Trending Strike-slip Faults Research Articles

THE ROLE OF FAULTS IN THE FORMATION OF THE OKHOTNICHYA CAVE (BAIKAL REGION)

The paper presents the results of an analysis of faults of different ranks near the Okhotnichya Cave in Pribaikalye, aimed at identifying their role in the formation and evolution of the cave and its adjacent areas. This was done using rank-wise structural-paragenetic analysis of faults, which forms the basis of a specialized mapping tool for fault zones. Factual evidence was obtained through several methods. The speleoinitiating fracture network was studied based on the results of the cave digital topographic survey performed using Leica DistoX 310 laser rangefinder. The therewith-generated 3D-model of the cave allowed making up a detailed plan of the passages for linking to the local geological-structural observations with mass fracture measurements and studying dip directions and strike orientations of the cave fractures. The results stated that the passages in the cave network correspond to the paragenesis of the right-lateral NNE trending strike-slip fault. Local analysis of rock fracturing within the cave made it possible to determine the type of kinematics of speleoinitiating fractures and to verify the reconstruction of the fault zone of the supra-local level. It has been stated that narrow tunnels follow the local NNE- and WNW-oriented strike-slip faults, and large chambers and grottoes follow the extension structures - ENE- and NE-striking normal faults. The lineament analysis of the cave-adjacent area revealed that the strike-slip fault network of the cave is an element of paragenesis of the regional normal fault, typical of the late-orogenic Baikal rift system. Thus, the conducted research showed that the genesis of the Okhotnichya Cave has a mixed character and provided the possibility of analyzing the karst caves' spatial patterns to reconstruct kinematic types of faults at different hierarchic levels - local, supra-local, and regional.

Origin of Early to Middle Triassic ultrapotassic syenites in South China: A record of block amalgamation in East Asia

Alkaline intrusions such as ultrapotassic syenites are typically formed in extensional tectonic settings including continental rift, post-orogenic and post-collisional regimes. Here we present two early Mesozoic ultrapotassic syenite plutons (Tieshan and Yangfang) in South China that were formed in a continent collisional setting. LA-ICP-MS zircon UPb chronological, major and trace elemental, and SrNd isotopic data of these syenites are used to explore their origin and to further constrain the geodynamics of early Mesozoic magmatism in South China. Our new data indicate that the Tieshan and Yangfang plutons were formed in Early Triassic (249 Ma) and Middle Triassic (240 Ma), respectively. The Tieshan and Yangfang syenites have SiO2 contents of 50.84–56.95 wt% and 59.13–68.34 wt%, respectively, both are enriched in alkalis with very high K2O (5.60–9.68 wt%) and K2O/Na2O (1.8–15.7) and in LILE (Ba = 2464–8813 ppm; Sr = 652–3499 ppm), REE (498–1355 ppm) and HFSE (Zr = 264–766 ppm). They show enriched SrNd isotopic compositions with 87Sr/86Sr (t) and εNd (t) of 0.7096–0.7102 and − 5.2 to −6.5, respectively for Tieshan and of 0.7112–0.7119 and − 8.8 to −9.7, respectively for Yangfang. Geochemical data suggest that the studied ultrapotassic syenites were derived by partial melting of ancient subduction-modified lithospheric mantle including slab-derived melt hybridization and slab-derived carbonate fluid metasomatism, with the source depth of 60–90 km for Tieshan and at least 90 km for Yangfang. We further suggest that their origins are related to the transtension of the regional NE–trending strike-slip faults caused by continental collisions during the early Mesozoic amalgamation in East Asia.

Contrasting origins of A-type granites in the Late Triassic-Early Jurassic Pitou complex, southern Jiangxi province: Implications for Mesozoic tectonic evolution in South China

