Newly obtained geochemical and geochronological data from the Saih Hatat Dome in northeastern Oman and the Betsiaka Group in northern Madagascar reveal compelling similarities in the Neoproterozoic geological evolution of these geographically distant regions. The Saih Hatat Dome serves as a tectonic window with a NW-SE extension of <95 km and an E-W extension of <50 km. It is encircled by the allochthonous Samail Ophiolite and the underlain nappes consisting of mostly sedimentary rocks from the Neo-Tethyan Hawasina Basin. The rocks within this window underwent Late Cretaceous high-pressure/low-temperature eclogite- and blueschist-facies metamorphism.

In contrast, the Betsiaka Group of northern Madagascar, located between the Neoproterozoic Bemarivo Belt (750-720 Ma) and the Permo-Mesozoic cover, includes amphibolites, garnet-sillimanite micaschists, quartzites, and rare calc-silicate rocks.

New U-Pb zircon LA-ICP-MS data from a quartzdiorite dyke, intruding the basal part of the Hatat schists of the Saih Hatat Dome, yielded a crystallization age of 845 +2/-4 Ma. Similarly, a U-Pb zircon age of 841 ± 5 Ma was determined from an orthogneiss within the Betsiaka Group. Both igneous suites exhibit a calc-alkaline geochemical signature characteristic of volcanic island arcs.

The quartzdiorite in the Saih Hatat intruded a volcanosedimentary sequence and is covered by Cryogenian to Ediacaran metasedimentary and metavolcanic formations. Two metatuffites contain igneous and detrital zircons with ages ranging from approximately 530 to 2872 Ma, featuring clusters around 750 to 850 Ma and 1010 to 1164 Ma. Ages exceeding 1.1 Ga are unprecedented from an Arabian Plate source. Conversely, a quartzite from the Betsiaka Group displays a youngest >90% concordant zircon age of 1771 ± 28 Ma, with age peaks at around 2.5, 2.4 Ga, 1.8 Ga, and 1.85 Ga, pointing towards a Late Paleoproterozoic deposition age. Zircon ages between 1.77 and 1.85 Ga are also absent from central Madagascan igneous rocks. We propose that these crustal fragments in Oman and Madagascar originated from an area previously proximate to the Aravalli Craton in NW India.

How to cite: Bauer, W., Rasaona, I. T., Jacobs, J., Collins, A., Edwards, L. E., Callegari, I., and Scharf, A.: Evidences for Neoproterozoic fragments with Indian origin in Oman and northern Madagascar, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1308, https://doi.org/10.5194/egusphere-egu24-1308, 2024.

In this study, we present enigmatic exposures of suspected Cambrian age deposits of the Haushi-Huqf High, Central Oman. The present study area is an uplifted horst-block bounded by north-south oriented normal faults, with onlapping Mesozoic carbonate deposits on its western and eastern flanks, covering an outcrop area of ~1 km². This exposure reveals decameter to kilometer-scale concentric, nested and coalescing ring-like structures superimposed within a clastic host rock, forming regularly spaced structural highs with lateral thicknesses and heights of one to several meters bounded by several meter wide troughs infilled with recent sediments. The host rock comprises fine to coarse grained, cross stratified quartz arenites, with basal pebbly lags, and with paleocurrents indicating a W-SW paleo-transport direction. The significant textural/mineralogical maturity of these sandstones suggests extensive recycling of older sediments, with the presence of frosted, well rounded grains signifying aeolian input. Establishing the stratigraphic position of the deposit within the regional context is challenging, owing a lack of body fossils, datable strata or correlatable stratigraphy proximal to the study site. However, Uranium-Lead Zircon dating of the host rock does reveal two geochronological populations: Neoarchaean to Paleoproterozoic (2.8-2.5 Ga), likely sourced from Precambrian basement rocks of Northern and Eastern Yemen, and Early Cambrian (~530 Ma), likely sourced from Cambrian-aged alkaline magmatism located within close proximity to the study site. Based upon the above, coupled with the observed textural, mineralogical and depositional characteristics of the deposit, we postulate that a Lower Paleozoic origin (esp. Amin Fm. Of the Haima Supergroup) is likely.

Interpreted as fluivial-plain / fluvio-deltaic in origin, these rocks exhibit bioturbation within a select interval in the form of large horizontal/vertical calcite cemented burrows, indicating marine influence and colonization by benthic macrofauna. Furthermore, a thin, laterally continuous deposit of botryoidal calcite is observed, which commonly pinches out between reactivation surfaces. We interpret this deposit as recrystallized bacterially induced precipitates of calcium carbonate, signifying the presence of microbial mats developed during a short-lived period of marine incursion. Petrographic analysis reveals that there is a strong association between the pronounced diagenetic overprint of the study area and the occurrence of this deposit. Ridges structural highs exhibit major chemical compaction and porosity collapse via the development of quartz overgrowths. Conversely, topographic lows between these structures are generally porous and poorly consolidated, being characterized by the presence of calcite cementation and hematite grain coatings. The contrasting mechanical competence of the sandstones forming the topographic highs and lows offer spatial controls over differential weathering and erosion of the study area, resulting in the remarkable diagenetic architecture observed therein. It is proposed that spatially disparate early calcite cementation associated with microbial mat colonization protected the pore system from pervasive chemical compaction, which was extensively removed by meteoric dissolution post-exhumation. The pronounced spatial organization of calcite precipitation and cementation controlling these structures poses fascinating questions regarding the self-organization of microbial mat communities during the Cambrian substrate revolution, hinting at the influence of internal feedback and environmental controls in their nucleation and propagation.

