Tectonic Environment Research Articles

Paleoproterozoic skarn mineralization events and geodynamic background in the Jiao-Liao-Ji Belt: Geological, geochemical and chronological evidence from the Daqinggou Fe–Cu polymetallic deposit in Ji'an, NE China

The Daqinggou Fe–Cu polymetallic deposit has been discovered in the Ji'an district, east of the Jiao-Liao-Ji Belt (JLJB). It consists of the Daqinggouli and Beigou ore sections, and the ore bodies are mainly magnetite ore bodies, followed by copper polymetallic ore bodies. Six metallogenic stages have been distinguished here: The dry skarn (I1), wet skarn (I2), iron oxide (I3), early quartz-sulfide (II1), late quartz-sulfide (II2), and quartz-carbonate stages (II3). There are also three types of fluid inclusions (FIs): gas-rich (W1-type), liquid-rich (W2-type), and daughter crystal (S-type) FIs. The ore-forming fluids here belong to a H2O–NaCl ± CO2 system with a medium-high temperature and medium-high salinity during the Stages I3 and II1, in addition to a H2O-NaCl system with a medium-low temperature and medium-low salinity in the Stage II2. In-situ S isotopes indicate that the Stage II1 sulfides were derived from magmatic sources, whilst the Stage II2 sulfides were derived from a mixture of magma and stratigraphic sources and Stage II3 was dominated by the sulfur source of the sedimentary strata. Additionally, the Pb isotope data reveal that the ore-forming minerals were of crustal or orogenic origin. By comparing the metallogenic elements of typical skarn deposits, we believe that the Daqinggou deposit is a calcareous skarn deposit, which originates from dimetasomatism between the microcline granite and marble of the Mayihe Formation in the Ji'an Group. The immiscibility and mixing of ore-forming fluids are the key mechanisms of metal precipitation within the deposit. Furthermore, the U-Pb ages of single zircons from microcline granites and hydrothermal apatite in the ores constrained the formation of rocks and deposit to the late Paleoproterozoic. Elemental geochemistry and zircon Hf isotope data further divided the microcline granite into I-type granite with high potassium and differentiation, originating from the partial melting of Neoarchean crustal materials in the region, which then underwent fractional crystallization. The diagenetic tectonic environment shows the characteristics of an active continental margin, which may have resulted from regional large-scale arc-continent collisions (Longgang Block and Nangrim Block), also implying the occurrence of ocean subduction during the evolution of the JLJB.

Zircon U-Pb and trace element constraints on the evolution of the Tonian (829–831 Ma) alkaline plutons within the Mercara Shear Zone, south India

The research sheds light on the age, origin, and tectonic environment of two significant alkaline plutons, Sullya and Angadimogar, located in the Mercara Shear Zone in the Southern Granulite Terrain of southern India. The zircon U-Pb dating indicates that the plutons crystallized at 829 ± 3.7 Ma and 831 ± 4.7 Ma, respectively. The zircon geochemistry suggests that Sullya and Angadimogar plutons underwent distinct crystallization processes, with zircons from Angadimogar samples crystallizing at varying temperatures over a prolonged period with limited fO2 levels and zircons from Sullya samples crystallizing at stable temperatures and variable redox conditions. Most of the zircons from both plutons have trace element characteristics indicating formation in the continental crust. In contrast, some zircons from Sullya have trace elements similar to those found in the oceanic crust. The presence of two distinct types of zircons in Sullya samples indicates that the parental melt of the Sullya pluton consisted of magma from multiple sources. The average estimated temperature for zircon crystallization in Sullya was 691 °C, while the mean temperature in Angadimogar was 802 °C. The research implies that the plutons were emplaced parallel to the shear plane during an extensional regime, reactivating the paleo shears during the late Proterozoic era. The study highlights the importance of using multiple geochemical and geochronological techniques to gain a better understanding of the complex geological evolution of the Precambrian terrains.

The Paleoproterozoic Evolution of Basement Rocks of the Taebaeksan Basin, Korean Peninsula, and Their Correlation to Those of the Paleoproterozoic Massifs in the Korean Peninsula

