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We formulate a numerical framework, in both 2d and 3d, to model the structural patterns emerging from creeping viscous flow typically encountered in long‐term ductile lithospheric deformation by coupling the discontinuous Galerkin level set method with a finite element Stokes‐like flow solver. The level set formulation has the advantage of retaining information on the interface geometry, decreased memory requirement and improved computational efficiency from the two‐way particle‐mesh information transfer compared to particle‐in‐cell methods. Furthermore, our formulation fully exploits the advantages of the finite element method (e.g., the flexibility of mesh geometry and the ease of handling anisotropic materials) by using a unified finite element framework. The novelty of our formulation is the capability to offer a fully dynamic approach for modeling structural patterns resulting from a tectonic flow that is non‐steady and inhomogeneous. The material distribution and the finite deformation patterns predicted from the numerical model can be directly compared with geological map patterns (e.g., lithological distribution at specified depths and on cross‐sections) and field structural analyses (e.g., foliation, lineation and strain patterns), thus offering the possibility of ground‐truthing the modeling results by field evidence. As examples for potential applications of our method, we apply our method to the modeling of a competent inclusion in simple shear flow, as well as a Rayleigh‐Taylor type density overturn. Our models demonstrate good agreement with previous 2d benchmark results and produce 3d lithological and deformation patterns comparable to field observations. Plain Language Summary: A novel modeling method is proposed to simulate the ductile deformation patterns resulting from viscous tectonic flow. Domains of different material properties are efficiently captured by the scalar level set function, which describes the signed distance to the domain interface. The level set field, paired with passive tracer particles, enables the modeling of the spatial distribution of lithological units, regional fold patterns of stratigraphic layers as well as finite deformation patterns (in terms of foliation/lineation patterns, strain history and strain intensity) in 3d block model, horizontal slices at certain depth level and vertical cross‐sections. Simulated cross‐sections and geological maps can be constructed along any direction and at any depth, thus allowing direct comparison between numerical models and field data obtained from geological mapping. Key Points: We implement a method for simulating tectonic flow in both 2d and 3d capable of predicting ductile deformation patternsAreas of different material properties are efficiently captured with the level set method on a stationary meshTracer particles record simulated strain ellipsoids, thus facilitating comparisons between model results and field data [ABSTRACT FROM AUTHOR]

The Pikwitonei Granulite Domain (PGD), located in the northwestern Superior Province, is one of the largest Neoarchean high‐grade metamorphic domains in the world, and is a key to understanding the Neoarchean crustal evolution of the Superior Province. Here we report results of a study on ultrahigh temperature (UHT) granulites with a sapphirine + quartz‐bearing peak assemblage from the Sipiwesk Lake area in the PGD. Three stages of metamorphic assemblage development are recognized based on petrographic observations: Pre‐peak stage is marked by garnet, sillimanite, K‐feldspar, and biotite inclusions within sapphirine and orthopyroxene. Peak stage is charactered by the typical UHT associations of sapphirine + quartz and sapphirine + orthopyroxene. The retrograde stage is represented by the retrograde formation of cordierite, biotite and sillimanite in the matrix. Phase equilibrium modelling based on the bulk compositions of sapphirine‐bearing granulites suggest that the rocks have experienced extensional UHT metamorphism in excess of 1035°C at pressures of 7.9–9.0 kbar, followed by isobaric cooling process. SHRIMP U–Pb dating of metamorphic zircons in sapphirine‐bearing granulite record the timing of the UHT event in the PGD with a weighted mean 207Pb/206Pb age of 2681 ± 13 Ma. This study in combination with other metamorphic P–T paths and age information reveals that this UHT metamorphism at 2.68 Ga in PGD was generated by upwelling asthenosphere due to slab break‐off in collision during the amalgamation of the Superior Province. [ABSTRACT FROM AUTHOR]

