Dextral Strike-slip Motion Research Articles

Activity and motion characteristics on the southern segment of the Red River fault zone, Yunnan province, China

The longer time for recording large earthquakes on a plate boundary fault, the better that understanding of large earthquake rupture behavior and seismic hazard on the fault zone. However, large earthquakes (M ≥ 7) are rarely recorded on the boundary fault with slow slipping rate, such as the Red River fault zone (RRFZ), which is an important plate boundary fault that marks the southwestern boundary of the Yangtze platform or south China block. There have been no large earthquake records on the southern segments (including the segment in Vietnam) of the RRFZ since historical earthquake records began in 886 AD, except the 1652 Midu M 7 earthquake and the 1925 Dali M 7 earthquake on the northern segment. The southern segment of the RRFZ will not have a large earthquake in the future or as a large earthquake seismogenic zone with a long period of recurrence, remains controversial, in part because of the absence of constraints from geological evidence. This controversial seriously restricts the risk assessment of future large earthquakes on the southern segment of the RRFZ. By careful interpretations of high resolution remote sensing images, in combination with a detailed field geological and geomorphic survey, we found a series of fault valleys and bedrock outcrops from Gasha toYaojie and Yuangjiang to Hekou on the southern segment of the RRFZ. Multiple trench excavation and radiocarbon dating sample analyses show that the mid valley trace in the southern segment of the RRFZ is an active fault. Geological and geomorphic evidence from Gasha to Yaojie and Yuanjiang to Hekou indicate that the mid valley trace in the southern segment of the RRFZ exhibits dip slip and dextral strike slip motion characteristics. This result is inconsistent with those of previous studies that the mid valley trace is purely strike slip. Furthermore, trenches opened on the range front trace in the southern segment of the RRFZ in Ejia are found to still be active, differing from previous studies. Thus, the seismic hazard on the southern segment of the RRFZ should be reevaluated.

Resolution analysis of the gravity survey network in the middle and south sections of Tan-Lu fault and recent changes in the gravity field

In this paper, we computed the fractal dimension of three survey areas within the central and southern sections of the Tan-Lu fault zone using fractal analysis. Subsequently, simulations were conducted to analyze the gravity response under a forward model of equivalent density changes. Additionally, we thoroughly investigated the seismic monitoring capabilities of the gravity network in the central and southern regions of the Tan-Lu fault. Expanding on these analyses. Recent gravity field variations were examined in the mid-southern segment of the Tan-Lu fault zone and its surrounding areas from 2013 to 2023. The results indicate that the observation capabilities of the northern network in the study area outperform those of the southern gravity network, with the northern network demonstrating a more evenly distributed coverage. The optimal gravity anomaly recovery effect for the entire study area is achieved at a resolution of 0.5° × 0.5°. With an equivalent observable signal in the range of 30 × 10−8 m/s2 to 40 × 10−8 m/s2, the spatial resolution of the gravity network's field source is estimated to be approximately 55 km. From 2013 to 2023, a significant positive change has been observed in the gravity field within the study area. The Tan-Lu fault zone plays a crucial role in governing the crustal movement in this region, with the dextral strike-slip movement trend of the fault persisting. Small earthquakes occur more frequently in the southern section of the fault zone, while strong earthquakes are less common. The alignment of gravity field changes with the fault strike indicates ongoing activity in the fault zone without any signs of locking. In the central segment of the Tan-Lu fault zone in the Shandong region, there appears to be a weaker correlation between gravity field changes and fault trends. This discrepancy may suggest that the area is locked, resulting in the accumulation of stress and strain. It is imperative to monitor the continuous evolution of the gravity field in this region to gain insights into potential seismic risks.

Facies controls and tectonic evolution on oil accumulation and entrapment in the Cenomanian Abu Roash G member, northern-central Egypt: Deltaic and channel sandstones as good reservoirs

