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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]

Hardly any previous studies have focused on the granitic dykes which intrude into the Paleoproterozoic Liaohe Group in the Liaodong Peninsula, northeast of the North China Craton. In situ zircon U-Pb dating, Lu-Hf isotopic and geochemical analyses on three representative monzogranite dykes were taken in this study. These dykes have relatively high content of SiO2 (72.20%–74.78%) and K2O (2.83%–6.37%), and have characteristics of high-K calc-alkaline to shoshonite series. Two dyke samples have I-type granite features and have high Sr/Y ratios and positive Eu anomalies, showing an adakitic feature. Another dyke has a high ratio of Ga/Al, but has a low Zr saturation temperature, which differs from the typical A-type granite. Zircon grains from these three dykes have typical magmatic zoning in CL images and yield consistent U-Pb ages of ~1859–1852 Ma, which are interpreted as the crystallization ages of these dykes. Hf isotopic analyses yield mainly negative εHf(t) values and TDM2 ages of 2782–2430 Ma, similar to those of the 2.2–2.1 Ga granitoids and meta-sedimentary rocks (the Liaohe Group), indicating these monzogranitic dykes may have been sourced from melting of Paleoproterozoic granitoids and meta-sedimentary rocks. The monzogranitic dykes were generated under a post-collisional geological setting after the Jiao-Liao-Ji orogeny process. [ABSTRACT FROM AUTHOR]

Special Issue on Tectonic, Magmatic and Metallogenetic Evolution of the Central China Orogenic Belt. [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]

The Neoarchean Pukaskwa batholith consists of pre-, syn-, and post-tectonic phases emplaced over an interval of 50 million years. Pre-tectonic phases are broadly synvolcanic and have a high-Al tonalite-trondhjemite-granodiorite (TTG) affinity interpreted to reflect derivation by partial melting of basaltic crust at lower crustal or upper mantle depths. Minor syn-tectonic phases slightly post-date volcanism and have geochemical characteristics suggesting some involvement or interaction with an ultramafic (mantle) source component. Magmatic emplacement of pre- and syn-tectonic phases occurred in the midcrust at paleopressures of 550-600 MPa and these components of the batholith are thought to be representative of the midcrust underlying greenstone belts during their development. Subsequent to emplacement of the syntectonic phases, and likely at approximately 2680 Ma, the Pukaskwa batholith was uplifted as a structural dome relative to flanking greenstone belts synchronously with ongoing regional sinistral transpressive deformation. The driving force for vertical tectonism is interpreted to be density inversion (Rayleigh-Taylor-type instabilities) involving denser greenstone belts and underlying felsic plutonic crust. The trigger for initiation of this process is interpreted to be an abrupt change in the rheology of the midcrust attributed to introduction of heat from the mantle attendant with slab breakoff or lithospheric delamination following the cessation of subduction. This process also led to partial melting of the intermediate to felsic midcrust generating post-tectonic granitic phases at approximately 2667 Ma. We propose that late density inversion-driven vertical tectonics is an inevitable consequence of horizontal (plate) tectonic processes associated with greenstone belt development within the Superior Province. Le batholite neeoarcheeen de Pukaskwa comprend des phases pre-, syn- et post-tectoniques mises en place durant une peeriode de 50 Ma. Les phases pre-tectoniques sont largement synvolcaniques et elles ont une affinite Al et TTG (<>) elevee qui est interpretee comme etant le reflet de la derivation par fusion partielle d'une croflte basaltique a des profondeurs de croflte inferieure ou de manteau superieur. Des phases syntectoniques mineures sont leegerement plus tardives que le volcanisme et elles ont des caracteristiques geochimiques qui suggerent une certaine implication ou interaction avec une composante de source ultramafique (manteau). La mise en place magmatique des phases pre;- et syntectoniques a eu lieu dans le milieu de la croflte a des paleeopressions de 550-600 MPa et ces composantes du batholite seraient representatives des ceintures de roches vertes sous-jacentes, au centre de la croflte durant leur deeveloppement. Apres la mise en place des phases syntectoniques, et probablement vers 2680 Ma, le batholite de Pukaskwa a ete souleve en dome structural par rapport aux ceintures de roches vertes de part et d'autre, et ce, de maniere synchrone avec la deformation transpressive regionale senestre en cours. La force motrice derriere le tectonisme vertical serait une inversion de densite (instabilitees de type Rayleigh-Taylor) impliquant les ceintures de roches vertes plus denses et la croflte felsique plutonique sous-jacente. Le declencheur pour l'initiation de ce processus est interprete comme etant un changement abrupt dans la rheologie de la croflte moyenne attribue a l'introduction de chaleur du manteau auxiliaire a la rupture de la dalle ou a la delamination lithospherique suivant la cessation de la subduction. Ce processus a aussi mene a une fusion partielle de la croflte moyenne intermediaire a felsique generant des phases granitiques post-tectoniques vers 2667 Ma. Nous proposons que la tectonique verticale poussee par l'inversion de densite tardive soit une consequence inevitable des processus tectoniques horizontaux (plaques) associesau developpement de ceintures vertes dans la Province du Superieur. [Traduit par la Redaction], Introduction Large, intermediate to felsic plutonic complexes of batholithic dimensions are a major component of the Superior Province and Archean cratons in general, but are poorly understood compared to the [...]