Slab Failure Research Articles

Influence of moisture content and intermediate principal stress on cracking behavior of sandstone subjected to true triaxial unloading conditions

The presence of water has been confirmed to play an important role in affecting the failure properties of underground surrounding rock when subjected to complicated stress circumstances. In the current study, the crack propagation behavior of red sandstone affected by various moisture contents and intermediate principal stresses were investigated by using the QKX-YB200 true triaxial test system with unloading minimum principal stress. The experimental results demonstrate that the failure mode can be divided into shear, tension with shear, and slabbing. A clear observation of the fractured specimen shows that the extensional cracks tend to increase while shear cracks gradually diminish with the increase of moisture content and intermediate principal stress. For natural sandstone (with lower moisture content), the transition of failure mode from shear to slabbing requires higher intermediate principal stress. However, with the increase of moisture content, the occurrence of slabbing failure requires lower intermediate principal stress. The analysis of failure process indicates that the presence of water may restrain the possibility of rockburst, and the intermediate principal stress exhibits distinct functions in the failure behavior of natural and saturated sandstone. The surface microscopic morphological characteristics and acoustic emission signal feature were also analyzed to validate the transformation of the cracking mode. The current research indicated that the water-induced micro defect and damage effect, “water wedge” effect, intermediate principal stress effect are the key factors that contribute to the final slabbing failure in immersed hard rocks under true‑triaxial unloading conditions.

Comparison of Punching Shear Behaviour of Two-Way Concrete Slab Reinforced with CFRP Grid and Steel Bars

Two punching shear failure tests of two-way concrete slab reinforced by CFRP grid and HRB 400 steel were studied in this paper. The reinforcement ratio of slab reinforced with CFRP grid and HRB400 is 0.33% and 0.37 respectively. The upper and lower surfaces of the concrete slab’s tensile and compressive strains, the reinforcement strains, the load deflection of the slabs, and the applied load value were analyzed. The results show that under approximately the same reinforcement ratio, the concrete slab reinforced with CFRP grid has higher bearing capacity. Both slab failure formed with punching cones, the punching cone angle of CFRP grid slab is 24.1°, which is far less than 38° for reinforced concrete slabs. The tests results indicated that there is a cooperative between longitudinal and transverse limb of CFRP grid.

Petrogenesis of late Ediacaran volcanic rocks of the Kerdous and Tagragra d’Akka inliers (Anti-Atlas Morocco): Involvement of slab-failure

Late Ediacaran rocks of the Ouarzazate Group define a thin pile of sediments and pyroclastic deposits between the Paleoproterozoic basement and the Cambrian sedimentary cover in the southern Kerdous and Tagragra d’Akka inliers. In the Tafeltast area, terrigenous sediments with volcano-sedimentary and pyroclastic rocks are located in grabens controlled by syn-sedimentary normal faults. The sedimentation is characterized by a maximum flooding outlined by the Agoujgal carbonates. In the Tagragra-n-Daouizid area, the Ouarzazate Group represents the surficial emission of rhyolitic pyroclastic flows. This pyroclastic activity was associated with continental coarse-grained sedimentary deposits. In the Tagragra Ouahallal area, the volcanic sequence is comparable to that observed in subglacial volcanoes. Massive ash layers, intrusive pillow lavas in waterlogged deposits, stacking of lava flows, alternation of emerged and submerged periods under shallow water, are characteristics described in sub-glacial mafic volcanoes.According to geochemical data, volcanic rocks of the Ouarzazate Group are: (i) mafic rocks with continental flood basalt and calc-alkaline basalt affinity; (ii) high-K calc-alkaline felsic rocks, generated by partial melting of crustal lithologies, or by an enriched mantle with involvement of crustal component; and (iii) intermediate to felsic slab failure rocks derived through mantle processes including melting of mafic upper portion of the subducted slab.