Along northern-central Egypt, the oil accumulation and entrapment were mainly controlled by variable parameters including the stratigraphic architecture, sedimentary features, and tectonic evolutions. The present paper presents a new model for oil occurrences in the Abu Roash G Member (Cenomanian) along Gindi, Abu Gharadig and to a few extents the Beni Suef basins, in the northern-central part of the Western and Eastern Deserts of Egypt. The studied concessions include the Wadi El Rayan, East Bahariya and El Diyur (Gindi basin and Abu Gharadig basins, Western Desert) and the Ghariboun (Beni Suef Basin, Eastern Desert) fields. Twenty sedimentary facies were recorded from the studied subsurface sections of the Abu Roash G Member and grouped into three facies associations. A new depositional model is achieved where estuarine, open marine, deltaic distributaries, and tidal channel deposits are the main facies associations recorded in the studied Abu Roash “G". These deltaic and channel deposits occurred as an arch like form between open marine and estuarine deposits. These deltaic and tidal channel sandstone deposits act as a good reservoir to accumulate oil from nearby areas. As well, these areas were subjected to the well-known Syrian arch compressional deformation that affected northern Egypt during the Mesozoic, up to late Senonian time. A regional NE-SW oriented fold system took place, forming NE-SW oriented ridges in addition to the dextral strike-slip movement that took place along these ridges because of this compressional deformation.To sum up, oil accumulation in the studied Abu Roash G Member was mainly controlled by facies distribution mainly of channel sandstone enhanced by the tectonic movements (Syrian Arc System) affecting the areas studied.

Evidence of Dextral Strike-Slip Movement of the Alakol Lake Fault in the Western Junggar Based on Remote Sensing

The NW-SE-trending dextral strike-slip faults on the north side of the Tian Shan, e.g., the Karatau fault, Talas–Fergana fault, Dzhalair–Naiman fault, Aktas fault, Dzhungarian fault, and Chingiz fault, play an important role in accommodating crustal shortening. The classic viewpoint is that these strike-slip faults are an adjustment product caused by the difference in the crustal shortening from west to east. Another viewpoint attributes the dextral strike-slip fault to large-scale sinistral shearing. The Alakol Lake fault is a typical dextral strike-slip fault in the north Tian Shan that has not been reported. It is situated along the northern margin of the Dzhungarian gate, stretching for roughly 150 km from Lake Ebinur to Lake Alakol. Our team utilized aerial photographs, satellite stereoimagery, and field observations to map the spatial distribution of the Alakol Lake fault. Our findings provided evidence supporting the assertion that the fault is a dextral strike-slip fault. In reference to its spatial distribution, the Lake Alakol is situated in a pull-apart basin that lies between two major dextral strike-slip fault faults: the Chingiz and Dzhungarian faults. The Alakol Lake fault serves as a connecting structure for these two faults, resulting in the formation of a mega NW-SE dextral strike-slip fault zone. According to our analysis of the dating samples taken from the alluvial fan, as well as our measurement of the displacement of the riser and gully, it appears that the Alakol Lake fault has a dextral strike-slip rate of 0.8–1.2 mm/a (closer to 1.2 mm/a). The strike-slip rate of the Alakol Lake fault is comparatively higher than that of the Chingiz fault in the northern region (~0.7 mm/a) but slower than that of the Dzhungarian fault in the southern region (3.2–5 mm/a). The Chingiz–Alakol–Dzhungarian fault zone shows a gradual decrease in deformation towards the interior of the Kazakhstan platform.

Cenozoic sedimentary archives of a strike-slip fault zone in the Tanhai Region, Bohai Bay Basin, Northeastern China

The Changdi fault, also known as the Changdi fault zone, is commonly proposed to be a branch of the Tan-Lu fault zone in the Tanhai region of the Bohai Bay Basin. Using three-dimensional seismic data, borehole data, isopach maps, and RMS maps, we attempted to provide a comprehensive understanding of the structural properties and sediment dispersal patterns occurring within the Changdi area from a source-to-sink perspective. Two distinct geomorphological factors were identified in the Changdi area and four types of strike-slip fault-controlled alluvial channels were proposed for the first time. Additionally, three types of sediment dispersal systems, characterized by various sediment infillings, source inputs, and source areas, were reported. The spatial and temporal variations in the geometry and kinematics of the Changdi fault zone were observed to regulate sediment dispersal within the subsag. Sediment dispersal systems in the Changdi area were regulated by sediment dispersal associated with faults resulting from strike-slip movement. The movement of the input port in the provenance area was controlled by strike-slip movements. The movement of the sedimentary center indicated that there was a dextral strike-slip distance of 3.24 km during the E2s3L period. This study suggests that dextral strike-slip movements occurred in the Changdi fault zone, forming a strike-slip fault-controlled basin. The findings of this study may prove useful in developing models to predict the patterns of sediment dispersal controlled by strike-slip faults as well as the location of areas rich in sand.

