Active Tectonic Setting Research Articles

Paleostress analysis of a gigantic gravitational mass movement in active tectonic setting: The Qoshadagh slope failure, Ahar, NW Iran

Abstract For better understanding of the dynamics of large slope failures, the slope-scale stress field reconstructions are eligible. A new approach of paleostress analysis of large gravitational mass movements, based on the multiple inverse method in 9D space and processed by a non-commercial code MARK2010, is demonstrated on the case of a gigantic gravitational slope failure in active tectonic setting at Mount Qoshadagh in NW Iran. The entire slope failure represents a very deep-seated gravitational slope deformation with relatively short displacement, roto-translational base and an estimated volume of about 83–110 km3 which is of the last glacial age. This gigantic slope failure has developed in an active-tectonic setting along the Qoshadagh Fault System (or called South Ahar Fault), which caused fast uplift of the entire mountain range of Qoshadagh, and it was probably seismically triggered. Using this paleostress approach, we were able to distinguish the mass-movement stress phase of NW compression in the rockslide's zone of compression and NW–SE extension in the upper part from a variety of other 8 regional-tectonic and 2 subsequent gravitational phases. Maximum principal stress of the slope-failure phase was in its compression zone sub-parallel to the estimated displacement vector; in the head it was sub-vertical. The paleostress analysis has been proved as a useful tool for reconstructing the stress field evolution of large slope failures.

Study of a Neogene basin dynamics: The “Bizerte basin”, northeastern Tunisia: relevance to the global Messinian Salinity Crisis

The Messinian sediments of northeastern Tunisia were deposited under an active tectonic setting. They are organized in sequences indicating a transitional deposit from margin – littoral to lacustrine – continental facies. These series unconformably overlie the Serravallian–Tortonian silty clays packages, and are overlain by the transgressive Early Pliocene marl (Zanclean). The presence of evaporitic strata points out to the Messinian Salinity Crisis described in the peripheral basins of the western Mediterranean. The Messinian sedimentation was found to have been closely controlled by transtensive tectonics and differential subsidence at a large spatio-temporal scale. It is organized in sequences typical of a depositional environment controlled by eustatism, tectonic and maybe by climate changes. Despite the existence of some local specific sedimentological characteristics, our results corroborate previous findings that pointed out to the Messinian times as a singular period all around the Mediterranean Basin. Field and subsurface seismic profile data helped reconstructing either the sedimentary or tectonic unconformities existing between the studied Messinian series and older Neogene successions.

Applying the Multiple Inverse Method to the analysis of earthquake focal mechanism data: New insights into the active stress field of Italy and surrounding regions

In order to obtain new insights into the active tectonic setting of the Italian territory and surrounding regions, the Multiple Inverse Method (MIM) has been applied to the analysis of fault plane solutions from more than 700 earthquakes with Mw≥4. The active stress field in the top 40km of the lithosphere has been defined for four 10km-thick layers, each including 810 square cells of 1.5° side. The obtained stress field maps point out that most of the upper crustal seismicity of the Western and Central Alps is controlled by a strike-slip regime, which is dominant also in part of the Dinarides, Albanides and Hellenides and in a large sector encompassing eastern Sicily and the Malta area to the eastern Tunisia offshore. On the other hand, the well-known extensional belt occurring in the interior of the Apennines appears to extend well beyond the backbone of Italy, potentially reaching the outer foothills of the northern Marche region, while the adjacent Adria block (extending to the eastern Po Plain and the outer Dinarides) sticks out as a major area characterised by dominant thrust faulting in the upper crust. A similar regime characterises also a large sector of the western Tyrrhenian Sea, from NE Tunisia through western Sicily and the west coast of Sardinia, to the Provence coast.Besides lateral variations, our analysis also points out a significant vertical heterogeneity of the stress field, the deeper levels (20 to 40km) investigated in this study being characterised by dominant horizontal maximum compression even in areas of upper crustal extension.The application of the MIM to a large seismological dataset, providing basic information for the compilation of active stress maps, contributes to a better understanding of active tectonic processes and may be used for improving seismotectonic zoning and reservoir management.

SEISMIC HAZARD IN TUSCANY: WHICH BEST DEFENCE STRATEGY?

