East-west Shortening Research Articles

Strain and kinematics within the Salmon River suture zone and western Idaho shear zone, Idaho, USA: Exploring the contribution of ductile stretching to mass transfer and exhumation in fold-thrust and transpressional systems

Measuring penetrative strain is critical for understanding the 3D strain field of structural systems. Here, we investigate ductile strain and kinematics in two Cordilleran structural systems in north-central Idaho: the Salmon River suture zone (SRSZ), which is a west-vergent ductile fold-thrust system that accommodated shortening associated with terrane collision between ∼144 and 105 Ma, and the north-striking, subvertical western Idaho shear zone (WISZ), which accommodated dextral-transpressional shearing between ∼105 and 86 Ma. We collected finite strain data from stretched clasts in three SRSZ thrust sheets, which define 56–87% average thrust-parallel stretching and 35–48% average thrust-normal thinning. Thrust-parallel stretching contributed >27 km of cumulative displacement to the up-dip portion of the fold-thrust system, comparable to the 34 km of total thrust displacement estimated at down-dip levels. In the WISZ, we documented dextral kinematics in lineation-normal planes, and we measured boudinaged and folded granitic dikes to estimate late-stage (∼91-86 Ma) strain, which yielded 65% minimum lineation-parallel stretching and 50% minimum east-west shortening. Subvertical stretching in the WISZ accommodated >9–10 km of exhumation relative to the Idaho batholith to the east. The SRSZ and WISZ both demonstrate the 1st-order importance of ductile stretching for accommodating the large-scale transfer of mass and exhumation in fold-thrust and transpressional systems.

2730–2670 Ma rifting triggers sagduction prior to the onset of orogenesis at ca 2650 Ma: implications for gold mineralisation, Eastern Goldfields, Western Australia

The dominant structural fabric in the Eastern Goldfields is the steep north- to north-northwest-trending S2 foliation that is axial planar to upright F2 folds, developed during intense horizontal east–west shortening (D2–4 event). These structures consistently overprint D1 structures, which comprise layer-parallel S1 foliation, extensional shears, thrusts and recumbent F1 folds. The D1 event represents a separate and distinct episode of deformation with a markedly different stress regime (dominant vertical σ1), compared with the stress regime during the D2–4 events (horizontal east–west oriented σ1). There is little evidence for pre-2670 Ma ductile deformation in the Eastern Goldfields, as: (1) the ca 2730–2670 Ma greenstone sequences are deposited conformably on the older ca 2800 Ma greenstone sequences, with the first significant angular unconformities observed at the base of the post greenstone late basins; (2) a lack of schist or gneiss clasts in the late basins suggests that the surrounding uplifted sequence was largely undeformed; (3) the layer-parallel S1 foliation is observed throughout the 2720–2670 Ma greenstone sequence; and (4) the dominant low north- and south-plunges of F2 folds suggest that the sequence was predominantly flat-lying prior to strong east–west shortening (D2–4 events). The ca 2670–2655 Ma D1 event represents a period of sagduction that occurred immediately after cessation of rifting as a result of gravitational instability from deposition of dense, cold, greenstone sequences onto thinned, light, hot felsic crust. Late basins represent depocentres on the sinking greenstones during sagduction. Marked contrasts in the structural style of gold deposits, metallogeny and fluid sources, typically attributed to progressive deformation during orogenesis, could instead reflect temporally distinct mineralising events during changing tectonic regimes. In the East Yilgarn, an early plumbing system dominated by north-northwest-trending basin-controlling structures was likely established during rifting and focused fluids during multiple hydrothermal circulation events.

Convergence and transpression along the paleo-Pacific margin of Australia during the Paleozoic: insights from the Pinnak Sandstone at Mallacoota, northeast Victoria

