Orogenic Research Articles

Mapping the Crustal Magmatic System and Regional Deformation of the Toba Region by Multiparameter Ambient Noise Adjoint Tomography

AbstractIn this study, we develop a multiparameter ambient noise adjoint tomography method, and apply it for the first time to image the crustal magmatic system and regional deformation of the Toba region. Using Rayleigh and Love waves at periods of 5–20 s extracted from ambient noise, we construct a new multiparameter 3D crustal model that includes shear‐wave velocity, radial and azimuthal anisotropy. The isotropic component of our model reveals (a) over 30% Vs reductions beneath the Toba caldera with a melt fraction ranging from to , and (b) two low Vs bodies located in the middle crust (10–20 km) beneath the Helatoba volcano and the upper crust beneath the Lubukraya volcano, suggesting a large transcrustal magmatic mush model beneath this volcanic arc region. Our anisotropic model shows positive radial anisotropy in the middle crust of the volcanic regions, indicating the presence of horizontally layered melt sills. In the upper crust, we find predominantly weak negative radial anisotropy and significant azimuthal anisotropy, suggesting subvertical rock fabrics dominate upper crustal anisotropy. The orientation of fast velocity directions (FVDs) mostly aligns with the Sumatran Fault due to fault fabrics resulting from shearing deformation along the plate boundary. In the Tarutung region with rich geothermal resources, FVDs shift to being fault‐perpendicular probably due to the alignment of stress‐induced, fluid‐rich microcracks. Our study provides new insights into crustal magmatic architecture and deformation regimes of the Toba region shaped by regional tectonics and magmatic processes.

Structure of the Barud Dome Complex, Eastern Desert, Egypt: Insights from Crustal Origins in the Northern Basement Terrains of the Arabian–Nubian Shield

AbstractThe Barud gneissic dome complex is situated along the ENE‐trending dextral shear zone of the Qena–Safaga Line that serves as a significant tectonic boundary between the basement terrains of the Northern and Central Eastern Desert. These terrains exhibit distinct differences in crustal composition and deformation style. The Northern Eastern Desert and its extension into Sinai are predominantly composed of gneissic granites that are intruded by large batholiths of calc‐alkaline and alkaline granites. Conversely, the Central and Southern Eastern Desert are commonly blanketed by a carapace of ophiolite‐bearing volcano‐sedimentary rocks of the Pan‐African cover nappes. These northern terrains, just north of the Barud dome complex, the crust underwent significant NW–SE regional crustal extension across the Qena–Safaga Line, which sharply delineates the northern limit of the transpressional deformations linked to the Najd fault system in the Central and Southern Eastern Desert. Through comprehensive geological mapping and the integration of various geophysical, geochemical and geochronological data, this paper offers explanations for the contrasting geological features of the basement terrains on both sides of the Qena–Safaga Line and its analogous Fatira Shear Zone that plays a significant role in tectonic modeling of the Barud dome complex region. The Barud gneissic protolith experienced crustal shortening approximately 697 million years ago in the NW–SE direction, initiating dextral motion along the Fatira Shear Zone. Large batholiths of granodiorite/tonalite complex intruded the Barud gneissic dome protolith around 630 million years ago along the Qena–Safaga Line, at relatively shallow crustal depths, following the same orientation as the earlier shortening direction. Ongoing magmatic activity along the Qena–Safaga Line indicates intense magmatic underplating, resulting in significant intrusions of granodioritic melts into the early rifted crust of the Northern Eastern Desert and Sinai terrains. The crust of these northern terrains likely underwent isostatic compensation through uplifting and subsequent erosion. The disappearance of ophiolite‐bearing belts and the presence of Paleo‐ to Mesoproterozoic continental‐derived cobbles and ignimbrites in Sinai metasedimentary belts and Northern Eastern Desert molasse basins suggest that the northern terrains, located north of the Qena–Safaga Line, originated as a cohesive, thin continental crust that rifted off the eastern passive margin of the Sahara Metacraton during the early Neoproterozoic rifting of the Rodinia supercontinent.