Evaluating the Relation of Cave Passage Formation to Stress-Field: Spatio-Temporal Correlation of Speleogenesis with Active Tectonics in Asprorema Cave (Mt. Pinovo, Greece)

Caves serve as time capsules, preserving significant markers of tectonic activity and offering insights into geological history. Fault geometries and past activations found in caves can be correlated with known deformational events in the broader area, temporally delimiting the speleogenesis. More specifically, cave passage formation is suggested to be affected by the regional stress-field. The Asprorema Cave in Northern Greece is a typical example of a fracture guided cave, with passage geometry influenced by relative sidewall movements, revealing these discontinuities as faults. This study constructs the timeframe and conceptual model of speleogenesis in relation to tectonic events, geomorphological evolution and hydrological zones, and verifies its relation to the stress-field. Active tectonics, mineralogy and cave geomorphology are investigated. Results suggest syntectonic speleogenesis under phreatic and epiphreatic conditions. The absence of corrosion on fault slip surfaces implies recent activations post cave’s shift to the vadose zone. Structural analysis identifies three main neotectonic phases: NNW-SSE striking faults (oldest group of structures), NE-SW striking faults with dextral strike-slip movement (post-middle Miocene), and NE-SW striking normal faults indicating extensional stress-regime (Quartenary). The last two phases affect cave passage shape causing wall displacement, highlighting passage formation along discontinuities perpendicular to the horizontal minimum stress axis.

Petroleum geological characteristics and exploration targets of the oil-rich sags in the Central and West African Rift System

Based on seismic, drilling, and source rock analysis data, the petroleum geological characteristics and future exploration direction of the oil-rich sags in the Central and West African Rift System (CWARS) are discussed. The study shows that the Central African Rift System mainly develops high-quality lacustrine source rocks in the Lower Cretaceous, and the West African Rift System mainly develops high-quality terrigenous organic matter-rich marine source rocks in the Upper Cretaceous, and the two types of source rocks provide a material basis for the enrichment of oil and gas in the CWARS. Multiple sets of reservoir rocks including fractured basement and three sets of regional cap rocks in the Lower Cretaceous, the Upper Cretaceous, and the Paleogene are developed in the CWARS. Since the Late Mesozoic, due to the geodynamic factors including the dextral strike-slip movement of the Central African Shear Zone, the basins in different directions of the CWARS differ in terms of rifting stages, intervals of regional cap rocks, trap types and accumulation models. The NE–SW trending basins have mainly preserved one stage of rifting in the Early Cretaceous, with regional cap rocks developed in the Lower Cretaceous strata, forming traps of reverse anticlines, flower-shaped structures and basement buried hill, and two types of hydrocarbon accumulation models of “source and reservoir in the same formation, and accumulation inside source rocks” and “up-source and down-reservoir, and accumulation below source rocks”. The NW–SE basins are characterized by multiple rifting stages superimposition, with the development of regional cap rocks in the Upper Cretaceous and Paleogene, forming traps of draping anticlines, faulted anticlines, antithetic fault blocks and the accumulation model of “down-source and up-reservoir, and accumulation above source rocks”. The combination of reservoir and cap rocks inside source rocks of basins with multiple superimposed rifting stages, as well as the lithologic reservoirs and the shale oil inside source rocks of strong inversion basins are important fields for future exploration in basins of the CWARS.

Structural and tectonic evolution between Indo-Myanmar ranges and central Myanmar basin: Insights from the Kabaw Fault

The Kabaw Fault is a north-south trending arcuate suture zone formed between the accretionary prism of the Indo-Myanmar Ranges (IMR), and the Central Myanmar Basin (CMB). The lineament of the Kabaw Fault is defined as a stratigraphic contact zone between flysch sediments of the IMR and molassic sediments of the CMB along the eastern base of the IMR. The accretionary prism of IMR was initially formed as a single wedge (pro-wedge) during Triassic, however, the forceful subduction of the Indian Plate resulted in the formation of an open wedge (double-sided wedge) during the Cretaceous. The double-sided wedge of the accretionary prism of IMR is revealed by the structural deformation pattern of the molassic sediments and the Triassic flysch exposures in the fore-arc basin of CMB, however, the eastern part of the wedge is buried under the fore-arc basin. At the eastern base of IMR, the ophiolite occurrences are close to the Kabaw Fault except in the Kabaw Valley where the ophiolites are associated with the Jurassic sedimentary rock units. The Kabaw Valley is generally occurred as a north-south elongated lowland basin, positioned along the western part of the Kabaw Fault. The east-dipping geometry of the Kabaw Fault is manifested by the evidence of east-verging synclinal folds of the fore-arc basin in the CMB, and the east-verging folding is due to slip up on the slope of the retro-wedge. The dextral strike-slip movement of the Kabaw Fault is displayed by the shifting of mud volcanoes in the Pyay to Kalaywa region and the two-phase folding and deformation within the Chindwin sub-basin and the Minbu-Salin sub-basin. The present study proves not only the Kabaw Fault as an east-dipping reverse fault with structural evidence, but also reveals the double-sided wedge system of the IMR accretionary prism.

