Active Margin Research Articles

Assessment of seismic liquefaction hazard and ground response in subduction zone: A 1D non-linear effective stress approach

Abstract The Makran Subduction Zone (MSZ) represents a convergent plate boundary where the Arabian Plate is subducting beneath the Eurasian Plate. This study assessed liquefaction susceptibility and ground response in Gwadar region, located on the eastern side of MSZ. A comprehensive dataset of seismic records, compatible with Pakistan design code BCP: 2021 rock spectrum, was used as input motions at bedrock. A series of one-dimensional (ID) non-linear effective stress analyses (NL-ESA) was conducted using DEEPSOIL v7 numerical tool. The findings revealed that pore water pressure ratio (ru) exceeded the threshold value for liquefaction onset (ru > 0.8) at various depths within the site profiles. A significant de-amplification of peak ground acceleration values was observed at liquefiable depths in soft soils. The liquefied stratum exhibited a non-linear response, with high shear strain values manifesting plastic deformations. A comparison of computed design spectra with code spectra revealed significant discrepancies. It is demonstrated that BCP: 2021 underestimated site amplification for site class D profiles in the 0.1 to 0.8 s period range, while overestimating it for site class E profiles across the entire period range up to 1.6 s. The findings will benefit infrastructure development in the region, particularly within the China-Pakistan Economic Corridor.

Analysis of stress changes on the Poso fault caused by large inland earthquakes: Case study of the 2017 Mw 6.6 Poso and the 2018 Mw 7.5 Palu-Donggala earthquakes

The 2017 Mw 6.6 Poso and the 2018 Mw 7.5 Palu-Donggala represent significant seismic events in central Sulawesi Island. These events transferred the stress to the surrounding faults, which can promote or inhibit the critical condition in a fault, thus evaluating the stress transfer from these earthquakes is crucial for a comprehensive understanding of fault behaviour. In this study, we investigate the effect of these large events by resolving the accumulated Coulomb stress change onto a multi-strike segment of the Poso fault. Additionally, we also used GPS measurement (Global Strain Rate Model) to estimate the increase in tectonic stress rate due to coupling of triple-junction plate convergence. The 2017 Poso earthquake induces positive stress changes (7 kPa to 27 kPa) in the central segment, negative changes (–4 kPa to –10 kPa) in the northern segment, and less significant effects in the southern segment. The 2018 Palu-Donggala earthquake imparts a notably high negative Coulomb stress (–16 kPa to –27 kPa) across the entire northern segment. Cumulatively, both earthquakes reduce Coulomb stress predominantly in the northern part of the Poso fault, suggesting a delayed critical point. Furthermore, the analysis of the Coulomb stress changes time function indicates that stress accumulation in the northern Poso fault is more modulated by large earthquakes, while stress accumulation in the southern segments may be more controlled by longterm tectonic stress loading. The stress accumulation model developed in this study can provide a guidance in better understanding further earthquake risk mitigation in central Sulawesi.

Sequence stratigraphic framework of carbonates in mixed siliciclastic–carbonate sequences: local versus external controls in a tectonically active basin (Lorca Basin, Miocene, SE Spain)

