NNW-trending Faults Research Articles

Magmatic evolution and sources of metals and fluids in the large granite-related Xiasai vein-type Ag–Pb–Zn(–Sn) deposit, northern Yidun terrane, SW China

The Xiasai Ag–Pb–Zn–(Sn) deposit in the northern Yidun terrane (eastern Tethys), hosted in Late Triassic metasandstones, is genetically associated with Late Cretaceous granites. We present chemical and Sr–Nd–Pb–Li–B isotope data of Late Cretaceous granites and their mafic microgranular enclaves (MME), late aplites, and Late Triassic metasedimentary rocks. The narrow range of 87Sr/86Sr99 (0.70627–0.70953) and εNd99 (–6.1 to –5.2) values of most Late Cretaceous granites reflects a mixed source with contributions from the mantle and Paleoproterozoic felsic crust. These granites have high SiO2 contents (>69 wt%) and strong depletions in Sr, Ba, and Eu. Major and trace element contents correlate with the fractionation index 1/TiO2, indicating that they experienced extensive fractionation. Local late aplite dikes were derived from similar source rocks, but seem to be younger.The Pb isotopic compositions reflect that the metal Pb was derived from the granite with variable contributions from the Late Triassic sedimentary rocks. Weakly and moderately altered metasandstones have similar δ7Li and δ11B values as most granites (δ7Li: 0.00 to 2.68 ‰; δ11B values: –14.93 to –12.36 ‰), indicating magmatic fluid sources. The magmatic fluids resulted in the initial enrichment of Sn, Cu, Pb, and Zn. Strong alteration of feldspar and biotite resulted in the metasandstones in negligible change of Li concentrations, significant loss of Sr, Na2O, CaO, MgO, and Fe2O3, but significant addition of B. This alteration lowered δ7Li from 1.01 to –3.65 ‰ and lowered δ11B from –9.43 to –19.18 ‰. The low δ7Li values and extremely low δ11B values reflect external fluids from the Late Triassic sedimentary wall rocks, which interacted with granites and mobilized metals (e.g., Sn, Ag, Pb, and Zn) from the granite and/or the sedimentary wall rocks. The location of the Xiasai deposit is controlled by regional NNW-trending faults induced by Late Cretaceous extension.

Особенности сульфидной минерализации гидротермальной системы мыса Фиолент (юго-западный Крым)

As a result of generalization of geophysical studies, petro-paleomagnetic and structural-geomorphological analyses, as well as thermodynamic modeling, some features of ore formation in the hydrothermal system of Cape Fiolent (southwestern Crimea) under island arc conditions were revealed. It has been established that the main transformations of rocks of the Middle Jurassic igneous complex of Cape Fiolent occurred under the influence of hydrothermal fluids during the introduction of felsic intrusions during 168–140 Ma. The zones contain sulfide mineralization, the main minerals of which are pyrite, sphalerite, pyrrhotite, galena, chalcopyrite and arsenic pyrite. In the central parts of the hydrothermal alteration zone, massive sulfides are strongly weathered; these zones contain many secondary sulfates. In the marginal parts of hypergenic limonite, yellow-brown goethite prevails in the oxidation zone, yellow jarosite in the center, which is probably due to the large amount of pyrite in the center of the system, which gave more sulfuric acid during oxidation. The presence of native sulfur in the section testifies to the mixing of the acidified hydrothermal solution with seawater. Complex petro-paleomagnetic and magnetometric studies have shown that contact changes and transformation of the contrasting basalt-rhyolite formation occurred along the NNW-trending faults.

Features and favorable exploration direction of normal faults in Jurassic strata in northern central Sichuan Basin, China

Studies focusing on the fault system in the Jurassic strata of the Sichuan Basin have been limited, restricting the understanding of the hydrocarbon accumulation mode of the Shaximiao Formation and the expansion of exploration. Through interpretation and coherent slice analysis of extensive seismic data, we have newly discovered that normal faults are widely developed in the northern central Sichuan Basin in the Jurassic strata. These faults mainly extend from the Lower to Upper Jurassic strata and are characterized by the continuous arrangement of NEE-trending small faults in the plane, with a few NNE-trending and NNW-trending faults also present. The distribution of Jurassic fault combinations varies within the basin, with normal faults mainly distributed in the low uplift areas of central Sichuan and the north of central Sichuan. Geochemical data comparisons indicate that these normal faults serve as conduits between the Jurassic source rocks and the Shaximiao Formation reservoir in these areas. Furthermore, the newly discovered normal faults are superimposed with the middle and lower Jurassic source rocks in the northern central Sichuan Basin, suggesting the formation of a new hydrocarbon accumulation model involving hydrocarbon generation from the middle and lower Jurassic, facilitated by communication through normal faults. Notably, one of the promising directions for exploration lies in the multi-stage channel superimposed development zone near these normal faults.