The effect of using shredded plastic on the behavior of reinforced concrete slab

The present work investigated the usage of recycled plastic waste in slabs. The mechanical properties of concrete were studied by testing 21 standard cylinders with 5 %, 10 %, and 15 % RPET and RPEP for the slump, density, compressive, and splitting tensile strengths. It shows that while RPET improved workability more than RPEP, both ingredients decreased concrete density by up to 9.8 %. The RPET group provided greater strength than the RPEP by 10 %. Slight variations in RPET and RPEP led to a decrease in splitting tensile strength. Seven 500x500x110mm reinforced concrete slab samples were tested experimentally to determine the influence of 5 %, 10 %, and 15 % RPET and RPEP substituting aggregate. The slabs were sorted into control, RPET, and RPEP groups and tested using a line load at midspan, comparing failure mode, initial crack load, ultimate load, and deflections for each group. All samples failed due to flexure. RPET slabs cracked less than the control and RPEP slabs. Replacing coarse aggregate with RPEP reduces first cracking loads by 3.2–34.3 %. The experimental flexural load tests showed that the ultimate load decreased by 13.9–21.6 % when RPET was employed and by 2.4 %, 7.9 %, and 14 % when RPEP was used. A decrease in deflection was observed when 5 % of RPET and RPEP were used, while deflection was increased for 10 % and 15 %. In experiments, slab failure and cracking loads were less than the expected theoretical loads. The work incorporates FEM slab simulation. The finite element method matches experimental data for computing the ultimate loads for RPET and RPEP slabs. The finite element method did not match how the slab responded to load. Finite element analysis generates more flexible slab behavior than experimental testing.

Petrogenesis, Sources, and Tectonic Settings of Triassic Volcanic Rocks in the Ela Mountain Area of the East Kunlun Orogen: Insights from Geochronology, Geochemistry and Hf Isotopic Compositions

The Ela Mountain area is located at the easternmost point of the East Kunlun Orogen, in which voluminous igneous rocks developed in the Triassic period, and it is a good place to investigate the tectonic evolution of the Paleo-Tethys Ocean. In this study, petrological, geochemical, zircon U-Pb geochronology and zircon Hf isotope studies were carried out on the volcanic rocks in the Ela Mountain area. Dacite (239.3 ± 1.4 Ma) exhibits calc-alkaline I-type characteristics, and rhyolite (237.8 ± 2.1 Ma) is similar to high-K calc-alkaline highly fractionated I-type volcanic rock. The petrogenesis shows that both rhyolite and dacite originated from the partial melting of the mafic lower crust of the Mesoproterozoic under relatively high temperature and low pressure. Dacite and rhyolite were derived from the same or similar parent magma, and they are volcanic rocks with different differentiation degrees formed in the same magmatic pulse activity. Differing from rhyolite and dacite, basaltic andesite shows a relatively young age (234 ± 1.2 Ma), mainly originating from the partial melting of the lithospheric mantle modified by subducted slab-derived fluids; the magma was contaminated with a small amount of crustal source components and experienced the fractional crystallization of mafic minerals before the eruption to the surface. This study on the tectonic environment of these volcanic rocks shows that they were formed in the environment of slab failure in the late stage of syn-collision, and that they are different types of volcanic rocks from different sources under similar tectonic environments. The volcanic rocks of the Ela Mountain area in this contribution provide important evidence for Middle Triassic to Late Triassic syn-collisional magmatism in the slab failure stages. The results of this study constrain the lower age limit of the closure of the Paleo-Tethys Ocean and the initial time of extension of the late stage of syn-collision, providing important information regarding regional tectonic evolution processes and volcanic activity history. They can be applied to regional tectonic evolution, petrology, volcanic stratigraphy and mineral deposits related to volcanic rocks.