The Neoproterozoic magmatism along the Jiangnan Orogen preserves significant information for understanding the tectonic evolution of the South China Block (SCB). We conducted a systematic zircon U–Pb geochronological and whole‐rock geochemical study on the basalts from the Yingchuan Formation in the eastern Jiangnan Orogen, SCB. The basalts yielded a weighted mean 206Pb/238U age of 817 ± 13 Ma, enriched in Rb, Th, U, LREE and HFSE (e.g., Zr and Ti). The basalts have positive εNd(t) (+1.9 to +2.1) and high (87Sr/86Sr)i (0.69853–0.70737), indicating a slightly depleted mantle source. The high La/Nb (2.14–2.35) and La/Ta (28.6–33.3) ratios indicate a lithospheric mantle source for the basalts. Their high Ba/Yb (7.85–44.3) and Th/Yb (0.59–0.74) ratios and high absolute Nb contents (7.64–11.6 ug/g) indicate that the lithospheric mantle source has been metasomatized by melts and fluids derived from a subducted slab. The basalts are characterized by (La/Yb) N ratios (3.0–3.5) and Sm/Nd ratios (0.24–0.26), comparable to intra‐continental back arc basin basalts (BABBs). Their Ta/Yb (0.14–0.16) and Th/Yb (0.59–0.74) ratios are similar to those of Okinawa Trough basalts and contemporary mafic rocks formed in the back‐arc basin in the Jiangnan Orogen. Combined with their source features, we propose that the basalts were formed in a back‐arc basin setting. The identification of BABBs from the Yingchuan Formation shows that there were Neoproterozoic back‐arc basins in the south‐eastern Yangtze Block, indicating that the final assembly between the Yangtze and Cathaysia blocks did not occur before ca. 817 Ma. [ABSTRACT FROM AUTHOR]

The 290–280 Ma mafic Liuyuan Complex, embedded in the terranes constituting the southern edge of the Central Asian Orogenic Belt, has been interpreted to be either an ophiolite or an intracontinental large igneous province. Our detailed mapping shows that the Liuyuan Complex preserves an almost complete oceanic crustal section, with basal troctolite cumulates, varitextured gabbro affected by intense sub‐seafloor hydrothermal circulation, a newly discovered, and laterally‐continuous sheeted dyke complex, capped by basaltic pillows. This architecture is inconsistent with a continental rift‐layered intrusion model for the Liuyuan Complex, which we interpret as oceanic crust formed by seafloor spreading. The trace element ratios (Th/Yb, V/Ti, La/Sm, and La/Nb) of the lavas is consistent with a back‐arc basin environment. We suggest that the slab subducting to the north and forming the Ganquan arc system rolled back around 292 Ma, opening a back‐arc basin (the Liuyuan Complex). This oceanic basin started to close from ca. 281 Ma, with north‐dipping subduction under the accreted terranes constituting the southern active margin of Composite Siberia. The Liuyuan Complex was eventually obducted southwards over the Ganquan arc as part of the upper plate during the final closure of the back‐arc basin. [ABSTRACT FROM AUTHOR]

Fault geometry, kinematics, geophysics, the tectonic stress field and tectonic evolution of the Zhouwang fault in the southern Jiangnan tectonic transition zone of the Lower Yangtze region, eastern China are examined. Field observations show the fault is composed of a series of nearly E–W trending, N–S dipping faults, and four stages of tectonism (sinistral strike‐slip, thrust nappe, normal fault, and dextral strike‐slip) developed in turn. Geophysical data show that the fault trends almost linearly E–W along a flat, steep gravity gradient at shallow depth, with distinct gravity anomalies to the north and south and different in the north and south. Also, the deep part is characterized by northward dip and a gradual slowing down. Tectonic stress field analysis indicates that the fault experienced four tectonic movements: NNE–SSW compression, NNW–SSE compression, NEE–SWW extension, and E–W compression. Combined with regional tectonic background and previous research results, this indicates that: (1) the Zhouwang fault experienced sinistral strike‐slip movement during the Indosinian Period (260–200 Ma); (2) thrust nappes developed during the early Yanshanian Period (163–145 Ma); (3) a normal fault occurred in the late Yanshanian Period (125–65 Ma); and (4) dextral strike‐slip movement occurred in the Himalayan Period (ca. 50–37 Ma). The results reveal the tectonic evolution of the fault during Mesozoic deformation in the area, and also reveal the geological evolution and tectonic transformation of the Lower Yangtze region, which is key to our understanding of intracontinental deformation in eastern China. [ABSTRACT FROM AUTHOR]