The origin of A-type granites is purely circumstantial. Granitic complexes are quite common and generally composed of different type granites. I- and A-type granite association in a granitic complex is often described in the literature. Here we present a granitic complex, i.e. the Pitou complex in southern Jiangxi province, South China that is composed of different varieties of A-type granites. Detailed zircon LA-ICP-MS U Pb chronology and in situ Hf isotope, mineral chemistry and whole-rock element and Sr Nd isotope data of this granitic complex are used to explore their origin and to further constrain the geodynamics of Mesozoic magmatism in South China. Our new data indicate that the Pitou complex was emplaced during the Late Triassic (237 Ma) (central to northern part) and Early Jurassic (188–185 Ma) (southern part), respectively and that both the Late Triassic and Early Jurassic granites belong to A-type but show contrasting origins. The Late Triassic granites show an association of alkali-feldspar granite-syenogranite-monzogranite and the rock type of the Early Jurassic granites is alkali-feldspar granite. All the granites are composed mainly of K-feldspar, quartz, plagioclase and biotite (ferri-biotite or annite) with biotite occurring as anhedral crystal, interstitial to quartz and feldspar. Both the Late Triassic and Early Jurassic granites have high SiO 2 (>70 wt%) and total alkalis (K 2 O + Na 2 O > 8 wt%) with high FeO T /(FeO T + MgO) and low Mg#. They are enriched in rare earth elements (except Eu) and depleted in Sr and Ba. They display Zr + Y + Ce + Nb >350 ppm, 10,000 × Ga/Al >2.6 and have high zircon saturation temperatures (>800 °C). Biotites in the granites are Fe-rich with very low Fe 3+ /Fe 2+ , indicating fairly reducing conditions. However, the Late Triassic and Early Jurassic granites also show some geochemical differences. The Late Triassic granites have lower FeO T /(FeO T + MgO) and higher Mg# than the Early Jurassic granites, with the Mg# of the former consistent with pure crustal melts and the Mg# of the latter much lower than pure crustal melts. In addition, the Late Triassic granites have lower zircon saturation temperatures (up to 843 °C, average 823 °C) than the Early Jurassic granites (up to 946 °C, average 875 °C). Furthermore, the Late Triassic granites have high 87 Sr/ 86 Sr (t) (0.7132–0.7226) and negative ε Nd (t) (−10.3 to −10.9) and ε Hf (t) (in situ zircon) (−11.5 to −11.6) that are similar to those of the early Paleozoic granitoids in the region whereas the Early Jurassic granites have low 87 Sr/ 86 Sr (t) (down to 0.7034) and positive ε Nd (t) (up to +3.0) and ε Hf (t) (in situ zircon) (up to +8.3) that are similar to those of the Early Jurassic gabbroic rocks in the region. Geochemical data and major element modeling suggest that the Late Triassic A-type granites were formed by shallow (ca. 15–20 km depth) dehydration melting of the early Paleozoic granitoids triggered by intraplating of basaltic magmas and the Early Jurassic A-type granites were produced by extensive fractionation (ca. 90% to 95%) from gabbroic magmas by removal of plagioclase, amphibole, K-feldspar, clinopyroxene and magnetite. We further suggest the origin of the Late Triassic A-type granites was related to the transtension of the regional NE–trending strike-slip faults caused by the early Indosinian continental collisions and the Early Jurassic A-type granites were emplaced in a back-arc extensional setting coupled with the slab rollback and subsequent slab break-off of the subducted Palaeo-Pacific plate. Our new data confirm that the early Mesozoic magmatism in South China was controlled by continental collisions during the Late Permian to Triassic amalgamation in Southeast Asia whereas the late Mesozoic magmatism was related to the northwestward subduction of the Palaeo-Pacific plate. A transition in the dominant tectonic regime from the Tethyan to the Pacific tectonic domain most likely took place during the Rhaetian. • The Pitou granitic complex emplaced during the Late Triassic and Early Jurassic. • Both Late Triassic and Early Jurassic granites are A-type but show contrasting origin. • Late Triassic granites formed by shallow dehydration melting of Paleozoic granitoids. • Early Jurassic granites formed by extensive fractionation from gabbroic magmas. • Origin of both A-type granites suggests different geodynamic mechanisms.

Fault-Related Fluid Flow Implications for Unconventional Hydrocarbon Development, Beetaloo Sub-Basin (Northern Territory, Australia)

This study assesses potential geological connections between the unconventional petroleum plays in the Beetaloo Sub-basin, regional aquifers in overlying basins, and the near surface water assets in the Beetaloo Sub-basin Northern Territory, Australia. To do so, we built an innovative multi-disciplinary toolbox including multi-physics and multi-depth imaging of the geological formations, as well as the study of potentially active tectonic surface features, which we combined with measurement of the helium content in water sampled in the aquifer systems and a comparative analysis of the surface drainage network and fault lineaments orientation. Structures, as well as potential natural active and paleo-fluid or gas leakage pathways, were imaged with a reprocessing and interpretation of existing and newly acquired Beetaloo seismic reflection 2D profiles and magnetic datasets to determine potential connections and paleo-leakages. North to north-northwest trending strike slip faults, which have been reactivated in recent geological history, are controlling the deposition at the edges of the Beetaloo Sub-basin. There are two spring complexes associated with this system, the Hot Spring Valley at the northern edge of the eastern Beetaloo Sub-basin and the Mataranka Springs 10 km north of the western sub-basin. Significant rectangular stream diversions in the Hot Spring Valley also indicates current or recently active tectonics. This suggests that those deep-rooted fault systems are likely to locally connect the shallow unconfined aquifer with a deeper gas or fluid source component, possibly without connection with the Beetaloo unconventional prospective plays. However, the origin and flux of this deeper source is unknown and needs to be further investigated to assess if deep circulation is happening through the identified stratigraphic connections. Few north-west trending post-Cambrian fault segments have been interpreted in prospective zones for dry gas plays of the Velkerri Formation. The segments located in the northern part of the eastern Beetaloo Sub-basin do not show any evidence of modern leakages. The segments located around Elliot, in the south of the eastern Beetaloo Sub-basin, as well as low-quality seismic imaging of potential faults in the central part of the western sub-basin, could have been recently reactivated. They could act as open pathways of fluid and gas leakage, sourced from the unconventional plays, deeper formations of the Beetaloo Sub-basin or even much deeper origin, excluding the mantle on the basis of low 3He/4He ratios. In those areas, the data are sparse and of poor quality; further field work is necessary to assess whether such pathways are currently active.