How Small Slip Surfaces Evolve Into Large Submarine Landslides—Insight From 3D Numerical Modeling

AbstractSubmarine landslides are a major marine geohazard affecting resilience of offshore infrastructure and coastal urban centers. Attention has previously been paid to quantifying post‐failure dynamics of catastrophic submarine debris flows and their consequences. However, pre‐failure initiation and growth of a small slip surface evolving into a large submarine landslide are still less understood. This study aims to explore the physical failure mechanism of submarine landslides initiated from small slip surfaces and to quantify key features of failure evolution. They are achieved by modeling the entire three‐dimensional (3D) landslide evolution, integrating the initiation and growth of slip surface, failure of slab above the slip surface, post‐failure mass movement and re‐deposition of transported sediments, using a novel numerical method. The characteristics of the slip surface growth within a favored layer and the patterns of the slab failure in the overlying layer have been thoroughly discussed. The transition from the pre‐failure slip surface growth to the diverse post‐failure mass movement are first observed and discussed with the 3D geometry effects, revealing the complex cascading mass movement mechanisms. The criterion for unstable growth of a planar slip surface and critical condition for slab failure are proposed. The findings from the study facilitate scientific understanding of the evolution of historic events and help safeguarding offshore developments against submarine landslide recurrence.

Extracting acoustic emission features that precede hard rock instability with unsupervised learning

The static and dynamic failure processes of hard rocks were simulated by compression tests to investigate the precursors of hard rock instability. In the tests, acoustic emission (AE) signals were acquired, and their clustering features were automatically extracted by the clustering unsupervised learning method. The results showed that a class of AE signals featured ‘high rise time, high ring count, high energy and low peak frequency and low quantity’ precede hard rock instability and can be used as an indicative precursor feature of hard rock instability. In addition, this class of signals can be used to predict the instability mode of hard rocks after occurrence of the slabbing failure phenomenon: the hard rocks eventually will experience spalling instability if the AE signals occur intermittently and tensile failure signals dominate; or rockburst instability if the AE signals occur continuously and shear failure signals dominate.

Eocene Volcanic Complex from Central British Columbia: The Role of Fractional Crystallization during the Magmatic Evolution

Abstract The Challis-Kamloops belt of south-central British Columbia is a regionally extensive (>65,000 km2) magmatic province that erupted within the North American Cordillera during the Eocene (55-45 Ma). The inland volcanic belt runs parallel to the coast, and the rocks were emplaced mainly within extensional basins indicating volcanism was attributed to rift-related decompressional melting. The rocks include both calc-alkaline and tholeiitic mafic and intermediate types (i.e., low-Fe, medium-Fe, and high-Fe suites). Voluminous volcanic units (Buck Creek, Goosly Lake, Swans Lake) of the Buck Creek volcanic complex (~3,000 km2 in area) within the Nechako plateau erupted within 1-2 million years and show significant internal chemical variability. All rock types have similar Sr-Nd isotopic (87Sr/86Sri=0.70435-0.70487; εNdt=+2.6-+4.0) ratios indicating they originated from the same sub-Cordilleran mantle source. Petrological modeling using the most primitive rocks of the Buck Creek, Goosly Lake, and Swans Lake magmatic pulses demonstrates that the chemical variability observed in each system can be explained by hydrous fractional crystallization in the upper crust (≤0.1 GPa) under moderately oxidizing to oxidizing conditions (ΔFMQ 0 to +0.7). The primary difference between the low-Fe to medium-Fe (calc-alkaline) Buck Creek suite model and the high-Fe to medium-Fe (tholeiitic) Swans Lake suite model is water content as the Swans Lake model has lower (H2O=0.75 wt.%) starting water than the Buck Creek and also the Goosly Lake models (H2O=1.25-2.00 wt.%). Moreover, the intermediate to silicic rocks of the complexes are compositionally similar to rocks associated with “slab failure” suggesting that rifting and mantle melting were related to asthenospheric upwelling through a slab tear. The implications are that the chemical variability of the rock suites are primarily related to fractional crystallization and that the mantle source is heterogeneous with respect to water content which is likely due to heterogeneities in the processes related to pre-Eocene subduction.

