Tectonic System Research Articles

ANALISIS PARAMETER KEGEMPAAN (NILAI-a DAN NILAI-b) DI WILAYAH BUSUR BANDA

Some areas in Indonesia are earthquake-prone areas, one of which is the Banda arc. The Banda arc has a complete tectonic system and is also an area with a high level of seismicity. One of the earthquake disaster mitigation efforts is by analyzing the a-values and b-values which are seismotectonic parameters. The a-values and b-values can be analyzed through the Gutenberg-Ritchter equation through the frequency-magnitude distribution. The gradient of the frequency-magnitude distribution is the b-value which is a stress distribution constant which indicates the level of fragility of the rocks in the area, while the a-value indicates seismic activity which is the seismicity constant. In determining the a-value and b-value depends on the Magnitude completeness (Mc). This study uses earthquake data from the USGS catalog from 2015–2020 and then uniformizes the magnitude to magnitude moment (Mw), declusters the earthquake catalog to eliminate the effects of foreshocks and aftershock to obtain the main earthquake data through ZMAP 6.0 software. After that, do a magnitude-frequency distribution plot to determine the completeness of the data in order to obtain the completeness of magnitude (Mc) which can be used to determine the a-value and b-value using ZMAP 6.0 software. The result of this research is the value of Magnitude Completeness (Mc) is 4.5, while the a-value is 9,07 and the b-value is 1,33. For the spatial variation of a-values and b-values, there are areas with a low a-value of 7 and a low b-value of 1,2 which have a chance of a large earthquake in the future due to the accumulation of energy that causes a high level of stress in the area.
 

Alpine convergence record in the Carboniferous Badstub Formation, Upper Austroalpine basement nappes, Austria

ABSTRACT Within the Carboniferous of Nötsch, the Badstub Formation is a clastic sequence of the Upper Austroalpine basement nappes exposed few kilometres north of the Periadriatic Fault System (Carinthia, Austria). Although these rocks preserve pristine sedimentary features, multi-scale structural analysis disclosed a syn-metamorphic foliation in fine-grained rocks, sets of mineralized faults, veins, and corona textures. Vein fillings and coronas contain equilibrium mineral assemblages with prehnite, pumpellyite, chlorite, phengitic mica, winchite, and riebeckite. Thermodynamic modelling and geothermometry constrain metamorphic conditions at 260–310°C and 0.25–0.50 GPa that are consistent with a temperature/depth ratio of about 20°C km−1. In a 2D thermomechanical model this thermal state is reached either in the upper or lower continental plate during convergence. Thus, during the Alpine convergence, the Badstub rocks were buried from the shallow crust at depths between 13 and 18 km either by ablative oceanic subduction or by continental subduction of the passive margin, and eventually stacked into the orogenic wedge at the Adria margin. During the downward and upward paths, the Badstub rocks were translated as a coherent poorly strained block. This first quantitative constraint on metamorphism for these Carboniferous rocks is consistent with the Upper Austroalpine basement nappes being a tectonic system that recorded the Alpine convergence under eclogite to prehnite–pumpellyite facies conditions.

Connection of Kryvbas tectonics with natural and technogenic seismicity

Purpose. Studying the tectonic features of the structure of the earth’s crust of Kryvyi Rih-Kremenchuk suture zone to clarify the nature of the origin of seismic events in the Kryvbas. Methodology. To analyze and generalize the data on the Kryvbas seismicity with reference to large-scale geological and tectonic maps of exploration work. To study its tectonic structure based on geological, geophysical studies and drilling of Kryvyi Rih superdeep well. Findings. In the period 2011–2021, about 1,200 seismic events were recorded on the territory of Kryvbas, the majority of which had a minor magnitude  2.0. Among them there were identified 13 powerful industrial explosions from mb = 2.7–3.5 and 20 earthquakes of tectonic origin with mb = 2.1–4.5. Powerful explosions in mines predominantly induce earthquakes. In recent years, local earthquakes began to occur in tectonic fault zones outside the ore mining area, which indicates a change in the elastic-deformation state of the geological environment. The analysis of the attributes of local earthquakes and their locations suggests that Kryvyi Rih tectonic system and the entire eastern flank of the earth’s crust of the West Inhulets-Kryvyi Rih-Kremenchuk suture zone are geodynamically active structures, where the processes of thrust and shear tectonics are also observed on a recent geological time scale. Originality. A detailed analysis of the earthquakes shows that some of them occur at significant depths in the zones of tectonic faults outside of Kryvbas. At the same time, faults in separate directions are activated, where brittle deformations and viscous-plastic formations are manifested in the past geological time. The location of local earthquakes made it possible to single out two sections and five linear zones of seismic activity in the region. Practical value. Based on the results from this research it is possible to create an applied model of the tectonic section of the earth’s crust to solve the problems of evolution and geodynamics of the lithosphere of the Ukrainian shield, mountain geology and to optimize mining. The identified faults of active inherited development are important in determining the development paths for quarries and mines in Kryvbas.