The Korean Peninsula mainly comprises the Paleoproterozoic Gwanmo, Nangnim, Gyeonggi, and Yeongnam massifs from north to south. The Paleoproterozoic basement is rarely exposed in the Paleozoic Taebaeksan basin, which is located in the northeastern part of the Okcheon belt between the Gyeonggi and Yeongnam massifs. One of the most important issues in the tectonic interpretation of the Korean Peninsula is whether Paleoproterozoic rocks in the Taebaeksan basin have an affinity with those in the Gyeonggi or Yeongnam massifs. To solve this problem, we focused on the petrogenesis of the Imgye gabbroic diorite, Jungbongsan granite, and Jangsan quartzite in the Imgye area of the Taebaeksan basin. The Imgye gabbroic diorite shows mafic to intermediate compositions with slightly enriched LREEs compared to HREEs, slightly positive Rb, K, and Pb anomalies, and negative Ta, Nb, and P anomalies. The Imgye gabbroic diorite formed in a volcanic arc tectonic setting. The geochemical compositions of the Jungbongsan granite show enriched LREEs compared to HREEs with negative Eu anomalies, and reveal strong positive Rb, Th, K, and Pb anomalies with negative Ba, Ta, Nb, Sr, P, Eu, and Ti anomalies. This Jungbongsan granite also formed in an arc tectonic setting like the Imgye gabbroic diorite. LA-ICP-MS zircon age dating of the Imgye gabbroic diorite gives an intrusion age of 1948 ± 21 Ma, whereas SHRIMP U–Pb zircon age dating on the Jungbongsan granite yields an emplacement age of 1873 ± 14 Ma. The εHf(t) values of the Imgye gabbroic diorite are from 3.5 to 9.7, whereas those of the Jungbongsan granite are from −2.9 to 0.6. These data imply that the Imgye gabbroic diorite formed from a depleted mantle in the arc tectonic environment, whereas the Jungbongsan granite formed by reworking pre-existing crust material in the arc environment. The detrital zircons in the Jangsan quartzite show ages ranging from 3.06 to 1.85 Ga, with a peak concentration of ca. 2.5 Ga. Previous studies have suggested that the northern Gyeonggi and Nangnim massifs underwent collision-related magmatism and metamorphism at ca. 1.93–1.90 Ga, and then post-collisional magmatism and metamorphism at ca. 1.89–1.83 Ga, whereas the southern Gyeonggi massif underwent subduction-related magmatism and metamorphism at ca. 1.94–1.92 Ga, and then post-collision-related magmatism and metamorphism at ca. 1.84–1.78 Ga. By contrast, subduction-related events were recognized in the northern Yeongnam massif at ca 2.02–1.96 Ga and 1.90–1.85 Ga. This work, combined with the previous studies, suggests that the Paleoproterozoic basement in the Imgye area of the Taebaeksan basin can be correlated with the Paleoproterozoic basement of the northern Yeongnam massif rather than with those of the Nangnim and Gyeonggi massifs.

Crustal anisotropy of the South China block and tectonic implications

Exploiting the teleseismic waveform data from permanent seismic stations distributed in the South China block, we obtained the crustal anisotropy parameters at 51 stations by fitting the azimuthal variations of arrival times of the PMs converted wave of radial receiver functions. The results show the dominant direction of fast wave polarity in the South China block is NW–SE, which is basically consistent with the absolute plate motion direction. Combining the shear wave splitting and GPS results, we speculated that the tectonic extension of the Paleo-Pacific plate subduction dominates the crust–mantle anisotropy, which reflects the large-scale tectonic stress setting of the South China block. The fast wave directions of NE–SW and E–W calculated by a few stations might represent a local complex tectonic environment, and the crustal anisotropy of NE–SW is well related to the tectonic deformation in Paleozoic. The delay time of slow waves caused by crustal anisotropy ranges from 0.14 s to 0.71 s, with an average of 0.33 s. The delay time of Jiangnan orogenic belt, which located in the southeast of Yangtze block, is particularly large, which reflects the complex and intense intra-continental tectonic movements since Neoproterozoic. The crustal anisotropy along the southeast coast can be contributed to the local lithosphere underplating caused by the upwelling of asthenosphere in Cretaceous.

Upper crust anisotropy of the 2020 Jiashi MS 6.4 earthquake

The 2020 Jiashi MS 6.4 earthquake occurred north of the 1997–1998 Jiashi earthquake swarm. Because of its complex tectonic environment and frequent strong earthquake occurrence, scholars have paid extensive attention to this area. To study the upper crustal anisotropy in the source area, we applied microseismic event detection and shear-wave splitting techniques to the seismic data recorded by five stations around the epicenter. First, the earthquake catalog of the Jiashi MS 6.4 earthquake sequence was rebuilt using the “Match & Locate” method. A total of 9,695 earthquake events were obtained, and the number of newly detected earthquakes was approximately 7.3 times the number in the officially released catalog. The newly identified microseismic data greatly increased the number of effective records and improved the reliability of the results. We analyzed shear-wave splitting according to the updated catalog. The results showed that the dominant polarizations of the fast shear waves were in NW or NNW at the stations BPM, XKR, L6505, and L6513, consistent with the stress near the source area. There are also blind faults with an NNW direction in the strike distributing en echelon and parallel to the main stress direction in the Jiashi seismic area. Thus, the fast shear-wave polarization of the four stations may also reflect the strike of multiple buried NNW faults in the study area. The fast shear-wave polarization of station HLJ, located at the Halajun Basin, was E–W, with the overall trend of the Kalpin thrust nappe structure. However, this station didn’t show the same NW or NNW fast-wave direction as the four stations previously mentioned. This finding may indicate that the NW-trending buried faults in the Jiashi seismic area have a limited size in both the length and the depth, only reaching northward near the second row of the Kapingtag nappe structure. The temporal trend of the delay time at station HLJ showed that a stress-release process occurred before the MS 6.4 earthquake and that stress-release occurred again after the mainshock. At station XKR, the delay time rapidly increased and then fell in the early period after the MS 6.4 earthquake, indicating that stress accumulated rapidly after the main earthquake but was released during the aftershock sequence. This study provides novel insights into the complex structural characteristics and seismogenic environment in the Jiashi area.