How to cite: Seers, T., Laya, J. C., Corradetti, A., Ewing, R., and Miller, B.: Enigmatic Kilometric Scale Diagenetic Structures of the Haushi-Huqf High, Central Oman, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19309, https://doi.org/10.5194/egusphere-egu24-19309, 2024.

In the United Arab Emirates, the Late Triassic events including the Carnian Pluvial Episode are relatively poorly studied compared to the carbon isotope excursion and extinction event at the Triassic-Jurassic boundary. This study presents an integrated approach using geochemical and sedimentological data to investigate the depositional and environmental changes through the Late Triassic into the earliest Jurassic. Upper Triassic sediments exposed in Wadi Milaha consists of the marine Milaha and Ghalilah formations. The upper part of the Milaha Formation comprises limestone (predominantly mudstones and wackestones), with subordinate sandstone, marl and shale deposited in a shallow marine environment with some evidence of high-energy shoal deposition represented by ooidal and bioclastic grainstones and packstones. Clastic input varies cyclically and correlates with higher-order sea-level fluctuations. Faunal content includes bivalves, green algae, echinoderms, and benthic foraminifers, and suggests deposition in a shallow semi-restricted to open marine environment. Elemental proxies including Fe and Mn enrichment factors show widespread oxygen deficiency during the Late Norian on this equatorial shelf of Panthalassa. The Late Norian-Hettangian Ghalilah Formation is further broken into the Asfal and Sumra members. The first of these members is dominated by floatstones and rudstones with a higher content of coarse siliciclastics, indicating deposition in regressive conditions. The Sumra Member shows a decrease in coarse siliciclastics and an increase in mudstones, wackstones and packstones indicating a transgressive sea level cycle following the sequence boundary at the top of Asfal. The XRF elemental data also indicate fluctuations in clastic input throughout the Asfal and Sumra members indicative of increased weathering fluxes likely associated with a change to more humid conditions through the Late Triassic. A loss of fauna as well as ooidal grainstones are present at the top of the Sumra Member and continue into the Sakhra Member of the Ghalilah Formation indicating the well-documented extinction at the Triassic–Jurassic boundary. These new data from the equatorial margin of Panthalassa highlight significant environmental and climatic shifts through the Late Norian to Hettangian.

How to cite: Shah, A., Hennhoefer, D., Al-Suwaidi, A., Alsuwaidi, M., and Thomas Steuber, T.: Environmental change and stratigraphy of the Upper Triassic sediment succession in Ras Al-Khaimah, UAE, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14336, https://doi.org/10.5194/egusphere-egu24-14336, 2024.

The Late Cretaceous emplacement of the Semail ophiolite and underlying thrust sheets onto the Arabian continental margin is well constrained by geochronological data. The stratigraphy and the development of the foreland basin in front of the advancing nappes is still poorly understood. This study aims to unravel the tectonostratigraphy of the foreland basin and link this to different stages of the nappe emplacement.

Obduction is associated with a major regional Turonian (92Ma) unconformity that ended the middle Cretaceous shallow water carbonate deposition on the passive margin. Locally this is related to the development of a foreland bulge in front of the southward advancing nappes. It caused collapse and erosional recession of the platform margin; the platform top was subaerially exposed and was incised by fluvial valley systems some 150 m deep.

Along the collapsed margin, a sedimentary mélange formed with re-deposited platform sediments and blocks. These were later incorporated into the thrust complex and returned tectonically onto the margin. The subaerial unconformity on the exposed carbonate platform was onlapped during the initial phase of foredeep development by a thin (150 m thick 150km wide) transgressive carbonate ramp as it subsided into a starved foredeep. Further forebulge onlap was by fine-grained coastal clastics that were sourced laterally from local uplift of the Huqf Basement along the eastern margin of the Arabian Plate.

Transgression ended in the Santonian (85Ma) and is followed by some 250 km northward progradation of a mud-prone delta complex of more than 1 km thick into the southeastern part of the foredeep. This deltaic wedge has been incised by deep canyons and slump scars suggesting slope collapse and sediment by-pass during the Early Campanian (83Ma). The eroded slope is onlapped by a sequence of laterally-derived siliciclastic turbidite siltstones and sands which onlap the nappes to the north demonstrating that nappe emplacement ended in the early Campanian. The clastics are sourced from exposed Upper Paleozoic clastics in the Huqf area. There is very little detritus from the orogen.

The Late Campanian to Maastrichtian deposition in the foredeep consists of hemipelagic chalks and marls which can be more than 1300 m thick. Influx of detrital sediments from the orogen is restricted to a strip just a few kilometers wide in front of the thrusts.  This sequence is affected by a latest Campanian tectonic uplift associated with incisions up to 150 m deep filled with redeposited hemipelagic carbonates. This event may be related to inversion in eastern Oman coinciding with slab break-off (ca 75Ma) and exhumation of the subducted continental margin in the northeast.

The foredeep along the ophiolite obduction complex was a persistently underfilled basin:  filled by hemipelagic carbonates and local clastic detritus from the forebulge. Lack of sediment input from the orogen suggest that this was mostly subaqueous. Limited uplift may be related the high density of the ophiolite slab and could be a general feature of obduction orogens. Erosion by dissolution could help explain the lack of sediment input from both the forebulge and the orogen.