Innovative design solutions for contemporary Tou-Kung based on topological optimisation

Tou-Kung, which is pronounced in Chinese and known as Bracket Set (Liang & Fairbank, A pictorial history of Chinese architecture, 1984), is a vital support component in the Chinese traditional wooden tectonic systems. It is located between the column and the beam and connects the eave and pillar, making the heavy roof extend out of the eaves longer. The development of Tou-Kung is entirely a microcosm of the development of ancient Chinese architecture; the aesthetic structure and Asian artistic temperament behind Tou-Kung make it gradually become the cultural and spiritual symbol of traditional Chinese architecture. In the contemporary era, inheriting and developing Tou-Kung has become an essential issue. Several architects have attempted to employ new materials and techniques to integrate the traditional Tou-Kung into modern architectural systems, such as the China Pavilion at the 2010 World Expo and Yusuhara Wooden Bridge Museum. This paper introduces the topological optimisation method bi-directional evolutionary structural optimisation (BESO) for form-finding. BESO method is one of the most popular topology optimisation methods widely employed in civil engineering and architecture. Through analyzing the development trend of Tou-Kung and mechanical structure, the authors integrate 2D and 3D optimisation methods and apply the hybrid methods to form-finding. Meanwhile, mortise and tenon joint used to create stable connections with components of Tou-Kung are retained. This research aims to design a new Tou-Kung corresponding to “structural performance-based aesthetics”. The workflow proposed in this paper is valuable for Architrave and other traditional building components.

Spatial–temporal influence of the Mongol–Okhotsk and Palaeo–Pacific tectonic systems in NE China: Evidence from geochronological and geochemical data of felsic rocks in the east‐Central Jilin Province and southern Great Xing'an Range

The temporal and spatial extents of the Palaeo–Pacific and Mongol–Okhotsk tectonic systems, which together dominated the Mesozoic tectonics of NE China, still remain unclear. Here, we present new zircon U–Pb ages, isotopic analyses and whole‐rock major‐ and trace‐element data for felsic rocks from west and east Songliao Basin to explore the above question. The granites in Shancheng area formed between 176 and 164 Ma and have εHf(t) values of −22.09 to −7.59 with a TDM2 age range of 3622–2336 Ma. The granites are dominated by adakites and I‐type granite whose primary magma is derived from a thickened ancient crust. The rhyolites in Wushijiazi area formed between 151 and 141 Ma and have εHf(t) values of 3.34–12.38 with a TDM2 age range of 517–1328 Ma. They are A‐type granite and have a flat rare‐earth‐element (REE) pattern with obvious negative Eu anomalies, suggesting they were derived from partial melting of lower crustal rocks. The above findings indicate that the middle–late Jurassic granite in the Shancheng area formed in a compression setting related to the subduction of the Palaeo–Pacific Plate beneath the Eurasian continent and the Late Jurassic to early Cretaceous rhyolites in Wushijiazi area formed in an extensional setting related to the collapse of the Mongol–Okhotsk belt. In combination with regional geologic data, we conclude that the Palaeo–Pacific tectonic system mainly affected the east side of Songliao Basin, while the Mongol Okhotsk tectonic system mainly affected the Erguna Block, through the GXAR to the northern margin of the North China Craton (NCC).