Orogens and detritus: unravelling the Mesoproterozoic tectonic geography of northern Australia through coupled detrital thermo- and geo-chronometers

This study presents detrital muscovite 40Ar/39Ar data from the Mesoproterozoic Roper Group and overlying informally named successions, in the Beetaloo Sub-basin, northern Australia. Detrital muscovite chronology reveals tectono-thermal processes within source regions and provides new constraints on the basin provenance, revising previous interpretations based on detrital zircon data. Detrital thermo- and geochronology, together demonstrate three main periods when the basin paleogeography was altered that correspond to the evolving tectonic history of the North Australia Craton (NAC) through the Mesoproterozoic. The first is characterised by an increased sediment contribution from source regions that lay along the eastern margin of Proterozoic Australia. These source regions are interpreted to have formed the uplifted rift-shoulders between Proterozoic Australia and Laurentia at ca 1.45 Ga. After that, sediments derived from eastern Proterozoic Australia sources become less voluminous up-section. The youngest analysed formation from the Roper Group, the Kyalla Formation, was predominately from sources to the south of the basin, representing another modification of basin geography. This is interpreted to result from the closure/subduction of the Mirning Ocean as the West Australian Craton (WAC) approached and collided with the NAC, resulting in an uplift of the southern margin of the NAC, at ca 1.35–1.31 Ga. The uppermost Mesoproterozoic to lower Neoproterozoic sandstone successions that overlie the Roper Group were derived from the Musgrave Province. Coupled detrital zircon and muscovite data imply a rapid cooling at ca 1.20–1.15 Ga that is interpreted to reflect syn-orogenic exhumation during the Musgrave Orogeny. Furthermore, data from the Beetaloo Sub-basin suggest that the changed basin tectonic settings reshaped basin geography and result in distinctive detrital zircon and muscovite geochronology records. In this study, we used the detrital U–Pb zircon and muscovite 40Ar/39Ar age data from the Beetaloo Sub-basin and a range of other basins deposited in different tectonic environments, including the convergent, collisional and extensional settings, to reconstruct the basin tectonic geography and illustrate various tectonic controls on basin formation in different tectonic backgrounds. KEY POINTS Detrital muscovite 40Ar/39Ar data provide thermochronological constraints on basin provenance, complementing previous interpretations based on detrital zircon data. Spatial and temporal variation of provenance reconstructs the basin tectonic geography, reflecting the Mesoproterozoic tectonic history of the North Australia Craton. Coupled thermo- and geochronology constrain tectonic settings of basin deposition.

Generating large volumes of crust-derived high δ18O rhyolites in the Chon Aike Silicic Large Igneous Province, Patagonia

Abstract The Jurassic Chon Aike Silicic Large Igneous Province (Patagonia and the Antarctic Peninsula) is dominated by voluminous, crust-derived magmas (235,000 km3) that erupted as predominately explosive silicic material over ~40 m.y. In this study, we combine petrological descriptions and bulk-rock major- and trace-element compositions with quartz oxygen-isotope measurements from multiple silicic units (primarily ignimbrites and some rhyolitic flows) from two of the five silicic formations in Patagonia. We have identified that quartz oxygen-isotope values are high (>9‰–12‰). Quartz pheno crysts analyzed by secondary ion mass spectroscopy (SIMS) are also homogeneous at the microscale with no measurable change in isotope value with respect to internal and often complex zoning textures. The ubiquity of widespread high δ18O rhyolites and their trace-element compositions support their origin from melting of a metasedimentary source with a similarly high δ18O value. Mass balance calculations require that an average of >75% melt derived from partial melting of the dominant basement lithology is needed to explain the isotopic and chemical composition of the rhyolites. The ideal P-T environment was identified by thermodynamic models for fluid-absent melting of graywackes at 900 °C and 5 kbar. Regional-scale crustal melting occurred during a widespread, high heat-flux environment within an extensional setting during the breakup of the Gondwanan supercontinent. The overlap of a unique tectonic and igneous environment, combined with a fertile crust dominated by graywacke and pelitic compositions in southern Patagonia, generated large volumes of some of the highest δ18O silicic magmas documented in the geologic record.