Underpinning almost every Paleozoic paleogeographic reconstruction and tectonic model of the Lachlan Orogen is the interpretation of the structural geology related to crustal collision and amalgamation. Bounding the eastern margin of the Lachlan Orogen is a north-trending corridor of Cambrian–Ordovician turbidites that in northeast Victoria are recognised as the Pinnak Sandstone or previously known as the Mallacoota Beds. This sequence contains an accretionary prism related early S* foliation, syn-sedimentary dykes, slump structures, early faults or décollements and early quartz veins. These indicate anisotropic compaction by fluid extraction in a shallow marine turbidite sequence that underwent localised deformation (D1), which can be attributed to the Benambran Orogeny (ca 450 Ma). There was a change in the rheological properties during the ensuing late Silurian D2 Bindian Orogeny (ca 420 Ma). This event produced north–south-trending upright, east-verging folds (F2) with a marked partitioning of strain between the different sedimentary units. Folds plunge south at ∼30°, are tight to isoclinal, with local collapsed hinges and limb thrusts. This D2 deformation along the paleo-Pacific margin involved dextral transpression and a southerly propagation of the deformation front. Superimposed on these structures is an east–west paleostress pattern and two episodes of faulting (D3 and D4). In the first, brittle strike-slip faults were accompanied by ductile folding related to east–west shortening during the Middle–Late Devonian Tabberabberan Orogeny (ca 385–370 Ma). These were accompanied by the emplacement of the Sandpatch Point Granite. The second episode (D4) of strike-slip faulting reactivated many of the earlier faults during further east–west shortening and was related to the Carboniferous Kanimblan Orogeny (ca 354–343 Ma). This is best seen close to the granite contact where the strong crystallised granite reinforced the contact metamorphosed greywacke sequence, inhibiting ductile deformation so that faults deformed in a brittle fashion.

The geological evolution of the Silala River basin, Central Andes

AbstractImproved understanding of the geology and stratigraphic architecture of the Silala River basin and its evolution, reviewed here, has been important in providing scientific evidence to an international dispute between Chile and Bolivia on the nature and origin of the waters of the Silala River. The dispute was submitted in 2016 to International Court of Justice (ICJ), which issued its judgment in 2022. The Silala River has evolved within an active volcanic chain, in the western region of the Andean plateau. Various volcanic structures, at different stages of their evolution, have determined the basin's development. The first evidence of alluvial drainage associated with the Silala fluvial system appeared in the Lower Pleistocene (ca. 2.6–1.6 Ma), a record of alluvial deposits with paleoflow directions toward the Southwest and South‐Southwest. These deposits had an important role in forming a highly permeable horizon, confined between two pyroclastic deposits (the Cabana and Silala Ignimbrites) which comprise the main regional aquifer in the basin, although there are other minor locally important aquifers. The second stage in the evolution of the river system occurred in the late Upper Pleistocene‐Lower Holocene (ca. 11–8.5 ka BP), when an erosive period carved the current trans‐boundary ravine in the Silala Ignimbrite. Morphological evidence clearly shows that the ravine was carved by fluvial action. The only documented tectonic activity during the development of the Silala River basin is the Cabana reverse fault and associated normal faults, representing an East–West shortening, which occurred between 2.6 and 1.6 Ma.This article is categorized under: Science of Water > Water and Environmental Change Science of Water > Hydrological Processes Water and Life > Nature of Freshwater Ecosystems Human Water > Water Governance

Geochemical and geochronological constraints on the Mesoproterozoic Red Granite Suite, Kunene AMCG Complex of Angola and Namibia

Anorthosite-mangerite-charnockite-granite (AMCG) suites form large batholiths emplaced during the Proterozoic Eon. Magma source(s), emplacement mechanisms, and the tectonic setting of AMCG suites remain poorly understood. We present new major and trace element geochemistry combined with U-Pb zircon geochronology and Lu-Hf isotopes for the Red Granite Suite, part of the Mesoproterozoic Kunene AMCG Complex (Angola and Namibia), and its Paleoproterozoic host rocks, to elucidate the petrogenesis and tectonic setting of the Kunene Complex granitoids. The studied samples are mostly granite with minor syenite and quartz monzonite. LA-MC-ICPMS U-Pb zircon dates indicate that felsic magmatism was active for at least 90 Myr (1450–1360 Ma) and shows spatial and temporal similarities with emplacement of the main anorthositic body. The geochemistry of the granitoids did not change substantially over time, with predominant alkali-calcic, A-type granites. The εHf(t) of zircon grains in the Red Granite Suite ranges between −11.3 and + 1.6. These results, when considered together with Hf isotopic compositions of zircon from the Paleoproterozoic host rocks (εHf(t) = -11.3 to + 0.4) and xenocrysts in the Red Granite, suggest the suite is derived from the mixing of a Paleoproterozoic crustal component with juvenile mantle-derived material. Syn-magmatic east–west shortening has been documented in both the anorthosites and Red Granites at the southwestern margin of the Kunene Complex in the period 1400–1380 Ma. The results from the Hf isotopes on zircon, combined with the long-lived nature of magmatism, the syn-contractional magmatism, at least locally, and the requirement for extensive crustal melting, suggest that the Red Granite Suite was formed in a convergent margin setting. This challenges the traditional view that A-type granitoids are restricted to anorogenic, extensional settings, and is in agreement with recent views on the petrogenesis of massif-type anorthosites and their associated MCG magmatism.