Crustal anisotropy and deformation in the South China Block

Crustal anisotropy and deformation in the South China Block

Intracontinental Deformation and Reactivation of the Southern Central Asian Orogenic Belt: Styles, Causes and Mechanisms

AbstractContinents are a mosaic of cratons, orogens and accreted terranes of various natures. They can either remain stabilized or become prone to reactivation or reworking. The Alxa region, at the southern margin of the Central Asian Orogenic Belt (CAOB), has undergone complex multistage Mesozoic deformation. Through structural mapping, paleostress inversion and low‐temperature thermochronological techniques, six deformation phases were identified in the central Alxa, revealing a close correlation between intracontinental deformation and plate‐margin interactions. A 240–200 Ma cooling event in the Alxa region, coinciding with regional exhumation, occurred within a large overlap zone formed by two synchronous sinistral shear systems traversing the CAOB. This suggests an intracontinental transpressional setting during the Middle–Late Triassic. The Triassic deformation was driven by the collision between the Yangtze and North China Cratons and the accretion of the Qiangtang Block to southern Eurasia continent. During the Jurassic to Cretaceous, the Alxa region experienced repeated episodes of extension and shortening reactivation. Paleostress data reveal Middle‐Late Jurassic N–S syn‐sedimentary shortening, Early Cretaceous syn‐rifting extension and Late Cretaceous shortening. The Middle‐Late Jurassic N–S shortening is related to the closure of the Mongol‐Okhotsk Ocean and the collision of the Lhasa Block with southern Eurasia. Late Cretaceous NW–SE compression in the southern CAOB is ascribed to stress transmitted from the eastern margin of Eurasia. The multidirectional and multiphase intracontinental deformation in the southern CAOB was shaped by the combined effects of far‐field effects, upper mantle modifications due to protracted subduction along the convergent plate margins and inherited structures.

Spatiotemporal variations of Early to Middle Paleozoic magmatism in northern Beishan: Implications for accretionary and collisional processes in the southern Central Asian Orogenic belt

Spatiotemporal variations of Early to Middle Paleozoic magmatism in northern Beishan: Implications for accretionary and collisional processes in the southern Central Asian Orogenic belt

Petrogenesis of the Xifanping Porphyries in the Sanjiang Orogenic Belt, SW China: Eastward Propagation of the Indo–Asian Collision

AbstractLarge‐scale Cenozoic alkali‐rich magmatic rocks are exposed at the eastern margin of Tibet due to the interaction between the Indian and Eurasian plates. However, their petrogenesis and associated geodynamic processes remain poorly understood. We analyzed the Xifanping porphyries in the Sanjiang orogenic belt to provide new insights. Our study shows a successive assembly of porphyry intrusions during three magmatic episodes. The magnitude and duration of the magmatic activities diminished sequentially, and mineralization occurred during the intermediate phase. Geochemically, the Xifangping porphyries display an adakitic affinity. According to zircon Hf isotope data, we propose that these porphyries originated from the partial melting of the thickened mafic lower crust beneath the western Yangtze Craton in response to lithospheric extension and asthenospheric upwelling. Analogous to the coeval alkali‐rich porphyries in western Yunnan, the petrogenetic model of the Xifanping porphyries indicates regional north–south and east–west fractures caused by the clockwise rotation of the continental lithosphere and the Jinshajiang–Red River strike‐slip during the post‐collision phase of the India–Eurasia collision. In this context, we argue that the collision in eastern Tibet may have extended eastward to southwestern Sichuan during the post‐collision period, persisting until approximately 30 Ma.

Petrogenesis and age of granitoids associated with the Dongshan Cu polymetallic deposit, East Kunlun Orogenic Belt, NW China: Implications for the Middle to Late Triassic tectonic setting and Cu polymetallic mineralization

Petrogenesis and age of granitoids associated with the Dongshan Cu polymetallic deposit, East Kunlun Orogenic Belt, NW China: Implications for the Middle to Late Triassic tectonic setting and Cu polymetallic mineralization

Controls of Neoproterozoic magmatism on Ni Cu sulfide mineralization in the Jiangnan Orogenic Belt, South China: An example from the newly discovered Sibao Ni Cu sulfide deposit

Controls of Neoproterozoic magmatism on Ni Cu sulfide mineralization in the Jiangnan Orogenic Belt, South China: An example from the newly discovered Sibao Ni Cu sulfide deposit

Apatite and Zircon as key indicators for effusive-explosive transition in the Leningcou Volcano: Middle Triassic Volcanic activity in the East Kunlun Orogenic Belt