Structural Behavior of Reinforced Lightweight Concrete Slabs

This paper presents an exploration of choosing the optimum density for concrete that achieves the best structural performance for two-way slabs made of concrete with fine aggregate in different proportions less than the ratio used in ordinary concrete to produce different densities, by taking advantage of the idea of fine aggregate concrete which considers as light-weight concrete to achieve lighter concrete with higher structural endurance. The experimental program includes constructing and testing five slabs, four of them made of concrete with different fine aggregate radios 75%, 50%, 25%, and 0% to get different densities (2207, 1792, 1536, 1310 kg/m3) as well as another slab made of normal concrete used as a reference slab with a density of 2414 kg/m3. The outcomes reveal that decreasing the density of the slab from 2414 kg/m3 to 1310 kg/m3 by reduction fine aggregate in concrete from 100% to 0% respectively has more effect on the first crack load than that on the ultimate load of two-way slabs as the first crack load decreases with percentages 16.7%, 33.3%, 38.9%, and 61.1% the while the ultimate load decreases with percentages 7.3%, 21.9%, 46.3%, and 56.1%, respectively as compared to the reference (normal wight concrete slab). Also, decreasing the density of the slab made the cracks form and spread quickly and the slab failure tends towards the brittleness, and the cracks diffused and grew faster and wider.

Critical Condition of Reinforced Concrete Roof Slab Failure Under Blast and its Blast Resistance Design Method

Critical Condition of Reinforced Concrete Roof Slab Failure Under Blast and its Blast Resistance Design Method

Cretaceous to Cenozoic controls on the genesis of the shelf-incising Perth Canyon; insights from a two-part geomorphology mapping approach

Perth Canyon is Australia's second largest submarine canyon, and its shelf-incising morphology contrasts with the more prolific slope-confined canyons that typify Australia's passive continental margin. The canyon has a sinuous course that extends 120 km from the shelf break (~180 m depth) to its fan at the foot of the continental slope (~4500 m). Though the canyon initiates only 50 km offshore from a major city, its genesis and geomorphic stability have not been well understood. Bathymetry data acquired in 2015 by the Schmidt Ocean Institute enabled the application of a new two-part seafloor classification approach to objectively map the complexity of the system in unprecedented detail. Part 1 used a semi-automated approach to classify the seafloor bathymetry into morphological categories, and Part 2 defined these units as geomorphological features through the interpretation of sub-bottom and seismic images, sediment samples and acoustic backscatter datasets. The resulting geomorphic map reveals an array of aggradational (cyclic steps and sediment waves), incisional (entrenched canyon floor and nick-points) and mass movement (slump and slab failures) features that for the first time provide detailed insights into the canyon's formative processes. Large faults and the Cretaceous palaeobathymetry appear to have strong influence on the canyon's planform, its depth of incision, and the distribution and types of mass failure that characterise its flanks. These data also reveal the Perth Canyon to be a predominantly relict feature; a large Late Cretaceous infilled incised valley (subaerial) beneath the canyon headwall likely initiated the canyon's development and represents its initial and most active phase. Two more infilled incised valleys are stacked above the first, and demonstrate a progressive decrease in scale, and presumably also canyon activity. Each incised valley represents lowstand incisions of the palaeo-Swan River, and their timing is linked to pronounced Late Cretaceous to Cenozoic sea level regression events, palaeoclimatic change, and onshore catchment enlargement. The disconnection of the modern Perth Canyon from the present day Swan River, and the low rates of sediment accumulation on the adjacent shelf and slope, ensure low rates of sediment supply to the canyon, and only infrequent ignition of turbidity currents. Low rates of sediment supply can similarly account for the entrenched morphology of the modern fan and only minimal headwall movement coincident with seismic events in 2018. However, additional core and bathymetry data for the lower canyon reaches are required to conclusively determine the extent of recent canyon activity.