Genesis of the Jinji gold deposit in the Jiangnan Orogen, South China: Constraints from geology, chlorite geochemistry, age and H-O-S-Pb isotopes

The Jinji gold deposit (northeastern Hunan province) is located in the central Jiangnan Orogenic Belt, South China. The auriferous sulfide-calcite-quartz vein orebodies, controlled by near NNW-trending faults, occur in the Lengjiaxi Group metamorphic rocks spatially associated with the Banshanpu granitic pluton. Metallic minerals include mainly pyrite, arsenopyrite, and pyrrhotite, with minor sphalerite, chalcopyrite, galena, and native gold. The main alteration types include K-feldspar, silicic, sericite, carbonate, and chlorite. The gold mineralization comprises three stages: (1) quartz–K-feldspar–chlorite–carbonate–arsenopyrite–pyrite, (2) quartz–carbonate–chlorite–polymetallic, and (3) quartz–carbonate–fluorite–pyrite. Geothermometry of chlorite yielded formation temperatures of 261–332 °C (stage 1) and 262–290 °C (stage 2), whereas the calculated oxygen fugacity of chlorite is −45 to −40 (stage 1) and −42 to −39 (stage 2). The δ18OH2O and δD values are 8.8–10.5 ‰ and −73.3 to −72.8‰ (stage 1), 3.2–4.8 ‰ and −83.6 to −80.7‰ (stage 2), and −1.4 to −0.4 ‰ and −82.2 to −78.6‰ (stage 3), respectively. These results indicate that the primary ore fluids (stages 1 and 2) were derived from a granitic magma and were mixed with meteoric water in stage 3. The gold-bearing sulfides (pyrite, pyrrhotite and galena) have δ34S values of −4.8 to +5.8‰, whilst their 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb ratios are of 35.975–36.204, 15.160–15.231, and 16.100–16.176, respectively. The sulfide S-Pb isotope compositions indicate that the metals were likely derived from the Banshanpu granitic magma, which was produced by partial melting caused by Early Paleozoic crustal thickening. The Jinji deposit exhibits many features of orogenic gold mineralization, such as the ore-controlling structures and mineralization styles (quartz-calcite-sulfide veins). The Jinji deposit is the first reported gold deposit in the central Jiangnan orogen with a genetic link to early Paleozoic granitic magma.

The Petilia-Sosti Shear Zone (Calabrian Arc, southern Italy): An onshore-offshore regional active structure

The integrated interpretation of different types of data, consisting of a detailed Digital Terrain Model, field structural and morphotectonic observations, high resolution seismic data, seismological and Synthetic Aperture Radar interferometry information (vertical and horizontal movements), associated with a review of the available literature, has allowed to analyze the shallow expression of the regional-scale Petilia-Sosti Shear Zone (PSSZ). It is one of the major NW-trending tectonic lineaments affecting the Calabrian Arc and is characterized by a present-day tectonic and gravity-driven deformation. This study investigated the portion of the PSSZ between the offshore Crotone Peninsula, located along the Ionian sea of Calabria, and the central part of the Sila Massif.A complex tectonic history is documented since middle Miocene onward for the PSSZ. It consists of an alternation of sinistral and dextral transpressional and transtensional tectonic phases correlated with the geodynamic events occurred during the SE migration of the Calabrian Arc.The shallow expression of the investigated part of the PSSZ consists of a roughly 14 km wide, ca. 80 km long NW-trending tectonic zone including synthetic NW- to NNW-trending faults and N-NE antithetic minor structures. The main identified NW-trending faults, which show a development between 30 and 50 km, are the Sila and Lakes faults in the Sila Massif, and the Marcedusa-Steccato, Fosso Umbro and Tacina faults located in the SW part of the Crotone Basin and in its offshore area. Currently, the fault segments of the Sila Massif exhibit a prevailing normal kinematics with a left-lateral component, whereas a more complex geological framework occurs in the south-western part of the onshore-offshore Crotone Basin. The latter is dominated by gravity-driven movements, associated with the SE migration of the Crotone Megalandslide and with the regional uplift of Calabria, whereas normal kinematics with a small left-lateral component of movement, locally replaced by reverse/transpressional tectonics, was observed along the southern coast in the late Pleistocene deposits of the Le Castella marine terrace.The seismological data highlight that some strong earthquakes occurred in 1638, 1744 and 1832, with magnitude Mw between 5.7 and 6.8, might be associated with the Lakes, Fosso Umbro and Tacina faults respectively. In this frame, the PSSZ is proposed as a new potential NW-oriented active composite seismogenic source for the central-northern Calabria.