Numerical Simulation of Underground Mining-Induced Fault-Influenced Rock Movement and Its Application

The F317 fault, as a major tectonic zone in the Jianshan mine area, influences the geotectonic features and geomechanical properties of the mine area. Mining operations need to be conducted within these tectonic systems, so it is important to fully study and understand the characteristics and evolution of these tectonic systems to develop reasonable mining plans and safety measures. Aiming at the problem that the existence of the F317 fault affects the stability of the west road during the mining of the security pillar at The Jianshan underground mine in Panzhihua Iron Mine, the mechanical model of the fault surface was established through the theory of material mechanics. The mechanical criterion of fault slip during the security pillar retrieval process was obtained and combined with the contact surface theory in the numerical analysis software FLAC3D. Two numerical calculation models with and without the F317 fault were established to analyze the change characteristics of the maximum tensile stress and displacement of the road protection zone under different simulation scenarios. The influence of the fault’s presence on the surface road’s stability during the security pillar retrieval process was obtained. The study results show that changes in positive and shear stresses at the fault face caused by the security pillar retrieval process are the main factors influencing the fault slip. The upper side of the fault tends to slip along the fault face during the security pillar retrieval process, which theoretically prevents the transfer of subsidence displacement caused by underground mining to the roadside (foot side of the fault). The presence of the F317 fault has less effect on the tensile stresses at the road protection zone. Still, the fault allows the tensile stresses to be concentrated at the top and bottom of the quarry and at the isolated pillar, which is more likely to cause the rock to be stretched and squeezed. Without the F317 fault, the maximum subsidence displacement at the road protection zone is 30.59 mm, the maximum X-directional displacement is 42.17 mm (both of which are greater than the safe displacement limit by 20 mm), and the maximum Y-directional displacement is 19.75 mm, which is less than the safe displacement limit by 20 mm. Compared with the case without the F317 fault, the displacement at the road protection zone with the F317 fault is smaller, with a maximum subsidence displacement of 16.92 mm, a maximum X-directional displacement of 19.63 mm, and a maximum Y-directional displacement of 3.35 mm, all of which are less than the safe displacement limits. Therefore, the presence of the F317 fault provides some protection to the west side of the road from collapse due to underground mining.

Southward continuation and slab rollback of the Neotethyan arc−back-arc system: Insights from Eocene mafic intrusions from North Sumatra, SE Asia

The Neotethyan subduction and collision with the Asian, Indian, and Australian plates is evidenced by a giant Andean-type arc system and a remarkable Neotethyan igneous belt along the southwestern Eurasian margin. However, the southward extent, and cause, of Neotethyan subduction is poorly understood. Here, a zircon U-Pb dating and whole-rock geochemical study of two groups of Eocene (50−48 Ma) mafic intrusions from Tangse, North Sumatra, helps to unravel the Neotethyan subduction story. Group 1 consists of diabase samples, which have mid-oceanic-ridge− and arc-like geochemical affinities, with low chondrite-normalized La/Yb(cn) (∼0.6) ratios and a high measured εNd(t) value of +8.7. Such geochemical signatures indicate that the magmatic rocks were derived from a refractory depleted mantle source that was metasomatized by slab melts. Group 2 consists of gabbro-diorites, which are enriched in the large-ion lithophile elements and depleted in some high field strength elements. These samples have high La/Yb(cn) (2.9−6.6), low Nb/La(cn) (0.2−0.3), εNd(t) values of +1.1 to +5.0, and εHf(t) values of +8.8 to +15.3. Group 2 samples were produced by the melting of a depleted mantle wedge metasomatized by slab fluids. The magmatism provides evidence for the southern continuation of the Neotethyan igneous belt and tectonic system, whereby slab rollback triggered melting and upwelling in an arc−back-arc geodynamic system from South Tibet to SE Asia.

