consumption.

Shoreline extraction and change estimation using geospatial techniques: a study of coastal West Bengal, India

Shoreline identification is a complicated and time-consuming process for larger and inaccessible areas such as the coastal region of West Bengal (India) using traditional and repetitive ground surveying techniques. Though the recent advancement of geospatial technologies has overcome many of these issues, low spatial resolution, mixed pixels, on-screen shoreline delineation accuracy are not entirely reliable. Moreover, coastal land changes along the shoreline, especially islands, are the major concern mainly related to mangroves destruction. normalised difference vegetation index (NDVI)-Tasseled-Cap transformation technique has been used to automatically generate shoreline using seven Landsat image pairs (1989–2018). The shorelines have been quantified and analysed by end point rate (EPR) and linear regression rate (LRR) algorithms in the digital shoreline analysis system (DSAS) add-in tool within the ArcGIS platform. The rate of shoreline change has been analysed for delineating zones of accretion and erosion. The result reveals that the coastal region of West Bengal has undergoing erosion at the rate of − 3.36 m/year and − 4.70 m/year as per EPR and LRR methods, respectively. Moreover, the study also shows the zone along the islands is more susceptible to erosion than the other zones. The island-wise shoreline study reveals except Lothian Island, the rest of the selected islands viz. Bulchery, Dalhousie, Bhangaduni, Sagar and Baghmara Reserve Forest are erosion-prone. The results would be valuable for coastal and forest conservation planners to identify the most vulnerable zones and propose appropriate policy measures.

Anthropogenic influences on the variation of runoff and sediment load of the Mahanadi River basin

ABSTRACT The emphasis of the present study is on trends and abrupt change points for the runoff and sediment load in a major river basin and anthropogenic factors that influence these trends. The methods adopted are the Mann-Kendall, Sen’s slope, and Pettitt tests for trend and change detection; the difference in digital elevation model for coastal morphological changes; and the double mass curve technique for relative proportions of anthropogenic factors. Significant decreasing trends in yearly runoff and sediment load are observed for 13% and 69% of the hydrological stations, respectively. The analysis found a 79% reduction in sediment discharge into the sea. A figure showing zones of vertical erosion and accretion is also displayed. Geomorphic changes indicate that the landforms susceptible to areal erosion are vulnerable to vertical land loss. Upstream damming, increasing demand, and water allocations are the crucial anthropogenic factors responsible for reducing the sediment load of the basin.

Distinct BSRs and their implications for natural gas hydrate formation and distribution at the submarine Makran accretionary zone

Distinct BSRs and their implications for natural gas hydrate formation and distribution at the submarine Makran accretionary zone

Isolation cementing of oil and gas wells of the Сarpathian region

The problem of reliable isolation cementing of oil wells belonging to non-operating stock is considered. It is shown that the oil and gas fields of the Carpathian region are characterized by unique mining, geological and geographical conditions, as well as a large number of old wells of complex design that require unconventional solutions when performing isolation works. The peculiarities of structure formation, technological properties of insu-lating materials based on oil well cement PCT I-100 and composite mixtures CREA, CREA-LF have been studied. It was found that in the first case, the hydration products are represented by ettringite, hexagonal AFm phases, calcium hydroxide and fibrous hydrosilicates. The following phenomena are characteristic for composite materials: a more uniform distribution of hydrates in the gel mass of hydrosilicates, better ordering of the contact zones of accretion, and an increase in the number of intergrown fibers in blocks of hydrosilicates. All of that ensures the formation of a stone of a denser structure, the closure of a larger number of hydrates surface active centers in contact interactions, controlled synthesis, improvement of the strength characteristics and deformation properties of the cement stone. It is shown that the improvement of the quality of composites is facilitated by the use of modern polyfunctional additives-modifiers applying the technology of manufacturing dry building mixtures. It has been found that to increase the efficiency of krents, it is advisable to use complex additives of multifunctional action, which, complementing each other, make it possible to achieve an additive and sometimes synergistic effect. A new generation plasticizer based on polycarbonates, stabilizing additives and micro-reinforcing fibers is used as a modifier of the CREA and CREA-LF composite mixtures. The ability to microplastic deformation of the composite matrix, reinforced by microreinforcement, causes higher energy consumption for the destruction of the stone. An improved technology for performing insulation works is proposed, taking into account the design features and the state of well support elements, which provides for the use of thermographenite and zeolite tuff in addition to the binder material.