ABSTRACT The sequence stratigraphic framework of initiation and growth of carbonates in environments impacted by siliciclastic inputs is highly variable because of the biogenic nature of the sedimentary production and its sensitivity to environmental conditions. Using panorama interpretations, logging, and characterization of benthic communities, the mixed carbonate–siliciclastic sedimentary succession of the Neogene Lorca Basin (SE Spain) has been studied to decipher the role of local and global controlling parameters on the sequence stratigraphic framework of carbonate production. Three different carbonate depositional models are distinguished: 1) retrogradational homoclinal ramps (type 1) dominated by heterozoan communities that developed lateral to alluvial fans, 2) progradational flat-topped coral platforms (type 2) with Porites and Tarbellastraea coral carpets with a coeval retrogradational pattern on basin margins, and 3) retrogradational narrow siliciclastic-rich coral platforms (type 3) with Tarbellastraea buildups intercalated with deltaic deposits. Onset of carbonate production systematically occurred during transgressions controlled by eustasy and was locally enhanced by extensional tectonics. In steep margins located in the vicinity of major marginal faults, transgressions were characterized by high terrigenous inputs, and only heterozoan-dominated ramps (type 1) developed. The flooding of these steep and tectonically active margins characterized by small drainage basins and immature, locally sourced alluvial systems led to lower terrigenous fluxes and the growth of coral flat-topped platforms (type 2) during subsequent highstands. Away from main marginal faults, deltaic environments were sourced by large drainage basins. They were characterized by a flat topography that permitted the occurrence of a shallow photic zone subject to low and irregular terrigenous inputs up to the distal part of the depositional profile during transgressions. In this deltaic configuration, the growth of narrow siliciclastic-rich coral platforms (type 3) were favored. On these platforms, coral buildups were regularly buried by terrigenous inputs during highstands. In the Lorca Basin, the dimensions of siliciclastic systems and the size of their drainage basins also directly impacted the sequence stratigraphic framework of carbonates intercalated in terrigenous units. This study illustrates the marked variability in: 1) the different types of carbonate depositional profiles and 2) the timing of these carbonates in a mixed carbonate–siliciclastic system because of the size, maturity, and location of siliciclastic systems, local tectonics, inherited topography, and global sea-level fluctuations.

Early Cretaceous to Eocene magmatic evolution of Livingston Island, South Shetland Archipelago: Geochronological and isotope geochemical constraints from intrusive suites

The magmatic products exposed across Livingston Island comprise a part of the South Shetland magmatic arc built on an active continental margin. The main magmatic phases of Livingston Island include the Early to Late Cretaceous plutonic and volcanic rock associations, the Eocene plutons, and some sporadically distributed intrusions of Paleocene to Eocene dykes. The intrusions were emplaced into the strongly deformed turbiditic sedimentary rocks of the Miers Bluff Formation. 40Ar39Ar and zircon UPb geochronologic data presented here define four distinct episodes of intrusive activity represented by the emplacement of the Hesperides (125 Ma), the Cerro Mirador (104–97 Ma), the Siddons Point (80 Ma) and the Barnard Point suites (42 Ma), in addition to some dyke intrusions with emplacement ages of 105 to 40 Ma. The intrusions are represented by mafic to intermediate compositions characterized by middle potassic, calc-alkaline affinities, with only a few samples from the Eocene activity exhibiting tholeiitic character. Trace element, Sr-Nd-Pb isotope and zircon Hf isotope variations indicate magma generation in a subduction setting with extensive involvement of continental crust-derived melts for the Early to Late Cretaceous activity. The effects of crustal input on melt chemistry appear to have diminished in time, especially from the Paleocene onwards, leading to magma generation with typical oceanic island arc geochemical signatures. This change in melt chemistry is likely partly related to the roll-back induced overriding plate extension which resulted in a time-integrated increase in the rate of melt movement and a decrease in the residence time in crustal levels. Slab steepening caused by the systematic decrease in plate convergence rate led to an enhanced involvement of isotopically depleted mantle component, producing a heterogeneous source with variable subduction signature.

The Diverse Habitats of Eclogite Formation: Insights From the Mesoproterozoic Glenelg Inlier, Scotland