Spatial distribution of porphyry copper deposits in Dehaj terrain: Implications for exploration

Magmatism is triggered and controlled by tectonic systems, and thus these processes play an irrefutable role in the deposition and emplacement of hydrothermal mineral systems. It is, therefore, paramount to recognize the tectonic processes that are genetically associated with hydrothermal mineral systems. This study seeks to address this caveat by recognizing the main tectonic processes that have controlled the distribution of porphyry copper deposits in Dehaj terrain, Central Iran. For this purpose, the spatial association of 31 known porphyry copper deposits, faults, and fractures were evaluated by fry, fractal, and distance-distribution analyses. The results of fry analysis revealed that mineralization has distributed through three different trends, namely NE, NW, and NS, which shows a clear association with the fault systems presented in the area. Also, the fractal method applied demonstrated that structural controls on mineralization have operated on two different scales, regional and local scales. Distance-Distribution analysis was further used to assess the spatial correlation between known porphyry Cu deposits and fault traces, supplementing the results of fry and fractal analyses by quantitative measurements. The synthesis of the results of these three methods shows that the NW-trending faults have plausibly controlled the magmatism at a regional scale; nevertheless, NE- and N-trending faults have probably operated at local scales controlling the channeling and emplacement of mineral-bearing fluids.

The proto-type basin and tectono-paleogeographic evolution of the Tarim basin in the Late Paleozoic

The Tarim basin is a large composite and superimposed sedimentary basin that has undergone complex multi-period and polycyclic tectonic movements. Understanding the proto-type basin and tectono-paleogeographic evolution of this complex superimposed basin is important for understanding the basin-mountain coupling and dynamical mechanisms of the Paleo-Asian and Tethys tectonic systems as well as hydrocarbon exploration and development. Based on previous works, together with the recent exploration, and geological evidences, three global plate tectonic pattern maps, four Tarim proto-type basin maps (in present-day geographic coordinates) and four regional tectono-paleogeography maps (in paleogeographic coordinates) during the Late Paleozoic are provided in this paper. Based on these maps, the proto-type basin and tectono-paleogeographic features of the Tarim basin during the Late Paleozoic are illustrated. The Devonian to Permian is an important period of terranes/island-arcs accretion and oceanic closure along the periphery of the Tarim block, and a critical period when the polarity of Tarim basin (orientation of basin long-axis) rotated at the maximum angle clockwise. During the Late Paleozoic, the periphery of the Tarim block was first collisional orogeny on its northern margin, followed by continuous collisional accretion of island arcs on its southern margin: on the Northern margin, the North and South Tianshan Oceans closed from East to West; on the South-Western margin, the Tianshuihai Island Arc gradually collided and accreted. These tectonic events reduced the extent of the seawater channel of the passive continental margin in the Western part of the basin until its complete closure at the end of the Permian. The Tarim basin was thus completely transformed into an inland basin. This is a process of regression and uplift. The Southwest of the Tarim basin changed from a passive to an active continental margin, through back-arc downwarping and eventually complete closure to foreland setting. The intra-basin lithofacies range from shelf-littoral to platform-tidal flat to alluvial plain-lacustrine facies. The tectonic-sedimentary evolution of the Tarim basin is strongly controlled by peripheral geotectonic setting.

Fluid evolution and ore genesis of the A'gui Cu deposit in southern Great Xing'an Range, Northeast China: Evidence from fluid inclusion and C–H–O–S–Pb isotopes