How to cite: Droste, H., Levell, B., and Searle, M.: The sedimentary record of ophiolite obduction in North Oman, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4386, https://doi.org/10.5194/egusphere-egu24-4386, 2024.

The Rus Formation consists of a succession of carbonate rocks deposited in the Southeastern Arabian foreland system during the Paleocene-Ypresian. Throughout the UAE, the Rus Formation is commonly restricted to the subsurface of the Abu Dhabi Emirate territory, with the exception near the western front of the Hajar Mountains close to Al Ain city. At this location, the Rus Formation is exposed and forms the core of the Jebel Hafeet km-scale anticline fold. This large-scale exposure allowed us to study its stratigraphic and tectonic evolution from deposition to the present-day tectonic framework. Lithostratigraphic and facies analyses of the outcropping portion of the Rus Formation at Jebel Hafeet identified a succession of approximately 150 m of limestones and dolostones characterized by three main depositional facies:

• platform facies, characterized by thick to massive carbonate beds with abundant shallow-water bioclasts;
• ramp facies, showing evidence for syn-depositional instability, with mass flows and collapse structures;
• ramp-basin facies, characterized by thin beds with marked downlapping geometries.

Thus, the studied succession forms a complete platform-to-foreland basin transition that is well-exposed along the hinge of the fold structure. The base of the Rus Formation is concealed beneath the widespread quaternary cover, whereas the top of the Rus consists of unconformable stratigraphic contact with the Dammam Formation.

During the Early Cenozoic, the depositional environment of the Rus Formation was probably subjected to far-field stress due to the migration of the foreland depocenter in response to the obduction of the ophiolite slabs onto the Arabian continental margin successions. Structural analyses of deformation features such as faults and folds and geochronological/geochemical analysis of the correlated calcite veins (U-Pb on calcite) within the Rus Formation revealed that compressive tectonics generated the main folding event and drove subsequent exhumation from c. 20 to 2 Ma. Thus, these new data suggest that the deformation and uplift of Jebel Hafeet succession occurred in the context of post-Oligocene tectonics simultaneously with the Zagros collision but were likely developed along a strike-slip system accommodating the push of the Eastern Makran Belt.

How to cite: Decarlis, A., Hennhöfer, D., Arboit, F., and Ceriani, A.: Stratigraphic and tectonic setting of the Rus Formation at Jebel Hafeet, UAE., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8861, https://doi.org/10.5194/egusphere-egu24-8861, 2024.

The geology of northern Oman and eastern Arabia is distinctive because of the emplacement of the Semail Ophiolite onto the stable Arabia platform in the late Cretaceous followed by the later development of the Jebal Akhdar and Saih Haitat domes. East of Muscat, the Wadi Kabir Fault forms an important structure along which the northern edge of the Saih Hatat domes was unroofed.  In the Bandar Jissah area, Triassic carbonates occur in the footwall of the NNE-dipping Wadi Kabir Fault while rocks of the Semail Ophiolite, newly discovered rocks of the metamorphic sole, and a sequence of Paleogene sedimentary rocks crop out in the footwall.  Some workers posit that the Wadi Kabir and associated faults form basin-bounding faults for the Bandar Jissah rift basin and that folds in the hanging wall cover sequence are the product of rollover during basin formation.

However, our detailed mapping and kinematic analysis illustrates that folds in the hanging wall are actually contractional structures that formed due to tectonic inversion along the Wadi Kabir and other faults.  The overall shortening is modest (~10%) and primarily confined to the hanging wall rocks, consistent with buttressing against mechanically rigid rocks in the footwall of the Wadi Kabir Fault.  These structures require an interval of N-S directed shortening in northern Oman  that post-dates the deposition of mid-Eocene marine sediments in the Seeb Formation. The Wadi Kabir Fault also has localized zones of listwaenite preserved in its damage zone derived from ophiolitic rocks. Collectively, the Wadi Kabir Fault is a long-lived structure that’s experience multiple episodes of extensional and contractional slip since the Paleocene.

How to cite: Bailey, C. and Driscoll, E.: Tectonic inversion in the Bandar Jissah Area: evidence for Cenozoic contraction in northern Oman, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18950, https://doi.org/10.5194/egusphere-egu24-18950, 2024.

Jebel Madar is located in the Adam Foothills of North Oman. It has been interpreted as a salt-cored, faulted anticline caused by the movement of the Precambrian-Cambrian Ara salt Fm, during the orogeny of the Oman mountains. The out-cropping Shuaiba and Natih carbonate rocks are reservoirs analogues for numerous Omani hydrocarbon fields. The maximum depth of burial is interpreted to be similar to those observed in the sub-surface fields. Therefore, Jebel Madar is considered a perfect structural analogue of fracture and fault dominated reservoirs above a salt dome in sub-surface conditions. Previous fracture studies focused mostly on the peripheral parts of Jebel Madar (i.e., Natih Fm.). Thus, fracture patterns are described as being radial, independent from regional fault and fracture pattern, and therefore, hypothesized as controlled by salt doming.

Recently, we conducted a high-resolution drone photogrammetry survey focused on the central parts of the jebel, in order (1) to update and detail fault and fracture patterns; (2) to refine our understanding of its structural evolution model; (3) to serve as a foundation for virtual reality field trips and courses.