Volcanic geosites assessment in the Plio-Quaternary Azrou-Timahdite Plateau (Middle Atlas, Morocco)

During the Plio-Quaternary, the Azrou-Timahdite Plateau (PAT), considered as “the land of lakes and volcanoes”, was the region of alkaline volcanism associated with the penecontemporaneous NE-SW trending strike-slip fault movements system. This volcanism is the most recent and the most extensive in Morocco. It occupies 7.8% of the Middle Atlas range area where the majority of volcanic edifices follow an NNW-SSE-oriented trend. The volcanic field occupies an area of about 1000 km2. The present study allowed us to inventory 76 volcanic geosites that comprise a range of volcanic structures that are unique in Morocco. 26 are retained during the quantitative assessment. 33% of the sites were filtered for the scientific assessment stage (26 sites out of 76), including 5 of high scientific value and 21 of medium scientific value. Of these 26 sites, 84% show a moderate to a high degree of deterioration (22 of 26). However, only 6 sites have a negative total value, having a deterioration value greater than the scientific value, demonstrating the considerable scientific importance of the sites in the region, which requires more attention and protection. It should be noted that only 3 steps (inventory, quantitative assessment, degree of deterioration) of the adopted methodology were applied. In fact, due to the large number of geosites with a medium to high risk of deterioration, the fourth step (usage value) was excluded. Besides, we have chosen to present the detailed geological, geomorphological, and volcanic specificities of 5 geosites of high scientific value. These geosites hold specific characteristics among the other volcanoes of the PAT: their eruptive dynamism, their size, their shape, their extent, and the nature of their pyroclastic products.

The Andaman Basin Central Fault Zone, Andaman Sea: Characteristics of a major deepwater strike-slip fault system in a polyphase rift

2D and 3D seismic reflection data from Thailand waters in the Andaman Sea have revealed a major NNE-SSW trending strike-slip fault (Andaman Basin Central Fault Zone, ABCFZ). This fault developed following a change from E-W to ENE-WSW extension during the Oligocene-earliest Miocene, to NNW-SSE transtension. The ABCFZ is interpreted to have formed subsequent to an extensional detachment translating the upper crust, including the extensional rift basins, to the west, leaving the ABCFZ to be developed on thinned, lower plate, lower continental crust. The ABCFZ was active during the Early and early Middle Miocene. A very extensive belt of ENE-WSW R′ shears up to 60 km wide, hundreds of kilometres in length (NNE-SSW direction), with faults spaced about every kilometer bounds both sides of the ABCFZ. R-shears occur more infrequently and predominantly occur close to the ABCFZ. The distinctive and unusual structural style of regionally dominant R′ shears is interpreted to be a result of NNW-SSE extension related to the northwards movement of the Indian Plate relative to SE Asia. The ABCFZ displays large-scale uplift (~100 km wavelength) on its eastern margin. If the uplift occurred at a restraining bend, then the nearest one requires at least 50 km of dextral displacement. Canyons mapped traversing this high provided pathways for gravity driven sediments to enter the deepwater area. The ABCFZ and the Sagaing Fault to the north are both associated with large basins whose depocentres lie parallel to the fault trace. They represent a different type of strike-slip basin from classic pull-apart basins, and are more laterally extensive than typical pull-apart basins. The East Andaman Basin margin shows regional variations in crustal thickness which have N–S trending contours related to Oligocene-age extension. The ABCFZ follows the location and trend of the necking zone within continental crust, suggesting this was a mechanically favourable location for development of the fault. The ABCFZ illustrates a type of strike-slip deformation and sedimentation pattern that can be expected on other hyper extended continental margins that have evolved from extension to highly oblique transtension.

Eurekan faults on northern Ellesmere Island, Arctic Canada: from Cenozoic strike-slip tectonics to recent seismicity

The Eurekan deformation is a partially contractional Cenozoic tectonic event that affected large parts of the Arctic region. In the study area on northern Ellesmere Island, major NE-SW trending strike-slip faults occur, which are related to the Eurekan deformation. The outcrop data show that left-lateral strike-slip kinematics slightly dominate, but also right-lateral kinematics were documented. Cross-cutting relationships of the individual faults give evidence for multiple fault reactivations within major strike-slip zones. The reconstructed paleostress fields show two phases. The first phase started with a N-S compression and shifted over a NNE-SSW compression into a NNW-SSE compression. The second phase was a WNW-ESE compression. The paleostress field evolution reflects the movements of Greenland. During the Eurekan phase 1, Greenland moved northward and during Eurekan phase 2 it moved to the WNW. These motions likely controlled the stress field on northern Ellesmere Island. From the paleostress field analyses and the orientation of the strike-slip faults in the study area, it can be derived that the Eurekan phase 1 deformation is characterized by left-lateral strike-slip faults, whereas most-likely during Eurekan phase 2 the majority of right-lateral strike-slip faults formed. The paleostress field analysis implies that many Eurekan faults are reactivated Ellesmerian faults. Recent seismic events indicate ongoing tectonic activity at some of the major strike-slip faults. This sheds new light on the geodynamics of northern Ellesmere Island, which was mechanically coupled to the Greenland plate, and implies that under the recent stress field, earthquakes at strike-slip faults are still possible and some of these faults were active in at least three phases over the last 350 Myr.