The A'gui Cu deposit is located in the eastern slope of the southern Great Xing'an Range (SGXR), and it is a vein-type Cu deposit spatially and temporally related to the Cretaceous monzogranite which intruded Pingshan Formation. Vein-type Cu orebodies are mainly hosted in the NE and nearly EW faults. Previous studies on the A'gui deposit mainly focused on geological exploration, and there was no study on its fluid evolution and genesis. Therefore, we carried out conducted fluid inclusion and stable isotope (C–H–O–S–Pb) analysis to study the fluid evolution, fluid and ore-forming material sources and genesis of the A'gui deposit. According to the field investigations and mineral crosscutting relationships, four paragenetic stages were identified: quartz–pyrite–chalcopyrite–pyrrhotite–arsenopyrite ± magnetite (Stage I), quartz–pyrite–chalcopyrite (Stage II), quartz–chalcopyrite ± pyrite–sphalerite–galena (Stage III) and carbonate ± quartz (Stage IV). From Stage I to Stage II, the assemblage of fluid inclusions (FIs) in quartz is characterized by the development of daughter mineral–bearing three–phase FIs (SL–type), vapour FIs (V–type), vapour–rich two–phase aqueous FIs (LV–type) and liquid–rich two–phase aqueous FIs (VL–type). Only VL–type FIs appeared in the Stage III quartz and Stage IV calcite. The homogenization temperatures of FIs in stages I, II, III and IV are 329–390 °C, 255–336 °C, 166–244 °C and 120–157 °C, with salinities of 3.37–45.33 wt%, 3.53–39.76 wt%, 4.17–7.86 wt% and 3.37–7.15 wt% NaCl eqv., respectively. The fluid inclusion type assemblage suggested that obvious fluid boiling occurred in the Stage I and Stage II. Fluid boiling may be the reason for the precipitation of useful minerals. According to the HO isotope analysis of stages I–II quartz (δ18OH2O = −2.1 to 3.2 ‰, δDV–SMOW = −128.4 ‰ to −110.6 ‰), the fluid was originally magmatic water. From Stage III to Stage IV (δ18OH2O = −12.3 to −2.3 ‰, δDV–SMOW = −129.6 ‰ to −104.2 ‰), the HO isotope value is obviously close to the meteoric water line, indicating that meteoric water is mixed with evolved magmatic solutions. The ore–forming fluid of the A'gui deposit represents a medium–high temperature NaCl-H2O magmatic hydrothermal system. The C isotope compositions (δCV–PDB = −5.74 ‰ to −4.76 ‰) in stage IV indicate that the C in the fluid was derived from a magmatic source and was affected by meteoric water. In addition, the measured S isotope compositions in stages I–III of the hydrothermal fluids (δ34SV–CDT = 2.2 to 3.7 ‰) indicate that S mainly comes from granitic magma. Further, the Pb isotope (206Pb/204Pb = 18.276–18.367, 207Pb/204Pb = 15.52–15.556, 208Pb/204Pb = 38.157–38.193) in stages I–III indicate that the ore-forming materials are derived from the mixture of mantle and orogenic material. In summary, this study showed the A'gui is a typical magmatic hydrothermal vein-type Cu deposit that related to Cretaceous monzogranite formed under the joint constraints of Mongolia-Okhotsk Ocean and Paleo-Pacific Ocean tectonic system. Fluid boiling and mixing are the main ore-forming mechanism.

SEISMIC IMAGING BENEATH SUMATRA ISLAND AND ITS SURROUNDINGS, INDONESIA, FROM LOCAL-REGIONAL P-WAVE EARTHQUAKE TOMOGRAPHY

Sumatra Island and its surroundings, Indonesia, are one of the most active tectonics in the world. The Aceh-Andaman earthquake, one of the most destructive earthquakes in the world, occurred there. It has attracted many earth scientists to apply various methods, including seismic tomography, to understand the island’s subsurface structure and tectonic system. This study is the first to delineate subsurface imaging beneath the island and its surroundings using a local-regional earthquake catalogue from the Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG) seismicnetwork. The tomographic imaging of P-wave (Vp) conducted in this study has successfully delineated subduction slabs (high Vp), partial melting zones (low Vp), volcanic arcs (low Vp), and Sumatran Fault zones (low Vp). The relationship between the subduction zone and the volcanic arc on the island can be seen on several vertical sections where a partial melting zone occurs at a depth of about 100 km, which functions as magma feeding for some volcanoes on the island. The oceanic slab model also exhibits a more pronounced and steeper slope towards the southern regions of Sumatra Island, possibly attributed to the slab’s aging process in that direction. The results highlight the importance of the BMKG seismic network in imaging local-regional subsurface structures beneath Indonesia’s archipelago, especially for the main islands such as Sumatra.

Using Sustainable Tectonics to Create a Long-lasting Architectural Framework with Artistic Dimensions and Expressive Design