Understanding the Deformation Structures and Tectonics of the Active Orogenic Fold-Thrust Belt: Insights from the Outer Indo-Burman Ranges

Abstract The tectonic deformation of the outer Indo-Burman Ranges (i.e., Chittagong Tripura Fold Belt, CTFB) is associated with the oblique convergence of Indo-Burmese plates since the latest Miocene. This article presents detailed field evidence of deformation structures and their kinematics in the exposed Tertiary successions in the CTFB. We combine observations made in this study with the published structural, geodetic, and seismic data sets to present an overview of the active tectonic framework of the region and its strain partitioning. To determine the kinematic evolution, décollement depth, and amount of strain, we combined geologic field mapping, structural analysis of fifteen anticlines, fracture/lineament analysis, and paleostress analysis of faults that define the ∼100 km wide CTFB. Structural data and kinematic analyses suggest subhorizontal plane strain with approximately 10% east-west shortening (oriented ~65°) that is perpendicular to the axial plane (oriented ~155°) of the CTFB anticlines. No evidence of significant transpression or strike-slip faulting has been observed in the CTFB and, therefore, suggests that full slip-partitioning is normal to the outer belt and parallel to the inner belt of the IBR. Paleostress analysis results are in good agreement with the present-day stress regime, and this implies that past and present deformation is dynamically related with the normal component of India-Burma oblique vector velocity motion.

Surface mapping, structural modelling and kinematics along the sinistral strike-slip fault zone, NE Potwar, Pakistan

AbstractThis research was carried out to understand the nature of strike-slip Jhelum Fault zone and to propose a model for the surface to subsurface deformation pattern. Field data along with satellite images are used to construct the geological map. Moreover, the subsurface model has been proposed using the mechanism of dip-isogons in computer application which connects points of equal inclination or dip on the outer and inner bounding surfaces of a folded layers. The proposed geological map and subsurface model shows that the Jhelum Fault when propagated in the south from Hazara-Kashmir Syntaxis forms a continuous shear zone on surface with some discontinuous exposure of splay faults rather than exposed as continuous discrete break. Likewise, the subsurface cross sections show that deformation along the fault zone is accumulated by splay faults from the main Jhelum Fault, which forms a positive flower structure with steep north-eastward dips, which is characteristics of strike-slip movement along Jhelum Fault Zone. The vertical stratigraphic throw along these faults shows small offsets and little east–west shortening, indicating that the major slip along the fault is strike slip.

Structural initiation along the frontal fold-thrust system in the western Indo-Burman Range: Implications for the tectonostratigraphic evolution of the Hatia Trough (Bengal Basin)

The Bengal Basin accommodates an extremely thick Cenozoic sedimentary succession that derived from the uplifted Himalayan and Indo-Burman Orogenic Belts in response to the subduction of the Indian Plate beneath the Eurasian and Burmese Plates. The Hatia Trough is a proven petroleum province that occupies much of the southern Bengal Basin. However, the style of deformation, kinematics, and possible timing of structural initiation in the Hatia Trough and the relationship of this deformation to the frontal fold-thrust system in the outer wedge (namely, the Chittagong Tripura Fold Belt) of the Indo-Burman subduction system to the east are largely unknown. Therefore, we have carried out a structural interpretation across the eastern Hatia Trough and the western Chittagong Tripura Fold Belt based on 2D seismic reflection data. Our result suggests that the synkinematic packages correspond to the Pliocene Tipam Group and the Pleistocene Dupitila Formation. This implies that the structural development in the western Chittagong Tripura Fold Belt took place from the Pliocene. In the Hatia Trough, the timing of structural activation is slightly later (since the Plio-Pleistocene). In general, fold intensity and structural complexity gradually increase toward the east. The presence of reverse faults with minor strike-slip motion along the frontal thrust system in the outer wedge is also consistent with the regional transpressional structures of the Indo-Burman subduction system. However, to the west, there is no evidence for strike-slip deformation in the Hatia Trough. The restored sections indicate that the amount of east–west shortening in the Hatia Trough is very low (maximum 1.2%). In contrast, to the east, the amount of shortening is high (maximum 13.5%) in the western margin of the Chittagong Tripura Fold Belt. In both areas, the key trapping mechanism includes anticlinal traps, although stratigraphic and combinational traps are possible, but this requires further evaluation.