The Cerro Negro epithermal district, northwestern Deseado Massif (Patagonia, Argentina): New insights from telescoped volcanic-hydrothermal systems

The Cerro Negro district, northwestern Deseado Massif (Patagonia, Argentina), is one of two world-class Au–Ag epithermal mines in the Patagonian region, with combined reserves, resources, and production of about 8 Moz of Au equivalent. The epithermal deposits are hosted by volcanic and intrusive rocks and are related to the evolution of distinct Jurassic magmatic events. Major WNW trending depocenters were filled by a thick sequence of andesitic-dacitic flows and ignimbrites. In the western part of the district, the sequence is intruded by subvolcanic bodies of the same composition and is grouped into the 159-156 Ma Eureka Volcanic Subvolcanic Complex (EVSC). Hydrothermal activity took place during the last stages of the EVSC, producing epithermal Au- and Ag-rich veins of low to intermediate sulfidation style in the Eureka West (156 Ma) and the Marianas-San Marcos veins (155-154 Ma) that were emplaced in NW striking extensional faults and in WNW to E-W trending strike-slip faults. In the eastern part of the district, basal units of the EVSC are overlain by a thick package of 154 Ma rhyodacitic ignimbrites, hosting the NW to EW-striking Vein Zone deposit and the NW-striking Bajo Negro, Silica cap and Gato Salvaje veins. NNE-trending block faulting formed horsts in the western and eastern parts of the district, separated by a central graben. Uplift of the western and eastern horst blocks lowered the water table and caused erosion, exhumation, and telescoping of the vein systems. Volcanism culminated in a late-to post-mineral rhyolitic event composed of lava-domes and volcaniclastic deposits grouped into the Eureka Rhyolitic Complex (ERC). Continued hydrothermal-volcanic explosive activity produced breccias which cap some of the Au–Ag vein deposits. The high geothermal gradient during ERC volcanism generated renewed hydrothermal activity, and hot springs discharged along the boundary faults of the central graben and within the graben in a fluvio-lacustrine environment.The Au–Ag epithermal veins associated with the EVSC (Eureka and Marianas-San Marcos) show a complex paragenetic history. High Au–Ag grades are related to early sulfide-rich ginguro bands formed at 290–230 °C from meteoric and volcanic fluids due to boiling/flashing mechanism at ~600–800 m below the paleowater table. Low-grade to barren quartz stages followed the early Au–Ag stage, and late calcite was deposited due to the collapse of steam heated CO2 waters. The highest Au–Ag grades are related to a late supergene event extending to 400 m depth. The eastern group of epithermal deposits (Vein Zone, Bajo Negro, Silica cap and Gato Salvaje) were emplaced ~300–400 m below the paleowater table indicated by a silica cap on Cerro Negro hill. They are dominated by silica replacement after lattice calcite texture with high Au grades related to low temperature quartz and late hematite-stained brecciation. We conclude that all deposits are genetically related to intrusive activity, and that additional Au–Ag mineralization may be concealed beneath post-mineral volcanic and sedimentary rocks in the central graben.

Risk-assessment of hydropower plant susceptible to seismic hazard by 3D spectrum analysis

Recently, new fault zones are identified in central Borneo due to the ongoing geomorphological anomalies along the Rajang-Crocker Belt. The Kapit-Belaga region along the Rajang River system are located in between active trending strike-slip faults. By 2025, this region will have 3 operational large hydropower dams namely, Bakun, Murum and Baleh which are approximately 120 km apart in radius. Even though central Borneo is known to be a stable area, the assessment of seismic risk for existing dams is vital. The seismic failure of Konya Dam, India in 1967 proved that occurrences of catastrophic earthquake in low seismicity region is possible. Furthermore, earthquake frequency model shows that it is plausible for the Crocker fault system to produce seismic ruptures of magnitudes ≥7.0. The research of risk-assessment for hydropower in this work is motivated by the possibility of larger seismic hazard within the Crocker fault system. Hypothetical seismic loadings from Tosya and Aydin earthquakes’ records are adopted as inputs to replicate long-distance waves for the Response Spectrum Analysis (RSA) by ANSYS© ACADEMIC. Results show that tensile zone develops at the reservoir bed, extending to the dam foundation. When the seismic load is at 0.625 g Peak Ground Acceleration (PGA) – which is equivalent to magnitude 6.0 earthquake, the mechanical responses of the dam body excitation and hydrodynamic pressure from the impact of the reservoir due to seismic excitation triggers structure failure at the mid crest and bottom of the dam.

Distinct tectonic activities in Guangxi, China due to large earthquakes on the Longmenshan fault zone

It is of great importance to study active tectonics in Guangxi, China which is a region with relatively high level of seismic hazard. In this work, we attempt to apply the Load/Unload Response Ratio (LURR) method to test stress state of tectonic field in Guangxi and find obvious difference in the periods before and after earthquakes on the Longmenshan (LMS) fault zone. The regions with higher stress accumulation indicated by LURR augmented significantly after the 2008 Ms8.0 Wenchuan earthquake and reduced gradually following the 2013 Ms7.0 Lushan earthquake. The movement of LURR was along a northwestern trending strike slip fault, the Bama-Bobai fault, showing the shear loading acting on the fault. To evidence this viewpoint, we construct GPS velocity profile on this fault. Results show that the fault manifested left lateral motion after the Wenchuan earthquake. This movement which, was never observed before the Wenchuan earthquake, faded away after the Lushan earthquake. We suggest that the detected changes, both in LURR and GPS velocity field, were probably caused by stress redistribution on the LMS fault zone due to occurrence of large earthquakes. The results may imply the potential seismic hazard zone in Guangxi.