The hypothesis that the probability of major earthquakes in a given zone is strongly influenced by the space-time distribution of previous seismic events in the surrounding area is supported by numerous and significant pieces of evidence. This work describes a particularly clear example of this phenomenon that occurred in the central-northern Apennines during the period 1915-1920. The fact that the strong 1915 Fucino earthquake in the central Apennines was followed by an exceptional seismic reaction of the northern Apennines (6 events of magnitude greater than 5.5 in the 1916-1920 time interval) is consistent with the active tectonic setting of these zones. Furthermore, it can be demonstrated that the time occurrence of each event in the northern Apennines is compatible with the arrival of the highest values of the perturbation induced by the previous shocks, as computed by numerical modelling of postseismic relaxation.

Engineering and Environmental Geology of Granada and its Metropolitan Area (Spain)

Research Article| August 01, 2012 Engineering and Environmental Geology of Granada and its Metropolitan Area (Spain) JOSÉ CHACÓN; JOSÉ CHACÓN a Department of Civil Engineering, University of Granada, Granada, Spain 1Corresponding author email: jchacon@ugr.es. Search for other works by this author on: GSW Google Scholar CLEMENTE IRIGARAY; CLEMENTE IRIGARAY a Department of Civil Engineering, University of Granada, Granada, Spain Search for other works by this author on: GSW Google Scholar RACHID EL HAMDOUNI; RACHID EL HAMDOUNI a Department of Civil Engineering, University of Granada, Granada, Spain Search for other works by this author on: GSW Google Scholar IGNACIO VALVERDE-PALACIOS; IGNACIO VALVERDE-PALACIOS b Department of Architectural Constructions, University of Granada, Granada, Spain Search for other works by this author on: GSW Google Scholar IGNACIO VALVERDE-ESPINOSA; IGNACIO VALVERDE-ESPINOSA b Department of Architectural Constructions, University of Granada, Granada, Spain Search for other works by this author on: GSW Google Scholar FRANCISCO CALVO; FRANCISCO CALVO a Department of Civil Engineering, University of Granada, Granada, Spain Search for other works by this author on: GSW Google Scholar JORGE JIMÉNEZ-PERÁLVAREZ; JORGE JIMÉNEZ-PERÁLVAREZ a Department of Civil Engineering, University of Granada, Granada, Spain Search for other works by this author on: GSW Google Scholar EVA CHACON; EVA CHACON b Department of Architectural Constructions, University of Granada, Granada, Spain Search for other works by this author on: GSW Google Scholar PAZ FERNÁNDEZ; PAZ FERNÁNDEZ a Department of Civil Engineering, University of Granada, Granada, Spain Search for other works by this author on: GSW Google Scholar JESÚS GARRIDO; JESÚS GARRIDO a Department of Civil Engineering, University of Granada, Granada, Spain Search for other works by this author on: GSW Google Scholar FRANCISCO LAMAS FRANCISCO LAMAS a Department of Civil Engineering, University of Granada, Granada, Spain Search for other works by this author on: GSW Google Scholar Environmental & Engineering Geoscience (2012) 18 (3): 217–260. https://doi.org/10.2113/gseegeosci.18.3.217 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation JOSÉ CHACÓN, CLEMENTE IRIGARAY, RACHID EL HAMDOUNI, IGNACIO VALVERDE-PALACIOS, IGNACIO VALVERDE-ESPINOSA, FRANCISCO CALVO, JORGE JIMÉNEZ-PERÁLVAREZ, EVA CHACON, PAZ FERNÁNDEZ, JESÚS GARRIDO, FRANCISCO LAMAS; Engineering and Environmental Geology of Granada and its Metropolitan Area (Spain). Environmental & Engineering Geoscience 2012;; 18 (3): 217–260. doi: https://doi.org/10.2113/gseegeosci.18.3.217 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEnvironmental & Engineering Geoscience Search Advanced Search Abstract Granada and its metropolitan area lie on the eastern edge of a basin where the foothills rise into the adjacent Sierra Nevada (3,482 m). On the west the valley is bordered by several faulted, Quaternary-age alluvial fans and by dissected terraces of the Genil River. Landscape evolution from about Tortonian to Pleistocene time is reflected by relict Quaternary glaciers preserved on a deeply eroded lower Paleozoic terrain and by terrace remnants and channels resulting from rapid Late Pleistocene and Holocene fluvial incision. This particular geological, geomorphic, and active tectonic setting, combined with a Mediterranean climate under continental influence, and the rapid urban development in the last 60 years have increased exposure to several natural hazards. Urban expansion has increased flash-flood and mass-wasting vulnerability, and seismic risk is similarly increasing with the 1884 Andalusian Earthquake (M 6.3), reflecting the last of several large, ∼500-year recurrence temblors that have affected the area since at least Roman times. Modern Granada and its metropolitan area, with about a half million inhabitants, are currently increasingly challenged by the highest levels of exposure to natural hazards, by strain on traditional society resulting from adapting to the changes produced by the three decades since the advent of democracy (1978) and by the consequences of the deep economic crisis. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Chemical indices (CIA and WIP) as proxies for integrated chemical weathering in China: Inferences from analysis of fluvial sediments