ABSTRACTEclogite‐facies rocks provide important constraints on the behaviour of convergent plate boundaries and the geometries of tectonic reconstructions due to the high to ultrahigh pressure conditions at which they form. Many eclogite occurrences are documented near the suture zone of active collisional settings where they are interpreted to mark the approximate location of former ocean basin subduction. Such observations influence tectonic interpretations for older eclogites within more deeply eroded and/or less well‐exposed terranes. The eclogitic Glenelg inlier in northwest Scotland is one such example, with c. 1 Ga eclogites having previously been interpreted as marking the trace of a Grenville‐aged collisional suture zone that defines a third ‘arm’ to the Grenville orogen alongside well‐defined sutures in North America and Scandinavia. Here we use a combination of geochronology, phase equilibrium modelling and accessory‐phase thermometry to show that the eclogite‐facies assemblages were produced at 18–19 kbar and 700°C–750°C from c. 1.1 to 1.0 Ga. Accounting for the foreland basin setting of equivalent‐aged sedimentary rocks in the region and demonstrating the thermal viability of this setting, we show that eclogite formation occurred in deforming foreland crust adjacent to the Grenville orogen, in a setting broadly analogous to fault‐bounded basement uplifts in the forelands of active deformation belts, such as the Himalayas and Andes. Our results demonstrate that eclogite‐facies rocks can form in a greater range of tectonic settings than are sometimes considered, with implications for tectonic reconstructions of collisional zones. In this instance, our results remove the need for a third ‘arm’ of the Grenville orogen by placing Glenelg in a foreland setting, reconciling the absence of plentiful Grenville‐aged metamorphic rocks in northwest Scotland, the sedimentological record and paleomagnetic data in the wider region.

Dynamic Emergence of Plate Motions and Great Megathrust Earthquakes Across Length and Time Scales

AbstractThe slow motion of tectonic plates over thousands of kilometers is intermittently interrupted by great earthquakes with sudden slips localized near convergent plate boundaries. We developed a subduction model that self‐consistently integrates buoyancy forces, diffusion and dislocation creep, and inter‐plate friction. From the nonlinear dynamics emerge long‐term plate motions that achieve velocities of cm/year, effective viscosities of Pas below plates, and sudden slips up to m repeating every several hundred years. Along‐strike resistance arising from long‐wavelength variation of coseismic slip is naturally incorporated with a rupture length scale, . Computations with km generate events with . When decreases, there is a commensurate decrease in the effective moment of rupture events. Predicted long‐term plate velocities, mantle viscosities, cycles of stress loading and release, and rupture event size and magnitude all show good agreement with observations.

METAL AND MINERAL MICROINCLUSIONS IN ADAKITES FROM THE FRAMING OF THE UTANAK MASSIF (STANOVOI SUPERTERRANE, RUSSIAN FAR EAST) AS EVIDENCE FOR METAL ENRICHMENT IN ADAKITIC MAGMAS

Porphyritic amphibole–plagioclase andesites at the southern margin of the Utanak ultramafic massif (Stanovoi superterrane, Russian Far East) show low yttrium and ytterbium contents and high Sr/Y and La/Yb ratios typical of adakites. Microinclusions in these volcanic rocks are Cu–Ag–Au alloys, native silver, composites of gold and silver with Cu, Zn, In, Mn, Ni, and Mo minerals, as well as microparticles of platinum, silver sulfides and chlorides, pyrrothite, chalcopyrite, barite, tungsten oxide, crocoite, and cassiterite. The structural features of some microinclusions and their association with primary amphibole and plagioclase suggest their magmatic origin, while other microinclusions hosted in the quartz–chlorite–K-feldspar groundmass formed during later metasomatism. The Utanak adakites are characterized by elevated gold contents (up to 134 ppb) and, together with other manifestations of Mesozoic adakitic magmatism within the Stanovoi superterrane (Il’deus, Lucha, and Gabbrovyi massifs), are classified as ore–bearing (fertile) adakites according to geochemical criteria. We suggest that common association of adakitic magmatism with large porphyry, epithermal, and skarn deposits at convergent plate boundaries is related not only to the high water content and the oxidation state of adakitic magmas but also to the initial enrichment of the latter in various ore components.

A Novel Event-triggered Practical Prescribed-Time Control for four Complex coupled Duffing-type MEMS resonators with Prescribed Performance