The North Qinling Orogen underwent subduction and collision processes during the Palaeozoic, but the tectonic framework remains unclear. To investigate the tectonic evolution of the North Qinling Orogen, we selected the Devonian granites from the northeastern margin of the North Qinling Terrane. Integrated petrographic, geochemical, and geochronological studies, as well as Sr–Nd–Hf isotopic analyses, were carried out on the newly identified Devonian granites from the Hengjian area in the northeastern North Qinling Terrane, Qinling Orogenic Belt. Zircon laser ablation inductively coupled plasma mass spectrometry U–Pb dating reveals that these granites were crystallized at 396–387 Ma. The granite samples are metaluminous to weakly peraluminous (A/CNK = Al2O3/(CaO+Na2O+K2O) = 0.86 to 1.12), with high SiO2 (60.6–76.5 wt%) and high total alkaline (Na2O + K2O = 8.45–11.0 wt%) contents. The granites are enriched in Th, rare‐earth element, Zr, and Hf and depleted in Sr, Nb, Ta, P, Eu, and Ti. They are characterized by high Zr + Nb + Ce + Y contents (511–990 ppm) and 10,000*Ga/Al ratios (2.71–3.32), as well as high zircon‐saturation temperatures (TZr = 819–885°C, average = 845°C), which indicate that they are typical A‐type granites. The granites have low Y/Nb (0.39–0.67) and Yb/Ta (0.56–0.83) ratios, resembling those of the A1‐type granite, which indicates that they are formed in anorogenic settings. They also have low (87Sr/86Sr)i ratios (0.7055–0.7071) and negative εNd(t) values (−10.1 to −8.40) and variable zircon εHf(t) values (−8.46 to +14.7), with the two‐stage model ages of 2.0–1.8 Ga and 1.9–0.4 Ga, respectively. These geological features suggest that the granites of the Hengjian area were most likely generated by partial melting of mafic lower crust induced by asthenospheric ascent. The A‐type granites were generated in a continental rift environment during 396–387 Ma, corresponding to the closure of the Shangdan Ocean and the opening of the Palaeo‐Tethyan Ocean during the Early Devonian. [ABSTRACT FROM AUTHOR]

We carried out an integrated study of zircon U–Pb geochronology, Hf isotopes and geochemistry on the paragneisses and amphibolites from the Chencai area, South China. The detrital zircon ages of four paragneisses range from 2974 to 501 Ma with the main peak at ca. 820 Ma. The detrital materials with Neoproterozoic age may derive from the Jiangnan Orogen and those of Palaeo–Mesoproterozoic age may come from the Wuyi terrane. The youngest age indicates that the protoliths of the paragneisses were formed after ca. 501 Ma. The εHf(t) values (−20.6 to +20.9) of the detrital zircons suggest that the detrital materials of the protoliths are composed of old crustal and juvenile materials. The geochemical characteristics suggest that the protoliths of the paragneisses are greywackes, which formed in an active continental margin or continental island arc environment. The metamorphic ages of the three amphibolites are 428 ± 4, 430 ± 4, and 438 ± 3 Ma. The protoliths of the amphibolites are tholeiites, which can be divided into two groups. Group 1 is characterized by low ∑REE contents and (La/Yb)N ratios showing left‐inclined REE patterns and Nb, Ta depletion which resembles N‐MORB. Group 2 has higher ∑REE contents and (La/Yb)N ratios, with Eu negative anomalies showing affinity to E‐MORB. The data show that the Chencai Group is composed of oceanic crust remnants and continental crust materials, indicating it should be a subduction accretionary complex rather than a metasedimentary sequence and thus it cannot be regarded as the Precambrian basement of the Cathaysia Block. [ABSTRACT FROM AUTHOR]