Rivers play a key role in earth surface processes by weathering and eroding the upper continental crust under variable climate regimes. How to quantitatively determine the chemical weathering intensity in the drainage basins using geochemistry of fluvial sediments remains unclear. The Chemical Index of Alteration (CIA) and the Weathering Index of Parker (WIP) have been used worldwide as proxies to evaluate the chemical weathering intensity in large watersheds and in specific weathering profiles. In this study, concentrations of major oxides in the suspended particulate matter (SPM) and fine-grained floodplain sediments from 13 major rivers in China from north to south were analysed and compiled for the estimation of chemical weathering in China. The gradual increase in CIA and decrease in WIP values with decreasing latitude of the catchments suggest enhanced weathering intensity in these river basins. A combined monsoon climate effect of temperature, runoff and precipitation primarily controls the chemical weathering in China. The provenance rock types and relief play minor roles in weathering, whereas an active tectonic setting and typhoon events play key roles in the weathering process in Taiwan. The CIA values of the finer SPM samples within a given river are overall greater than those in the corresponding coarser floodplain sediments, underscoring the effect of sediment grain size on CIA values.The irregular seasonal variation of the CIA within a specific river further confirms the notion that the CIA does not reflect the instantaneous chemical weathering on continents. Although it is impossible to build a general model for regulating the chemical weathering of continents, this study reveals that the integrated chemical weathering intensity in large latitudinal watersheds can, with careful application, be quantitatively estimated using the proper geochemical proxies of river sediments.

Asthenospheric flow and lithospheric evolution near the Mendocino Triple Junction

The migration of the Mendocino Triple Junction in northern California creates a complicated lithosphere–asthenosphere boundary system at shallow depths (<60km), following the progressive transition from Cascadia subduction to San Andreas transform motion. It provides a natural laboratory to examine lithospheric evolution associated with slab removal in an active tectonic setting. However, pathways of the asthenospheric sources that fill the slab-free region created by the triple junction migration remain unclear. Previous active source profiles and body-wave tomography are limited to either crustal or a deeper upper mantle scale, respectively. In this study, we present a three-dimensional shear velocity model from joint inversion of ambient noise (8–30s) and ballistic Rayleigh wave dispersion curves (22–100s), as well as Ps receiver functions, using 111 stations from the Flexible Array Mendocino Experiment, USArray Transportable Array and the regional Berkeley Digital Seismic Network. In the crust, we have observed the low-Vs Franciscan Complex in the Coast Ranges and the relatively high-Vs Great Valley ophiolite abutting the low-Vs Sierran basement. The low-Vs uppermost mantle imaged near the sudden steepening of the subducted oceanic slab extends seismic evidence for forearc mantle serpentinization further south along the Cascadia margin. In addition to the asthenosphere beneath the Gorda plate, the joint inversion Vs model further identifies three other young asthenospheres resulting from different partial melting mechanisms. Northward motion of the triple junction causes asthenospheric flow both from under the Gorda plate and from the cooling former mantle wedge left under the Great Valley and Sierra Nevada, imaged from the joint inversion as a relatively deep (>75km) low-Vs anomaly. These two mantle flows appear to begin mixing ~100km south of the southern edge of the Gorda plate in the slab window region. We speculate that the latter provides the wedge-type geochemical signature seen in the Coast Range volcanic rocks, reconciling slab window models and volcanic geochemistry. This ‘staggered’ upwelling model proposed here also explains the ~3Myr delay in onset of volcanism after triple junction migration.