This paper explores the dynamic characteristics and a novel event-triggered practical prescribed-time controller for four complex coupled Duffing-type MEMS resonators. Initially, the effects of mechanical coupling stiffness, electrostatic coupling stiffness, and internal system parameters on the system's dynamic behavior are examined. The analysis results provide guidance for selecting system parameters. Furthermore, the dynamic analysis reveals that chaotic oscillations may occur in the system without input, significantly affecting system performance. To mitigate these chaotic oscillations, a novel event-triggered practical prescribed-time controller with prescribed performance is proposed, utilizing interval type-3 fuzzy system (IT3FS) to estimate unknown nonlinear functions. By employing a more relaxed practical prescribed-time stability (PPTS) criterion and a novel time-varying scale transformation function (STF), the designed controller ensures that all signals converge within a prescribed time. Additionally, a prescribed performance function (PPF) is employed, allowing for more flexible convergence boundary settings. A dynamic event-triggered mechanism is implemented to reduce the frequency of control signal updates. The stability analysis demonstrates that all signals converge within a prescribed time, and the tracking errors remain within their prescribed boundary. Finally, simulations validate the effectiveness of the proposed scheme.

Tectonostratigraphic models of an extensional back-arc basin: inferences for the evolution of the Pannonian Basin System

The subsidence history and sedimentary architecture of extensional basins are controlled by the interplay between tectonics, mantle dynamics and climatic variations. Observations from outcrop to regional seismic scales coupled with numerical modelling techniques, including basin-scale stratigraphic, crustal-scale tectonic and mantle-scale subduction models, contribute to the quantification of basin evolution. Here, we review and discuss both tectonic and stratigraphic applications of such models and compare them with observations from the Pannonian Basin system of Central Europe. We show that diachronous localization of back-arc extension, crustal thinning, asthenospheric upwelling and subsequent thermal relaxation are superimposed on an overall slow plate convergence. These processes result in contrasting subsidence and uplift patterns and a variable heat flow evolution in different parts of the basin system. The crustal stress-field of the sub-basins does not always reflect their contrasting vertical motions. Extensional deformation generally migrates from the basin margins towards the basin centre. Structural inversion is localized along hot and weak inherited zones from the Middle Miocene to Present. Tectonic subsidence focuses sedimentation along deep depocentres, sourced by exhumed footwalls and from the neighbouring orogens. The overall post-rift sediment progradation is influenced by inherited bathymetries from the preceding syn-rift stage and by enhanced differential vertical motions.

The new insight of tectonic setting in Sunda–Banda transition zone using tomography seismic. Case study: 7.1 M deep earthquake 29 August 2023

Abstract The Sunda–Banda arc transition zone features the collision of the Indo-Australian oceanic plate and the Australian continent, resulting in intricate geological and geodynamic conditions. Tectonic activity in this region is shaped by the convergence of multiple major plates, including the Indo-Australian oceanic plate and the Eurasian plate. The crustal structure along the Sunda–Banda arc transition zone is complex and influenced by various factors such as subduction, continental collision, and volcanic activity. The tectonic complexity of the region in eastern Indonesia makes it an interesting area for study. In this research, International Seismological Centre-Engdahl-van der Hilst-Buland catalogue data from 1964 to 2020 were used, which include recorded information on 69.705 earthquake events from 1.185 recording stations and consist of 2.943.974 P phases. Resolution testing was performed using various velocity grids, and optimal results were obtained with a medium resolution of ∼100 km × 100 km × 80 km for the inversion process. The tomographic inversion analysis provided valuable insights into subsurface structures within Earth’s crust and mantle up to a depth of approximately 750 km. The occurrence of deep earthquakes in the study area has provided valuable insights into complex dynamics associated with subduction and plate tectonics. The results of the tomographic inversion analysis reveal that earthquakes are concentrated in areas with high-velocity anomalies, indicating intense tectonic activity near the subduction zone. This study offers the perspective on the structural complexities and earthquake origins in the Sunda–Banda arc transition zone following the 2023 Mw 7.1 Bali Sea earthquake, which occurred on August 29, 2023, at 02:55:32 UTC + 7, approximately 163 km northeast of Lombok, Indonesia. This earthquake was caused by slab pull activity from the Australian Plate and involved a combination of downward and oblique-normal movement. These characteristics indicate the convergence and interaction between tectonic plates in the subduction process occurring in the Bali Sea area. As a result, there have been frequent occurrences of various tectonic and volcanic activities including earthquakes of different magnitudes. These results highlight the significance of the high-velocity anomaly connected to this occurrence, offering valuable insights into seismic behaviour and tectonic phenomena in the region. The findings of this study indicate that the deep earthquakes in the Bali Sea may be induced by faulting due to the transformation of metastable olivine into denser spinel at significant depths, along with shear instability caused by phase transitions within Earth’s mantle layers. This theory proposes that stress-induced changes in phase can initiate shear instabilities and subsequently lead to deep earthquakes.