Petrology and geochemistry of adakitic intrusions and dykes at Sarcheshmeh porphyry Cu‐Mo ± Au deposit, Iran: Insights into their source

AbstractThe Sarcheshmeh porphyry copper deposit (PCD) is located in the southeast part of the arc‐related Urumieh‐Dokhtar volcano‐plutonic belt. This PCD was formed by intrusion of a Middle Miocene granodiorite to tonalite stock into the volcano‐sedimentary rocks that are mainly andesite exhibiting Early Tertiary thrusting and faulting. On the basis of geochemistry of intrusive rocks, they are calc‐alkalic and alkali‐calcic suites that are consistent with oxidized I‐type magmas. The Fe2O3/FeO ratio in the Sarcheshmeh PCD is 1 to 3, consistent with a high oxygen fugacity. The igneous rocks of Sarcheshmeh PCD belong to a mature arc, but related to a post‐collision arc setting. Considerable evidence supports adakitic affinities of the Sarcheshmeh rocks, including geochemical values of Sr > 300 ppm (ave., 594 ppm), high ratios of Sr/Y > 20 (ave., 75), La/Yb > 20 (ave., 30), and enrichment of LREE and LILE relative to HREE and HFSE. The adakites of Sarcheshmeh belong to high‐silica adakites (HSA) that can be formed by melting of subducting seawater‐altered oceanic plate, which interact with the mantle wedge then followed by slab break‐off with local transtension in the middle part of the Dehaj‐Sarduieh belt. In rocks of the region, the ratios of Th/Ce > 0.12 and Nb/Zr > 0.05 suggest that the subducting crust has a role in forming different groups of these rocks. Geotectonic discrimination diagrams are used to distinguish between normal arc and slab failure magmatic systems, including Nb versus Y, La/Sm versus Sm/Yb, La/Yb versus Gd/Yb, and Rb versus Nb + Y diagrams. The plutonic rocks of the Sarcheshmeh PCD have characteristics consistent with adakites derived via slab failure, which are obviously metallogenically favorable magmatic systems. Adakitic melts generated rapidly during sinking of a broken slab (into higher temperature mantle), buoyantly migrate through the subcontinental lithospheric mantle (SCLM), which is related to structural evolution of that SCLM with local extension or transpression.

Petrogenesis of the Early Silurian Renda appinite suite in the southeastern Qilian Orogen, NW China: Implications for the evolution of a Proto-Tethys magmatic arc

ABSTRACT Early Paleozoic subduction beneath peri-Gondwana microcontinents formed a major Proto-Tethys magmatic arc system. Appinite suite rocks constitute important components within that magmatic arc. Herein, we report hornblende 40Ar/39Ar and zircon U–Pb geochronology data, zircon Hf isotope, mineral chemistry, whole-rock geochemistry, and Sr–Nd–Pb isotope data for the rocks of hornblende gabbro-diorite-quartz diorite-quartz monzodiorite from the Renda appinite suite and adjacent granite porphyry in the southeastern Qilian Orogen. Hornblende 40Ar/39Ar and zircon U–Pb isotopic data constrain ages of the intrusions of the Renda appinite suite to 439–435 Ma. Rocks in this suite represent the calc-alkalic to alkali-calcic series, and they are enriched in large-ion lithophile elements and depleted in high-field-strength elements. The hornblende gabbros exhibit moderate initial 87Sr/86Sr ratios (0.7046–0.7055) and higher whole-rock εNd(t) (–1.3 to +1.7) and zircon εHf(t) (+7.2 to +11.2) values relative to the other rocks of the suite (0.7047–0.7064, – 7.7 to – 1.1, and – 6.6 to +6.8, respectively) as well as Pb isotopic features similar to EM2 lithospheric mantle. These geochemical characteristics suggest that the Renda appinite suite originates from partial melting of an enriched lithospheric mantle, with subsequent fractional crystallization and hybridization with crustal components. The granite porphyry formed by partial melting of the crust coeval with the emplacement of juvenile magma. This study suggests emplacement occurred during a short-lived collision with slab failure (breakoff) after latest stage (cessation) of Proto-Tethys oceanic subduction along the northern side of the southeastern Qilian Orogen. The heat supplied by the asthenospheric upwelling through a gap in the subducted slab induced melting in lithospheric mantle and deep crust producing Renda appinite suite rocks and granite porphyry.