The dataset comprises ~ 37,000 drone photographs with a total aerial coverage of ~ 6 km² and a resolution between 3cm and 1 mm. This enables us to develop 44 Digital Outcrop Models (DOMs), with a total of ~ 10.2 billion points. This unique database allows us to quantify the fault and fracture networks of Jebel Madar, in terms of orientation, intensity and 3D arrangement. The DOMs also provide a unique opportunity to map, analyze and interpret fractures and faults that are not accessible by field geology, but only accessible by drone.

This contribution shows early results of the high-resolution Digital Outcrop Model-based fault and fracture analysis. We will illustrate the impact of mechanical stratigraphy on fracture distributions in 3D and re-evaluate the impact of regional tectonics on the structural rise of the dome.

How to cite: Menegoni, N., Panara, Y., Iakusheva, R., Lamarche, J., Richard, P., and Finkbeiner, T.: Fracture network analysis of Jebel Madar (North Oman): new perspectives from very-high resolution Digital Outcrop Modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16878, https://doi.org/10.5194/egusphere-egu24-16878, 2024.

Oman is situated in the southeastern Arabian plate, just behind the Makran subduction zone. The internal stability of this portion of the Arabian plate must be questioned, however, based on recent studies focusing on long-term observations. These studies provide evidence of active deformation in the Hajar mountains of northern Oman and the UAE. Specifically, recent studies that focused on vertical deformation, yielded temporally and spatially variable vertical rates ranging from 0.01 to 0.89 mm/a in northeastern region of the Arabian Peninsula (Hoffman et al., 2020). Others presented evidence of the continuing uplift of some domes in the Hajar mountains. Furthermore, a significant seismic contrast is well-documented along the Makran subduction zone in Iran and Pakistan. This provides an opportunity to study whether the regional-scale uplift pattern of the Hajar mountains correlates with the variability in deformation style along the Makran plate interface or is caused by driving forces unrelated to horizontal plate motion and subduction. Monitoring the contemporary motions of the northeastern boundary of the Arabian plate can, therefore, enhance our understanding of the complex kinematics of the Makran region. Here, we provide first results of our space-geodetic study in which we combine, both, vertical and horizontal motion analysis to determine the present-day 4D-temporal and spatial strain variability across Oman.

The National Survey Authority (NSA) that runs the GNSS reference network across the Sultanate of Oman, established a continuously operating network of 47 sites in 2016. Since its establishment, the network served numerous positioning and mapping activities within the country, providing a precise tool to study the internal deformation of the southeastern Arabian plate. Six-and-a-half years of continuous data acquisition were utilized in our study, combined with 26 IGS stations, to derive horizontal and vertical displacement rates, initially in ITRF20.

A new regional reference frame for Oman was realized by rotating ITRF20 so that the horizontal velocities of the Oman CORS stations are minimized in the new reference frame ONGD23. As a result of this process, the average rigid-body rotation of the Arabian plate was estimated and eliminated. The residual velocities illustrate internal horizontal and vertical deformation across Oman, ranging from fractions of millimeters per year to a few millimeters per year. The spatial pattern varies from 1.5 mm/a subsidence in the north to 0.1 mm/a uplift in the northeast. Subsidence of 1.2 to 1.8 mm/a is documented around oil fields. The results also yield uplift rates of up to 0.8 mm/a near certain domes of the Hajar mountains. A noticeable pattern of subsidence transitioning to uplift, from west to east, is observed across the Hajar mountains. Surprisingly, however, the southern flanks of the mountains yield gradual uplift rates. The Arabia – Eurasia plate convergence cannot be directly responsible for such regional scale uplift. Additional mechanisms must be invoked to explain this enigmatic intra-plate strain.

How to cite: Abolghasem, A. M., Friedrich, A. M., Al Balushi, F., Al Sheidi, I., Al Musalhi, A., and Al Wardi, Y.: Present-day deformation rates across Oman based on space Geodesy , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18604, https://doi.org/10.5194/egusphere-egu24-18604, 2024.

In the first phase of the International Deep Profiling of Tibet and the Himalaya the INDEPTH project an over 90 km long deep seismic reflection profile was acquired. This was an interdisciplinary program of geophysical and geological studies focus to increase the understanding of the internal architecture and mechanics of the Himalaya-Tibet region. Reprocessing of INDEPTH-I deep seismic reflection image resolves the South Tibetan Detachment System (STDS) as composed by few laterally displaced ramp structures. These can be interpreted to be structurally related to the outcropping gneiss domes. The STDS is recognized as complex extensional shear zone most probably coeval with the emplacement of the leucogranitic bodies. Geologic data indicates that the latter are pre-, syn- and post- kinematic with the deformation and, are generally controlled by the system of detachment faults (including the STDS). The interpreted STDS is broken up, and the individual segments are tilted revealing compressional deformation. Underneath, and down to 42 km depth, two prominent high amplitude, multi cyclic, north dipping events are imaged: the Tethyan Himalayan Sequence (THS) and, the Greater Himalayan Sequence (GHS). Above the GHS the north-dipping reflection fabrics appear imbricate and are seldom interrupted by weak/transparent zones. The existing geological knowledge and, the geometrical relationships (unraveled by the internal architecture constrained by the seismic image suggest that the transparent areas in the GHS could be indicative of leucogranite emplacements. Thus, the latter can be interpreted as the product of rapid exhumation of the upper GHS together with magma along the High Himalayan Thrust (HHT), repeated in-situ remelting due to strain heating by exhumation of the lower GHS and Lesser Himalayan Sequence (LHS), and extension of the South Tibetan Detachment System (STDS). This mechanism is consistent with interpretation of seismically transparent zones as the seismic response of granitic plutons.