Reconstructing the tectono-sedimentary evolution of the Early–Middle Jurassic Tlaxiaco Basin in southern Mexico: New insights into the crustal attenuation history of southern North America during Pangea breakup

Abstract During Pangea breakup, several Jurassic extensional to transtensional basins were developed all around the world. The boundaries of these basins are major structures that accommodated continental extension during Jurassic time. Therefore, reconstructing the geometry of Jurassic basins is a key factor in identifying the major faults that produced continental attenuation during Pangea breakup. We reconstruct the tectono-sedimentary evolution of the Jurassic Tlaxiaco Basin in southern Mexico using sedimentologic, petrographic, and U-Pb geochronologic data. We show that the northern boundary of the Tlaxiaco Basin was an area of high relief composed of the Paleozoic Acatlán Complex, which was drained to the south by a set of alluvial fans. The WNW-trending Salado River–Axutla fault is exposed directly to the north of the northernmost fan exposures, and it is interpreted as the Jurassic structure that controlled the tectono-sedimentary evolution of the Tlaxiaco Basin at its northern boundary. The eastern boundary is represented by a topographic high composed of the Proterozoic Oaxacan Complex, which was exhumed along the NNW-trending Caltepec fault and was drained to the west by a major meandering river called the Tlaxiaco River. Data presented in this work suggest that continental extension during Pangea breakup was accommodated in Mexico not only by NNW-trending faults associated with the development of the Tamaulipas–Chiapas transform and the opening of the Gulf of Mexico, but also by WNW-trending structures. Our work offers a new perspective for future studies that aim to reconstruct the breakup evolution of western equatorial Pangea.

Multiple isotope (He-Ar-Zn-Sr-Nd-Pb) constraints on the genesis of the Jiawula Pb-Zn-Ag deposit, NE China

• Mantle fluid and atmospheric water are two most important sources for the ore-forming fluid of the Jiawula deposit. • Zn isotopic variation was most likely caused by kinetic Rayleigh fractionation. • Coeval magma played a key role in the formation of the deposit. The large Jiawula Pb-Zn-Ag deposit is located in the Manzhouli area, northeast China. The Pb-Zn-polymetallic mineralization in the Jiawula deposit is present as ore veins distributed in Early Mesozoic sedimentary and magmatic rocks and was controlled by NWW to NNW trending faults. He and Ar isotope analysis results of fluid inclusions hosted in pyrite show that 40 Ar/ 36 Ar ratios are 280.5–300.1, which is close to the atmospheric value (295.5). 3 He/ 4 He ratios vary from 40.15 × 10 −7 to 71.68 × 10 −7 . The calculated mantle He are in a range of 35.8–64.0%, with an average of 51.0%. He-Ar isotopic data reveals that the ore-forming fluids of the Jiawula deposit were derived from mixture of two fluid end-members: (1) mantle-derived fluid, which has provided a considerable proportion of He; and (2) crustal fluid, which is characterized by almost atmospheric Ar and crustal He. The sphalerite from the Jiawula deposit have a narrow range of δ 66 Zn JMC values, varying from 0.15 to 0.307‰, with a mean value of 0.236‰. We suggest that the variation of Zn isotope values of sphalerite from the Jiawula deposit was most likely caused by kinetic Rayleigh fractionation. The Zn isotope analysis result, combined with previous S isotopic data, indicate that the ore-forming material of the Jiawula deposit was derived from a single source. The intrusive rocks in the deposit have low initial 87 Sr/ 86 Sr ratios, relatively high ε Nd (t) values, and young T DM2 Nd model ages, indicating a high proportion of juvenile material in the petrogenesis. Combined with Sr-Nd-Pb isotopic data of intrusive rocks that are coeval with mineralization in the deposit, He-Ar-Zn isotope analysis results, and previous studies, we propose that the mantle component in the ore-forming fluid and material of the Jiawula deposit was most probably derived from the simultaneous magma, which was derived from partial melting of crust with involvement of mantle magma in an extensional setting during the late Jurassic to the early Early Cretaceous.