Neotectonics of the Avaj region (NW Iran): left-lateral strike-slip and range-parallel reverse faults

The aim of this study is the geomorphological analysis of neotectonic deformation in the Avaj region in the NW part of the Iranian Plateau. We use observations from detailed field surveys and the analysis of digital elevation model (DEM) and satellite images (Landsat-7 ETM+, 30-m resolution) to explore a new E-W trending strike-slip fault system in the study area. The major active faults of the Avaj region are the NW-SE trending Avaj and Hassanabad fault zones. The Avaj Fault is a SW-dipping reverse fault with a transport toward NE and the Hassanabad Fault is a NE-dipping reverse fault that has moved Paleozoic rocks over Cenozoic sedimentary units. Moreover, there are some E-W trending left-lateral strike-slip faults which cut Late Quaternary deposits. The relationship between the NW-SE and E-W faults indicates that the slip at the termination of the NW-SE faults changes from reverse to left-lateral strike-slip faults. The activity of the left-lateral faults has formed a series of offsets and displacements in drainage paths. These left-lateral faults probably initiated in 5±2 Ma because of the convergence between the Central Iran and the South Caspian blocks.

Petrogenesis and tectonic significance of early Indosinian A-type granites in the Xinxing pluton, southern South China

The Xinxing granitic pluton is a large batholith cropping out in southern South China with its long axis parallel to the regional NE–trending faults. We conduct the first comprehensive study of zircon laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U–Pb chronology and trace element chemistry, rock-forming mineral chemistry and whole-rock element and Sr–Nd isotope geochemistry for this pluton. Our new data indicate that the pluton was emplaced during the interval 234–232 Ma, i.e. early Indosinian rather than late Mesozoic as previously considered. The southern pluton consists of syenogranite and monzogranite, which are composed of K-feldspar, oligoclase, quartz and ferri-biotite. The northern pluton consists of monzogranite and granodiorite, which are composed of andesine, K-feldspar, quartz and magnesio-biotite. The southern granites have high SiO2 contents (72.5–79.2 wt%) and high FeOT/(FeOT + MgO) (T refers to total) ratios with low Mg# [atomic Mg/(Mg + FeT)]. They are enriched in rare earth elements and depleted in Sr and Ba with Zr + Y + Ce + Nb >350 ppm and 10,000 × Ga/Al >2.6. Their initial magma temperatures are unusually high (>886 °C). All those features strongly suggest an affinity with A-type granites. The northern granites have lower SiO2 contents (63.4–72.5 wt%) and lower FeOT/(FeOT + MgO) ratios as well as higher Mg# than the southern granites. They are also enriched in rare earth elements and depleted in Sr and Ba, with high Ga/Al ratios and high Zr + Y + Ce + Nb contents. Geochemical data and major element modeling confirm that the southern A-type granites were generated by the moderate degree (~49%) shallow (ca. 15–20 km depth) dehydration melting of the early Paleozoic granitoids triggered by intraplating of basaltic magmas. Subsequent moderate degree (~57%) fractionation of such crustal melts produced the more felsic granites in the southern pluton, whereas subsequent mixing of such crustal melts with about 8 to 48% intraplated mafic magmas generated the less felsic granites in the northern pluton. Interaction of mafic magmas with A-type crustal melts causes the northern granites to lose some diagnostic geochemical features of A-type granites such as high FeOT/(FeOT + MgO) ratios and to be transitional towards I-type granites. We further suggest their origin to have been related to the transtension of the regional NE–trending strike-slip faults coupled with the early Indosinian continental collisions.

Sediment transport mechanisms revealed by quantitative analyses of seafloor morphology: New evidence from multibeam bathymetry of the Israel exclusive economic zone