Devonian–Carboniferous regional deformation in the northeastern Lachlan Orogen, southeastern Australia

The timing of regional deformation of the turbiditic Silurian–Devonian Hill End Trough in the northeastern Lachlan Orogen has been a contentious issue with one view ascribing the regional north–south folds and axial planar foliation to Middle Devonian basin inversion. Alternatively, it has been argued that given the low-angle discordance between Lower and Upper Devonian units on the Capertee and Molong highs, and the development of a dominant episode of folding mapped from the Hill End Trough into the adjoining highs, the major regional deformation is latest Devonian to early Carboniferous and predates intrusion of Bathurst-type granites at 358–314 Ma. We have approached the problem by analysing the gentle, upright, southeast-trending folds and deformation patterns in Devonian units of the northern Capertee High (Cudgegong area), drawing a cross-section across the Hill End Trough and reviewing the structure of two areas in the Molong High (west of Orange, and south of Wellington). Upper Devonian units on the highs are affected by fold patterns that extend into the underlying successions and have been interpreted as continuous into the central Hill End Trough, confirming the extent of the latest Devonian to early Carboniferous regional deformation in the northeastern Lachlan Orogen. Constraints from timing of deposition and radiometric ages are ambiguous and imply deformation was overlapping with sedimentation, as has also been inferred from sedimentary features of the Upper Devonian succession. Steeply dipping faults along the highs predated the Late Devonian and were probably formed in extension during formation of the Hill End Trough and were reactivated during basin inversion and potentially during Upper Devonian sedimentation. Our conclusion is that the simplest hypothesis is that the regional east–west shortening was of latest Devonian to early Carboniferous age, although poorly understood basin inversion occurred in the Middle to Late Devonian. KEY POINTS The timing of the development of regional north–south folds in the northeastern Lachlan Orogen has been a contentious issue and is difficult to resolve, given the broad stratigraphic constraints and ambiguous radiometric ages. The simplest hypothesis remains that the regional deformation was of latest Devonian to early Carboniferous timing. Middle to Late Devonian deformation included reactivation of basin-forming steeply dipping faults during basin inversion and ongoing sedimentation.

A revised age, structural model and origin for the North Pennine Orefield in the Alston Block, northern England: intrusion (Whin Sill)-related base metal (Cu–Pb–Zn–F) mineralization

Mineralization and associated fluid migration events in the c . 1500 km 2 North Pennine Orefield (NPO) are known to be associated with tectonic activity, but the age of these tectonic events and origins of the base metal sulfide mineralization remain unresolved. New fieldwork in the Alston Block shows that mineralization post-dates a weakly developed phase of north–south shortening consistent with far-field Variscan basin inversion during the late Carboniferous. New observations of field relationships, coupled with microstructural observations and stress inversion analyses, together with Re–Os sulfide geochronology show that the vein-hosted mineralization (apart from barium minerals) was synchronous with a phase of north–south extension and east–west shortening coeval with emplacement of the Whin Sill ( c . 297–294 Ma). Thus the development of the NPO was related to an early Permian regional phase of transtensional deformation, mantle-sourced hydrothermal mineralization and magmatism in northern Britain. Previously proposed Mississippi Valley Type models, or alternatives relating mineralization to the influx of Mesozoic brines, can no longer be applied to the development of the NPO in the Alston Block. Our findings also mean that existing models for equivalent base metal sulfide fields worldwide (e.g. Zn–Pb districts of Silesia, Poland and Tennessee, USA) may need to be reassessed.