Cenozoic Subsidence History of the Northern South China Sea: Examples from the Qiongdongnan and Yinggehai Basins

The Qiongdongnan and Yinggehai Basins are important petroliferous basins. To study the Cenozoic subsidence characteristics of these two basins, their controlling factors, and their implications, we studied the basins’ subsidence characteristics via one-dimensional, two-dimensional, and holistic subsidence. Then, we compared the basins’ subsidence characteristics based on the evolution of several particular geological processes that occurred in the South China Sea (SCS) and adjacent areas. The results indicated that the change in the holistic subsidence of both basins occurred episodically. In addition, the subsidence in these two basins differed, including their subsidence rates, the migration of the depocenters, and the changes in the holistic subsidence. The dynamic differences between the two basins were the main factors controlling the differences in the subsidence in the two basins. In the Qiongdongnan Basin, the subsidence characteristics were primarily controlled by the mantle material flowing under the South China Block in the Eocene and the spreading of the SCS from the Oligocene to the Miocene. In the Yinggehai Basin, the subsidence characteristics were primarily controlled by the coupling between the uplift of the Tibetan Plateau and the strike-slip motion of the Red River Fault before the Early Miocene and by only the effect of the strike-slip motion of the Red River Fault from the Middle Miocene to the Late Miocene. Since the Pliocene, the subsidence characteristics of both basins have been principally controlled by the dextral strike-slip motion of the Red River Fault. The major faults contributed to the spaciotemporal variations in the subsidence within each basin.

Seismotectonics, Geomorphology and Paleoseismology of the Doroud Fault, a Source of Seismic Hazard in Zagros

In this study, the active tectonics, paleoseismicity, and seismic hazards of the Doroud Fault are examined through high-resolution satellite image interpretations, field investigations, outcrop and trench excavations, and the dating of geochronology samples. The Doroud Fault (DF), one of the essential segments of the Main Recent Fault in the northern margin of the Zagros mountain range, has a historical and instrumental background of high seismicity. We present the first constraints from tectonic geomorphology and paleoseismology along the Doroud Fault near the capital city of Dorud. Detailed observations from satellite imagery, field investigations, real-time kinematic (RTK) measurements, paleoseismological trenching, the radiocarbon (C14), and optically stimulated luminescence (OSL) as ages allowed us to map the fault in detail, describe and characterize its kinematics, and document its recent activity and seismic behavior (cumulative displacements, paleoseismicity, and magnitude, as well as recurrence interval) relevant to the recent seismic activity of the Doroud Fault during the late Holocene as one of the most important seismogenic faults in Zagros. Modern alluvial terraces of gullies and loess accumulations are systematically deflected and/or offset with co-seismic rupture, landslides, and scarps, indicating that the Doroud Fault has been active in the late Quaternary and is characterized by dextral strike–slip movements with a normal component. In addition, our findings provide a comprehensive analysis of the fault displacement, the timing of paleoearthquakes, and the right-lateral slip rate of the Doroud Fault. The late Holocene slip rate of the Doroud Fault using the OSL dating the gully is as follows: the minimum and maximum horizontal slip rates are estimated to be 1.82 and 2.71 mm/yr, and vertical slip rates of 1.03 and 1.53 mm/yr are calculated for the past 4600 ± 900 years in the middle segment of the fault. This study focused on a paleoseismological trench within the archeological sites of Darbe-Astaneh. The central portion of the fault has historically hosted more than nine earthquakes in the last 66 ka years, according to the study’s findings. According to paleoseismology studies, the Doroud Fault has the seismic capability to cause earthquakes with a magnitude of more than 7.4 and a total slip rate of about 3.83 ± 0.1 m. The average recurrence interval for the identified paleoearthquakes is approximately 104 ± 7 years.