Modal and Geochemical Compositions of the Lower Silurian Clastic Rocks In North Qilian, Nw China: Implications For Provenance, Chemical Weathering, and Tectonic Setting

Abstract The North Qilian orogenic belt records the transition from Ordovician marine back-arc basin to Early Devonian terrestrial molasse basin as the Central Qilian Block was sutured to the North China Craton. The detrital framework and geochemical composition of Lower Silurian sedimentary rocks within the North Qilian Belt record the provenance, tectonic setting, and a variety of sedimentary processes that operated during transport from source to sink. The petrological and geochemical characteristics of sandstones, siltstones, and shales in the western segment of the North Qilian Belt indicate a generally low degree of chemical weathering of source area(s) and limited sorting prior to deposition. These characteristics suggest an active tectonic setting. In contrast, samples studied from the eastern part of the North Qilian Belt indicate low to moderate chemical weathering and low to moderate hydraulic sorting. Such characteristics imply a more stable tectonic setting. Geochemical data including Eu/Eu*, Ti/Nb, Th/Sc, and Co/Th ratios suggest contrasting source regions for the western and eastern segments of the North Qilian Belt. Sources in the west included basement rocks of the Central Qilian Block and the North China Craton. In addition, western sources may have included mafic rocks located within the North Qilian arc. In contrast, data derived from eastern samples suggest a felsic provenance that probably formed part of the basement complex in the Central Qilian Block and the North China Craton. Overall, detrital and geochemical data, combined with the regional geology, suggest a foreland basin setting that formed during collision of the Central Qilian Block with the North China Craton.

PECULIARITIES OF COAL SEAM &lt;i&gt;L&lt;sub&gt;3&lt;/sub&gt;&lt;/i&gt; STRUCTURE IN THE KRASNOARMEYSKY COAL-MINING DISTRICT, DONETS BASIN

Formation of l3 coal seam rock massif in the Krasnoarmeysky district occurred in active tectonic setting that evidenced by its thickness and one of interlayers and composition. Identical interlayer characteristics of CC Krasnolymanska and Almazna coal mine production fields speak about simultaneous and drastic changes of peat sedimentation. The studies have proved decreasing of coal seams thickness and increasing of their quantity westward to the Ukrainian Shield. Present-day structure of coal rock massif testifies of significant tectonic impact onto sedimentation processes during a basin formation and post-formation period.

An alternative model for the recent evolution of the Northern–Central Apennines (Italy)

The aim of this paper is to propose an alternative model for the Pliocene-Quaternary to present evolution of the Northern–Central Apennines by combining geometrical requirements (Riedel shear system) with existing structural and geological geometries (fault systems and their tectonic associations). We define three sectors characterized by different geological, seismological, geodetic and geothermal signatures: the North-Western Sector (NWS), the Western Central Sector (WCS) and the Eastern Central Sector (ECS). According to GPS data derived from literature the three blocks move independently. In particular, the NWS is bound between the ECS/WCS and the Alps; this constraint leads to a stress accumulation responsible for a fragmentation into further several blocks, which move either to the NE or SW. The WCS is relatively stable; the ECS moves towards NE and is characterized by the presence of numerous releasing and restraining bends, which can be related to the action of a main NNW–SSE left-lateral shear zone. Accordingly, the recent and active tectonic setting of the Northern–Central Apennines is rather related to the dynamics of the introduced blocks, caused by the push of the African plate against Europe, than to subduction processes.

No correlation between Anderson Reservoir stage level and underlying Calaveras fault seismicity despite calculated differential stress increases

Concerns have been raised that stresses from reservoir impoundment may trigger damaging earthquakes because rate changes have been associated with reservoir impoundment or stage-level changes globally. Here, the idea is tested blindly using Anderson Reservoir, which lies atop the seismically active Calaveras fault. The only knowledge held by the author going into the study was the expectation that reservoir levels change cyclically because of seasonal rainfall. Examination of seismicity rates near the reservoir reveals variability, but no correlation with stage-level changes. Three-dimensional finite-element modeling shows stress changes sufficient for earthquake triggering along the Calaveras fault zone. Since many of the reported cases of induced triggering come from low-strain settings, it is speculated that gradual stressing from stage-level changes in high-strain settings may not be significant. From this study, it can be concluded that reservoirs are not necessarily risky in active tectonic settings.