The Evolution of the REE-Bearing Özvatan Nepheline Syenite-Carbonatite Complex, Central Turkey: Mineralogical, Geochemical, and Stable Isotopic Approaches

Carbonatite complexes and associated fenite zones are famous for their high-grade rare metal ores. The carbonatite–fenite complexes generally contain high concentrations of light rare earth elements (LREE), thorium (Th), and uranium (U). While most carbonatites are closely related to continental rift zones, some complexes can be observed in post-collisional tectonic environments. The Özvatan nepheline syenite–carbonatite complex is an example of post-collisional carbonatitic magmatism in Central Anatolia, Turkey. The magmatic suite is generally composed of silica-undersaturated ultra-alkaline rocks and carbonatite dikes accompanied by high-intensity fenite zones. The carbonatites of the complex are generally dominated by coarse-grained calcite minerals accompanied by fluorite phenocrysts and may also contain minor amounts of rock-forming silicate minerals. The metasomatic aureole zones (fenites) are mainly composed of euhedral nephelines, K-feldspars, aegirines, augites, and garnets. Carbonatites of the Özvatan complex show enrichments in Ca and F with depletion of alkaline (K and Na) elements. Carbonatites and fenite zones of the Özvatan complex host a variety of incompatible elements, including La, Ce, Nd, Th, U, and Nb. The isotopic composition and general geochemical properties of carbonatites in the study area represent mantle-derived carbonatites rather than crustal limestones/skarns.

Seismic anisotropy in the upper crust around the north segment of Xiaojiang faults in the SE margin of Tibetan Plateau

The Xiaojiang faults located in the SE margin of the Tibetan Plateau is a fault system of left-lateral strike-slip, striking NS, between the 2nd-order Sichuan-Yunnan block and the 1st-order South China block. The Xiaojiang faults and the surrounding areas are characterized by strong tectonic movements and intense seismic activities. Using seismic data from January 2013 to November 2020 recorded at the stations of the temporary QiaoJia seismic Array (QJ Array), deployed by the Institute of Geophysics, China Earthquake Administration, this study investigates the upper crustal anisotropy by the shear-wave splitting analysis on small local earthquakes, discusses the deformation patterns in the upper crust in the north segment of the Xiaojiang faults, evaluates the stress distribution in the study area, and analyzes its relationship with the regional tectonic structure. Adopting the data processing technique of shear-wave splitting, a total of 875 effective records were obtained at 50 stations. The mean direction of polarizations of fast shear-wave (PFS) is 162° ± 44° in the study areaand the mean normalized time-delay is 4.96 ± 2.38 ms/km. Based on the spatial distribution of the PFS and the regional geologic structure, the study area is divided into two zones: the zone N and the zone S. The PFS in the zone N is scattered, but the dominant PFS direction is in NNW, which is consistent with the direction of the regional maximum principal compressive stress. In the zone N, there are a few smaller local areas (i.e., subzones A, B, C, and D) in which the orientations of the PFS are quite different from the surrounding area. In the zone S, the dominant directions at most stations are in nearly NS, consistent with the strike of the Xiaojiang fault. It reveals the detailed spatial distribution of seismic anisotropy in the upper crust, as well as in situ principal compressive stress, indicating the influence of the regional stress, the complex tectonic environment, and maybe also the impact of the South China block. It also reveals that there also might be an upper-crust scale of tectonic line at near 26°20′N under Xiaojiang faults, which coincides with the north-south tectonic boundary in the lithospheric anisotropy.

Studi Batuan Asal (Provenance) Batupasir Formasi Simpangaur Daerah Way Krui, Lampung

Bengkulu basin is the one of fore arc basin which formed in Sumatra island. The basin formation is inseparable from tectonic activity of the Sumatra Island from the Pre-Tertiary era to present day. The relationship between tectonic activities and the basin filling can be identified by conducting a provenance study on the sedimentary rocks. The Simpangaur Formation is a Tertiary sedimentary rock that has filled the Bengkulu Basin in the southern Sumatra. The aim of this research is determining the provenance of Simpangaur Formation existed in Way Krui area, Lampung, and its tectonic environment. The observations of thin section were carried out on eleven sedimentary rock samples obtained from field. The provenance of these rocks is analyzed by quantifying the mineral composition microscopically. The result analysis show that the grains originated from a magmatic arc environment, specifically the transitional arc and undissected arc. Based on the presence of polycrystalline quartz in eleven rock samples, it is interpreted as originating from the Orogen Arc. In addition, it is also interpreted that the provenance for sandstone samples of the Simpangaur Formation are plutonic and metamorphic rocks in a semi-arid climate, based on ancient climate.