Neotectonic evidence for Late Quaternary reverse faulting in the northern Chile outer forearc (22.5°S-23°S): Implications for seismic hazard

In the northern Chile outer forearc (19°S to 23°S), extension is the dominant deformation style conducted by crustal faults during the Neogene-Quaternary. Most of this extension has been produced by normal faulting along submeridian branches of the Atacama Fault System (AFS). During the Late Quaternary, several of these faults have built conspicuous metric-scale normal faulting scarps in alluvial deposits; the construction of these scarps has been related, in some cases, to M~7 normal faulting paleoearthquakes. On the contrary, shortening during this time span has only been locally reported. Until now, no metric-scale reverse faulting scarps have been documented along submeridian strands of the AFS. This study presents novel evidence corresponding to reverse fault scarps produced during the Late Quaternary by three NNE and NNW trending faults in the outer forearc between 22.5°S and 23°S: the El Toro (ETF), Caliche (CF), and Sierra Valenzuela (SVF) faults. These scarps, with up to 2.5 m height, developed in basement rocks, pre-Quaternary, and/or Quaternary alluvial deposits. Based on their characteristics and the evidence suggesting that similar fault scarps in the Andean forearc have a seismogenic origin, we interpret that these neotectonic landforms were produced by single reverse faulting paleoearthquakes. Considering the maximum scarp height as a proxy for the coseismic slip and fault length as a proxy for surface rupture length, we have estimated magnitudes between M6.2 and M6.9 for the causative rupture events. To discuss how reverse crustal faulting may be related to the interseismic and/or coseismic stages of the subduction cycle, we perform elastic dislocation models to calculate the horizontal displacement fields (at 0 and 20 km depth) induced by the interplate locking distribution in the area (over a seismic cycle) and three megathrust earthquakes (Antofagasta, 1995, Tocopilla, 2007, and a synthetic rupture). Modeling results suggest that the studied faults may experience reverse slip during both stages of the subduction cycle. We propose that the ETF, CF and SVF are faults capable of producing moderate-to-large earthquakes in the future. Finally, we reinforce the need to address the earthquake potential of the studied faults, and others similar to them, to acquire a complete assessment of the seismic hazard in the northern Chile outer forearc.

Main constrains and dynamic process of Ordovician hydrocarbon accumulation, central and western Tahe Oil Field, Tarim Basin

Diversified types of oil and gas resources have been discovered in the Ordovician strata of central and western parts of the Tahe Oil Field, Tarim Basin. The formation contains oil in the direction as a whole, and its accumulation process appeared to be extremely complicated. The dynamic process of oil and gas accumulation in the central and western parts of Tahe Oil Field were re-studied on the basis of combination of approaches including perspective of multiple reservoir-forming factors and their temporal and spatial dynamic configuration relationships, the discussion of typical reservoir profiles, thermal evolution of source rocks and consequent hydrocarbon generation history, paleo-structural evolution, hydrocarbon accumulation period and transport system, thus, a model of compound accumulation was established following an idea that paleo-structures and strike-slip faults together constrained reservoir formation and hydrocarbon generation as well as accumulation. Studies have shown that the main constrains for hydrocarbon accumulation in the study area includes the long-term hydrocarbon generation and expulsion from source rocks, multi-stage charging and accumulation and mixing transformation, paleo-structural controlling the migration and accumulation direction, conduction and lateral adjustment by strike-slip faults, and multiple types of fractures and caves. The dynamic process of hydrocarbon accumulation has the characteristics of vertical transportation, lateral accumulation, paleo-uplift controlling enrichment in the early stage, and in-situ hydrocarbon source, migration and accumulation, and fault controlling enrichment in the late stage. The mixed accumulation of oil and gas of different stages and different properties has created the present complex oil and gas appearance of the Ordovician strata. The heavy oil area was dominated by early accumulation, which was related to the high paleo-structures in the middle and late Caledonian periods, and the later charging was relatively weaker. The light oil area was dominated by late accumulation, mainly constrained by the transport and short-range lateral adjustment of strike-slip faults. It is most developed in the NNE-trending fault zone and the intersection with the NNW-trending fault.