Abstract This study synthesizes 15 years (2001–2016) of detailed multibeam hydrographic mapping covering the entire 26,500 km2 of the Israeli Exclusive Economic Zone (EEZ). Multibeam data were collected on-board three research vessels across the continental shelf, slope, and the deep Levant basin; between water depths of about 15 m to 2100 m. Single-channel 3.5 kHz seismic reflection chirp profiles were collected simultaneously with the multibeam surveys in selected parts of the area. The new data enabled the first comprehensive quantitative seafloor morphological analysis of the slope and deep basin. Using GIS techniques on the high-resolution multibeam data, we analyze the spatial distribution and quantitatively describe the seafloor morphologies in detail. High-resolution chirp seismic profiles demonstrate the underlying shallow structure. Results indicate that the seabed comprises five main morphologies: folds, faults, sediment waves, deepwater channels, and sediment fan lobes. Quantitative morphological analysis and seismic data interpretation were used to derive field relations between these morphologies, which along with previously collected multi-channel seismic reflection data, suggest that a concentric fold geometry formed around the Nile outlet during the late Pliocene to early Pleistocene, as part of a general thin-skin radial salt-tectonic deformation above the Messinian mobile unit. This radial motion was accompanied by displacement along NNE-trending strike-slip faults in the basin, and an extensional component across E-W trending strike-slip faults along the Levant margin. While some of these displacements continue to deform the modern seabed (across Area A), others are covered by a wedge of Quaternary deposits, mainly in the northeastern part of the basin (Area B). Areas A and B also differ in grain size distribution, as indicated by backscatter analysis of the multibeam data. These observations divide the Israeli EEZ into two distinct areas: (Area A) Nile derived siliciclastic sediments transported directly into the deep basin via confined (forming meandering channels and overbank deposits) and unconfined flows (forming fans and lobes). The wedge consisting of Area B was fed by erosion products of the Nile outlet that were transported northwards along the continental shelf by seafloor currents of the Levant Jet System, and glided down the northern Levant continental slope as turbidity currents. This supply built at least seven sequences of Quaternary sediment waves that form upslope migrating cyclic steps. The complete data coverage and quantitative morphological analysis presented here introduce new spatial and temporal constraints that call for a reexamination of previous seabed sampling locations not accounting for detailed bathymetry, and to augment future seabed sampling efforts, understanding the sediment supply paths across the basin, and the geomorphological footprint of salt tectonics processes.

Ore Forming Fluid of Epithermal Quartz Veins at Cisuru Prospect, Papandayan District, West Java, Indonesia

The Cisuru area is located in Talegong Sub-district, Garut Regency, West Java, Indonesia which is belongs to the central part of Southern Mountain Slope. The aim of this research is to understand the nature and characteristic of fluid inclusion from quartz veins (especially drill core samples) in the study area. Rock units in the area are characterized by Tertiary volcanic rocks and volcaniclastic sequence which is mainly composed of andesite, andesitic breccia, volcanic breccia, lapilli tuff, dacite and related to the intrusion of diorite. The Cisuru epithermal mineralization is dominantly hosted by andesite, dacite, breccia and lapilli tuff, and would probably be controlled by both permeable rocks and NS and NE-SW trending strike-slip faults. The mineralization is shown as void filling and replacement within the silica zone, veinlets along with the open space/fractures and dissemination. Fluid inclusion from quartz veins was studied to know nature, characteristics and origin of hydrothermal fluids. Microthermometric measurements of fluid inclusions were realized by using a Linkam THMSG 600 combined freezing and heating stages. Homogenization temperature and final ice melting temperature were measured for primary two-phase inclusion from quartz veins. Base on the study of the fluid inclusion, the value of homogenization temperature (Th) range from 200 ºC to 395 °C and ice melting temperature range from -0.1 to - 4.5 where salinity range from 0.2 to 7.2 wt. % NaCl equivalent. Fluid inclusion petrography and microthermometric measurement data exhibit that fluid mixing, dilution and boiling were main processes during the hydrothermal evolution. The formation temperature of each quartz vein is 260 ºC to 290 ºC and also their formation depth is estimated between 560m to 925m respectively. Combination of fluid inclusions petrography, microthermometric measurement, and estimate paleo depth from Cisuru area were suggested under the epithermal environment.

Geology and structure of the Reykjanes volcanic system, Iceland

The Reykjanes Peninsula is a trans-tensional plate boundary with several volcanic systems from the centers of which fissure swarms extend to the NE and SW. The fissure swarms accommodate the extensional component, whereas north-south trending strike-slip faults accomodate the transform component. The fissure swarms release stress during volcano-tectonic episodes that occur at intervals of several hundred years. Stress is released by the strike-slip faults by microearthquake swarms at intervals of a few decades.The fissure swarms are segmented along their trend. The segments include a volcanic center with a clustering of fissure eruptions and extensional faults. A proximal zone of 20–40 km follows were faults become dominant with distance from the center. Linear anomalies of a high geothermal gradient extend further still, into the marginal area of Early Quaternary to Miocene rocks indicating dyke propagation for another 30–40 km beyond visible faults.The Reykjanes volcanic center is nested in a 5–6 km wide rift zone with boundary faults of just over 20 m visible throw. Volcanic production keeps pace with extension and subsidence to fill the rift. The last three volcano-tectonic episodes occurred at Reykjanes in the 13th century, about 2000 years ago and about 3200 years ago. The lavas from these three fissure eruptions cover >2/3 of Reykjanes by area, largely smoothing over faults of the rift floor. During the Weichselian glacial maximum the ice margin may have reached 75–100 km beyond Reykjanes. It had become ice free 14,500 years ago. There is evidence of at least 10 eruptions on the Reykjanes volcanic system since, of which the first ones were of lava shield type. A similar eruption frequency may have prevailed at Reykjanes during its postglacial time interval.There are three volcanic fissure zones within the Reykjanes center. The middle zone of 1.5 km2 hosts the main geothermal resource of the system. Recently the western zone proved to host an exploitable resource also. It may be restricted to a narrow zone of dykes. The reservoir temperatures of these two lie in the range 280–310 °C. The eastern zone has not proved productive so far. It has erupted olivine rich shield lavas on most of its trace whereas the others have erupted slightly evolved tholeiite. Feed zones in the main production zone have been correlated partly with the axis of the eastern of two tindars. They cluster also in near horizontal intervals which may suggest that density controlled offshots also play a role.