Throughout history, architecture has changed to reflect the increasing expressive capacities of ideas, elements, and structural systems as a result of this development, explains the development of structural systems as a result of the accumulation of construction and architectural experiences, and thus how structural thought transforms from a purely functional perspective. Structural tectonic to generate closed or semi-closed architectural spaces fulfills functional requirements and achieves structural and aesthetic conditions without sacrificing the role of shaping architecture and structural cohesiveness. The goal of the research is to investigate new architectural design methodologies emerging from the combination of tectonic systems and sustainable architecture to better understand tectonic architecture patterns in both traditional and digital forms. Tectonics organizes the analytical criteria for analyzing the constituent layers of architecture's formal structure in both designs and practice. By analyzing the theoretical and practical aspects and developing a clear mechanism to achieve a distinctive expressive sustainable architecture by integrating traditional tectonic factors in traditional sustainable practices and digital tectonic factors in technical sustainability, the study provides a conceptual framework under the theme of Sustainable Tectonics to define the formal structure of sustainable designs, traits, and layers detectable in sustainable architectural design. The study looked at key analytical features that may be utilized to analyze the underlying assumptions systematically. The analytical technique is a research strategy.

Direct Evidence for Dextral Shearing in the Shanxi Graben System: Geologic and Geomorphologic Constraints From the North Liulengshan Fault

AbstractThe Shanxi Graben System (SGS) is one of the first‐order Cenozoic tectonic features in North China. Understanding the kinematics of this tectonic system is crucial for deciphering the mechanism of continental rifting and the deformation pattern across North China. Although the SGS has long been thought to be a right‐lateral, transtensional shear zone, the geologic and geomorphologic evidence for dextral strike‐slip along its internal faults was slim and even controversial. Field investigations, interpretations of satellite imagery, and construction of decimeter‐scale digital elevation models from unmanned aerial vehicle surveys were used in this work to investigate the tectonic geomorphology of the eastern segment of the North Liulengshan Fault (NLSF) in the northern SGS. Although this fault segment was previously thought to be a pure normal fault, the presence of geomorphic features such as right‐laterally offset terrace risers and gullies, along with an analysis of fault‐slip data, suggests a component of right‐lateral strike‐slip displacement. Combined with optically stimulated luminescence dating of offset fluvial terraces, the late Quaternary right‐lateral strike‐slip and vertical slip rates of this fault segment are both estimated to be ∼0.2–0.3 mm/yr. The discovery of dextral strike‐slip along the NLSF provides compelling direct evidence for determining the dextral transtensional kinematics of the SGS. This puts new constraints on our knowledge that the evolution of the SGS is primarily driven by the outward expansion and growth of the Tibetan Plateau and supports the “bookshelf” rotation kinematic model for North China.

Seismicity clustering of sequence phenomena in the active tectonic system of backthrust Lombok preceding the sequence 2018 earthquakes

Seismicity clustering of sequence phenomena in the active tectonic system of backthrust Lombok preceding the sequence 2018 earthquakes

Geophysical evidences on reactivation of NE faults in southern Arabian Shield and its tectonic implications

The Eastern flank of the Red sea represents an uplifted Precambrian basement that is known as the Arabian Shield. Different tectonic events were activated since the collisions among continental fragments that occurred during the period 630–550 Ma, showing very old NE ophiolite-suture zones, North trend shear zones, belts, folds, and NW Sinistral fault system known as Najd shear zones. Thus, heterogeneities and inherited faults are expected in the old basement; however, based on surface observations, NE trend faults are not described in the Arabian Shield. Despite the inconsistency with the background tectonic model of the Red Sea rifting, recent seismological studies show that active NE faults may exist in western Arabian Shield. This study aims to investigate and map the fault system in southern Arabian Shield and then better understand the tectonic system acting in the region. We provide an analysis that incorporates gravity, magnetic, and seismological data in Namas area, where earthquake sequence occurred in 2017. Using the regional-residual separation, filtering and edge detector function techniques, we identified NE trend inherited faults within the Precambrian basement that might be seismically active, as shown by the obtained distribution of epicenters and focal mechanism solutions of strike-slip style among the 2017 Namas Earthquake sequence. This result emphasizes the preexistence of a potential local tectonic process that is incongruous with the regional stress regime.