How to cite: Carbonell, R., Li, H., Gao, R., and Lu, Z.: Revisiting the INDEPTH-I Deep seismic profile in Himalayan Orogen: Constraints on structure and leucogranites emplacement, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22363, https://doi.org/10.5194/egusphere-egu24-22363, 2024.

The Indian collision has deformed the eastern Asian continent in a multifaceted way, uplifting Tibet and surrounding mountains, activating ≥ 1000 km-long strike-slip faults, and opening Tertiary rifts and oceanic basins up to ≈ 3000 km away from the Himalayas. Modelling such broad-scale tectonics has been challenging. While continent-scale, lithospheric deformation appears to have been primarily taken-up by long, narrow, inter-connected shear-zones with large offsets, the contribution of processes such as channel-flow, collapse, delamination, etc… has remained contentious. Here, based on increasing ⁴G (Geological, Geophysical, Geochronological, Geodetic) evidence including kinematic and timing constraints on the main mechanisms at play, we use Discrete Element (DE) Modelling to simulate and further understand the evolution of 3D strain across east Asia since the onset of collision, ≈ 55 Ma ago. The planar, 50 million km², 125 km-thick models are scaled for gravity. The approach permits mega-fault generation and evolution without pre-arranged initial settings. The results provide insight into fault birth, propagation, and motion, as well as mountain building and plateau growth. They corroborate that continental crustal thickening across Tibet alternated with the extrusion of large blocks that rifted apart in the far field. Remarkably, without changes in boundary conditions or indentation rate, the DE model also vindicates slip reversal along initial strike-slip shear zones.

How to cite: Jiao, L., Donze, F.-V., Tapponnier, P., Scholtes, L., Gaudemer, Y., and Xu, X.: Discrete Element Modelling of Southeast Asia’s 3D Lithospheric Deformation during the Indian Collision, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4476, https://doi.org/10.5194/egusphere-egu24-4476, 2024.

In seminal papers Paul Tapponnier revealed the existence of several hundred-km-long active strike-slip faults in and around the Tibetan plateau where, the India-Asia collision was expected to only produce reverse faults and folds (e.g., Tapponnier et Molnar, 1977). He latter further stressed out the role of such large strike-slip faults in the long-term building of the plateau, especially on its eastern side, (e.g., Tapponnier et al., 1982; 1990; 2001). the so-called extrusion tectonics model rises major discussions in particular on how SE Tibet evolved through time and in a more general way how the continental crust deforms. Completely different, sometime antagonistic, models have since been proposed for the geological and topographic evolution of SE Tibet, such as the channel flow hypothesis (e.g.; Royden et al., 1997; Clark and Royden, 2005). Central to this discussion are the Ailao Shan – Red River (ASRR) metamorphic belt and the eastern topographic margin of the Eastern Tibetan plateau.

The ASRR has been interpreted as a major left-lateral faults allowing the ≥500 km lateral escape of Sundaland toward the SE during the Miocene (e.g.; Tapponnier et al. 1990, Leloup et al., 1995, 2001), linked with the opening of the South China Sea (Briais et al., 1993). On the other hand, other propose that the ASRR as a limited offset and / or is an exhumed piece of a lower crustal channel (e.g. Searle, 2006; Mazur et al., 2012; Chen et al., 2023).

The eastern margin of the Tibetan plateau geological history is also disputed. It has been interpreted as a topographic step passively uplifted by eastward propagation of lower crustal channel flow during the Upper Miocene (e.g., Clark et al., 2005; Royden et al., 2008; Burchfiel et al., 2008). Other favour the existence of a ~800 km long thrust belt where thrusting take place since the Oligocene linked to crustal shortening (e.g.; Tapponnier et al., 2001; Liu-Zeng et al., 2008; Zhu et al., 2021; Pitard et al., 2021; Ge et al., 2023) in complex interaction with the Xianxuihe left-lateral fault since ~9 Ma (e.g.; Zhang et al., 2017).

At the light of the thermochronological and geochronological data allowing to better constrain the timing of exhumation and deformation in the ASRR, the Xianshuihe fault and along the Eastern Tibetan margin we will discuss how the channel flow model appear flawed and how large strike-slip fault have interacted with reverse faults to shape eastern Tibet since the Oligocene.

How to cite: Leloup, P. H.: Interaction between large strike-slip faults and reverse faulting shapes East Tibet since the Oligocene, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21522, https://doi.org/10.5194/egusphere-egu24-21522, 2024.

As part of his sabbatical at Schlumberger in the ARAMCO in 2008-2009, Paul Tapponnier started a complete reassessment of the plate tectonic structure, age and evolution of the Red Sea.  Public and industrial geophysical data, including gravity, magnetics, and seismics, covering the whole Red Sea, have been (re)interpreted in view of recent concepts.  This study concluded that oceanic lithosphere covers a large part of the Red Sea, although the expression of seafloor spreading in the whole ultraslow-spreading northern Red Sea and on the earlier stage of opening in the central and southern Red Sea is hidden by the thick salt cover.  We have been associated to this research between 2009 and 2013 and beyond, and will present some highlights of this exciting period.