Structural Control of High-Grade Gold Shoots at the Reward Mine, Hill End, New South Wales, Australia

Abstract The Reward mine at Hill End hosts structurally controlled orogenic gold mineralization in moderately S plunging, high-grade gold shoots located at the intersection between a late, steeply W dipping reverse fault zone and E-dipping, bedding-parallel, laminated quartz veins (the Paxton’s vein system). The mineralized bedding-parallel veins are contained within the middle Silurian to Middle Devonian age, turbidite-dominated Hill End trough forming part of the Lachlan orogen in New South Wales. The Hill End trough was deformed in the Middle Devonian (Tabberabberan orogeny), forming tight, N-S–trending, macroscopic D2 folds (Hill End anticline) with S2 slaty cleavage and associated bedding-parallel veins. Structural analysis indicates that the D2 flexural-slip folding mechanism formed bedding-parallel movement zones that contained flexural-slip duplexes, bedding-parallel veins, and saddle reefs in the fold hinges. Bedding-parallel veins are concentrated in weak, narrow shale beds between competent sandstones with dip angles up to 70° indicating that the flexural slip along bedding occurred on unfavorably oriented planes until fold lockup. Gold was precipitated during folding, with fluid-flow concentrated along bedding, as fold limbs rotated, and hosted by bedding-parallel veins and associated structures. However, the gold is sporadically developed, often with subeconomic grades, and is associated with quartz, muscovite, chlorite, carbonates, pyrrhotite, and pyrite. East-west shortening of the Hill End trough resumed during the Late Devonian to early Carboniferous (Kanimblan orogeny), producing a series of steeply W dipping reverse faults that crosscut the eastern limb of the Hill End anticline. Where W-dipping reverse faults intersected major E-dipping bedding-parallel veins, gold (now associated with galena and sphalerite) was precipitated in a network of brittle fractures contained within the veins, forming moderately S plunging, high-grade gold shoots. Only where major bedding-parallel veins were intersected, displaced, and fractured by late W-dipping reverse faults is there a potential for localization of high-grade gold shoots (>10 g/t). A revised structural history for the Hill End area not only explains the location of gold shoots in the Reward mine but allows previous geochemical, dating, and isotope studies to be better understood, with the discordant W-dipping reverse faults likely acting as feeder structures introducing gold-bearing fluids sourced within deeply buried Ordovician volcanic units below the Hill End trough. A comparison is made between gold mineralization, structural style, and timing at Hill End in the eastern Lachlan orogen with the gold deposits of Victoria, in the western Lachlan orogen. Structural styles are similar where gold mineralization is formed during folding and reverse faulting during periods of regional east-west shortening. However, at Hill End, flexural-slip folding-related weakly mineralized bedding-parallel veins are reactivated to a lesser degree once folds lock up (cf. the Bendigo zone deposits in Victoria) due to the earlier effects of fold-related flattening and boudinage. The second stage of gold mineralization was formed by an array of crosscutting, steeply W dipping reverse faults fracturing preexisting bedding-parallel veins that developed high-grade gold shoots. Deformation and gold mineralization in the western Lachlan orogen started in the Late Ordovician to middle Silurian Benambran orogeny and continued with more deposits forming in the Bindian (Early Devonian) and Tabberabberan (late Early-Middle Devonian) orogenies. This differs from the Hill End trough in the eastern Lachlan orogen, where deformation and mineralization started in the Tabberabberan orogeny and culminated with the formation of high-grade gold shoots at Hill End during renewed compression in the early Carboniferous Kanimblan orogeny.

Late Carboniferous dextral transpressional reactivation of the crustal-scale Walls Boundary Fault, Shetland: the role of pre-existing structures and lithological heterogeneities

The Walls Boundary Fault in Shetland, Scotland, formed during the Ordovician–Devonian Caledonian orogeny and underwent dextral reactivation in the Late Carboniferous. In a well-exposed section at Ollaberry, westerly verging, gently plunging regional folds in the Neoproterozoic Queyfirth Group on the western side of the Walls Boundary Fault are overprinted by faults and steeply plunging Z-shaped brittle–ductile folds that indicate contemporaneous right-lateral and top-to-the-west reverse displacement. East of the Walls Boundary Fault, the Early Silurian Graven granodiorite complex exhibits fault-parallel fractures with Riedel, P and conjugate shears indicating north–south-striking dextral deformation and an additional contemporaneous component of east–west shortening. In the Queyfirth Group, the structures are arranged in geometrically and kinematically distinct fault-bounded domains that are interpreted to result from two superimposed tectonic events, the youngest of which displays evidence for bulk dextral transpressional strain partitioning into end-member wrench and contractional strain domains. During dextral transpressional deformation, strain was focused into pelite horizons and favourably aligned pre-existing structures, leaving relicts of older deformation in more competent lithologies. This study highlights the importance of pre-existing structures and lithological heterogeneity during reactivation and suggests the development of a regional transpressional tectonic environment during the Late Carboniferous on the Shetland Platform.