U–Pb SHRIMP zircon dating and geochemistry of metapelites from the Shillong Meghalaya Gneissic Complex, NE India: Implications for nature of protolith and tectonic setting

The Sonapahar area of Shillong Meghalaya Gneissic Complex (SMGC) is an extension of the Central India Tectonic Zone within the Precambrian Indian shield. The study area mainly consists of metapelites, basic granulites, granitic gneisses and high-grade gneisses as metamorphic imprints. U–Pb SHRIMP zircon dating yields a late Paleoproterozoic age of 1672 ± 6 Ma, which is age of the metapelites protolith. The petrochronology and geochemistry of metapelites and granitic gneiss basement rocks have been studied to learn more about the SMGC's tectonic environment, involvement in the supercontinent cycle, crustal development and geodynamic context. In the NCKFMASHTO system, phase equilibria modelling of metapelites shows peak metamorphic stage at P-T conditions of 8.25 kbar/ 820°C. Cordierite is formed during retrograde metamorphism during the decompression phases. The negative anomalies in Nb, Sr and Ti indicate that crustal sources played a significant role in magmatic emplacement. Geochemical data from metapelites indicate that protoliths were trachy-andesitic in nature, generated during the syn-orogenic environment by subduction tectonism. The SMGC experienced significant tectonic activity throughout the Paleoproterozoic age when the subduction tectonic setting coincided with orogenic activity. The presence of Paleoproterozoic age in the study area, as well as Southwestern Australia and East Antarctica correlates the Sonapahar granulite with the Columbia supercontinent history.

Deciphering influencing processes in a tropical delta system (middle-late Eocene? to Early Miocene, Colombian Caribbean): Signals from a well-core integrative sedimentological, ichnological, and micropaleontological analysis

Deltaic depositional systems are characterized by a complex interaction of physical, chemical, and biological factors. Although fluvial-, wave- and tidal-dominated deltaic environments have been extensively studied, evaluation of the processes in tropical mixed sedimentary systems has not been fully documented. Tropical regions with active margins are tectonic environments where these multiple factors act on the development of coastal systems. An onshore well-core from this tropical setting (Sinú-San Jacinto Basin, Colombian Caribbean) revealed that a middle-upper Eocene?-lower Oligocene coarse-grained deltaic setting is replaced by a thick coal-bearing mixed-energy fine-grained deltaic succession from the Oligocene to Early Miocene. The integrated analysis of facies associations, ichnological data, and terrestrial/marine micropaleontological assemblages (palynomorphs, foraminifera, and calcareous nannofossils) of this well-core allowed us to identify changes in dominance and influence of coastal processes (fluvial-, wave- and tide) and shoreline evolution. Using this information, as well as the sediment supply and accommodation space ratio, we were able to distinguish three intervals from the bottom to the top of the siliciclastic succession: (i) middle-late Eocene?–early Oligocene, prograding, fluvial-dominated, wave- and tide-influenced coarse-grained deltas with amalgamation of hyperpycnal-dominated mouth bars with hyperconcentrated flow input, (ii) Oligocene, retrograding to prograding, hyperpycnal-dominated heterolithic delta deposits punctuated by transgressive pulses, and (iii) late Oligocene to Early Miocene, aggradational, coal-bearing fine-grained delta plain with a higher proportion of transgressive phases over the continental environment. The complete succession represents long-term (∼14 Myr) mixed-energy nearshore siliciclastic systems, showing different lithological arrangements and sedimentation styles. A long-term evolution is observed from a middle-late Eocene? steep, short and coarse-grained sedimentary system with tropical humid lowland forest and punctual development of macrobenthic tracemaker communities (Interval I) to an Early Miocene gently (poorly drained), well-developed delta plain with mangroves and wave- and storm-influence record through trace fossils assemblages (Interval III). A combination of factors, including subsidence, relief uplifting, and possible relative sea level changes, are interpreted as the main controls on the stratigraphic evolution of sedimentary styles throughout the entire succession. Minor-order sedimentary successions into each interval (e.g., prograding distributary mouth-bar channel) revealed short-term cycles presumably controlled by an internal delta dynamic. Multidisciplinary analysis is essential for recognizing the influence of fluvial, wave, and tidal processes on tropical deltas, where high spatial and temporal variability makes it difficult to determine dominant processes for long periods of time.