Fault kinematics at the Hengill Triple Junction, SW-Iceland, derived from surface fracture pattern

The Hengill Triple Junction in Iceland is formed by the intersection of the Western Volcanic Zone (WVZ), Reykjanes Peninsula Oblique Rift (RPOR) and a transform zone, the South Iceland Seismic Zone (SISZ). The 19 × 13 km2 study area thus contains extensional structures related to volcanic systems of the two rift zones, Hengill and Hrómundartindur, as well as strike-slip structures characteristic of the transform zones. High definition aerial photographs, satellite images, and digital elevation models are used, supported by field studies, to accurately map and classify tectonic features in an effort to separate N-S trending strike-slip faults from the fissure swarms of the volcanic systems. A portion of the southern Hengill fissure swarm lies within the area. It trends NE-SW and exhibits extensional features characteristic of spreading ridges, i.e. normal faults, open fractures, and eruptive fissures. It is clearly delineated by surface fractures, and is traced a length of 28 km southwest from the central volcano, terminating before reaching the coastline. The fissure swarm is 2–3.5 km wide in the study area, widening southwards. Elevation profiles across the fissure swarm suggest a spreading rate comparable to the southern WVZ, which spreads at 4–5 mm/year. A portion of the Nesjahraun eruptive fissure is anomalously smooth and may represent secondary rifting. East-west shearing in the RPOR and SISZ is accomplished by many smaller and less conspicuous, northerly oriented strike-slip faults in a ‘bookshelf faulting’ manner. These parallel faults are overprinted on the volcano-tectonic structures of the RPOR. Evidence of 11 northerly striking strike-slip faults is found within the study area. The zone of bookshelf faulting is thus shown to be continuous across the triple junction area, from the SISZ to the RPOR. Finally, several structures (eruptive fissures, exposed dikes, and faults) strike near-perpendicular to the fissure swarm and may be the result of changes in the direction of maximum stress caused by rifting events, however, their tectonic significance remains uncertain.

Petrogenesis of Plio-Quaternary basanites in the Gandom Beryan area, Kerman,Iran: geochemical evidence for the low-degree partial melting of enriched mantle

In the Gandom Beryan area, basanitic lava flows erupted from fractures in the Nayband fault zone and formed an area of about 300 km2 of basanitic rocks in the western part of the Lut Block. Olivine and clinopyroxene are the major phenocrysts in a microlitic groundmass for these basanitic rocks. The geochemical data show that Gandom Beryan rocks are basanite in composition and belong to intercontinental rifts related to alkali basanites. These rocks have low Fe/Mg ratios (Fe2O3t/MgO = 1.07-1.43) with low silica content (SiO2 = 44.89-48.26 wt.%) and are high-Ti basanites. The investigated rocks are characterized by a significant enrichment of total REE and LREE relative to chondrite. Moreover, the REE patterns of these rocks are linear without any negative Eu anomalies. The low abundances of HREE in basanitic rocks and the REE modeling together reflect the relation between these elements and residual garnet in the partially melted mantle. The 207Pb/204Pb and 206Pb/204Pb ratios of the basanitic rocks fall near the field of enriched mantle II (EM-II). The Gandom Beryan volcanism, which was related to partial melting of mantle within an extensional setting, resulted from a left-step, pull-apart basin in the Nayband N-S trending strike-slip fault system. Although the fault system is older than Gandom Beryan volcanism, it seems that it has been reactivated during and after the volcanism.

Basement–cover structural relationships in the Kaladgi Basin, southwestern India: Indications towards a Mesoproterozoic gravity gliding of the cover along a detached unconformity

Structural relations between the Archaean basement and overlying Mesoproterozoic sedimentary cover were examined in the Kaladgi Basin of south western India. The basement, that forms a part of the western Dharwar craton, is an assemblage of the Archaean Peninsular Gneissic Complex (PGC), late Archaean Hungund Schist Belt (HSB) and granites (Closepet granite). The HSB, composed of Banded Iron Formations, quartzites, metapelites and mafic metavolcanics have undergone multistage deformation (D1, D2, and D3 respectively) with the development of refolded plane-non-cylindrical folds, transposed compositional banding and schistosity, crenulation lineations − all of which developed during the D1–D2 stage. These were mildly cross-folded along NE–SW during the D3 stage with an overall orientation of the structural grain along the NW–SE (310°) direction. The PGC consisting of granitoid gneisses are deformed in phase with the HSB. The Closepet granite that is intrusive within the PGC and the HSB is relatively younger (c. 2.5Ga) and is massive and undeformed, in general.Based on type, geometry, distribution, association of structural elements, variation and relative chronology of development, the deformation structures of the Mesoproterozoic sedimentary cover rocks of the basin can be grouped to define an extensional domain in the northern sectors and a contractional domain in the south–central sectors of the basin. The extensional domain is characterized by development of a gently dipping (10°−15° due south) homocline that is affected at places by normal faults, tensile and hybrid joints, and contain torn – apart segments of the cover. In the south–central sectors of the basin, an association of WNW–ESE trending, both northerly and southerly verging, asymmetric-to-overturned, plane non-cylindrical, gently plunging folds with axial planar cleavages, E–W trending thrusts, and N–S trending strike-slip faults, together define the contractional domain. Distribution, variation and interrelationship of structural elements in the cover rocks, reveal that, the extensional and contractional domains, are spatially linked, laterally pass on to each other continuously and are related to a single deformation event of the cover.The contrasting structural anatomy of the basement vis-a-vis Mesoproterozoic sedimentary cover indicate that (1) the Mesoproterozoic cover of the Kaladgi Basin, during its deformation, became detached from the basement and the basement thereby remained unaffected during deformation of the cover and (2) the deformation of the Mesoproterozoic sedimentary cover originated by a southerly-directed gravity gliding of the cover over the basement along the basement–cover contact (unconformity) that served as a surface for detachment.The Mesoproterozoic gravity gliding event in the Kaladgi Basin is inferred to result from a tectonic uplift of the basement in the northern sectors, due to possible crustal flexure of the South Indian Block during terminal phases of amalgamation of North Indian Block and East Antarctica with the South Indian Block during the Grenvillian.