On the role of trans-lithospheric faults in the long-term seismotectonic segmentation of active margins: a case study in the Andes

Abstract. Plate coupling plays a fundamental role in the way in which seismic energy is released during the seismic cycle. This process includes quasi-instantaneous release during megathrust earthquakes and long-term creep. Both mechanisms can coexist in a given subduction margin, defining a seismotectonic segmentation in which seismically active segments are separated by zones where ruptures stop, classified for simplicity as asperities and barrier, respectively. The spatiotemporal stability of this segmentation has been a matter of debate in the seismological community for decades. In this regard, we explore in this paper the potential role of the interaction between geological heterogeneities in the overriding plate and fluids released from the subducting slab towards the subduction channel. As a case study, we take the convergence between the Nazca and South American plates between 18–40° S, given its relatively simple convergence style and the availability of a high-quality instrumental and historical record. We postulate that trans-lithospheric faults striking at a high angle with respect to the trench behave as large fluid sinks that create the appropriate conditions for the development of barriers and promote the growth of highly coupled asperity domains in their periphery. We tested this hypothesis against key short- and long-term observations in the study area (seismological, geodetic, and geological), obtaining consistent results. If the spatial distribution of asperities is controlled by the geology of the overriding plate, seismic risk assessment could be established with better confidence.

Porphyry copper formation driven by water-fluxed crustal melting during flat-slab subduction

The prevailing view of the formation of porphyry copper deposits along convergent plate boundaries involves deep crustal differentiation of metal-bearing juvenile magmas derived from the mantle wedge above a subduction zone. However, many major porphyry districts formed during periods of flat-slab subduction when the mantle wedge would have been reduced or absent, leaving the source of the ore-forming magmas unclear. Here we use geochronology and thermobarometry to investigate deep crustal processes during the genesis of the Late Cretaceous–Palaeocene Laramide Porphyry Province in Arizona, which formed during flat-slab subduction of the Farallon Plate beneath North America. We show that the isotopic signatures of Laramide granitic rocks are consistent with a Proterozoic crustal source that was potentially pre-enriched in copper. This source underwent water-fluxed melting between 73 and 60 Ma, coincident with the peak of granitic magmatism (78–50 Ma), porphyry genesis (73–56 Ma) and flat-slab subduction (70–40 Ma). To explain the formation of the Laramide Porphyry Province, we propose that volatiles derived from the leading edge of the Farallon flat slab promoted melting of both mafic and felsic pre-enriched lower crust, without requiring extensive magmatic or metallogenic input from the mantle wedge. Other convergent plate boundaries with flat-slab regimes may undergo a similar mechanism of volatile-mediated lower-crustal melting.

Late Paleoproterozoic within-plate mafic magmatism in the western Yangtze Block, South China Craton: Implications for the initial break-up of the Columbia supercontinent