Petrogenesis and Tectonic Significance of Late Triassic A1-Type Granite from the West Section of North Qinling Orogenic Belt: Constraints from Geochronology and Geochemistry

The North China Block and the South China Block collided in the Middle Triassic, but there is still a lack of consensus regarding the end of collisional orogeny and the closure time of the Paleo-Tethys. In this paper, we report zircon U–Pb ages and geochemistry for the Shimen pluton in the northern margin of the West Qinling Orogenic Belt to investigate its genesis and tectonic environment. The new findings allow to constrain the end time of the Triassic orogeny in the Qinling Orogenic Belt and the closure time of the Paleo-Tethys. The weighted average 206Pb/238U ages of the Shimen pluton are 218.6 ± 1.5 Ma and 221.0 ± 1.7 Ma. Thus, we suggest that the Shimen pluton crystallized at the 218.6 Ma and 221.0 Ma and was formed during the Late Triassic (Norian). The Shimen pluton is mainly syenogranite and has alkaline dark minerals aegirine–augite. It is composed of 73.45 to 77.80 wt.% SiO2, 8.28 to 9.76 wt.% alkali, and 11.35 to 13.58 wt.% Al2O3, with A/CNK ranging from 0.91 to 1.02 and 10,000 Ga/Al ranging from 2.39 to 3.15. These findings indicate that the Shimen pluton is typical A-type granite. The plutons have low rare earth element contents, ranging from 73.92 to 203.58 ppm, with a moderate negative Eu anomaly. All the samples are enriched in large-ion lithophile elements, such as Rb, Nd, Th and U, and light rare earth elements, and are depleted in high field strength elements, such as Nb, P, Zr, Ba, and Sr. The depletion of Ba, Sr, and Zr may be related to the fractionation and evolution of the granite. According to the petrological and geochemical characteristics, the Shimen pluton is an A1-type granite formed in an anorogenic extensional environment. Combined with its tectonic characteristics and petrogenesis, the Shimen pluton was probably formed by the partial melting of the crust under high temperature and low pressure in the intraplate environment after the subduction of the South China Block beneath the North China Block. This observation indicates that the Triassic orogeny in the Qinling Orogenic Belt had ended and the Paleo-Tethys-Mianlve Ocean had also closed by the Late Triassic (Norian).

Complexity of Recent Earthquake Swarms in Greece in Terms of Non-Extensive Statistical Physics.

Greece exhibits the highest seismic activity in Europe, manifested in intense seismicity with large magnitude events and frequent earthquake swarms. In the present work, we analyzed the spatiotemporal properties of recent earthquake swarms that occurred in the broader area of Greece using the Non-Extensive Statistical Physics (NESP) framework, which appears suitable for studying complex systems. The behavior of complex systems, where multifractality and strong correlations among the elements of the system exist, as in tectonic and volcanic environments, can adequately be described by Tsallis entropy (Sq), introducing the Q-exponential function and the entropic parameter q that expresses the degree of non-additivity of the system. Herein, we focus the analysis on the 2007 Trichonis Lake, the 2016 Western Crete, the 2021-2022 Nisyros, the 2021-2022 Thiva and the 2022 Pagasetic Gulf earthquake swarms. Using the seismicity catalogs for each swarm, we investigate the inter-event time (T) and distance (D) distributions with the Q-exponential function, providing the qT and qD entropic parameters. The results show that qT varies from 1.44 to 1.58, whereas qD ranges from 0.46 to 0.75 for the inter-event time and distance distributions, respectively. Furthermore, we describe the frequency-magnitude distributions with the Gutenberg-Richter scaling relation and the fragment-asperity model of earthquake interactions derived within the NESP framework. The results of the analysis indicate that the statistical properties of earthquake swarms can be successfully reproduced by means of NESP and confirm the complexity and non-additivity of the spatiotemporal evolution of seismicity. Finally, the superstatistics approach, which is closely connected to NESP and is based on a superposition of ordinary local equilibrium statistical mechanics, is further used to discuss the temporal patterns of the earthquake evolution during the swarms.

Geochemistry and Sr–Nd isotopic characteristics of ferroan-magnesian metaluminous granites of the NW Sanandaj–Sirjan zone, Iran: granite formation in a compressional–extensional setting during Late Jurassic time

AbstractThe Almogholagh–Dehgolan region is in the North Sanandaj–Sirjan zone of NW Iran. The granites of the region are metaluminous and display geochemical and textural characteristics of transitional granites between ferroan (A-type) and I-type granites. In geotectonic discrimination diagrams, the Almogholagh–Dehgolan granites plot mainly in the fields of within-plate granites and volcanic arc granites. With the exception of the Qalaylan granites, parts of other granites resemble A2-type granites. Granites of the Qalaylan intrusive body have petrographic and geochemical features close to I-type granites and are not A-type. Primary mantle and chondrite-normalized spider diagrams show enrichments in light rare earth elements relative to heavy rare earth elements. For an age of 150 Ma, the initial87Sr/86Sr and143Nd/144Nd ratios vary from 0.702769 to 0.706545 and from 0.512431 to 0.512558, respectively. Epsilon Nd values vary in a relatively limited range between −0.3 and +2.2, which corresponds to a mixed mantle–crustal source. On the basis of new geochemical and isotopic data, we suggest a geodynamic model involving partial melting of lower crustal rocks with the contribution of mantle magmas in a weakly extensional tectonic setting for the generation of the A-type granites of the region. The occurrence of ferroan (A-type) granites in this region of the Sanandaj–Sirjan zone indicates the existence of a partly extensional tectonic environment in a mainly compressional subduction-related regime in Late Jurassic time.