Sedimentary and tectonic evolution of the Banquan pull-apart basin and implications for late Cenozoic dextral strike-slip movement of the Tanlu Fault Zone

Sedimentary and tectonic evolution of the Banquan pull-apart basin and implications for late Cenozoic dextral strike-slip movement of the Tanlu Fault Zone

Depositional environments of the Miocene sediments in northern Song Hong basin

Northern Song Hong Tertiary Sedimentary basin is a classic case study of a pull-apart basin in southeast Asia, whose formation was controlled by the India-Eurasia collision, sinistral and dextral strike-slip motion of the Ailao Shan-Red River Shear Zone and Opening of the East Vietnam Sea during the Cenozoic. Unlike the central and southern parts of the basin, the northern Song Hong Basin experienced a very strong inversion during the Late Miocene. This rapid uplift of the region has led to significantly change in lithofacies and sedimentary environments, which are now still poorly understood. This uncertainty is considered one of the main challingings in prediction of the non-structural traps in the region. The recent results derived from well logging and 2D/3D seismic interpretation allowed us to define the Miocene formation in northern Song Hong basin, which are subdivided into three substrata, namely: the Lower, Middle and Upper stratum, which are characterized by typical characteristics of lithology and depositional environments. The Lower Miocene formation is dominated by deltaic environment at the bottom, transitioning to the overlying shelf environment. Lithology of the section varies from coarse-grained sediment (sandstone) to fine grained material such as shale and mudstone upward; The Middle Miocene stratum demonstrate sandier, coalic materials of the delta plain and delta front environments intercalated with swampy shale. In contrast, the Upper Miocene section is characterized by more fluvial and nearshore elements. It is illustrated by presence of the channel-filled sand bodies and mouth/longshore sand bars. These sand bodies demonstrate good porosity and horizontal permeability, which are considered to be good potential reservoir for both structural and non-structural traps in the Miocene formation.

Tectonic dynamics of the Zhongjiannan Basin in the western South China Sea since the late Miocene

The Zhongjiannan Basin is located west of the South China Sea (SCS) and was affected by the left-lateral strike-slip of the Red River Fault (RRF), the West Edge Fault of the South China Sea (WEFSCS) and the continental rifting of the South China Sea in the early Cenozoic. The Zhongjiannan Basin formed in a strike-pull basin with an S‒N distribution. During the middle Miocene, the sea spreading of the SCS stopped, but the dynamic mechanism of the Zhongjiannan Basin, which controlled the sedimentary and the structural evolution after the late Miocene, remains unclear. In this paper, through the segment interpretation of the latest seismic section in the Zhongjiannan Basin, we conduct a comparative study of the sedimentary structure in the southern and northern Zhongjiannan Basin since the late Miocene. Combined with the regional tectonic dynamics analysis, we propose that the sedimentary and structural evolution of the Zhongjiannan Basin since the late Miocene was mainly controlled by residual magmatic activity in the Southwest Subbasin (SWSB) after expansion stopped, and the compressional structure stress field weakened gradually from south to north. The compressional tectonic stress field from north to south was formed in the northern basin under the dextral strike-slip movement of the RRF. The sedimentary and structural environment was relatively stable in the middle basin. Therefore, the sedimentary-structure evolution of the Zhongjiannan Basin since the late Miocene was controlled by the two different structural stress fields. The above knowledge not only has guiding significance for oil and gas exploration in the Zhongjiannan Basin but also provides a reference for studying the initiation time of dextral strike-slip along the Red River Fault Zone, as well as the junction position between the RRF and the WEFSCS.

A previously unidentified fault revealed by the February 25, 2022 (Mw 6.1) Pasaman Earthquake, West Sumatra, Indonesia

A destructive earthquake (Mw 6.1) struck Pasaman, West Sumatra, Indonesia, on 25 February 2022, resulting in at least 18 deaths and damage to 1765 buildings. Our relocated foreshock, mainshock, and aftershocks and their source mechanisms reveal a previously unknown ∼20 km long segment of the Sumatran Fault as a result of dextral strike-slip motion (strike N132oE and dip 72oSW) along what we have called the Kajai Fault. The inverted rupture model indicates a single, compact asperity with an approximate depth range of 2–11 km. This asperity extends ∼14 km along strike, and ∼9 km in the down-dip direction. The Coulomb stress change of the mainshock shows that areas to the north and south experienced an increase in stress, which is consistent with the observed aftershock pattern. The nearby Great Sumatran Fault segments (Angkola and Sumpur) experienced a significant increase in stress without any accompanying aftershocks, which likely increases the risk of them rupturing in the future.