Apatite and Zircon as key indicators for effusive-explosive transition in the Leningcou Volcano: Middle Triassic Volcanic activity in the East Kunlun Orogenic Belt

Provenance of the Middle–Late Triassic Successions in the Eastern Sichuan Basin, South China: Implications for the Evolution of the Qinling Orogenic Belt

AbstractThe Qinling orogenic belt in central China underwent long‐term tectonic evolution during an amalgamation between the North China and South China cratons. However, intense compressional deformation and uplift erosion resulted in the transformation and disappearance of much geological record from the Qinling orogenic belt, and the tectonic evolution of this belt remains poorly constrained during the Triassic. Located in the northernmost margin of the South China Craton, the Sichuan Basin preserves the complete Triassic sedimentary succession, and can provide significant information for understanding the Triassic tectonic evolution of the Qinling orogenic belt. We present detrital zircon U‐Pb dating, trace element and in situ Lu‐Hf isotope data for the Middle Triassic Leikoupo Formation and the Late Triassic Xujiahe Formation samples from the eastern Sichuan Basin, South China. The detrital zircon U‐Pb ages of the Leikoupo Formation show seven age clusters of 280–242, 350–300, 500–400, 1000–800, 2000–1750, 2100–2000 and 2600–2400 Ma, while those of the Xujiahe Formation show five age clusters of 300–200, 500–350, 1050–950, 2000–1750 and 2600–2400 Ma. Combined with published paleocurrent and paleogeographic data, the sediments of the Leikoupo Formation are interpreted to be sourced from the North China Craton, Yangtze Craton and North Qinling orogenic belt, and the potential main source regions of the Xujiahe Formation included the South and North Qinling orogenic belts. Provenance analysis indicates that the North Qinling orogenic belt was in inherited uplift and coeval denudation in the Middle Triassic. The proportion of the detritus formed in the South Qinling orogenic belt increases gradually from the Leikoupo to Xujiahe formations. This significant provenance change indicates that rapid tectonic uplift and extensive denudation of the South Qinling orogenic belt occurred in the early Late Triassic, which is related to the collision between the North China and South China cratons during the Triassic.

Petrogenesis of Jurassic granitoids from the Yanshan orogenic belt: Implications for crustal evolution in the northern North China Craton

Petrogenesis of Jurassic granitoids from the Yanshan orogenic belt: Implications for crustal evolution in the northern North China Craton

Apatite and zircon compositions as petrogenetic and metallogenic indicators for late Ordovician porphyries in the Songshunangou gold district, North Qilian orogenic belt (China)

Apatite and zircon compositions as petrogenetic and metallogenic indicators for late Ordovician porphyries in the Songshunangou gold district, North Qilian orogenic belt (China)

Differences in the Meso–Cenozoic Tectonic Evolution between the Huangling Paleo‐uplift and the Surrounding Areas in the Middle Yangtze Block, South China

AbstractApatite (U‐Th)/He and fission track dating and tectono‐thermal history modeling were used to reconstruct the Meso–Cenozoic tectonic evolution of the Huangling paleo‐uplift in the Middle Yangtze Block, South China. The tectonothermal evolution showed different tectonic exhumation/subsidence processes in the tectonic evolution of the foreland basin. The apatite (U‐Th)/He ages ranged from 31.3 to 77.8 Ma, recording the thermal events of the Cenozoic Himalayan movement and indicating progressive exhumation extending from the southeast to the northwest. The thermal information of the Mesozoic Yanshan movement period was recorded by the apatite fission track age with a pooled age of 93.8 to 147 Ma. The exhumation of the Huangling paleo‐uplift began in the Late Jurassic. The tectono‐thermal evolution was characterized by a rapid uplift during 140–115 Ma, subsidence during 115–60 Ma, a rapid uplift during 40–30 Ma, and a slow uplift from 30 Ma to the present. The western Hunan–Hubei Depression was exhumed in the Middle Jurassic, and the tectono‐thermal evolution was characterized by a rapid uplift during 160–135 Ma, a slow uplift during 135–50 Ma, a rapid uplift during 50–25 Ma, and a slow uplift from 25 Ma to the present. This Cenozoic exhumation was a response to the far field effect of the eastward growth of the Tibetan Plateau. The Cretaceous basins exposed in the surrounding areas of the Huangling paleo‐uplift (Zigui basin, Yichang slope, and Huaguoping synclinorium) are foreland basins formed by the bi‐directional compression of the Qinling–Dabie orogenic belt and the Xuefengshan intracontinental deformation system.