Experimental study on failure characteristics of slabbing failure model specimen and rockburst mechanism

Rockburst is a common dynamic disaster in underground engineering under high ground stress. A large number of rockburst examples show that there is a strong correlation between the instability failure of slab cracking surrounding rock and rockburst during the excavation process of hard and brittle surrounding rock. Seven cracks were made in a 150 mm × 150 mm × 35 mm granite cube sample, the lengths of cracks were reduced from the free face to the inside according to a certain proportion. The granite is cut to form a slab-like structure with the same thickness, and the slap cracking sample model was made. The uniaxial compression test was carried out on the cracking samples. Combined with the numerical simulation results, the crack initiation, propagation characteristics and failure process of the cracked rock samples were analyzed, and the relationship between the instability of the slab cracking surrounding rock and rockburst was revealed. The results show that the cracking of surrounding rock plate is easy to induce sudden rockburst disaster, but it also provides the possibility for monitoring and early warning of rockburst disaster. With the increase of the distance between surrounding rock and the excavation face, the failure mode of slab crack structure becomes complex and the degree of failure increases gradually. It is found that there are three types of failure mechanism in the process of slab rockburst formation. The rock slab on the sample that is a certain distance from the excavation frontage is the first to rupture. The failure of the rock slab far away from the excavation free face is relatively rapid, and its fracture mechanism is more complex, with the largest degree of damage, resulting in a large number of rock blocks and cuttings. The slabs close to the excavation face are mainly bent and broken, forming large blocks or slab-like blocks. Once the rock slab is bent and broken at the face of excavation, the slab-like rock block formed at the face of excavation and the inside of surrounding rock will pop out at a high speed instantly, resulting in a rockburst disaster. The results reveal the process of rockburst of slab cracking hard rock structure under high stress condition, which can provide a scientific basis for the prevention and control of rockburst.

Upslope Failure Mechanisms and Criteria in Submarine Landslides: Shear Band Propagation, Slab Failure and Retrogression

AbstractThe volume of a submarine landslide is likely to be amplified by shear band propagation along a basal surface or spreading failure extension in the sliding layer. Although the mechanism of translational submarine landslides has been understood using the interpretation of shear band propagation, assessment of the limits of failure extension, either through shear band propagation or retrogressive spreading, remains a challenge due to the diversity of post failure mechanisms. The paper aims to explore all post failure possibilities and quantify failure initiation and extension accordingly, focusing on the upslope conditions. The different failure mechanisms are explored with the aid of the large deformation finite element modeling. Original criteria for scarp position, shear band length at slab failure, retrogression conditions and ultimate spreading limits are proposed, following the process zone approach considering force equilibrium of the sliding mass. Simplified analytical predictions are shown to agree well with the numerical observations. The findings and criteria presented in the study are expected to help assess the ultimate scale of upslope failure in submarine landslides, which is important in determining geohazard zonation of submarine landslides.