Genesis of the Xiaoyuzan epithermal Au deposit in the Yelimodun volcanic basin, Western Tianshan, China: Constraints from geology, geochronology, isotopes and mineralogical compositions

The Tulasu and Yelimodun volcanic basins are two important Au districts in the northwestern Chinese Western Tianshan. Two large Au deposits have been discovered in the Tulasu basin, whereas only small-sized Au deposits and prospects, including the Xiaoyuzan deposit, were found in the Yelimodun basin. The purpose of this study is to examine the genesis of the Xiaoyuzan deposit and its implications for further exploration through geological, geochronological, geochemical and mineralogical studies of the host rocks and ores. The orebodies are mineralized veins and veinlets and are structurally controlled by NW- and NNW-trending faults within the Lower Carboniferous Dahalajunshan Formation volcanic rocks (DF). Sulfides are abundant (10–20 vol%) in the ores and consist of pyrite, sphalerite, galena, chalcopyrite and minor tetrahedrite. Electron microprobe analysis (EMPA) indicates that pyrite and sphalerite are both auriferous. Three ore-forming and alteration stages were distinguished: (I) quartz-pyrite stage with silicification and propylitization, (II) quartz-polysulfide stage with silicification and phyllic alteration, and (III) quartz-carbonate stage with carbonatization.The mineralization age is constrained to 357–331 Ma by a LA-ICP-MS U-Pb age of 357.3 ± 4.0 Ma for zircon from the ore-hosting tuff and the unconformably overlying Lower Carboniferous Aqialehe Formation containing fossils of the Visean period. The zircons from the tuff have highly positive εHf(t) values ranging from 5.9 to 10.1, indicating a magma source of depleted mantle with limited crustal contribution. The values of δ18OH2O-VSMOW calculated from δ18Oquartz and δDH2O-VSMOW measured from fluid inclusions of stage II quartz range from −4.0‰ to −2.9‰ and −117‰ to −109‰, respectively. The values of δ13CCO2 calculated from δ13Ccal and δ18OH2O calculated from δ18Ocal range from −1.6‰ to −1.4‰ and −9.8‰ to −2.7‰, respectively. The in-situ δ34S values range from 2.6‰ to 3.7‰ for pyrite and 2.7‰ to 4.1‰ for sphalerite, respectively. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of pyrite vary from 18.196 to 18.253, 15.564 to 15.642, and 38.063 to 38.300, respectively, similar to those of ore-hosting DF and granites from the Tulasu-Yelimodun volcanic belt. The above geochemical characteristics suggest that the ore-forming fluids were mixtures of magmatic and meteoric waters, and the metals and sulfur may have been derived partly from magmatic fluids generated from the hidden causative intrusions and partly from the hosting volcanic rocks. These, together with high sulfide abundance and development of sulfide assemblages representing intermediate-sulfidation state, suggest that Xiaoyuzan is an intermediate-sulfidation epithermal Au deposit. Considering the limited erosion for the Au mineralization within the interior of Yelimodun basin and close spatio-temporal relationship between intermediate-sulfidation and porphyry mineralization, it is inferred that there may be concealed porphyry Cu-Au mineralization underneath the Xiaoyuzan deposit and its vicinity.

Cenozoic tectonic inversion in the Northern Depression, South Yellow Sea Basin, East Asia: Structural styles and driving mechanism

The Northern Depression of the South Yellow Sea Basin underwent two episodes of tectonic inversion from the latest Eocene to Oligocene and in the Pliocene, respectively. During the inversion, the structural depression controlled previously by extensional faults was subjected to compression and erosion. Structural interpretation on 2D marine seismic data suggests that the structural styles associated with inversion are predominantly reactivated NNW-trending faults, fault-related folds, newly-formed reverse faults and unconformities. Here we used structural restoration technique to illustrate the sequential development of these inversion structures and to estimate the amount of deformation. To explore the mechanism of the basin inversion, the finite element modeling was employed to reproduce the inversion deformation in the Northern Depression. The deformation features predicted by modeling are well consistent with our structural observations. Based on a combination of these results and regional tectonic history, we propose that the inversion deformation in the South Yellow Sea Basin was predominantly driven by the enhanced dextral strike-slip motion along the Tan-Lu Fault. The interactions between the Eurasian plate and the Pacific realm resulted in the varying dextral movement along the Tan-Lu Fault, and the Cenozoic tectonic inversion in the South Yellow Sea Basin was a tectonic response to these processes.

3D hydrogeological reconstruction of the fault-controlled Euganean Geothermal System (NE Italy)