Early to Middle Miocene Dissectec Arc of Karangsambung Area: A Case Study of Waturanda and Penosogan Formations Provenance

This study undertakes a comprehensive analysis of the geological conditions within a specific region, with a dual objective. Firstly, it aims to detail the geophysical attributes, structural aspects, and formation processes of the region. Secondly, it strives to establish a connection between the provenance, or origin, of the sedimentary materials in the region and its geological characteristics. The primary subjects of the research are the Waturanda and Penosogan Formations. These formations were selected due to their unique geological properties that offer insights into the geological history of the region. The primary method employed in the study was petrographic analysis. This technique, involving a microscopic examination of rocks, facilitated a detailed investigation into the rock samples from both formations, highlighting their mineralogical constitution and overall textures. The study also involved a thorough examination of the original rock or parent material of the Waturanda and Penosogan Formations. This analysis provided important information about their inherent geological attributes and formation processes. One of the key findings was the identification of the tectonic environment in which these formations were developed. The study revealed that the tectonic setting was a magmatic arc, specifically a dissected arc. This significant insight into the geological conditions has profound implications for understanding the geological evolution and history of the region, thereby enriching our knowledge of Earth's dynamic geological processes.

First acceptance testing of multiple A10 absolute gravimeters in China and analysis of the comparison results

Three A10 absolute gravimeters (AGs) were first acquired in China by the Hubei Earthquake Agency under the Belt and Road Seismic Monitoring Network Project. Although AG measuring and testing technique is not new, the purchase and simultaneous testing of 3 A10 absolute gravimeters is unprecedented in China. This study conducted the first acceptance testing of the AGs at 3 locations (the Jiufengshan Gravity Observation Station, the Global Navigation Satellite System Observation Station in Wuhan, and the Jiugongshan Observation Station in Xianning). The results were compared using a method based on expert validation, and the acceptance testing scheme was formulated by referring to the Technical Regulations for Tectonic Environment Monitoring Networks in China and Specifications for Gravimetry Control. Based on the repeatability, precision, and consistency of the measured g values, the results from each instrument were evaluated using the air pressure precision test. Comparing the instrument reference values, the final test results can identify the indicator parameters for 3 A10 AGs, the effects of the surrounding environment, and the related parameters on measurement precision. The precision of A10-059, A10-058, and A10-057 exceeded 0.78 μGal, 0.79 μGal, and 0.42 μGal, respectively. This testing scheme can be used as a reference for conducting acceptance testing of AGs in the future and obtaining absolute gravimetric measurements.

Geochemical Assessment of River Sediments at the Outlets of Eastern Makran, Pakistan; Implications for Source Area Weathering and Provenance

The river sediments in the eastern Makran were investigated to determine the influence of climate, tectonics, and source rocks based on the geochemistry of sediment delivery to the offshore marine basin. Samples were collected at the outlets of four major drainage basins. The specimens were analyzed by XRF, ICP–MS, and ICP–AES. The geochemical concentrations of major, trace, and rare earth elements show great variation among the four outlets. The Rakhshan Kaur (RK), Shadi Kaur (SK), and Dasht Kaur (DK) represent more sorted and matured detrital sediments than those of the Hingol Kaur (HK). The detrital sediments at all outlets represent mostly humid climates except for the DK which falls at the junction of humid and semi-arid conditions. The studied samples show a low level of source area weathering. The sedimentary provenance of the RK and DK is due to the heterogeneous sources of detritus from Iran in the west and the older Eocene-Holocene sedimentary successions in the east. The sediment carried by SK is probably from the late Oligocene–Holocene succession from central and coastal Makran. The HK represents a heterogeneous provenance from the Kirthar-Sulaiman Belt, Bela Ophiolites, and sedimentary successions of central and coastal Makran. The tectonic environments of all river sediments signify a continental arc rather than an active continental margin.