Geochemistry and Nd isotopic composition of the Early Paleozoic flysch sequence in the Chinese Altai, Central Asia: Evidence for a northward-derived mafic source and insight into Nd model ages in accretionary orogen

Although Nd isotopic composition of sedimentary rocks is considered as a useful tool to trace the provenance, their Nd model age (TDM) is usually misused to discuss the timing of crustal formation in accretionary orogen. In the Central Asian Orogenic Belt, an Early Paleozoic flysch sequence extensively occurs in the Chinese Altai and adjacent western Mongolian terranes. Sedimentary rocks in the northwestern Chinese Altai were collected from the flysch sequence for geochemical and Nd isotopic studies. Although these rocks show different geochemical characteristics (e.g., arenaceous and argillaceous), they all have relatively low CIA (Chemical Index of Alteration) values (49–75), indicating a relatively weak weathering source or the absence of compositionally mature alumina-rich minerals produced by chemical weathering processes. Their relatively high ICV (Index of Compositional Variability) values (0.95–1.35) reveal an immature source and indicate that these rocks were probably deposited in an active tectonic setting. The sedimentary rocks from the flysch sequence have high MgO, Sc, Co and low Y, Nb, which suggest significant addition of mafic rocks into the source. Modeling based on Nb–Cr and Zr–MgO contents displays nearly 20% to 50% addition of mafic materials. In combination with the age and distribution of mafic rocks in the Chinese Altai and adjacent terranes, a northward-derived mafic source is recommended for the sedimentary sequence. Although the sedimentary rocks have Nd model ages (TDM=1.44–1.57Ga) older than Devonian granites (TDM=1.6–1.1Ga), young detrital zircons from the sediments and inherited zircons from the granites (450–500Ma) suggest a mixed source consisting of both old crust components and juvenile or less evolved crustal components. This reveals that Nd model ages (TDM) of metasedimentary rocks and igneous rocks can hardly provide close constrains on the timing of crustal formation in accretionary orogen. With the progresses in adjacent western Mongolian terranes, a tectonic scenario dominated by subduction-accretionary process is suggested to interpret the formation of the Early Paleozoic flysch sequence in the Chinese Altai and adjacent terranes.

A 36Cl age determination for Mystery Creek rock avalanche and its implications in the context of hazard assessment, British Columbia, Canada

The Sea to Sky Corridor has experienced hundreds of historic and prehistoric landslides. The most common types of historical landslides are rock falls and debris flows, which are relatively small in volume but can be damaging. These types of failures are more common in the southern part of the corridor, between Horseshoe Bay and Porteau, where infrastructure has been built in close proximity to steep slopes. Farther north, fewer landslides have been reported historically, but those that have been recorded are usually large and date to prehistoric time (e.g., Cheekye fan and Mystery Creek rock avalanche). As part of a Geological Survey of Canada surficial geology and landslide inventory mapping study, Mystery Creek rock avalanche, near Whistler, British Columbia, was sampled for 36Cl dating. Samples were collected from three large flat boulders of quartz diorite in the rock avalanche deposit to test a correlation with the previously reported radiocarbon age of 800 ± 100 years BP on charcoal. One sample revealed a mean age of 2,400 years and the other two, 4,300 and 4,800 years, respectively. These new results point to four possible interpretations: (1) Mystery Creek landslide is about 800 years old; (2) Based on the overlapping 2σ uncertainties, the rock avalanche took place between 2,200 and 3,600 years ago; (3) The rock avalanche deposit is 2,400 years old and the other two blocks are too old; and (4) The rock avalanche is between 4,300 and 4,800 years old. Although there is strength in numbers and it is likely that the age varies between 4,300 and 4,800 years, we favor the second interpretation where the age range is broader and statistically significant for all three samples. Moreover, at this time, we favor discounting the radiocarbon age based on a greater number of samples analyzed for 36Cl analysis and lack of detailed information on the charcoal sampling. The causes and triggers of the Mystery Creek rock avalanche remain unknown, but direct glacial debuttressing can be ruled out. Some of the causes are likely a combination of the regional tectonic setting which produced preferential planes of weakness reflected in the trend of major faults, headscarp, and reverse scarps. Yearly cycles of freezing and thawing are considered a plausible cause based on present-day climate records. Finally, a large earthquake still remains a possible trigger because of the active tectonic setting and the presence of potentially contemporaneous landslides in the same area. Mystery Creek rock avalanche and other historic and pre-historic landslides contributed to validation of a heuristic rock fall/rock slide/rock avalanche susceptibility mapping study, in which their headscarps correlated well with medium-high to high susceptibility zones. In terms of hazard assessment, Mystery Creek rock avalanche, although pre-historic in age, occurred in present-day climatic and geological conditions. This poses a threat to infrastructure such as the Sea to Sky Highway, railway, and power line.