Crustal structure and magmatism of the Marvin Spur and northern Alpha Ridge, Arctic Ocean

SUMMARYThe Marvin Spur is a 450-km-long east–west trending escarpment along the northernmost periphery of the Alpha Ridge, starting about 500 km from the coasts of Ellesmere Island and Greenland off the Arctic Ocean margin of North America and running subparallel to the Amerasian margin of the continental Lomonosov Ridge. This region was investigated as part of the Canada–Sweden Polar Expedition in 2016, from which two seismic profiles are presented. The first is a 165-km-long line along the crest of the Marvin Spur. The second is a 221-km-long line extending southwestward from the spur to the northern flank of the Alpha Ridge within the Cretaceous High Arctic Large Igneous Province (HALIP). Multichannel seismic reflection data were acquired along both lines using a 100-m-long streamer, and the airgun shots were also recorded using 16 sonobuoys and 5 stations on the sea ice to calculate a velocity model for the crust from forward modelling of seismic traveltimes. The Marvin Spur profile reveals up to 1100 m of sedimentary rocks on top of a 1-km-thick series of basalts (4.5–5.1 km s−1). Upper and lower crust have velocities of 5.8–5.9 km s−1 and 6.2–6.3 km s−1, respectively, with the upper crust being 1–2 km thick compared to around 13 km for the lower crust. A wide-angle double seismic reflection manifests the top and base of a 6-km-thick lower crustal layer that we interpret as magmatic underplating beneath the continental crust of the Marvin Spur. We correlate a high-amplitude magnetic anomaly on Marvin Spur with a comparable anomaly on Lomonosov Ridge by invoking 110 km of dextral strike-slip motion. Assuming that HALIP-related magmatic deposits generate these anomalies, the strike-slip motion pre-dates the main phase of magmatism (latest Cretaceous, 78 Ma). On the northern Alpha Ridge, sediments are around 1-km-thick and cover a 700 to 1700-m-thick series of basalts with velocities of 4.4–4.8 km s−1. Below is a 3-km-thick layer with intermediate velocities of 5.6 km s−1 and a lower crust with a velocity of 6.8 km s−1. Moho depth is not resolved seismically, but gravity modelling indicates a total thickness of 13 or 18 km for the igneous crust except for the Fedotov Seamount where Moho deepens by about 5 km. Construction of the seamount occurred in multiple magmatic phases, including flow eruptions during deposition of the Cenozoic sedimentary succession post-dating the main HALIP magmatism.

Characteristics of stress field and crustal kinematics of the southern region of Sichuan-Yunnan block, southern Tibet Plateau

The Red River fault is a massive tectonic shear zone of the Sichuan-Yunnan block, southern Tibet Plateau. The target area of this study is the Red River fault's middle-northern section and adjacent areas. Considering the spatial difference of tectonic structures and the inhomogeneity of focal mechanism solutions, we divided the target area into three structural units: the northern extension area, the middle strike-slip movement area, and the west complex rupture area. The study is carried out on the basis of zoning. Using the CAP method to invert the focal mechanism of moderate earthquakes and the principal compressive and tensile stress. Restoring the seismic source spectrum of small and medium earthquakes, then inversion the stress drops in three sub-units based on Brune model using digital waveform records. Our study suggests that: (1) Many high-stress drop earthquakes occurred in the transitional areas from the Weixi-Qiaohou fault to the Red River fault and from the Chuxiong fault to the Qujiang fault, also occurred in the Changning-Baoshan-Yongping area, revealing a large accumulation of local tectonic stress. (2) Some events with Δσ ≥ 20 MPa have occurred in the prominent low-speed anomaly area, indicating that a passive deformation crossed the Red River fault and extended to the west. Yangbi MS 6.4 earthquake (2021) occurred in a strongly locked area with high potential earthquake risk. (3) In the north of the study region, the movement of the Sichuan-Yunnan block to SE-SSE orientation was governed by the dextral strike-slip movement of the NW strike fault; in the middle region, the SE-orientated movement of the block relative to the South China block was governed by the sinistral slip movement of the SN-strike faults; and in the west region, the tectonic stress was governed by clockwise rotation of the block and the sinistral slip movement of the NE strike faults. We suggest that strike slip and rotation of the Red River fault's middle section may drive and aggravate passive movement in the north section, resulting in locally geophysical field responses. Therefore, the potential risk of a large earthquake in the middle-northern section of the Red River fault should be monitored.