The Paleoproterozoic was an important period for the tectonic-magmatism evolution of the Yangtze Block, which coincided with the assembly and break-up of the global Columbia (also known as Nuna) supercontinent. However, an essential issue, when the Yangtze Block initiated rifting from the supercontinent, remains controversial. This paper presents new zircon chronology, Lu-Hf isotopic data, and whole-rock geochemical analyses of the Bajiaojing and Xiaoqingshan meta-diabases in the western Yangtze Block to address this issue. The magmatic zircons from the Bajiaojing and Xiaoqingshan meta-diabases yielded U-Pb ages of 1675 ± 38 Ma and 1719 ± 10 Ma, representing an episode of mafic magmatism during the Late Paleoproterozoic. Moreover, the abundances and elemental ratios of high-field-strength elements (HFSEs, e.g., Y, Ta, Th, and Hf) in both meta-diabases are very similar to those of within-plate and mantle plume magmas. This implies that these Late Paleoproterozoic mafic rocks were likely derived from a mantle plume source in a continental within-plate extensional setting. Their magmatic source was relatively heterogeneous in isotopic and geochemical compositions, as inferred from significant differences in εHf(t) values and certain HFSE ratios (e.g., Nb/Yb, Ta/Yb, Th/Yb, Nb/Y, and Zr/Y) among samples. Such source heterogeneity might be attributed to interactions between the mantle plume and the overlying lithosphere. Combined with published εHf(t) values of detrital zircons and whole-rock εNd(t) values of (meta-)magmatic rocks, we speculate that the Yangtze Block experienced a tectonic transition from plate convergence to continental extension at ∼ 1.7 Ga. This means that the block began to rift from the Columbia supercontinent as early as 1.7 Ga. The Yangtze Block then evolved progressively as an isolated fragment until it was amalgamated into the Rodinia supercontinent.

Spatiotemporal evolution of post-seismic deformation caused by large earthquakes around the Pacific and its impact on plate movement

SUMMARY The fully relaxed deformation caused by an earthquake refers to the total deformation of the earth caused by the earthquake, including the coseismic deformation and the total effect of post-seismic stress relaxation in the mantle on crustal deformation. An in-depth investigation into post-seismic and fully relaxed deformation resulting from large earthquakes is conducive to comprehending the feedback effect of earthquakes on plate motion. In this paper, we first calculated theoretically the coseimic, post-seicmic and fully relaxed deformations caused by the Tohoku-Oki Mw9.0 earthquake using the spherical dislocation theory. The post-seismic displacement caused by the great earthquake leads to the continuous convergence of plates on both sides of the seismogenic fault, which will certainly facilitate the downward insertion of the subduction plate. As time goes by the influence range of seismic deformations becomes larger and larger. The Tohoku-Oki Mw9.0 earthquake can produce >5 cm of cumulative post-seismic horizontal displacement at a far place like the East Pacific Rise over 100 millenniums. Then, we built slip models of 375 earthquakes with Mw7.0 and above in the circum-Pacific seismic belt, calculated the cumulative post-seismic deformations of them, and found that significant post-seismic horizontal displacements covered the entire Pacific Ocean. The post-seismic deformation field caused by the 2011 Tohoku-Oki Mw9.0 earthquake, the 2010 Chile Mw8.8 earthquake, the 1964 Prince William Sound Mw9.1 earthquake and the 1960 Chile Mw(9.3–9.4) earthquake determines the overall distribution pattern of the deformation field in the Pacific region. Those large earthquakes around the Pacific make the total Pacific Plate present a tension strain in the northwest–southeast direction. The one at the East Pacific Rise reaches 300–400 nstr, with orientation of principle strain approximately perpendicular to the Rise. This tensile strain is bound to encourage transverse expansion of the mid-ocean ridge. By a logical extension, the post-seismic stress relaxation in the mantle caused by past earthquakes should be an important driving force for the current plate movement, in addition to the classic driving force like negative buoyancy and plate material phase transition. This study proves theoretically that there is a two-way relationship between great earthquakes and plate movement, and the viscous structure of mantle plays a key role in the relationship.

Crustal melting and continent uplift by mafic underplating at convergent boundaries.

The thick crust of the southern Tibetan and central Andean plateaus includes high-conductivity, low-velocity zones ascribed to partial melt. The melt origin and effect on plateau uplift remain speculative, in particular if plateau uplift happens before continental collision. The East Anatolian Plateau (EAP) has experienced similar, more recent uplift but its structure is largely unknown. Here we present an 80 km deep geophysical model across EAP, constrained by seismic receiver functions integrated with interpretation of gravity data and seismic tomographic, magnetotelluric, geothermal, and geochemical models. The results indicate a 20 km thick lower crustal layer and a 10 km thick mid-crustal layer, which both contain pockets of partial melt. We explain plateau uplift by isostatic equilibration following magmatism associated with roll-back and break-off of the Neo-Tethys slab. Our results suggest that crustal thickening by felsic melt and mafic underplate are important for plateau uplift in the EAP, Andes and Tibet.