Assessing the renewability of geothermal and hydrogeological resources is a particular requirement for their future preservation. The sustainable exploitation of a geothermal resource for its long-term utilization is related to both the water demand and the hydrogeological characteristics of the geothermal field, while its renewability is influenced by the geological and hydrogeological processes that enhance the groundwater flow. Numerical modeling can be successfully used to assess both the impacts of processes occurring in the geothermal system and the renewability of associated resources. However, the reliability of a numerical simulation is influenced by the accuracy of the dataset used to reproduce the geological system. A 3D hydrogeological reconstruction model, rather than a simplified conceptualization of the geological setting, can increase the consistency of the modeling results. In the case of the Euganean Geothermal System (NE Italy), a detailed reconstruction was performed to quantitatively reproduce the hydrogeological elements that allow the development of the geothermal system and to estimate the amount of thermal waters stored in the reservoir. The structural setting of the central Veneto region, in particular the high-angle NNW-trending faults of the Schio-Vicenza Fault System, plays a fundamental role in the existence of the Euganean Geothermal System, permitting hydraulic connection between the recharge area and the exploitation field. In addition, regional- and local-scale faults and fractures favor fluid convection, which represents the main process that warms thermal fluids. Reproducing such a complex geological setting in a 3D model allows improving knowledge about the features that characterize the geothermal system and attaining a solid framework for the construction of a 3D regional numerical model that will be used to assess the renewability of the system.

Surface ruptures database related to the 26 December 2018, MW 4.9 Mt. Etna earthquake, southern Italy

We provide a database of the surface ruptures produced by the 26 December 2018 Mw 4.9 earthquake that struck the eastern flank of Mt. Etna volcano in Sicily (southern Italy). Despite its relatively small magnitude, this shallow earthquake caused about 8 km of surface faulting, along the trace of the NNW-trending active Fiandaca Fault. Detailed field surveys have been performed in the epicentral area to map the ruptures and to characterize their kinematics. The surface ruptures show a dominant right-oblique sense of displacement with an average slip of about 0.09 m and a maximum value of 0.35 m. We have parsed and organized all observations in a concise database, with 932 homogeneous georeferenced records. The Fiandaca Fault is part of the complex active Timpe faults system affecting the eastern flank of Etna, and its seismic history indicates a prominent surface-faulting potential. Therefore, this database is essential for unravelling the seismotectonics of shallow earthquakes in volcanic areas, and contributes updating empirical scaling regressions that relate magnitude and extent of surface faulting.

Ouansimi copper mineralization (Western Anti-Atlas, Morocco): Paragenetic sequence and circulation of gangue hosted paleofluids.

The Ouansimi copper deposit, located South of the Kerdous inlier in Morocco, is an example of vein-type mineralization hosted in the Adoudou Formation limestone of the Lower Cambrian Taroudant Group. The copper-bearing veins are mainly controlled by Variscan NNW-trending faults and are subdivided here into Eastern, Western, and Central structures. On the basis of mineralogical, metallographic, and fluid inclusion studies, two mineralizing processes are proposed. A primary process is interpreted for the chalcopyrite, digenite, galena, sphalerite, carrollite, and pyrite with quartz and dolomite as gangue minerals. A secondary process is proposed for chalcocite, bornite, covellite, native copper, copper carbonate and oxide. Microthermometric analysis of fluid inclusions was carried out on quartz and dolomite gangues. Primary fluid inclusions trapped in quartz show the existence of fluids with temperatures of 175°C–275 °C and salinities of 10–15 wt % NaCl eq. However, fluid inclusions in dolomite indicate fluids with temperatures of 200°C–250 °C and salinities of 20–25 wt % NaCl equiv. Combining ore mineralogy and fluid inclusion microthermometry, two main hypogene sulphide mineralization stages can be distinguished in the Ouansimi copper deposit. The first Cu–Fe stage, with quartz as a gangue mineral, was related to hydrothermal fluids with moderate temperature and low salinity. The second Cu–Zn–Pb–Co–Ni–Fe stage was associated with dolomite as a gangue mineral and infilled cavities and fractures cutting quartz. This second phase was related to hydrothermal fluids with moderate temperature and high salinity. The tectonic evolution of the Ouansimi deposit was characterized by thrusting of the south limb over the north limb and by dextral and sinistral offsets of the mineralized structures along late-stage ENE-WSW-trending faults.

3D Coseismic Deformation Field and Source Parameters of the 2017 Iran-Iraq Mw7.3 Earthquake Inferred from DInSAR and MAI Measurements