Improved 3‐D P Wave Azimuthal Anisotropy Structure Beneath the Tokyo Metropolitan Area, Japan: New Interpretations of the Dual Subduction System Revealed by Seismic Anisotropy

AbstractThe Tokyo metropolitan area, in the Kanto region of Japan, lies on the Okhotsk plate. Historically, the city has suffered severe damage as a result of megathrust ruptures and intra‐plate earthquakes (M ≥ 7) caused by the dual subduction of the Philippine Sea (PHS) slab and the Pacific slab. To understand the unique seismotectonics of the region, we constrain the three‐dimensional (3‐D) P wave isotropic and azimuthal anisotropic velocity structure beneath the Kanto district, by applying a high‐resolution anisotropic tomography method to travel time data from a dense seismic network consisting of ∼500 stations (including the Metropolitan Seismic Observation network, MeSO‐net). The seismic structure, derived from 1,877 local earthquakes, suggests that the basement of the Okhotsk plate consists of an old accretionary zone formed when the NE Japan arc was part of the Asian continent. The anisotropy observed in the oceanic crust of the subducting PHS slab suggests the presence of a well‐developed system of bending‐related faults, oriented parallel to the axis of the Sagami Trough. We identify a low‐velocity anomaly within the PHS slab mantle, located beneath the Boso Peninsula, which has previously been interpreted as representing the overlying continental plate or the oceanic crust of the PHS slab. Lateral variations in the anisotropy structure suggest that the NE limit of the PHS slab lies farther south than previously thought. Anisotropy directions can be used to identify heterogeneities embedded in low‐velocity anomalies within the PHS slab, which have not been identified in previous studies using only isotropic velocity models.

Ab initio studies of propane dehydrogenation to propene with graphene

First principles calculations are employed to study the dehydrogenation of propane to propene using graphene. The interrelationship between the thermodynamic stability, the catalytic activity and the intrinsic capacity for hydrogen abstraction is employed to identify active graphene nanosheets. The atomistic nature of propyl species anchor sites in active graphene ribbons is clarified as a partially delocalised radical formed on one orbital, and not a typical dangling bond defect state associated with an open-volume defect. Redistribution of charges into zones of accretion and depletion, in the vicinity of the adsorption site, suggests that the delocalisation of the active site at finite temperatures is a distinct possibility that cannot be overruled. Since the active graphene models are obtained from geometrical variants of locally reconstructed carbon divacancies, results of this study suggest that the large-scale synthesis of narrow strips is the key step in the rational design of graphene-based active catalysts instead of large-area sheets.

Cretaceous–Early Cenozoic Geodynamics of the Olyutorka–Kamchatka Accretionary Zone

Within the Olyutorka–Kamchatka accretionary zone, several terranes of an island-arc, marginal-sea, and oceanic nature are distinguished. The igneous complexes of these terranes were formed within the active margin of the Western Pacific type. New data on the opening age of the marginal basins, as well as on the composition and age of the volcanic and terrigenous lithologic complexes of the terranes composing the Olyutorka–Kamchatka region, give grounds to propose a new refined model of the evolution of this region. The geodynamical reconstructions for the K2st-km1, K2km-m, and ₶1–₶2 times are presented.