Metasomatized lithospheric mantle beneath Turkana depression in southern Ethiopia (the East Africa Rift): geochemical and Sr–Nd–Pb isotopic characteristics

Mantle xenoliths entrained in Quaternary alkaline basalts from the Turkana Depression in southern Ethiopia (the East Africa Rift) were studied for their geochemical and Sr–Nd–Pb isotopic compositions to constrain the evolution of the lithosphere. The investigated mantle xenoliths are spinel lherzolites in composition with a protogranular texture. They can be classified into two types: anhydrous and hydrous spinel lherzolites; the latter group characterized by the occurrences of pargasite and phlogopite. The compositions of whole-rock basaltic component (CaO = 3.8–5.6 wt%, Al2O3 = 2.5–4.1 wt%, and MgO = 34.7–38.1 wt%), spinel (Cr# = 0.062–0.117, Al2O3 = 59.0–64.4 wt%) and clinopyroxene (Mg# = 88.4–91.7, Al2O3 = 5.2–6.7 wt%) indicate that the lherzolites are fertile and have not experienced significant partial melting. Both types are characterized by depleted 87Sr/86Sr (0.70180–0.70295) and high 143Nd/144Nd (0.51299–0.51348) with wide ranges of 206Pb/204Pb (17.86–19.68) isotopic compositions. The variations of geochemical and isotopic compositions can be explained by silicate metasomatism induced by different degree of magma infiltrations from ascending mantle plume. The thermobarometric estimations suggest that the spinel lherzolites were derived from depths of 50–70 km (15.6–22.2 kb) and entrained in the alkaline magma at 847–1,052°C. Most of the spinel lherzolites from this study record an elevated geotherm (60–90 mW/m2) that is related to the presence of rising mantle plume in an active tectonic setting. Sm–Nd isotopic systematic gives a mean TDM model age of 0.95 Ga, interpreted as the minimum depletion age of the subcontinental lithosphere beneath the region.

Deformation mechanisms, rheology and tectonics: microstructures, mechanics and anisotropy: introduction

This special publication of the Geological Society of London presents recent advances in the study of deformation mechanisms and rheology and their application to tectonics. We have subdivided the papers into two themed sections. The inference of deformation processes, conditions and rheology at depth in active tectonic settings is of fundamental importance to a quantitative geodynamic understanding of deformation in the Earth. The papers in the section on Lattice Preferred Orientations and Anisotropy are extremely important as they underpin our ability to make such geodynamic interpretations from global seismic data. These papers reflect the growing emphasis on the determination of elastic properties from microstructures, from which acoustic properties can be computed for comparison with in situ seismic measurements. The component of the microstructure that receives most attention is the lattice preferred orientation (LPO), otherwise known as the crystallographic preferred orientation (CPO) or the texture (the term used in material science and metallurgy). The papers include new LPO measurements (made almost exclusively by the relatively new technique of electron backscatter diffraction or EBSD), exploration of the significance of these data for seismic properties of both the crust and the mantle and modelling of LPO generation. An invited contribution from Mainprice and colleagues introduces a computational toolbox to help researchers calculate anisotropic physical properties from their LPO data. Rock microstructures evolve during deformation and rock physical properties, including both elastic properties and creep rheology, evolve with the microstructures as a function of strain and time. The section on Microstructures, Mechanisms and Rheology reflects the fundamental importance of understanding microstructural evolution to our ability to estimate deformation processes and conditions from recovered samples or geophysical data and to our modelling of tectonics. An invited contribution from Austin focuses on some of the key issues from the last few decades: how different mechanisms (grain size sensitive and grain size insensitive) compete and interact to control the evolution of grain size and LPO. Many of the other papers touch on these issues and make use of combinations of laboratory experiments, field studies and computational methods to explore the controls on microstructural evolution and to relate microstructural evolution to rheology and largescale tectonic processes. It is clear from this collection of papers that resolution of the controls on microstructural evolution in rocks remains at the cutting edge of Earth sciences.