The coseismic slip on the main fault related to the 2017 Iran-Iraq Mw7.3 earthquake has been investigated by previous studies using DInSAR (differential interferometric synthetic aperture radar) ground deformation measurements. However, DInSAR observation is not sensitive to the ground deformation in the along-track (AT) direction. Therefore, only the one-dimensional (1D) DInSAR coseismic deformation field measurements, derived in the LOS (line-of-sight) direction of radar, was applied in source parameters estimation. To further improve the accuracy of the fault slip inversion, the 3D (three-dimensional) coseismic deformation fields were reconstructed in the first place, by a combined use of the DInSAR and MAI (multiple aperture InSAR) measurements. Subsequently, the LOS and 3D deformation data sets were used as the constraint respectively, to perform a two-step inversion scheme to find an optimal geometry and slip distribution on the main fault. The comparative analysis indicated that the 3D coseismic deformation data sets improved the inversion-accuracy by 30%. Besides, the fault invention results revealed a deep dislocation on a NNW trending fault (the strike is 352.63°) extending about 60 km, along the fault dips 14.76° to the ENE. The estimated seismic moment is 8.44 × 1019 Nm (Mw7.3), which is close to the solution provided by USGS (United States Geological Survey). The slip distributed at the depth between 12 and 18 km, and the peak slip of 6.53 m appears at the depth of 14.5 km left near the epicenter. Considering the geological structure in the earthquake region and fault source-parameters, it comes to a preliminary conclusion that the ZMFF (the Zagros Mountain Front fault) should be responsible for the earthquake. In general, this paper demonstrated the superiority of using the 3D coseismic deformation fields on source parameters estimation.

Strain Accommodation in the Daliangshan Mountain Area, Southeastern Margin of the Tibetan Plateau

AbstractThe Xianshuihe‐Xiaojiang fault system (XXFS) plays a crucial role in accommodating relative motions of the south China block and the expanding Tibetan Plateau. Compared to the narrow southern and northern segments of the XXFS, the central section (also referred to as the Daliangshan mountain area) is broader and dissected by a network of faults. Geologic studies suggest that three major NNW trending faults may dominate slip partitioning of more recent faults in this region. However, due to accessibility issues, sparse geodetic studies have constrained geodetic fault slip rates with contradictory results. In this study, we use 17 new Global Navigation Satellite System sites combined with existing solutions to investigate slip partitioning of the region. We derive a tectonic velocity solution, develop a block kinematic model constrained by Euler pole clustering technique, and calculate geodetic fault slip rates to compare with geologic fault slip rates. We confirm that the Anninghe‐Daliangshan sliver (ADS) is a distinct, rigid block, and we resolve a new, rigid Daliangshan‐Yingjing‐Mabian block (DYB). Kinematic modeling predicts long‐term slip rates that suggest both the ADS and the DYB partition (~10.0–12.0 mm/year) relative motion between the Tibetan Plateau and south China block in the central XXFS, reconciling geologic observations. We suggest that both the continuum and microplate deformation patterns are present in our study area, of which the local tectonics is better explained by the microplate model, but scale of the kinematics makes its motion more consistent with the continuum model.

The Miocene Atastra Creek sinter (Bodie Hills volcanic field, California and Nevada): 4D evolution of a geomorphically intact siliceous hot spring deposit

The Atastra Creek siliceous hot spring deposit, or sinter, occurs in the Paramount-Bald Peak alteration zone, due north of the Bodie precious metals mining district in the Miocene Bodie Hills volcanic field, California and Nevada, U.S.A. Distinctive features include its geomorphically intact geyser vent mounds, the presence of growth-fault-stepped sinter terraces that developed westward along a NNW trending fault, and atypical Hg, Sb and As concentrations. High-temperature (>75 °C), subaerial, proximal apron sinter occurs in two settings – (1) radiating botryoidal geyserite in vent mounds and (2) bedded geyserite (columnar, nodular, size-sorted geyser eggs) intercalated with mid- to low-temperature (<60 °C), middle to distal apron terrace sinter. The active geyser vent mounds migrated from south to north across the apron terrace through time. A newly recognized, visually striking type of sinter – termed silica infiltrate herein – formed directly beneath the subaerial geyserite deposits. It is characterized by mainly parallel, thin, irregular beds of white silica with narrow borders of dark blue-gray silica, as well as swirly to globular white silica, all chaotically linked together by silica ‘necks’ and ‘bridges’. The silica infiltrate permeates the pre-existing sinter, and is interpreted to represent super-heated fluid injections into the immediately overlying geyser vent mounds and pools. The adjacent sinter sheets preserve fluid-flow directions of warm-water channels that traversed the discharge apron, including microbial streamer fabric and wavy laminated sinter with flattened bubbles. More distal sinter textures are recorded by rimmed terracettes with mammillated and palisade microbial fabrics and rare, warm pool-related stromatolites. However, plants are absent, probably due to the high metalloids, in particular As. Post-depositional events include an inferred hydrothermal eruption breccia and an interpreted drop in the water table accompanied by incursion of steam acid condensate, as evidenced by pervasive hydrothermal alteration of the Atastra Creek deposits. Hence, the well-exposed sedimentary facies distributions, well-preserved geomorphology, and stratigraphic and structural relationships together allow an unusually complete, paleoenvironmental reconstruction of the Atastra Creek paleohydrothermal deposit.