Newly discovered youngest UHT metamorphism on Earth, Western Sulawesi, Indonesia

Ultrahigh-temperature (UHT) metamorphism represents an extreme crustal thermal event with peak conditions exceeding 900 °C at 7–13 kbar. In the modern-style plate tectonic system, records of the UHT metamorphism are relatively rare due to the secular cooling of Earth. In the Palu region of Western Sulawesi, we newly discovered a series of HT-UHT metamorphic rocks including amphibolite, granulite, eclogites and gneiss. Of them, two granulite samples (18CS14-2, 18CS14-4) with high garnet content (>50 mol%) are chosen for petrographic observation, phase equilibrium modelling, and zircon U-Pb dating. These rocks are characterized by a relic M1 assemblage of Grt + Ky + Bt + Rt and a M2 assemblage of Grt + Sil + Pl + Spl + Crd ± Qtz + Ilm + melt. Phase equilibrium modelling based on effective bulk compositions yields UHT conditions of 7.2–8.5 kbar/940–1080 °C (18CS14-2) and 7.0–7.3 kbar/1000–1040 °C (18CS14-4). U-Pb analysis reveals two generations of metamorphic zircon with evolving REE content that is intimately related to garnet growth and decomposition. Zircon age of 36–5.3 Ma is ascribed to syn- to post-M1 metamorphism, whereas the young zircon age of 5.1–3.8 Ma is linked to syn- and post-M2 stage. The UHT metamorphism was probably the consequence of the upwelling of asthenospheric mantle triggered by post-collisional delamination of lithosphere in the Miocene-Pliocene (ca. 5 Ma). It could represent the youngest known UHT metamorphism on Earth.

Volcano‐Tectonic Evolution of the Christiana‐Santorini‐Kolumbo Rift Zone

AbstractLocated on the Hellenic Arc, the Christiana‐Santorini‐Kolumbo (CSK) rift zone represents one of the most active and hazardous volcano‐tectonic systems in the Mediterranean. Although this rift zone has been intensively studied, its tectonic evolution and the interplay of volcanism and tectonism are still poorly understood. In this study, we use high‐resolution reflection seismic imagery to reconstruct the opening of the rift basins. For the first time, we relate the activity of individual faults with the activity of specific volcanic centers in space and time. Our analysis shows a pre‐volcanic NNE‐SSW‐oriented paleo basin underneath the CSK volcanoes, representing a transfer zone between Pliocene ESE‐WNW‐oriented basins, which was overprinted by a NE‐SW‐oriented tectonic regime hosting Late Pliocene volcanism that initiated at the Christiana Volcano. All subsequent volcanoes evolved parallel to this trend. Two major Pleistocene tectonic pulses preceded fundamental changes in the volcanism of the CSK rift including the occurrence of widespread small‐scale volcanic centers followed by focusing of activity at Santorini with increasing explosivity. The observed correlation between changes in the tectonic system and the magmatism of the CSK volcanoes suggests a deep‐seated tectonic control of the volcanic plumbing system. In turn, our analysis reveals the absence of large‐scale faults in basin segments affected by volcanism indicating a secondary feedback mechanism on the tectonic system. A comparison with the evolution of the neighboring Kos‐Nisyros‐Yali volcanic field zone and Rhodos highlights concurrent regional volcano‐tectonic changes, suggesting a potential arc‐wide scale of the observed volcano‐tectonic interplay.

Crust and upper mantle electrical structure of the eastern Central Asian Orogenic Belt revealed by the MT line from Zhangwu County to East Ujimqin Banner

The Central Asian Orogenic Belt is bounded on the north by the Siberian Craton and on the south by the North China Craton and the Tarim Craton. It is one of the largest Phanerozoic accretionary orogenic belts on Earth. Since the early Paleozoic, its eastern part has experienced the compound orogenesis and mineralization of three major tectonic systems: the closure of the Paleo-Asian Ocean, the closure of the Mongolian–Okhotsk Ocean, and the subduction of the Paleo-Pacific Plate. From Zhangwu County in the south to East-Ujimqin Banner in the north, a 500 km magnetotelluric profile adjacent to Northeast China has been studied. With 100 sites of magnetotelluric data processing and analysis, we apply a two dimensional inversion in TE and TM modes and obtain a resistivity model up to a 100 km depth. We have discovered two high-resistivity anomalies with opposite dip directions in the upper mantle on both sides of the Solonker Suture Zone, which provide an evidence of the bi-directional subduction pattern of the oceanic crust and the position of the closure of the Paleo-Asian Ocean. In addition, the whole study area presents an approximate basin-range coupling relationship. In the northern part of the study area, the low-resistivity anomalies below it have an apparent north-dipping characteristic, which may be related to the asthenosphere upwelling from west to east. In addition, they may be related to the upwelling of mantle materials, and provide sources of ore-forming material for the Baiyinnuoer mining area through post-collision extension. In the central part of the study area, there are several large-scale high-resistivity anomalies below the Baolidao Belt. The different dip directions reveal the experiences of several subductions and collisions. In the southern part of the study area, the Bainaimiao Belt is located between the southern margin of the Songliao Basin and the northern margin of North China Craton. The main resistivity anomalies below are all south-dipping.Graphical