Neoarchean structural evolution of the Murchison Domain (Yilgarn Craton)

The progressive strengthening of the continental lithosphere triggered a secular transition in tectonic style during Neoarchean times, allowing the progressive establishment of Plate Tectonics on our planet. Structural investigations in Neoarchean cratons offer therefore a critical tool to constrain how such transition took place. The highly-mineralized Yilgarn Craton of Western Australia exposes one of the largest and best preserved portions of Archean continental crust worldwide. The Yilgarn crust was intensely deformed during the c. 2730–2650 Ma Neoarchean Yilgarn Orogeny, which was accompanied by widespread granitic magmatism, and was mostly unaffected by post-Archean pervasive tectonic events, representing therefore an ideal area for the study of Neoarchean tectono-magmatic events. Here, I combine new structural data with a re-examination of the recent regional structural literature, to offer an updated view of the structural evolution of the Murchison Domain, one of the best-exposed and mineralized portions of the Yilgarn Craton. The result is a new fourfold scheme for the structural evolution of the domain, supported by a detailed and structurally-controlled geochronological dataset. The preserved tectono-magmatic evolution of the domain started with a pre-orogenic period of dominant polydiapirism, during times of prevailing tectonic quiescence. This was followed by a sequence of orogenic deformation events that produced north-striking large-scale shear zones, along which syntectonic plutons, up to 100 km in size, were emplaced during three major tectonic pulses characterized by bulk east–west shortening, between 2730 and 2660 Ma. The deformation events identified here at the scale of the Murchison Domain are likely the local expression of Yilgarn-wide tectono-magmatic events, highlighting the importance of syntectonic granitic magmatism in shaping Neoarchean orogens.

Structural evolution and medium-temperature thermochronology of central Madagascar: implications for Gondwana amalgamation

Madagascar occupied an important place in the amalgamation of Gondwana and preserves a record of several Neoproterozoic events that are linked to orogenesis of the East African Orogen. In this study, we integrate remote sensing, field data and thermochronology to unravel complex deformation in the Ikalamavony and Itremo domains of central Madagascar. The deformation sequence comprises a gneissic foliation (S 1 ), followed by south- to SW-directed, tight to isoclinal, recumbent folding (D 2 ). These are overprinted by north-trending upright folds that formed during an approximately east–west shortening event (D 3 ). Together these produced type 1 and type 2 fold interference patterns throughout the Itremo and Ikalamavony domains. We show that the Itremo and Ikalamavony domains were deformed together in the same orogenic system, which we interpret as the c . 630 Ma collision of Azania with Africa along the Vohibory Suture in southwestern Madagascar. In eastern Madagascar, deformation is syn- to post-550 Ma, and probably formed in response to final closure of the Mozambique Ocean along the Betsimisaraka Suture that amalgamated Madagascar with the Dharwar Craton of India. Apatite U–Pb and novel laser ablation triple quadrupole inductively coupled plasma mass spectrometry (LA-QQQ-ICP-MS) muscovite and biotite Rb–Sr thermochronology indicates that much of central Madagascar cooled through c . 500°C at c . 500 Ma. Supplementary material: A detailed geological map of central Madagascar (Supplementary A), detailed methods and geo- and thermochronology results (Supplementary B), isotopic data for geo- and thermochronology (Supplementary C) and Landsat images and structural interpretation examples (Supplementary D) are available at https://doi.org/10.6084/m9.figshare.c.4840575

The inception of the Maliac Ocean: Regional geological constraints on the western Circum-Rhodope belt (northern Greece)