GNSS Observations of the Land Uplift in South Africa: Implications for Water Mass Loss

AbstractContinuously operating Global Navigation Satellite System (GNSS) base stations in South Africa show a spatially coherent vertical displacement. While one hypothesis attributes this vertical motion to crustal deformation from mantle flow and dynamic topography (Hammond et al., 2021, https://doi.org/10.1029/2021jb022355), we propose an alternative explanation. Our evidence suggests that land water loss from multiple droughts is a major driver of the observed uplift. In this study, we analyze daily Global Positioning System (GPS) height time series from 2000 to 2021. We use singular spectral analysis (SSA) to separate long‐term trends and annual and semi‐annual signals from noise. The processed time series were inverted into water mass loading on a uniform grid, with the Earth's crust's rheological properties defined by the Preliminary Reference Earth Model (PREM). Our experimental approach show that a 2 2 grid resolution provides suitable results for most of South Africa. The GPS‐derived total water storage change reconcile well with a GRACE‐assimilated solution and a hydrological model at the monthly scale across different provinces, showing correlations of up to 90% and 94%, respectively. The long‐term trend averaged over the country shows a considerable correlation of 46% and 53%, respectively. These long‐term total water storage trends provide strong evidence that the observed land uplift in South Africa is primarily of hydrological origin.

Fault Geometries of the 2024 Mw 7.5 Noto Peninsula Earthquake From Hypocenter‐Based Hierarchical Clustering of Point‐Cloud Normal Vectors

AbstractThe elucidation of intricate fault geometries provides fundamental and essential information regarding seismology and other fields of solid Earth sciences. Hypocenter alignments typically reflect complex crustal fault structures, so spatial clustering of hypocenter distributions has been used to construct planar fault geometries. However, conventional spatial clustering inherently struggles with the complexity of hypocenter distributions. In this study, we integrated point‐cloud normal vectors, commonly used in object recognition to reflect the local surface geometry of an object, into a hypocenter‐based hierarchical clustering to construct intricate planar fault models. We applied this method to the aftershock sequences of the Mw 7.5 Noto Peninsula earthquake in central Japan on 1 January 2024, which caused notable crustal deformation. We identified fault planes aligning with the coastline from the western to northern coast. A southeast‐dipping plane was located between the two south‐southeast‐dipping planes along the northern coast, correlating with gravity anomalies and surface geology or reflecting the complexity of fault ruptures and dynamic stress perturbations. The east‐dipping fault in the southwestern area showed a different distribution from the aftershocks of the 2007 Mw 6.7 earthquake, suggesting that the 2024 earthquake did not reactivate the 2007's fault plane. The NS‐trending aftershock focal mechanisms in the southwestern area suggest that a reverse‐fault slip probably occurred on the plane. Further investigations based on the intricate fault planes will contribute to a deeper understanding of the spatial characteristics of the coseismic slip of the 2024 earthquake and seismotectonics of the Noto Peninsula.

Crustal structure and tectonic evolution of the Pranhita-Godavari Rift: A comprehensive study using edge enhancement techniques and 2D gravity modeling

Crustal structure and tectonic evolution of the Pranhita-Godavari Rift: A comprehensive study using edge enhancement techniques and 2D gravity modeling

Inferring 3‐D Rheology of Low‐Viscosity Zone Around Quaternary Volcanoes of NE Japan From Postseismic Deformation of the 2011 Tohoku‐Oki Earthquake