How to cite: Dyment, J., Afifi, A., and Briais, A.: Working with Paul Tapponnier on the Structure, Age and Evolution of the Red Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18476, https://doi.org/10.5194/egusphere-egu24-18476, 2024.

The India-Eurasia collision zone is the largest deforming region on the planet with numerous faults and widespread earthquakes, extending from the Himalayan Front to north of the Tien Shan. Developed from plate tectonic theory, block models have long been used to describe the crustal deformation in the collision zone, and GPS data are often invoked to constrain and test the models. Although previous block models perform well against GPS data on the whole, the detailed performance in many areas of the collision zone remains uncertain due to sparsity of GPS data and the low resolution of the fault database used to define the blocks.

In this study, we process the raw GPS data collected via regional continuous GPS observation networks and Crustal Movement Observation Network of China (CMONOC) up to 2021, mainly located in Tibet, and obtain our core GPS velocity field with 420 continuous and 872 campaign stations. We further incorporate published GPS velocities, mainly located in the Himalaya and Tien Shan regions. We convert these velocities into our core solution to keep all the velocities in a consistent reference frame. As a result, we provide the densest and up-to-date GPS velocity field in the India-Eurasia collision zone including 2811 stations. Although the stations from CMONOC have been presented before, our updated velocities are more robust as they are derived from a longer time span, e.g., 5 years more than Wang and Shen [2020]. Also, we add an extra 351 stations for the collision zone compared to Wang and Shen [2020], most of which are continuous stations, over 300 of which have never been published. Wright et al. [2023] presented the first high-resolution InSAR velocity field for whole Tibet. Constraints from the InSAR data enable us to effectively evaluate the detailed performance of block modeling in Tibet, especially in the remote regions where the GPS data are sparse.

We incorporate the GPS and InSAR velocity fields, and 170 Quaternary fault slip rates into a recently-developed high-resolution block model with 237 blocks by Styron [2022] to predict block motion and fault slip rates throughout the collision zone. The block model fits the data well in general, although there are some significant residuals. The predicted slip rates along ~900 faults from the model are generally small except for those along several major faults, including the major Tibetan strike-slip faults, which have larger slip rates but still within the level of 10 mm/yr, and the Main Himalayan Thrust, which has a convergence rate at the level of about 15 mm/yr. The predicted slip rates show along-strike variations, and are consistent with previous geodetic studies. We then use our results to assess the limitations of tectonic block modelling for applications in seismic hazard assessment and in understanding the geodynamics of continental tectonics. The results suggest that tectonic strain has two modes: a few major faults exhibit focused strain and high slip rates; between these major structures, deformation is more continuous.

How to cite: Zheng, G., Wright, T., Styron, R., Fang, J., Ou, Q., Wang, D., Geng, J., Zhao, B., Wang, D., and Liu, J.: Testing high-resolution block modeling of the India-Eurasia collision zone with GPS, InSAR and geological fault slip rate data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18578, https://doi.org/10.5194/egusphere-egu24-18578, 2024.

Quantitative and high-precision vertical movements are indispensable for resolving the geological diversity of the Tibetan Plateau. In this study, we proposed a joint geodetic adjustment with Helmert iteration algorithm, systematically analyzed its merits with simulated data, and then jointly processed the datasets, including 116,000 km of leveling data, 21 continuous GNSS data sets, and their connecting surveying data, to get a high-precision vertical velocity field for the Tibetan Plateau. The primary results are as follows: (a) Compared with the single leveling data adjustment, the joint Helmert adjustment results of leveling data (i.e., the leveling data and errors are generated by simulation under the first order leveling regulations, which includes 55,708 km, 4605 segments, 4584 points, 22 loops and 40 nodes) and 500 geodetic simulated data (including 2–4 mm/yr errors) demonstrate that the Helmert adjustment can reduce the residual distribution range by roughly 46%; (b) Vertical uplift is dominant on the southern, northeastern, and southeastern margins of the plateau, with uplift rate ranges of 2.0–3.0, 1.0–3.8, and 1.0–2.0 mm/yr, respectively; (c) Conspicuous subsidence is located along the southern portion of the Ganzi fault, with vertical rates ranging from −3.3 to −0.5 mm/yr; (d) Velocity profiles show that vertical deformation varies in different parts of the Tibetan Plateau, which is mostly accommodated by large strike-slip and thrust faults, such as the Kunlun, Ganzi, and Longmenshan faults. Most of the surface uplift is accommodated by crustal shortening in the interior of the Tibetan Plateau; abrupt changes in vertical rates in eastern Tibet and the widely distributed surface subsidence of southeastern Tibet are consequences of crustal flow and gravitational collapse. Overall, the Tibetan Plateau is characterized by continuous deformation, with large spatial variations accommodated by complicated tectonic processes.

How to cite: Wu, Y., Su, G., Li, J., Pang, Y., Chen, C., Jiang, Z., and Bo, W.: High-Precision Vertical Movement of the Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5218, https://doi.org/10.5194/egusphere-egu24-5218, 2024.