Study on the ductility of open‐rib and re‐entrant composite slabs

AbstractComposite slabs with profiled steel sheeting and cast‐in‐place concrete are a conventional structural flooring system worldwide. The partial connection method (PCM) is a design method limited to slabs showing a ductile longitudinal shear failure. The ductility is defined in Eurocode‐4 in terms of additional strength after certain initial slip is produced, regardless of the steel sheet profiling shape. This article shows that the slip behavior is significantly different depending on the shape of the sheeting profile. On the one hand, the slip magnitude in reentrant slabs can be large enough to drive the two materials to their yielding stresses; on the other hand, in open‐rib profiles, the slab failure is due to the vertical release of the concrete, when the slip overpasses certain geometric limit. This failure mode is generally produced much before the materials reaches their yielding stresses. This finding is consistent with both the experimental and FEM results carried out in this study.

Neoproterozoic tectonics of the Jiangnan orogen: The magmatic record of continental growth by arc and slab-failure magmatism from 1000 to 780 Ma

The Neoproterozoic NE-striking Jiangnan orogen in the South China Block (SCB) separates the Cathaysia microcontinent on the southeast from the Yangtze craton in the northwest. The origin and evolution of the Jiangnan orogen is unresolved, with individual models explaining part of the history, such as various magmatic, deformational, metamorphic, and sedimentary events including extensional, contractional, and transpressional modes. Here, we present detailed geochronological and Nd-Hf isotopic data for Neoproterozoic mafic and felsic intrusions in the Jiangnan orogen and identify three episodes of Neoproterozoic magmatism. The first stage ranging from ~1013–942 Ma is preserved predominantly in the eastern segment of the orogen, including a series of mafic rocks with ages of ~1010–952 Ma, contrasting with weak magmatic activity in the western segment with a peak at ~997 Ma. The second stage ranges from ~906 Ma to ~820 Ma, with intensive and extensive bimodal magmatism occurring in the eastern and western parts. The last stage mainly occurred in the western Jiangnan orogen in the period from ~800 to 780 Ma, associated with drastic mafic magmatism and weakly bimodal volcanic activities. The bimodal volcanism in the eastern segment exhibits a striking weak trend after ~823 Ma, distinctly different from the western segment where the magmatism lasted until ~785 Ma, indicating its syn- to post-collisional in nature. The pre-800 Ma magmatic rocks in western Jiangnan orogen have a dominant negative Nd isotopic signature but exhibit a significant positive trend after 800 Ma, different from those in east, which have a decreasing trend. Both parts display a roughly decoupled Nd-Hf isotopic character presented by a dominant positive pattern in Hf isotopes of the Neoproterozoic intrusive rocks, indicating a significant addition of previous slab-derived components or accretionary wedges in the pre-800 Ma magma evolution, and more depleted materials involved in the source in the later stages. Oceanic subduction under the northwestern Cathaysia Block occurred around ~1.0 Ga, slightly earlier than the subduction to the southeastern Yangtze. A gradual tectonic transition from post-orogenic extension to intracontinental rifting dominated the tectonics in Jiangnan orogen in the middle-late Neoproterozoic, followed by slab failure after ~790 Ma. Arc magmatism was the dominant source of crustal growth before 820 Ma in the SCB, but was exceeded in volume by later slab failure magmatism after ~790 Ma.

Depth integrated modelling of submarine landslide evolution

Submarine landslides are a major geohazard among worldwide continental slopes, posing significant threats to offshore infrastructure, marine animal habitats and coastal urban centres. This study establishes an original numerical package for time-efficient modelling of the entire submarine landslide evolution covering the pre-failure shear band propagation, slab failure and post-failure dynamics. The numerical scheme is based on the conservation of mass and the conservation of momentum and combines the shear band propagation theory and the depth-integrated method, with the consideration of the drag force from the ambient water. Shear band propagation in the weak layer and slab failure in the sliding layer are controlled by the strain softening and rate dependency of the corresponding undrained strength parameters. The post-failure behaviour in the sliding layer, such as retrogression upslope and frontally confined and frontally emergent mechanisms downslope, is also simulated. The numerical results from the proposed method are comparable to the analytical solutions and the large deformation finite element analysis. Application of this method to a back analysis of the St. Niklausen slide in Lake Lucerne reproduced the observed shape of the mass transport deposits, the position of the main scar and the travel distance. Because of its easy implementation and efficiency, the proposed numerical method for modelling of submarine landslides seems promising for practical applications.