Deep-water Tectono-Stratigraphy at a Plate Boundary Constrained by Large N-Detrital Zircon and Micropaleontological Approaches: Peninsular Ranges Forearc, Baja California, Mexico

The distribution of sedimentary systems on Earth’s surface is intimately linked to tectonics, therefore, at plate boundaries the stratigraphic archive can unlock the timing and style of tectonism and relative plate motions. Using large-n detrital zircon and micropaleontological analyses, tied to field mapping and data collection, we unravel the timing of strike-slip motion and its influence on the development of a Cretaceous submarine canyon on a long-lived oblique-convergent margin. Structural analysis demonstrates that the canyon bedrock, composed of fluvial rocks (La Bocana Roja Fm., of maximum depositional age (MDA): 93.6±1.1 Ma), underwent both syn- and post-depositional contractional and extensional deformation during the Cenomanian-Turonian in response to dextral strike-slip movement. Relative sea-level rise associated with basin subsidence and hinterland uplift was coincident with incision and fill of a submarine canyon system (Punta Baja Fm., MDA 87.1±1.5 Ma to 84.9±2.0 Ma), which exploited structural lineaments in the bedrock. The canyon was filled by sediment derived from an uplifted magmatic arc during the Coniacian to Santonian, most likely shed from erosional topography associated with plutonic intrusions to the NE. Structural data suggest that oblique dextral strike-slip motion on the Pacific margin controlled the development and location of submarine erosion, and had ended by the earliest Santonian, significantly earlier than previously estimated. Basinward tilting led to uplift, followed by transgression and wave ravinement of the canyon fill, which was then overlain by a shallow-marine to fluvial system. Thus, the canyon was cut, filled, buried, uplifted and rotated basinward, planed off through wave ravinement, and onlapped by shallow-marine to fluvial sediments within an 8 Myr period. Our findings, in part, reconcile contrasting basin evolution models for the Late Mesozoic Pacific margin.

The Kalaotoa Fault: A Newly Identified Fault that Generated the Mw 7.3 Flores Sea Earthquake

AbstractWe reveal the existence of a previously unknown fault that generated the Mw 7.3 Flores Sea earthquake, which occurred on 14 December 2021, approximately 100 km to the north of Flores Island, in one of the most complex tectonic settings in Indonesia. We use a double-difference method to relocate the hypocenters of the mainshock and aftershocks, determine focal mechanisms using waveform inversion, and then analyze stress changes to estimate the fault type and stress transfer. Our relocated hypocenters show that this earthquake sequence ruptured on at least three segments: the source mechanism of the mainshock exhibits dextral strike-slip motion (strike N72°W and dip 78° NE) on a west–east-trending fault that we call the Kalaotoa fault, whereas rupture of the other two segments located to the west and east of the mainshock (striking west-northwest and southeast, respectively) may have been triggered by this earthquake. The Coulomb stress change imparted by the rupture of these segments on nearby faults is investigated, with a focus on regions that experience a stress increase with few associated aftershocks. Of particular interest are stress increases on the central back-arc thrust just north of Flores and the north–south-striking Selayar fault in the northwest of our study region, both of which may be at increased risk of failure as a result of this unusual earthquake sequence.

Rapid Exhumation Processes of the Gaoligong Mountain Range in the Southeastern Margin of the Qinghai–Tibet Plateau Since the Late Cenozoic

Three continent-scale ductile shear zones trending N-S are distributed in the southeast margin of the Qinghai–Tibet Plateau. Their tectonic deformation and exhumation histories are of great significance to understanding the orogenic processes within the continent and the growth as well as expansion mechanism of the plateau. The Gaoligong shear zone (GLGSZ) is the westernmost zone near the boundary of the Indian subduction plate and is less well studied than the Ailaoshan–Red River shear zone (ASRRSZ) in the east. In this study, low-temperature thermochronological methods including apatite (U-Th)/He (AHe), zircon (U-Th)/He (ZHe), and apatite fission track (AFT) were used to date the vertical profile samples from the Gaoligong Mountain to understand the exhumation processes that occurred in the late Cenozoic. Our results show that the GLGSZ has experienced two stages of rapid exhumation events since the late Cenozoic: in the middle Miocene (∼14.5 Ma) and early Pleistocene (∼2.9 Ma). Based on our data, we divided the late Cenozoic tectonic deformation and exhumation processes in the Gaoligong Mountain area into two stages: 1) From the middle to the late Miocene, large-scale regional dextral strike-slip movements and lateral compressions controlled the ductile shear zone and continuously denuded the mountain surface; 2) in the Pleistocene, rapid river erosion and undercutting caused by fluctuations of the monsoon system, together with the continuous activity of brittle faults, drove the latest rapid exhumations. A comparison of the thermochronological data of the different areas along the Gaoligong Mountain shows that the exhumation rate in its northern transect is significantly higher and the time of the onset of exhumation is earlier than that in the southern transect. These results indicate that the deformation processes began in the north and continued southwards and controlled the geomorphological characteristics of the Gaoligong Mountain, whose elevation is higher in the northern part than in the southern part.