Detrital Zircon U‐Pb Ages and Geochemistry of the Silurian to Permian Sedimentary Rocks in Central Inner Mongolia, China: Implications for Closure of the Paleo‐Asian Ocean

The Solonker suture zone has long been considered to mark the location of the final disappearance of the Paleo‐Asian Ocean in the eastern Central Asian Orogenic Belt (CAOB). However, the time of final suturing is still controversial with two main different proposals of late Permian to early Triassic, and late Devonian. This study reports integrated whole‐rock geochemistry and LA‐ICP‐MS zircon U‐Pb ages of sedimentary rocks from the Silurian Xuniwusu Formation, the Devonian Xilingol Complex and the Permian Zhesi Formation in the Hegenshan‐Xilinhot‐Linxi area in central Inner Mongolia, China. The depositional environment, provenance and tectonic setting of the Silurian‐Devonian and the Permian sediments are compared to constrain the tectonic evolution of the Solonker suture zone and its neighboring zones. The protoliths of the silty slates from the Xuniwusu Formation in the Baolidao zone belong to wacke and were derived from felsic igneous rocks with steady‐state weathering, poor sorting and compositional immaturity. The protoliths of metasedimentary rocks from the Xilingol Complex were wackes and litharenites and were sourced from predominantly felsic igneous rocks with variable weathering conditions and moderate sorting. The Xuniwusu Formation and Xilingol Complex samples both have two groups of detrital zircon that peak at ca. 0.9–1.0 Ga and ca. 420–440 Ma, with maximum deposition ages of late Silurian and middle Devonian age, respectively. Considering the ca. 484–383 Ma volcanic arc in the Baolidao zone, the Xuxiniwu Formation represents an oceanic trench sediment and is covered by the sedimentary rocks in the Xilingol Complex that represents a continental slope sediment in front of the arc. The middle Permian Zhesi Formation metasandstones were derived from predominantly felsic igneous rocks and are texturally immature with very low degrees of rounding and sorting, indicating short transport and rapid burial. The Zhesi Formation in the Hegenshan zone has a main zircon age peak of 302 Ma and a subordinate peak of 423 Ma and was deposited in a back‐arc basin with an early marine transgression during extension and a late marine regression during contraction. The formation also crops out locally in the Baolidao zone with a main zircon age peak of 467 Ma and a minor peak of 359 Ma, and suggests it formed as a marine transgression sedimentary sequence in a restricted extensional basin and followed by a marine regressive event. Two obvious zircon age peaks of 444 Ma and 280 Ma in the Solonker zone and 435 Ma and 274 Ma in Ondor Sum are retrieved from the Zhesi Formation. This suggests as a result of the gradual closure of the Paleo‐Asian Ocean a narrow ocean sedimentary environment with marine regressive sedimentary sequences occupied the Solonker and Ondor Sum zones during the middle Permian. A restricted ocean is suggested by the Permian strata in the Bainaimiao zone. Early Paleozoic subduction until ca. 381 Ma and renewed subduction during ca. 310–254 Ma accompanied by the opening and closure of a back‐arc basin during ca. 298–269 Ma occurred in the northern accretionary zone. In contrast, the southern accretionary zone documented early Paleozoic subduction until ca. 400 Ma and a renewed subduction during ca. 298–246 Ma. The final closure of the Paleo‐Asian ocean therefore lasted at least until the early Triassic and ended with the formation of the Solonker suture zone.

Petrogenesis and tectonic implications of Late Carboniferous continental arc high-K granites in the Dongwuqi area, central Inner Mongolia, North China