The northern Appalachian terrane wreck model

Ordovician and Siluro-Lower Devonian magmatic rocks in the northern Appalachians south of the Iapetus suture are currently interpreted as distinct belts composed of multiple, small, peri-Gondwanan terranes that amalgamated during the sequential closures of Iapetus (latest Ordovician), the Tetagouche backarc basin (early Silurian), the Acadian seaway (Siluro-Devonian), and the Rheic Ocean (Devono-Carbonferous) (multiple terrane model). Here, the Siluro-Lower Devonian magmatic belts are shown to have slab failure affinities and together with the Ordovician arcs form paired belts parallel to the Iapetus suture, which suggests that they were emplaced along the common, peri-Avalonian margin during pre- and post-collisional processes. The Iapetan suture and the paired belts are inferred to repeat in Atlantic Canada due to dextral, strike-slip processes of mid-Late Devonian or younger age (terrane wreck model). In Newfoundland, the repetition is inferred to be the result of oblique, dextral offset of ca. 250 km. In the Quebec Embayment, the Iapetan paired magmatic belts are repeated twice in the limbs of a Z-shaped orocline related to oblique, dextral offsets of ca. 1200 km of the southern limb. Limited Siluro-Devonian paleomagnetic data indicate no paleolatitudinal differences across the Iapetus suture, however ca. 100° post-mid Silurian clockwise rotation is indicated for the middle fold limb; these data favour the terrane wreck model. The terrane wreck model results in a simple tectonic scenario of southerly subduction of Iapetus beneath a single ribbon continent (Avalonia sensu lato) that was subsequently deformed.

The mid-Cretaceous Peninsular Ranges orogeny: a new slant on Cordilleran tectonics? I: Mexico to Nevada

The Peninsular Ranges orogeny occurred during the mid-Cretaceous at ∼100 Ma and affected rocks from southern Mexico to Alaska. The event resulted from the closing of an Early Cretaceous marine arc trough, named the Bisbee–Arperos seaway in Mexico and Arizona, and the Cinko Lake arc trough in the Sierra Nevada. The trough was an ocean that formed after the Late Jurassic – Early Cretaceous Nevadan orogeny and associated post-collisional magmatism. It was open for ∼40 million years and closed by westward subduction. Here, we focus initially on the most complete cross section, located in southwestern Mexico, where a west-facing Albian carbonate platform, with subjacent siliciclastic rocks built on the western margin of North America, was pulled down into a trench at 100 Ma, buried in hemipelagic mud and Cenomanian flysch, then overthrust from the west by rocks of the 140–100 Ma Santiago Peak – Alisitos arc and its substrate, the Guerrero Superterrane, which collectively document westerly subduction. This tectonically thickened collision zone was exhumed and intruded by 99–84 Ma distinctive post-collisional tonalite–granodiorite plutonic complexes, all with Sr/Y > 20, Sm/Yb > 2.5, Nb/Y > 0.4, and La/Yb > 10. These geochemical features are typical of slab failure, not arc magmas. The post-collisional plutons, previously considered to represent arc flare-ups, were derived from melting of the descending slab following arc-continent collision. Remnants of the arc, basin, related east-vergent 100 Ma thrusts, flexural foredeep, and 99–84 Ma slab failure plutons are traced from the Peninsular Ranges, through the Mojave Desert to the Sierra Nevada where similar rocks, relations, and ages occur. Along the western, back-arc, side of the orogen after collision and slab break-off, but during exhumation, east-dipping reverse faults with >10 km of east-side up movement shed 100–85 Ma plutonic and other debris westward from the hinterland into troughs such as the Valle and Great Valley. We extend our synthesis northward, from west-central Nevada to Alaska, in Part II.