Paleotectonic setting of basaltoid volcano-plutonic belts with porphyry copper deposits

The article considers geotectonic position and geological features of basaltoid volcano-plutonic belts (VPBs) associated with porphyry copper and gold-copper deposits. Three types of the belts, the oceanic, perioceanic, and riftogenic ones, are distinguished among these VPBs. The oceanic and peri-oceanic belts were incorporated into the composition of ensimatic island arcs and formed at a late stage of their development, after inversion of the basaltoid troughs. The riftogenic belts appeared in island-arc oceanic settings at a late stage of filling the spreading zones. VPBs of the first two types with porphyry gold-copper deposits are located over the convergent boundaries of tectonic plates in an above-subduction position, while belts of the third type form extended linear zones within individual rift structures and contain smallscale porphyry copper objects with poor gold and molybdenum contents. As examples of the structures, the Sunda, Philippine archipelago, New British, Solomon, Alaska, and Antilles ensimatic island arcs and the Irendyk and Novoalekseevsky belts of rift zones of the Southern Urals are described. Volcanic-plutonic associations participating in the structure of these VPBs (including those productive for porphyry copper mineralization), as well as structural-lithological complexes of their basement, are characterized. It is noted that repeated magmatism manifestations during the long-term development of the ensimatic island arcs lead to appearance of several basaltoid VPBs with porphyry gold-copper deposits, while basaltoid belts with porphyry copper objects in the rift settings are formed only once.

Tectonics of the Mw 6.8 Al Haouz earthquake (Morocco) reveals minor role of asthenospheric upwelling

A reliable identification of the fault responsible for the magnitude 6.8 Al Haouz earthquake that struck Morocco on 8 September 2023 has so far been hampered by a lack of accurate tectonic analyses. Here we provide the first updated tectonic framework of the earthquake epicentral area based on original field data. We cast our results into the context of available geomorphological, thermochronological and geophysical constraints, and discuss the earthquake characteristics within the framework of competing tectonic models either based on asthenospheric upwelling or transpressional tectonics. We found that the Al Haouz earthquake was likely generated by rupture along a north-dipping high-angle fault, linking former fault planes belonging to an orogen-scale WSW-ESE transpressional shear zone. The geological evolution and seismotectonic structure of the region are largely governed by the oblique convergence of tectonic plates. The impact of asthenospheric upwelling, if any, remains limited and may only influence the geomorphological evolution of the Western High Atlas, but cannot explain the seismotectonic and geological features observed today at the surface, which are instead effects of transpressional tectonics.

Crustal seismicity and updated stress mapping in the Bolivian Orocline, Central Andes

The Central Andes region, with significant seismic activity, has distinct faulting mechanisms across its varied topography. Notably, the sub-Andean province predominantly features reverse faulting, whereas the high Andean plateau shows a predominance of normal and strike-slip faults. Despite the importance of this extensive orogenic plateau, Bolivia remains under-documented in seismic studies. We used data from recently installed seismic stations in Bolivia and regional stations in Brazil to determine 13 new focal mechanisms of shallow crustal earthquakes in Bolivia, some of them felt in major cities. Employing probabilistic full waveform moment tensor inversion and P-wave polarities, we mapped the stress distribution across the Central Andes. The main patterns of faulting mechanisms were: reverse faulting along the NW-SE trending sub-Andean belt north of the Orocline (north of Cochabamba) with NE-SW compression; reverse faulting along the N-S trending sub-Andean belt south of the Orocline (south of Santa Cruz) with ∼ E-W oriented compression; strike-slip faulting within the Eastern Cordillera with NE-SW P axes. The results indicate that the sub-Andean belt experiences compressional forces perpendicular to the front of the Andean plateau, arising from both the spreading stresses of the plateau and the broader plate-wide compression. On the other hand, the high plateau (Altiplano) is characterized by normal and strike-slip mechanisms, suggesting a dynamic equilibrium between local extensional gravitational stresses and regional compressional forces due to the Nazca plate convergence.