The Jiangshan‐Shaoxing‐Pingxiang Fault (JSP Fault) is traditionally considered as the boundary between the Yangtze and Cathaysia blocks in South China. Whether the previously defined Shenshan and Kuli formations located along the JSP fault and near the Xinyu City, Jiangxi Province, are continuous strata or parts of a tectonic mélange is important for understanding the geological history of South China. A carbonaceous phyllite from the area, previously considered as part of the Neoproterozoic Shenshan and Kuli formations, is analyzed palynologically in this study. The Asteridium‐Comasphaeridium acritarch assemblage found in the slate can be correlated with the basal Cambrian Asteridium‐Heliosphaeridium‐Comasphaeridium (AHC) acritarch assemblage in Tarim and the Yangtze Block. The early Cambrian biostratigraphical age assignment for the carbonaceous phyllite indicates the presence of both Neoproterozoic and Cambrian rocks in the sedimentary package, and supports that the package is a part of tectonic mélange rather than a continuous Neoproterozoic strata. The Cambrian slate is the youngest known lithology in the mélange at present. [ABSTRACT FROM AUTHOR]

The nature of the Precambrian basement in the Cathaysia Block of South China is controversial, which inhibits our understanding of the pre‐Devonian tectonic evolution of the region. In this study, a suite of amphibolites and marbles in northern Fujian area located in the north of the Cathaysia Block were subjected to LA–ICP–MS U–Pb zircon geochronological and geochemical analyses. Results show that the protolith of the amphibolite formed after ca. 459 Ma, and its metamorphism happened at ca. 429 Ma. The protolith of the marble was deposited after ca. 518 Ma, and its metamorphic age is ca. 437 Ma. The amphibolites are divided into two groups based on geochemical data. Group 1 has an OIB‐like feature that might have formed in an environment characterized by oceanic islands and seamounts. Magmas associated with Group 1 were derived from an enriched mantle source with OIB characteristics. The protolith of Group 2 shows IAB feature that formed in an island arc environment. Marbles are interpreted to represent metamorphosed marine carbonate rocks. Integration of geochronological and geochemical study indicates that the marble and amphibolite should be an early Palaeozoic oceanic island–seamount association. It suggests the Cathaysia Block underwent oceanic subduction during collisional orogenesis in the early Palaeozoic. This subduction is thought to have initiated prior to ca. 437 Ma. The U–Pb zircon ages of younger intrusive granites indicate that final amalgamation occurred before ca. 392 Ma. During this process, east and west Wuyi were amalgamated to form the unified Cathaysia Block. Thus, it suggests that there was no unified pre‐Devonian basement in the Cathaysia Block. The pre‐Devonian tectonic setting of the Cathaysia Block was an accretionary orogeny. [ABSTRACT FROM AUTHOR]

Abstract: Large‐scale magmatism affected the Tongbai‐Dabie orogenic belt during post‐collisional lateral tectonic extension in the Cretaceous, which was suggested to account for the widespread deformation and migmatization in the Tongbai‐Dabie complexes. However, it cannot explain the most deformations in the shear zones. The northwest‐southeast shear zones are developed around or wrapped the Tongbai‐Dabie complexes. They play an important role for the interpretation of the tectonic evolution of the Tongbai‐Dabie orogenic belt. By a systematically observation and description of the geometry and kinematics of these shear zones, we found that the shear zones to the north dip NE and have a uniform sinistral shear sense, the shear zone to the south dips SW and has a uniform dextral shear sense, and the shear zones at the core are sub‐horizontal and have a uniform top‐to‐NW sense of shear. Combining with the comparison of previous and our geochronological studies, we interpret these associations as indicating that these shear zones were originally a single, more flat‐lying and sub‐horizontal shear zone with a uniform top‐to‐NW shear sense before the folding‐doming of the Tongbai‐Dabie complexes and suggest that the Tongbai‐Dabie orogenic belt experienced a uniform top‐to‐NW orogen‐parallel extension in the ductile lithosphere before the widespread magmatism in the Cretaceous. [ABSTRACT FROM AUTHOR]