In the nearly 50 years since Paul Tapponnier first recognized that eastward motion of Asian lithosphere played a key role in accommodating ongoing convergence between India and Eurasia (Molnar and Tapponnier, 1975, Science), the debate over the mechanical processes governing plateau growth have been a source of both inspiration and controversy.  Along the eastern margin of the Tibetan Plateau, adjacent to and north of the Sichuan Basin, a robust debate continues as to whether massifs substantially elevated above the plateau interior developed largely along upper-crustal faults or, alternatively, were built by flow and thickening in the lower crust.  We explore constraints on the timing, rates, and patterns of mountain building along the eastern margin of the Tibetan Plateau provided by over two decades of thermochronologic and geomorphologic studies.  Early models attributed mountain building along the plateau margin to extrusion along the left-lateral Kunlun fault; however, recent work has shown that slip along the Kunlun fault dies out eastward and is absorbed by deformation and rotation about the fault tip.  Rates of shortening across the plateau margin in the Longmen Shan region are low (< 1-2 mm/yr), but multi-thermochronometer relief transects (age-elevation) from three separate localities across the plateau margin imply that moderate to high rates of rock uplift and exhumation have been sustained along the plateau margin since ~30 Ma.  Forward modeling of the thermal response to exhumation reveals details of spatial differences in the exhumation history.  In the Pengguan Massif, immediately adjacent to the Sichuan Basin, these data require a two-phase exhumation history, separated by a hiatus or significant reduction in exhumation rate (Wang et al., 2012).  To the west, however, in the Xuelongbao Massif, new thermochronologic data require continuous (but temporally variable) exhumation rates >500 m/Myr during the entire late Cenozoic (Furlong et al., 2021).  Such rapid, localized exhumation coincident with high relief along the plateau margin requires a sustained influx of crustal mass at depth.

North of the Sichuan Basin, the topographic margin of the plateau is defined by the Min Shan.  The lack of a direct association between topography and upper crustal faults affords an opportunity to evaluate the patterns of differential rock uplift in the absence of inherited crustal anisotropy.  Here, correlations among topography, channel steepness, and erosion rate indicate a locus of moderate (300-500 m/Myr) erosion rate coincident with the Min Shan.  Fluvial incision rates inferred from dated strath terraces along the Bailong Jiang confirm spatial gradients in fluvial incision, with the highest incision rates (1000-2000 m/Myr) localized along the axis of the range.  This locus of incision has been sustained for 80-100 ka, and we interpret it to reflect differential rock uplift along the plateau margin.  The wavelength of rock uplift is consistent with thickening in the deep crust.  Collectively, the spatial patterns and rates of exhumation and erosion along the eastern margin of the plateau suggest that crustal thickening in the deep crust is ongoing today and may have been sustained since the late Oligocene.

How to cite: Kirby, E., Furlong, K., Shi, X., Danisik, M., Kamp, P., Hodges, K., and Zhang, H.: Cenozoic growth of the Tibetan Plateau: insights from exhumation and geomorphology along the eastern margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13574, https://doi.org/10.5194/egusphere-egu24-13574, 2024.

In the southeastern Tibetan Plateau, a series of region-scale dextral strike-slip shear zones play important roles in accommodating the continental collision and continental subduction during India-Asia convergence. This study provides structural, kinematic and geochronological data along the Dulongjiang shear zone, a newly recognized region-scale dextral strike-slip zone around the Eastern Himalayan Syntaxis (EHS) region. The structures and kinematic indicators record dextral lateral shearing within the zone in the Dulongjiang and Nabang regons of western Yunnan, China. The temperature range for dextral ductile shearing is estimated to be between 550 and 450 ℃, based on ductile feldspar deformation and CPO patterns of quartz in the granitic mylonites. Zircon U-Pb dating of syn-shearing leucogranites indicateds a period of dextral strike-slip movement between 30 and 18 Ma. The ⁴⁰Ar/³⁹Ar dating results from the mica fragments in mylonitic granites suggest rapid cooling since approximately 17-14 Ma. Combining these findings with previously published data on other dextral strike-slip faults/shear zones around the EHS and southeastern Asia, it is concluded that the Dulongjiang shear zone is connected with the Parlung shear zone in Tibet, the Nabang shear zone in western Yunnan and Sagaing Fault in the southeastern Asia. The Parlung-Dulongjiang-Nabang shear zone, along with other dextral strike-slip zones, forms a regional-scale Cenozoic dextral shear system around the EHS, extending into southeastern Asia. In addition, our study, in conjuncation with high wavespeed tomographic anomalies beneath the India-Asia collision zone, emphasizes the distinct evolution at lithospheric scales in  the southeastern and eastern parts of the collision zone. The intracontinental continuous strike-slip shearing indicates a tectonic transformation from extension in Tibet to block rotation around the EHS. From 30 to 18 Ma, the slab tear is associated, spatially and temporally, with a clockwise rotation and dextral strike-slip shearing around the EHS. These characteristics suggest a warmer geodynamic setting during the rotation and the influence of  a hot mantle flow associated with the tear in ongoing India lithosphere subduction. The Oligocene-Miocene dextral strike-slip shearing around the EHS and their linkage southwards with the dextral Sagaing Fault may correspond to the rotation required for the slab to bend, stretch and eventually tear beneath the EHS region.