AbstractSeveral geological and geophysical studies suggest the small‐scale presence of low viscosity zone (i.e., LVZ) beneath the Quaternary volcanoes of northeastern Japan. Before the 2011 Mw9.0 Tohoku‐oki earthquake, scientists hypothesized that these LVZs cause localized crustal deformations around the Quaternary volcanoes. However, the deformation‐signals related to these LVZs were too weak to properly understand the LVZ rheology. After the 2011 Tohoku‐oki earthquake, InSAR and Global Navigation Satellite System (GNSS) observations reported significant ground movements around five Quaternary volcanoes including the Mt. Akitakoma, Mt. Kurikoma, Mt. Zao, Mt. Azuma, and Mt. Nasu. Using the early years of postseismic GNSS displacements, we extracted the short‐wavelength components of strain‐rate distribution, which clearly show the localized crustal contraction near the five volcanoes. To explain such spatial pattern of localized contraction, we propose a 3‐D rheological model of LVZs near the five volcanoes, using power‐law Burgers rheology. Most of our modeled LVZs have narrow tops (width of 20–40 km), wide roots (width of 80–100 km), limited arc‐parallel dimensions (≤80 km), and are located at the depth range of 15–55 km in the lower crust‐upper mantle. Based on the localization of postseismic strain rate, newly proposed 3‐D LVZ models highlight an arc‐parallel heterogeneity of subsurface rheology along the volcanic front of northeastern Japan, which is consistent with previously reported clusterization pattern of late Cenozoic calderas and high geothermal gradient near the five Quaternary volcanoes.

Ten Questions of East Asian Tectonics

AbstractEast Asian continental tectonics challenges the plate tectonics paradigm with its diffuse intraplate deformation, magmatism, and earthquakes. Despite extensive studies, fundamental questions persist. This review examines ten critical questions of East Asian tectonics, including the thickness of the continental lithosphere, the origin of the North–South Gravity Lineament, and the northern extent of the Indian plate beneath the Tibetan Plateau. Additional questions address the Tibetan Plateau's lateral growth, the Tianshan mountain building, the mantle flow in response to the Indo‐Asian collision, and the formation of the Shanxi Rift. The review also explores the subduction along the eastern margins of the East Asian Continent and the origins of the Changbaishan volcanic field, the destruction of the North China Craton, and the development of the Mesozoic Large Granitic Province in South China. Originally presented at the DEEP2024 workshop to stimulate discussion of how SinoProbe‐II research initiatives could advance our understanding of Asian tectonics, this review provides context for each question, summarizes current knowledge, and identifies promising research directions.

Perched on the Plateau: Speciation in a Cape Fold Mountain Velvet Worm Clade, With the Description of Seven New Species (Onychophora: Peripatopsidae: Peripatopsis) From South Africa

ABSTRACTDuring the present study, we re‐examined species boundaries in three mountain‐dwelling velvet worm species complexes (Peripatopsis balfouri s.l., P. bolandi s.l. and P. purpureus s.l.) along the Cape Fold Mountains of South Africa. We obtained DNA sequence data for both the mitochondrial cytochrome c oxidase subunit one (COI) and the nuclear 18S rRNA loci. Phylogenetic inferences were derived with the use of maximum likelihood and Bayesian inference coupled with a divergence time estimation. Four species delimitation methods (ASAP, bPTP, bGYMC and STACEY) together with gross morphological analyses and scanning electron microscopy (SEM) were used to validate the diagnosis of novel species. Combined phylogenetic results demonstrated the presence of three geographically discrete clades (A‐C). Corroborative evidence for the novel lineages could be derived from the dorsal integument colour of live specimens and fixed dorsal and ventral papilla scales rank counts. The four species delimitation methods produced variable results. Divergence time estimations indicated that the Miocene epochs was a major period of cladogenesis. The seven novel velvet worm species, P. barnardi sp. nov., P. fernkloofi sp. nov., P. jonkershoeki sp. nov., P. kogelbergi sp. nov., P. landroskoppie sp. nov., P. limietbergi sp. nov., and P. palmeri sp. nov., are herein described.

The Impact of Mélange Formation on the Rheology and H2O Budget of the Subduction Zone Interface, With Implications for Diapir Nucleation

AbstractAt the subduction zone interface, a combination of mechanical deformation and (fluid‐mediated) chemical mixing of oceanic crust, sediment and mantle lithologies yields heterogeneous mélange lithologies. These mélanges have compositions and metamorphic mineral assemblages dissimilar to their endmember source lithologies, resulting in a subduction zone interface with physical properties (e.g., H2O capacity, density, and viscosity) that are distinct from both the source lithologies and simple mechanical mixtures of these lithologies. Using phase equilibria modeling, we find that a large range of mélange compositions carry more H2O to sub‐arc depths and are less dense compared to equivalent mechanical mixtures. We further show that mélange is much weaker than the overlying mantle but remains stronger than quartzite deforming by dislocation creep. Lastly, we synthesize these results and find that at all subduction zones, a range of mélange compositions are likely to form diapirs at sub‐arc depths and sub‐solidus temperatures.