Central Inner Mongolia is located in the southeastern segment of the Central Asian Orogenic Belt (CAOB), and controversy has long surrounded its late Paleozoic tectonic evolution. Here, we present an integrated study of zircon U-Pb ages, whole rock major and trace elements, and zircon Hf isotopes for five less studied alkali feldspar granitic plutons in the Dongwuqi area to the north of the Erenhot-Hegenshan-Heihe suture zone. Zircon U–Pb dating by laser ablation-inductively coupled plasma–mass spectrometry (LA–ICP–MS) indicates that these granitic plutons were emplaced in the Late Carboniferous (315–300 Ma). The Late Carboniferous alkali feldspar granites belong to high-K calc-alkaline series and are evolved I-type granites. They are high in SiO2 (73.22–77.36%), and low in MgO (0.07–0.49%) with enrichments in light rare earth elements (LREEs), Zr, Hf, Rb, Th, and U, and depletions in Ba, Nb, Ta, Sr, and Eu. The Dongwuqi granitic rocks are characterized by high positive zircon εHf(t) values (+7.6 to +15.1), and relatively young two-stage Hf model (TDM2) ages (364–835 Ma). These geochemical data, together the common miarolitic texture, indicate that they were derived from partial melting of juvenile arc-related mafic to intermediate rocks in the lower crust, and eventually emplaced in low-pressure conditions or at shallow crustal levels, with involvement of extensive fractional crystallization during magma evolution. Our new results, along with the published regional data, delineate a NE-trending Carboniferous continental arc belt (more than 1700 km) in the northern accretionary zone of the Erenhot-Hegenshan-Heihe suture. Accordingly, we invoke that the Dongwuqi Late Carboniferous high-K granites were emplaced in an active continental margin setting, which was probably related to the northwestward subduction of the Hegenshan oceanic plate beneath the Xing'an-Uliastai-Nuhetdavaa block.

Spatio-temporal analysis of decadal-scale patterns in barrier island response to storms: Perdido Key, NW Florida

The ability to accurately quantify shoreline variability is essential in order to establish aggressive mitigation strategies, based on recent global climate change projections. This investigation employed a suite of coastal data (topographic maps, aerial photography, satellite imagery and lidar) to establish decadal trends of shoreline movement along Perdido Key, a sandy barrier island off Florida’s northwest coast. The technique used to detect morphologic change with time was a recently developed tool, Analyzing Moving Boundaries Using R. This innovative methodology improves our understanding of the evolution of coastal systems by modeling shoreline variance using a method that is sensitive to shoreline shape. Results show that the barrier shoreline is a highly dynamic feature with distinct zones of erosion and accretion that are pervasive over time. In general, the island is displaying a mechanism of rotational instability with the eastern half retreating, and the western portion advancing. The inflection point, around which this rotational shifting is taking place, lies at the center of a Pleistocene headland located along the island’s midpoint. The results of this study suggest that coastal evolution along the island may be meta-stable, with trends in shoreline variance corresponding mainly to discrete storm events in time.

Nature and provenance of the Beishan Complex, southernmost Central Asian Orogenic Belt

The ages and origins of metasedimentary rocks, which were previously mapped as Precambrian, are critical in rebuilding the orogenic process and better understanding the Phanerozoic continental growth in the Central Asian Orogenic Belt (CAOB). The Beishan Complex was widely distributed in the southern Beishan Orogenic Collage, southernmost CAOB, and their ages and tectonic affinities are still in controversy. The Beishan Complex was previously proposed as fragments drifted from the Tarim Craton, Neoproterozoic Block or Phanerozoic accretionary complex. In this study, we employ detrital zircon age spectra to constrain ages and provenances of metasedimentary sequences of the Beishan Complex in the Chuanshanxun area. The metasedimentary rocks here are dominated by zircons with Paleoproterozoic–Mesoproterozoic age (~1160–2070 Ma), and yield two peak ages at 1454 and 1760 Ma. One sample yielded a middle Permian peak age (269 Ma), which suggests that the metasedimentary sequences were deposited in the late Paleozoic. The granitoid and dioritic dykes, intruding into the metasedimentary sequences, exhibit zircon U–Pb ages of 268 and 261 Ma, respectively, which constrain the minimum deposit age of the metasedimentary sequences. Zircon U–Pb ages of amphibolite (274 and 216 Ma) indicate that they might be affected by multi-stage metamorphic events. The Beishan Complex was not a fragment drifted from the Tarim Block or Dunhuang Block, and none of cratons or blocks surrounding Beishan Orogenic Collage was the sole material source of the Beishan Complex due to obviously different age spectra. Instead, 1.4 Ga marginal accretionary zones of the Columbia supercontinent might have existed in the southern CAOB, and may provide the main source materials for the sedimentary sequences in the Beishan Complex.