How to cite: Zhang, B., Li, Z., and Zhang, J.: Slab tear of subducted Indian lithosphere beneath the Eastern Himalayan Syntaxis region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9668, https://doi.org/10.5194/egusphere-egu24-9668, 2024.

As a product of continental collision, the Himalaya developed major thrust and fold structures to accommodate convergence.  With the continental subduction of the Indian continent beneath Asia, the deformation front has migrated southward over time.  The result of these tectonic and structural processes is the world’s highest mountain belt that exposes rocks of a large span of ages and has had a dynamic geomorphological evolution for the past 50-60 million years.  The Himalaya is now home to more than 53 million people.  These people face the ongoing threat of earthquakes, landslides, and floods due the active landscape in which they live.  While most earthquake events are caused by thrust fault activity, it has been recognized that there are faults that cut across the range, cross faults, that also play a role in hazards.  In the central and eastern Himalaya, cross faults have been identified where the range front transitions from salients to recesses.  Examples of these structures in Sikkim and Nepal include the Gish and Kosi faults.  Similar structures have also been identified north of the range front in the Lesser and Greater Himalayan regions.  A map of aftershock data from the 2015 earthquake shows an abrupt termination of aftershocks in the region east of Kathmandu that aligns with a proposed cross fault known as the Gaurishankar lineament.  Geophysicists suggested that a cross fault could be responsible for blocking of the lateral propagation of the thrust rupture.  The Dudh Kosi valley that drains the Khumbu or Everest region has had historic and pre-historic large landslides that may have originated on the Benkar cross fault structure.  In 2021, the Melamchi valley east of Kathmandu experienced a devastating flood that was in part tied to the reactivation of a large landslide.  That landslide site is co-located with north-south striking shear zones or cross fault structures.  While cross faults are not the major structures accommodating convergence, our work suggests that there are implications for hazard occurrence due to the presence of these structures.

How to cite: Hubbard, M., Mukul, M., and Gajurel, A.: Himalayan deformation and its connection to geologic hazards: cross fault examples, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13521, https://doi.org/10.5194/egusphere-egu24-13521, 2024.

Anatexis (i.e., partial melting) commonly occurs during crustal thickening, post-collisional collapse or exhumation and tectonic regime transition. It plays a crucial role in the evolution processes of tectono-thermal, rheological, and deformation behavior of the continental crust in orogenic belts. Continental-scale strike-slip shear zones often record significant tectono-magmatism and dynamic deformation processes of the crustal lithosphere. However, the genetic relationships and timing among the anatexis, deformation, and initial shearing along a strike-slip shear zone have not been well defined. The Chongshan shear zone (CS-SZ) is an important hundred-kilometer-long continental scale strike-slip shear zone on the Southeastern Tibetan Plateau. The CS-SZ involved contemporaneous activity with the adjacent sinistral Ailaoshan–Red River shear zone and dextral Gaoligong shear zone during the Cenozoic. In this study, we present a combined result of detailed field, microstructural, zircon U–Pb geochronology, geochemical and EBSD texture analyses of leucogranites and migmatites in the CS-SZ. The results indicate that most migmatites and leucogranites exhibit strong shear deformation and well-developed high-temperature mylonitic microstructures. The quartz aggregated from foliated leucogranites developed dominant high-temperature prism and prism

How to cite: Li, W., Cao, S., Dong, Y., Zhan, L., and Tao, L.: Deep crustal deformation, anatexis and rheological significance of the Continental-Scale Chongshan Strike-Slip shear zone on the Southeastern Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11406, https://doi.org/10.5194/egusphere-egu24-11406, 2024.

The formation of the Tibetan Plateau as a result of the Cenozoic India-Asia collision had a profound impact on the Asian tectonics configuration and climate dynamics. The kinematics and deformation pattern along the Altyn Tagh fault (ATF), marking the Plateau’s northern boundary, is of great significance for resolving the dispute on the deformation mechanisms of the Tibetan Plateau. However, the timing and configuration of the initial rupture along the ATF remains debated given the limited constraints on the depositional age of associated Cenozoic syntectonic strata.

Here we investigated the syntectonic Cenozoic strata in the Xorkol Basin, the pull-apart basin of the ATF. New uranium-lead analyses of the carbonate deposits yield dates of 58.9 ± 1.29 Ma. Therefore, we propose that the initiation of strike-slip motion along the ATF occurred no later than 58.9 Ma, leading to the formation of the Xorkol Basin as a composite pull-apart basin. This finding clarifies the timing and location of the initial ATF activity, indicating that the modern configuration of the ATF was established as early as the early Cenozoic.

This research provides the first yet oldest radioisotopic age along the ATF and surrounding area. This age estimate is also indicative of the depositional age of the Lulehe Formation in the Qaidam Basin, suggesting that the syntectonic sedimentation in the northern Tibetan Plateau initiated during the Paleogene. This timing coincides with the ca. 60 Ma onset timing of India-Asia collision, highlighting its far-field effect. We infer stress triggered by the India-Asia collision has propagated across the entire plateau in ca. 1-2 Ma, resulting in Paleocene strike-slip faulting along the ATF and other deformation in North Tibet.

How to cite: Yi, K., Cheng, F., Jolivet, M., Li, J., and Guo, Z.: Carbonate U-Pb ages constrain Paleocene initiation along the Altyn Tagh fault in response to the India-Asia collision, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2532, https://doi.org/10.5194/egusphere-egu24-2532, 2024.