Tectonic evolution and structural geology of the Jurassic succession in the Zubair oil field, southern Iraq

This study investigates the structural style and tectonic evolution of Jurassic succession in southern Iraq, within the Zubair oil field, which are crucial for charging oil to the Cretaceous reservoirs, utilized 3-D seismic reflection data to explore its complex geological history. The field is located in the Mesopotamian plain on the northeast Arabian Plate in southern Iraq. Four folds recognized: Hammar, Shuaiba, Rafdyia, and Safwan, each shaped by specific geodynamic processes. Hammar, Shuaiba, and Safwan are characterized as salt-related folds, influenced by salt tectonics. Rafdyia is identified as a compression-related fold formed due to the convergence of the Arabian and Eurasian plates. Forty-seven faults were identified, with diversity patterns and spatial distributions suggesting a tectonic history marked by three distinct phases: extensional tectonics, extensional with concurrent salt activity, and plate convergence. These phases have created a series of graben structures that, along with the identified folds, highlight the role of three primary tectonic processes: basement tectonics, salt dynamics, and plate interactions in shaping the structural style of the Zubair oil field during the Jurassic time.

UPPER CRETACEOUS–LOWER EOCENE MUDSTONES OF THE OUTER CARPATHIANS (PETROCHEMICAL AND PALEOGEODYNAMIC ASPECTS)

The mineral types of the Upper Cretaceous–Lower Eocene greenish-gray mudstones of the Skyba and Boryslav-Pokuttya nappes of the Outer Carpathians were studied. According to sedimentological features, these mudstones belong to hemipelagites and contain information about the background sedimentation conditions of the deep-sea oceanic basin. The purpose of the work is to clarify the paleogeodynamic features of the basin based on the results of studying the material composition of the Upper Cretaceous–Lower Eocene background mudstones, which in particular are part of the variegated-colored horizons. Research methods were geological mapping, X-ray structural, sedimentological, lithostratigraphic, petrogeochemical, geodynamic analysis. On the classification module diagram (Na2O+K2O)/Al2O3–(FeO*+MnO+MgO)/SiO2, the figurative points of the contents of the Upper Cretaceous–Lower Eocene mudstones of the Stryi, Yamna, and Manyava suites fall into the fields corresponding to two mineral types: a mixture with a predominance of montmorillonite and three-component mixture of chlorite+montmorillonite+hydromica composition. According to the obtained data, a gradual change in the conditions of the sedimentary environment from the Late Cretaceous to the Eocene can be traced, with a successive increase in the normalized alkalinity modulus and a decrease in the phemic modulus. On the paleogeodynamic discriminant diagrams (FeO*+MgO)–TiO2 and F1–F2, figurative points of Upper Cretaceous–Lower Eocene mudstones form petrochemical distribution trends that cover the fields of geodynamic conditions from passive to active margins of the sedimentation basin. The Cretaceous–Paleogene pelagic mudstones of the Sicilian domain of the Alpine Belt have a similar distribution of petrochemical components. The mineral assemblages found in the mudstones of the Skyba and Boryslav-Pokuttya nappes are typical for deep-sea clay sediments of modern oceans. The presence of montmorillonite and chlorite in the background argillites indicates a high probability of a contribution to the background petrofund of the sedimentatary basin by a femic magmatic component of endogenous origin, realized as a manifestation of volcanic and hydrothermal activity, synchronous to sedimentogenesis. An exogenous source could be the magmatic material transferred or changed by the processes of halmyrolysis, which is not synchronous with sedimentation. The Late Cretaceous–Early Eocene geodynamic events of the Outer Carpathian sedimentary basin developed in front of the ALCAPA and Tisza-Dacia terranes of the Alpine Tethys. Convergence, which caused the formation of the accretionary prism in front of the terranes, could contribute to the riftogenic (?) opening, deepening of the Outer Carpathian Basin, where the penetration of synsedimentary endogenous material, mainly of the basic composition, took place. This material could be the rock-forming source of the basin substrate, on which the mineral assemblages of the background hemipelagic mudstones were formed.