The article presents a research report conducted on the Nd (Neodymium) isotopic characteristics of granitoids rocksfrom the New foundland Appalachians. It mentions the general characteristics and composition of the granitoids which include its spatial-temporal variation and deep crustal composition. The National Natural Science Foundation carried out field surveys of granite rocks for the characteristics.

This article expands upon detrital zircon geochronology with a sampling and analysis strategy dating variably tectonized granitoid conglomerate clasts. Its purpose is to elucidate details of the provenance's tectonomagmatic history from deformation-relative age distributions. The method involves bulk samples of clasts, sorted based on the degree of internal ductile deformation. Isolating granitoid clasts, we divide them into three subsets: undeformed, slightly deformed, and deformed. Laser ablation, inductively coupled plasma mass spectrometry U-Pb geochronology is performed on zircon separates of each subset. Our case study, involving the Permian Hongliuhe Formation in the southern Central Asian Orogenic Belt, analyzes each of the three clast subsets, as well as sandstone detrital samples, at three stratigraphic levels and yields a profile of the unroofed provenance. Clast age distributions exhibit different, wider-age spectra than sandstone samples, an effect of proximity to the respective provenance. They indicate a minimal lag time, implying rapid exhumation rates, whereas sandstone data alone would indicate a 90 Myr lag time. Early Paleozoic arc-building episodes appear as Ordovician peaks in sandstone data and Silurian-Devonian peaks in clast data, indicating a younging of magmatism toward proximal provenance. A magmatic hiatus starts in the Devonian, correlating with the latest age of deformed clasts, interpreted as timing of collisional tectonics. The detailed age spectra provide regional tectonic context and interpretation of processes, as well as more robust provenance interpretation than could be determined from sandstone samples alone. The variably tectonized clast detrital geochronology method removes human sampling bias and the practical limits of studying regional granitoid distributions. [ABSTRACT FROM AUTHOR]

The Chinese Altai, a typical region of the Central Asian Orogenic Belt (CAOB), has been envisaged as subduction-accretion complex or Precambrian microcontinent. Thick metasedimentary rocks crop out extensively in the Central Altai and Qiongkuer domains, but their depositional age is not well constrained. Most workers have regarded these sedimentary rocks as passive continental margin sediments deposited on a Precambrian microcontinent. However, our studies of U-Pb and Hf isotopes of detrital zircons separated from these rocks reveal that a predominant population has 206Pb/238U ages between 460 and 540 Ma and most grains of this population possess positive εHf(t) values. Zircons of the population have oscillatory zoning, possess high Th/U ratios, and are enhedral to subhedral crystals with sharp edges, showing short distance of transportation from an igneous provenance. The above results indicate that these metasedimentary rocks were deposited on an active continental margin not prior to the Middle Ordovician. Therefore the Chinese Altai orogen was an active continental margin in the Early Paleozoic, which is inconsistent with a Precambrian microcontinent model and reveals an arc accretionary history. [ABSTRACT FROM AUTHOR]

Opinion. Comments on Gregory Lynch's article `Tectonic Burial, Thrust Emplacement, and Extensional Exhumation of the Cabot Nappe in the Appalachian Hinterland of Cape Breton Island, Canada,' published in a 1996 issue of `Tectonics.' Evidence in the Eastern Cape Breton Highlands for a folded highlands shear zone.

The article focuses on study with formation of Shirenshan block and its relationship with Luoluan fault with the study of Mesozoic intracontinental orogeny of the north Qinling. It mentions geological mapping with structural analysis and other conventional construction methods and vorticity analysis and tectonic chronology test. It also mentions analyze shear type, formation time and the protolith or metamorphic ages and strain decomposition theory.