Interaction between trench retreat and Anatolian escape as recorded by neogene basins in the northern Aegean Sea

The evolution of the North Aegean Sea is studied through the development of three deep basins: the North Aegean Trough, the North Skyros Basin and the Ikaria Basin. Bathymetric data, a 2D seismic dataset and the well-investigated stratigraphic records of the onshore deep basins of northern Greece and Western Turkey were used to make structural and seismic stratigraphic interpretations. The study area shows two sharp unconformities that correspond to the Eocene-Oligocene transition and the Miocene-Pliocene shift. These discontinuities were used as marker horizons for a more detailed structural and seismic stratigraphic interpretation resulting in the identification of several seismic units. A general seismic signature chart was established using onshore basin stratigraphy and well data, which was then used to constrain the ages of the different seismic units. The main features observed in the basins are interpreted as: 1) trans-tensional growth patterns in Pliocene and Quaternary sediments that combine NE–SW trending and steeply dipping fault zones that likely correspond to strike-slip corridors and E-W/WNW-ESE trending normal faults, 2) regional erosional truncations of Miocene sediments, likely related to the Messinian Salinity Crisis (MSC), 3) thick delta-turbidite deposits of Neogene age. Only the North Aegean Trough shows evidence of earlier development and polyphase deformation through inversion structures, and additional seismic units. Extension processes in the Aegean region have been driven by the Hellenic slab rollback since the middle Eocene. The widespread development of Neogene basins at the whole Aegean scale attests to a major tectonic change due to an acceleration of the trench retreat in the middle Miocene. The present study shows that the Neogene basins of the North Aegean Sea developed in dextral transtension with the northward migration of the associated NE-SW trending strike-slip faults. At regional scale, this tectonic pattern indicates that the westward escape of Anatolia started to interact with the trench retreat in the middle Miocene, around 10 Myr before the arrival of the North Anatolian Fault in the North Aegean Sea.

Palaeoenvironmental implications of geochemistry and radiolarians from Upper Devonian chert/shale sequences of the Truong Son fold belt, Laos

A new locality of Frasnian radiolarian chert and siliceous shale is reported in the Vilabouly area, within the Truong Son fold belt of central Laos, in the eastern part of the Indochina Terrane. Samples from this locality, together with previously described radiolarian–bearing siliceous shale from Ban Phonxai, 100 km further north, have been geochemically analysed. Most of the Ce anomalies from Vilabouly and Ban Phonxai exhibit negative normalized values suggesting deposition in an open–marine basin and in a transition zone between open–marine and continental margin environments, respectively. NASC and chondrite-normalized REE and La/Ce plots and trace element contents support this interpretation. Normalized La/Yb values indicate removal of LREEs relative to HREEs from the water column, suggesting deposition far from terrigenous sources for the Vilabouly samples. The Eu/Eu* values are not pronounced which, with the high values of Al2O3/(Al2O3 + Fe2O3), indicate minimal hydrothermal influence. Both sections are characterized by a distinctive Frasnian radiolarian and tentaculitid assemblage. The new radiolarian fauna from Vilabouly includes 23 species including Ceratoikiscum sp. cf. C. bujugum, Archocyrtium sp., Astroentactinia cf. stellata, Helioentactinia aster, H. perjucunda, Spongentactinella corynacantha, S. veles, Spongentactinia concinna, S. exquisita, Stigmosphaerostylus profundisulcus, Trilonche davidi, T. echinata, T. elegans, T. hindea, T. palimbola, T. vetusta, Palaeoscenidium cladophorum and others. The tentaculitids, Homoctenus ultimus and Costulatostyliolina vesca, have been previously described from South China and from Ban Phonxai. The similarity of the radiolarian fauna to those from South China, northern Thailand and Western Australia suggests free interchange of species. Based on geochemistry, stratigraphic sequences and structural geology, the radiolarian chert/siliceous shales are interpreted as highstand deposits in pull-apart basins. This was possibly caused by transtension along the NW–SE–trending strike–slip fault of the Thakhek–Danang Shear Zone during the Late Devonian. Copyright © 2015 John Wiley & Sons, Ltd.