Pacific Man – A Future Speculation Developed from Pacific Architectonics

Characterised by flexible joints and renewable use of materials, Pacific Architecture contains an integrated tectonic system that is historically used to construct both buildings and highly efficient watercrafts, enabling civilizations to flourish in Oceania. However, its significant architectural languages are widely dismissed in today’s utilitarian society. Witnessed in museum, cultural faculties and resorts, Pacific Architecture is often perceived as a cultural artefact that lacks of practical application. As a celebration of Pacific Architecture, the paper aims to discover how tectonics and construction systems from the Pacific could be revived, radically developed and utilised to accommodate “Future Pacific Living” in the rapidly changing world. Through a collective of speculative architectural propositions, the paper proposes alternatives to the existing postcolonial built environment while fully embracing future technologies. The first part of the paper is a review of the author’s past project ‘The Lomipeau Speculation’, a macro-scale visionary proposal to conceive of a city formed by Pacific tectonics. The second part, Pacific Men, is a narrative developed from the past project, exploring how Pacific Architecture can re-define humans’ relationship with the Ocean at a micro-scale. The speculation will be presented through architectural drawings with references to ekistic units.

Analogical simulation of salt flow and associated structures in different extensional conditions

The salt layer thickness variability and the timing of salt deposition in relation to rifting (prerift salt, synrift salt, and late synrift/postrift salt) influence salt flow and the resulting growth, geometry, and kinematics of salt bodies under different extensional conditions. We apply analogue modelling to analyze the influence and interplay of each of these parameters through three series of experiments focusing on extensional salt tectonics. The first (Series I) simulates thick-skinned extension of a tabular salt layer in the absence of basement structures and explore the effects of variable salt thicknesses and extensional structural styles. Series II tests the degree of mechanical coupling of sub- and supra-salt faults according to contrasting salt thicknesses over a rotating rift block. Series III explores thin-skinned, gravity-driven deformation implementing models of i) pure-gliding (S1), ii) pure-spreading (S2) and iii) a combination of both (S3). Series I shows that the degree of symmetry and the kinematics of the structures vary due to the influence of the thickness of the salt layer. Thick salt layers tend to nucleate symmetric rifts and associated diapirs, while thin salt layers form rifts that are strongly asymmetric and rotated towards the direction of extension. Series II demonstrates that the number and dimensions of peripheral post-salt grabens, rollers, and reactive diapirs depends on the degree of coupling between sub- and supra-salt, which in turn is controlled by how the salt layer is distributed over active rift structures. Series III shows that deformation is compartmentalized into proximal, transitional, and distal domains which are characterized by extension, translation and contraction, respectively. The style and lateral extent of these domains however vary. In models where deformation is driven exclusively by tilting of the salt layer (S1) and open-toe salt advance, there is development of linear grabens cored by reactive-passive diapirs throughout most of the model length. This produces a more abrupt transition between the extensional and contractional domains and limited downdip salt inflation. In the pure-spreading model (S2), where deformation is driven solely by differential loading there is formation of a wide zone of salt inflation at the toe-of-slope and an overall greater number of contractional structures at the downdip end of the model, beyond the slope. In S3 there is development of a more variable suite of salt and overburden structures as typically observed along salt-bearing passive margins. In this model, deformation is characterized by the development of rollover and normal growth faults in the proximal domain that transition downdip onto upright diapirs associated with bowl-shaped minibasins, halokinetic sequences rotated and megaflaps. Our study improves our understanding of the extensional salt tectonic systems and the controls on different salt and post-salt geometries and kinematics.