Reconstruction of Late-Quaternary sea- and lake-level changes in a tectonically active marginal basin using seismic stratigraphy: The Gulf of Cariaco, NE Venezuela

The Gulf of Cariaco is a marginal basin located between the Cariaco Basin and the Paria Gulf, offshore NE Venezuela, along a system of active right-lateral strike-slip faults. It is connected to the Caribbean Sea via a shallow 58-m-deep sill implying that the gulf was disconnected from the global ocean during eustatic lowstands. A dense grid of high-resolution reflection seismic profiles has been used to determine the overall tectonic structure of the gulf and to establish the seismic stratigraphy of its sedimentary infill. Six unconformity-bounded seismic–stratigraphic units were identified in the upper ~200m of the sedimentary infill. Detailed seismic–stratigraphic and seismic-facies analysis allowed defining a series of sedimentary features that can be used as indicators of past sea or lake level in the Gulf of Cariaco: i) delta offlap breaks, ii) evaporites, and iii) erosional unconformities. Using accurate measurements of these various indicators at several locations in the gulf and a simple total subsidence model, a relative sea/lake-level history encompassing the last 130kyr could be reconstructed. In periods of connection with the open ocean, reconstructed relative sea level correlates well with eustatic sea level. In times of disconnection, distinct lake-level fluctuations occurred, which sometimes resulted in total dessication of the gulf. Lake-level fluctuations appear to correlate with major Heinrich Events, stadials and interstadials. MIS 4, the LGM and the Younger Dryas were thus identified in the Gulf of Cariaco sedimentary record. The last reconnection to the Caribbean Sea occurred during MWP1b (around 11.5kyr). The very good fit of the Cariaco sea/lake-level curve with the eustatic sea-level curves (both in terms of amplitude and of timing) underscores potential for future paleoclimate research of the sedimentary record contained in this marginal basin, despite its active tectonic setting.

Falling rock hazard index: a case study from the Marun Dam and power plant, south-western Iran

Rock fall phenomena are a major hazard during construction in mountainous regions. At the Marun Dam site, rock falls occur almost every day on the downstream side. The left flank power plant and access roadways as well as the right flank roadways are susceptible to rock falls from the 100 m high cliffs with slopes of 70–90°. The cause is a combination of the orientation of the bedding planes and joint sets and the active tectonic setting of the area. The paper reports the use of RocFall and Dips software to simulate the conditions in order to define the potential risk of rock falls at the Marun Dam site, which could affect workers as well as structures. In the light of the Falling Rock Hazard Index obtained, preventative and remedial measures are suggested.

Impacts of the tectonic stress field on natural gas migration and accumulation: A case study of the Kuqa Depression in the Tarim Basin, China

Stress, fluid and temperature are three of the major factors that impact natural gas migration and accumulation. In order to study the influences of tectonic stress field on natural gas migration and accumulation in low-permeability rocks, we take the Kuqa Depression as an example and analyze the evolution of the structure and tectonic stress field at first. Then we study the influences of tectonic stress field at different tectonic episodes on fractures and fluid potentials through the numerical simulation method on the section across the KL2 gas field. We summarize two aspects of the impact of the tectonic stress field on natural gas migration and accumulation. Firstly, under the effects of the tectonic stress field, the rock dilation increases with the added stress and strain, and when the shear stress of rock exceeds its shear strength, the shear fractures are well developed. On one hand, the faults which communicate with the hydrocarbon source rocks become the main pathways for natural gas migration. On the other hand, these positions where fractures are well developed near faults can become good reservoirs for natural gas accumulation. Secondly, because fluid potentials decrease in these places near the faults where fractures are well developed, natural gas can migrate rapidly along the faults and accumulates. The impact of tectonic stress fields on natural gas migration and accumulation allows for hydrocarbon migration and accumulation in the low-permeability rocks in an active tectonic compressive setting.