The Coles Hill Uranium Deposit, Virginia, USA: Geology, Geochemistry, Geochronology, and Genetic Model

Abstract The Coles Hill uranium deposit, with an indicated resource of about 130 Mlb of U3O8, is the largest unmined uranium deposit in the United States. The deposit is hosted in the Taconian (approx. 480–450 Ma) Martinsville igneous complex, which consists of the Ordovician Leatherwood Granite (granodiorite) and the Silurian Rich Acres Formation (diorite). The host rock was metamorphosed to orthogneiss during the Alleghanian orogeny (approx. 325–260 Ma), when it also underwent dextral strike-slip movement along the Brookneal shear zone. During the Triassic, extensional tectonics led to the development of the Dan River Basin that lies east of Coles Hill. The mineralized zone is hosted in brittle structures in the footwall of the Triassic Chatham fault that forms the western edge of the basin. Within brittle fracture zones, uranium silicate and uranium-bearing fluorapatite with traces of brannerite form veins and breccia-fill with chlorite, quartz, titanium oxide, pyrite, and calcite. Uranium silicates also coat and replace primary titanite, zircon, ilmenite, and sulfides. Sodium metasomatism preceded and accompanied uranium mineralization, pervasively altering host rock and forming albite from primary feldspar, depositing limpid albite rims on igneous feldspar, altering titanite to titanium oxide and calcite, and forming riebeckite. Various geothermometers indicate temperatures of less than ~200°C during mineralization. In situ U-Pb analyses of titanite, Ti-oxide, and apatite, along with Rb/Sr and U/Pb isotope systematics of whole-rock samples, resolve the timing of geologic processes affecting Coles Hill. The host Leatherwood Granite containing primary euhedral titanite is dated at 450 to 445 Ma, in agreement with previously obtained ages from zircon in the Martinsville igneous complex. A regional metamorphic event at 330 to 310 Ma formed anhedral titanite and some apatite, reequilibrated whole-rock Rb/Sr and U-Pb isotopes, and is interpreted to have coincided with movement along the Brookneal shear zone. During shearing and metamorphism, primary refractory uranium-bearing minerals including titanite, zircon, and uranothorite were recrystallized, and uranium was liberated and mixed locally with hematite, clay, and other fine-grained minerals. Uranium mineralization was accompanied by a metasomatic episode between 250 and 200 Ma that reset the Rb-Sr and U-Pb isotope systems and formed titanium oxide and apatite that are associated and, in places, intimately intergrown with uranium silicate dating mineralization. This event coincides with rifting that formed the Dan River Basin and was a precursor to the breakup of Pangea. The orientation of late-stage tectonic stylolites is compatible with their formation during Late Triassic to Early Jurassic basin inversion, postdating the main stage of uranium mineralization and effectively dating mineralization as Mesozoic. Based on the close spatial and temporal association of uranium with apatite, we propose that uranium was carried as a uranyl-phosphate complex. Uranium was locally reduced by coupled redox reactions with ferrous iron and sulfide minerals in the host rock, forming uranium silicates. The release of calcium during sodium metasomatic alteration of primary calcic feldspar and titanite in the host rock initiated successive reactions in which uranium and phosphate in mineralizing fluids combined with calcium to form U-enriched fluorapatite. Based on the deposit mineralogy, oxygen isotope geochemistry, and trace element characteristics of uranium silicate and gangue minerals, the primary mineralizing fluids likely included connate and/or meteoric water sourced from the adjacent Dan River Basin. High heat flow related to Mesozoic rifting may have driven these (P-Na-F-rich) fluids through local aquifers and into basin margin faults, transporting uranium from the basin or mobilizing uranium from previously formed U minerals in the Brookneal shear zone, or from U-enriched older basement rock.