Causes of unusual distribution of coseismic landslides triggered by the Mw 6.1 2014 Ludian, Yunnan, China earthquake

The Mw 6.1 2014 Ludian, Yunnan, China earthquake triggered numerous coseismic landslides that do not appear to be associated with any previously known seismogenic fault. Traditional models of triggering for seismically generated landslides do not provide a reasonable explanation for the landslide pattern observed here. Here the Newmark method is applied to a grid to calculate the minimum accelerations required for slope failures throughout the affected region. The results demonstrate that for much of the study area, the distribution of failure prone slopes is similar to the actual pattern of coseismic landslides, however there are some areas where the model predicts considerably fewer failures than occurred. We suggest that this is a result of the complex source faults that generated the Ludian earthquake, which produced a half-conjugate rupture on nearly EW- and NNW trending faults at depth. The rupture directed much of its seismic moment southeast of the epicenter, increasing ground shaking and the number of resulting landslides.

Geochronology and Ore Mineralization of the Dzheltula Alkaline Massif (Aldan Shield, South Yakutia)

The Dzheltula alkaline massif is located in the Tyrkanda ore region of the Chara–Aldan metallogenic zone of the Aldan–Stanovy Shield (South Yakutia). The region contains separate placer gold objects, which are being explored at the present time, and ore-bearing Mesozoic alkaline intrusions, which are weakly studied due to their poor accessibility. The Dzheltula massif (DM) is the largest exposed multiple-ring intrusion within the Tyrkanda ore region; therefore, it is considered as a typical object for geological, petrological, geochronological, and metallogenic studies. The DM consists of five magmatic phases of syenite composition. 40Ar–39Ar dating has established that the crystallization age of the oldest phase, the leucocratic syenite porphyry (pulaskite), is 121.1 ± 1.3 Ma. The crystallization age of the cross-cutting phases represented by syenite–porphyry dikes (laurvikites and pulaskites) ranges from 120.1 ± 2 to 118.3 ± 2.1 Ma. The youngest phase of the massif, trachyte, crystallized at 115.5 ± 1.6 Ma. According to the mineralogical and geochemical studies, two types of ore mineralization, namely gold and uranium–thorium–rare-earth (U–Th–REE), are established within the DM. The gold mineralization was found in the quartz–chlorite–pyritized metasomatites. It is confined to the NNE- and NNW-trending fault zones and coincides with the strike of the syenite porphyry dike belt. Uranium–thorium–rare-earth mineralization has been established in the quartz–feldspathic metasomatites localized in the outer contact of the massif. The juxtaposition of mineralization of different types in some zones of the Dzheltula syenite massif significantly increases the ore potential of the studied object within the Tyrkanda ore region.

Evolution of the northern tip of Afar triangle: Inferences from the Quaternary succession of the Dandiero — Massawa area (Eritrea)

The Afar region is a triangular area located at the triple junction between the African, Somalia, and Arabian plates, which are currently diverging at different rates. Currently, the extension vector is roughly oriented in a NE-SW direction in the Afar, Red Sea and Gulf of Aden, in respect to Arabia plate, whereas the Nubian–Somalian divergence, evidenced by the Main Ethiopian Rift (MER), is approximately WNW-ESE (N95-100°E).This study focuses on the tectono-sedimentary evolution of a sector from Massawa to the north up to the continental Early-Middle Pleistocene Dandiero Basin to the south. This basin is filled with approximately 500m thick fluvial-lacustrine deposits and includes six formations. Sedimentation occurred mainly along the basin axis and allowed accumulation of sand and mud deposits with subordinate gravels close to the basin margin. The age of the basin infill succession is well constrained through integration between paleomagnetic and paleontological data and ranges between ~1.2 and 0.75Ma.The Dandiero Basin is controlled by two main roughly NNW-SSE trending, east dipping normal faults. The westernmost fault delimits the basins from the plateau, whereas the easternmost marks the limit between the basin succession and the Late Pleistocene Samoti Plain. We infer that the NNW-trending faults were progressively activated as a consequence of the Danakil Block counter clockwise rotation and were superimposed to the N-S trending faults that delimited the basin at the time of its inception as a marginal graben roughly aligned to the Eritrean-Ethiopian plateau. The timing of deformation (1.2Ma up to Present) is well constrained by the age of syntectonic sediments of the Dandiero Basin and volcanic products of the Alid Volcano. These relations allowed us to refine the timing and evolution of this sector of Afar and giving some insights on the geodynamics of the area.