Upper Riphean and Vendian sandstones of the Bashkirian anticlinorium

The analysis of lithogeochemical data on the Upper Riphean and Vendian sandstones from the Bashkirian anticlinorium showed that sandstone associations formed in a passive sluggish tectonic regime in the middle Late Vendian were replaced by associations accumulated in the more active tectonic settings. This is well seen in the SiO2-K2O/Na2O and (Fe2 + MgO)-TiO2 diagrams reflecting the particular and median compositions of psammites. The lithochemical characteristics of sandstones were examined to deter� mine the compositional variation of rock complexes eroded on paleodrainage areas. Quartzrich sedimentary, metasedimentary, and metamorphic rocks, as well as felsic igneous rocks prevailed in the paleodrainage areas throughout the entire Late Riphean and Early Vendian, while the main sources of clastic material in the Late Vendian were igneous intermediate and basic rocks. With allowance made for the previous comparativelitho� logical data and some other materials, significant similarity in the position and orientation of compositional fields of psammites from the middle and upper levels of the Asha Group (Bashkirian anticlinorium) with fields of psammites from different syncollisional (flysch and molasse) basins in the SiO2-K2O/Na2O, K2 O/Na 2 O-SiO 2 /Al 2 O 3 , F1-F2 and other diagrams suggests that the middle Late Vendian (beginning from the Basa level) was marked by a variation in tectonic/geodynamic settings of sandstone accumulation and in composition of the eroded paleodrainage systems. The revealed trend agrees well with concept of the exist� ence of the Late Riphean-Vendian Pechora paleocean.

Provenance of the Novo Oriente Group, southwestern Ceará Central Domain, Borborema Province (NE-Brazil): A dismembered segment of a magma-poor passive margin or a restricted rift-related basin?

Integrated field, LA-MC-ICP-MS geochronology and geochemical data from the Novo Oriente Group have been investigated in order to determine their provenance and possible tectonic setting. This group in the southwestern portion of the Ceará Central Domain, is a well-preserved metavolcanosedimentary sequence, in part exhalative, composed of two distinct formations. The proximal coastal Bonsucesso Formation comprises mainly quartzite and minor basic metavolcanic rocks and is in gradational contact with the distal Caraúbas Formation which constitutes a metapelitic–volcanic-carbonate sequence, including metabasic rocks with pillow structure and sheared serpentinized ultrabasic rocks. The youngest detrital zircon found in the quartzite of the Bonsucesso Formation yielded an age of ca. 2.1 Ga and well-defined peaks around 2.2, 2.3–2.4 and 2.5 Ga. In addition, zircons from a related metabasalt yielded an upper intercept age of 2083 ± 28 Ma. We interpret the zircons found in this metabasalt as inherited from the host quartzite. This fact is supported by depleted-mantle Nd model ages ( T DM age) from correlated metabasic and metaultrabasic rocks from other places in the Novo Oriente sequence, which have yielded ages between 1.36 and 1.69 Ga, that is younger than the zircon age obtained in the metabasalt extruded over the Bonsucesso quartzite. Geochemical data of the metasedimentary rocks from the Caraúbas Formation indicates a provenance composed of a mixture of felsic and intermediate sources typical of old stable cratons and older continental roots of active tectonic settings. The rocks of the Granja (Médio Coreaú Domain) and Bacajá Complexes (southeastern Amazonian Craton) exposed to the west of the Novo Oriente Group, and largely covered by the Phanerozoic Parnaíba intracratonic basin, are the most likely source rocks. Since the precise age of the Novo Oriente Group is not yet well constrained, two distinct settings may be proposed: (1) it may represent a more evolved basin developed from extensional processes during the Mesoproterozoic (ca. 1.5–1.3 Ga); and (2) it could constitute part of the passive margin systems developed during the break-up of the Rodinia crown copyright supercontinent (ca. 0.95–0.8 Ga), associated with a pre-Brasiliano/Pan-African ocean (e.g. Pharusian Ocean).