Geological Significance of Neoproterozoic Intrusive Rocks in the South Section of the Ailaoshan Orogenic Belt, SW China: Insights from Petrology, Geochemistry, and Geochronology

The Ailaoshan orogenic belt is one of the most significant orogenic belts in the southeastern margin of the Qinghai–Tibet Plateau. The widely developed magmatic rocks in this belt preserve the multi-stage tectonic evolution records of the South China Plate. As an important response to the Rodinia breakup tectonic event, the study of Neoproterozoic magmatic rocks in the area is of great significance for reconstructing the Neoproterozoic tectonic process of the Ailaoshan orogenic belt and the tectonic evolution of the South China Plate. Petrology, geochemistry, zircon U-Pb, and Lu-Hf isotopes of the Daping pluton in the Ailaoshan orogenic belt are studied in this paper. The Daping pluton is mainly divided into gabbros and granites. Gabbros and granites belong to the sub-alkaline series, which are relatively enriched in large ion lithophilic elements and depleted in high-field strength elements. The ΣREE contents of the gabbro are low with enrichment in LREEs and depletion in HREEs, and the degree of differentiation of light and heavy rare earth is low, with positive δEu and weak negative δCe anomalies. The ΣREE contents of the granite are low with enrichment in LREEs and depletion in HREEs, and the degree of light and heavy rare earth differentiation is high, with medium–weak negative δEu and weak positive δCe anomalies, suggesting an A2-type granite with A1-A2 transition characteristics. The weighted average age of the gabbro is 816.1 ± 4.1 Ma (MSWD = 0.11), with zircon εHf(t) values of −7.5–5.5. The magma source is a mixture of an ancient crust source and a new mantle source; the weighted average age of the syenogranite is 783.7 ± 8.1 Ma (MSWD = 1.4), with zircon εHf(t) values of −4.3–0.4. The magma source is mainly ancient crustal material (Ailaoshan Group), mixed with a small amount of mantle-derived material; the weighted average age of the monzogranite is 754.8 ± 6.1 Ma (MSWD = 3.0), with positive zircon εHf(t) values of 1.65–10.36. The magma source is a mixture of a large number of mantle-derived materials and a small number of crust-derived materials (Ailaoshan Group). The Daping pluton was formed in the transitional tectonic environment from post-collision to intraplate continental margin rift, corresponding to the Rodinia breakup process in the western margin of the South China Plate.

Age and petrogenesis of Ni-Cu-(PGE) sulfide-bearing gabbroic intrusions in the Lausitz Block, northern Bohemian Massif (Germany/Czech Republic)

The Lausitz Block, located in the northernmost part of the Bohemian Massif, hosts a large number of dike- to stock-shaped gabbroic intrusions that mainly comprise brown hornblende-poor (Group I; i.e. olivine gabbronorite, olivine gabbro, gabbro and diorite) and subordinately brown hornblende-rich lithologies (Group II; i.e. olivine-hornblende gabbro and hornblende gabbro). Several of these intrusions host small-scaled magmatic Ni-Cu-(PGE) sulfide accumulations. The intrusions are part of interconnected mafic–(ultramafic) plumbing systems that intruded Cadomian granodiorites of Lausitz Block in the Middle to Late Devonian during the early stages of the Variscan Orogeny. The previously inferred Devonian age of the intrusions is refined by biotite Ar-Ar dating that yield ages between 389.1 ± 3.9 Ma and 372.2 ± 3.7 Ma (2σ). Group I and Group II lithologies differ in their mineralogical and geochemical composition. Compared to the Group I lithologies those of Group II are characterized by higher modal contents of primary brown hornblende, Fe-Ti oxides and apatite, by Ti- and Al-enriched clinopyroxene and by lower contents of SiO2 and increased contents of TiO2, P2O5, LILE, HFSE and LREE. The differences suggest at least two different magmatic series where Group I rocks are linked to tholeiitic basaltic magmas with low to moderate Ti and volatile contents, whereas Group II rocks are derived from Ti- and volatile-enriched alkaline basaltic magmas. The magmas experienced clinopyroxene fractionation during their crustal ascent and storage, but were only minor affected by crustal contamination (< 5%) according to Sr-Nd-Pb isotope systematics. The tholeiitic and alkaline basaltic magmatism could be explained by a tectonic environment between a subduction and intraplate setting. Group II rocks have an intraplate chemical signature and their parental magmas are clearly originated from a deeper-seated mantle source with melting of garnet peridotite, likely associated with an asthenospheric upwelling. By contrast, precursor magmas of Group I rocks are originated from partial melting of a less-enriched source, presumably spinel peridotite, from a subduction-related environment. Trace elements systematics suggest that both groups at least partly resulted from an interaction (mixing) of the alkaline and tholeiitic magmas. Partial melting estimates for both groups vary between 5 and 20%. The proposed tectonic setting could have been related to a subduction slab retreat within the framework of the Variscan orogeny, which led to an upwelling of the asthenospheric mantle. Cu/Zr ratios <1 of gabbroic rocks from several intrusions suggest a previous segregation of magmatic sulfides in other sections of the magmatic plumbing system and give rise for a vertical and lateral Ni-Cu exploration potential.