Abstract Considerable debate surrounds the early-Alpine paleogeographic significance of the Circum-Rhodope belt (CRB, Greece), in particular, whether it was a rifted section of the southern Euroasian foreland, or of the late Mesozoic back-arc system of the Vardar Ocean or of both. In the attempt to clarify the complex nature of the CRB, nine new lithostratigraphic formations (with its members) in consideration of the spatiotemporal and regional geological context are constrained by tracing the changes in regional plate interactions and linked magmato-sedimentary record. The analysis of the stratigraphic data in combination with the highly complex, yet poorly constrained regional geology is employed to reconstruct the late Permian, Triassic, and latest Jurassic developments of this part of the southern European foreland. A continuum between the rifting and Triassic opening of the Maliac Ocean, the Carnian Eo-Cimmerian docking, is supported by the consolidated new data embedded into a collection of the nine distinct lithostratigraphic formations. The terminal Vardar plate approach during the latest Jurassic - earliest Cretaceous and the convergence with the investigated portion positioned to the south of the Balkan-Hellenic foreland thrust belt configured this regional Neotethyan flysch trough, whereas the Paleocene - Eocene east-west shortening and nappe stacking ejected the incoherent early Alpine system referred to as the CRB. The ejected Permo-Triassic, including the early Jurassic ophiolite-bearing formations of the CRB, are matched to be in line with those of the regional Southeast European importance. In fact, the results place the western CRB or eastern Maliac Ocean to lie at the distal southern margin (promontory) of the Eurasian craton aligned with the early- and late Paleozoic crystalline terranes: Paleozoic to Lower Triassic Variscan basement (segment of the Pelagonian Unit), “Veles Series” and Lower Complex of the Serbo-Macedonian Unit (Vertiskos Unit).

Episodic gold mineralisation correlated with discrete structural events at Ballarat East, southeast Australia

New 40Ar/39Ar geochronological data suggest orogenic gold mineralisation at the Ballarat East deposit, southeast Australia, occurred in three main episodes at ca. 445–435Ma, ca. 420–415Ma and ca. 380–370Ma. The gold mineralisation is localised in muscovite-bearing quartz and quartz-carbonate veins hosted in the steep faults (70–90°), on limbs of tight and isoclinal folds in an Ordovician turbidite sequence, and within west-dipping (≤45°) faults, historically known as leather jacket lodes. Initiation of the ≤45° faults that are confined to fold culminations, begins at ca. 445Ma, with peak metamorphic conditions at 440Ma. The earliest vein sets (V1), were emplaced on limb thrusts at ca. 445–435Ma and are characterised by arsenopyrite-dominated quartz veins. These V1 veins parallel arsenopyrite-rich shale units, historically referred to as ‘indicator beds’. Both the steep and ≤45° faults were reactivated during fold amplification with deposition of the V2 auriferous veins at ca. 420–415Ma. A later set of auriferous veins (V3–V4) with ages of 380–370Ma, dominated by pyrite-sphalerite-galena-white-mica quartz-(V3) or carbonate-rich (V4) veins are predominantly associated with reactivation of the ≤45° west-dipping faults. This new geochronological data constrains the local kinematic history of the Ballarat East deposit and has regional implications. The V1–V2 vein development appears to be synchronous across the entire western section of the Lachlan Orogen, where previous studies have suggested that initial gold mineralisation was linked to orogenesis at ∼440Ma, asa result of metamorphic devolatilisation reactions in the lower crust. In contrast, a close spatial and temporal relationship exists between the felsic dykes and the mineralisation recognised in the V3–V4 veins. The deformation that accompanies V3–V4 vein development is attributed to small, localised events during east-west shortening, utilising pre-existing fold and fault structures. The origin of the fluids producing the V3–V4 veins may be metamorphic devolatilisation associated with widespread felsic magmatism that occurred at this time across central Victoria.

New insight of the geological structures and tectonic framework of Ahnet and northwestern part of Tin Zaouatine terranes (western Hoggar, Algeria) constraints from aeromagnetic, gamma ray, and remote sensing data

The Ahnet and Tin Zaouatine terranes are located in the southern sector of the Algerian Desert and are part of the Tuareg Shield, which was built up during east-west shortening (Pan-African orogeny). This paper presents a new 1/200,000 geological and tectonic map of the Tin Tanet Firt sheet map (mainly of the Ahnet terrane and the northwestern part of the Tin Zaouatine terrane). Enhancement and processing of multispectral satellite data (Landsat 7 ETM+) combined with field campaign and airborne geophysics was used to discriminate geological lithologies and tectonic structures. We define six geological domains: (i) Palaeozoic formation and Cambrian continental facies and plutonic rocks, (ii) Late- to post-orogenic plutonic rocks, (iii) synchronous orogenic plutonic rocks, (iv) Neoproterozoic formation, (v) Mesoproterozoic volcanics, metasedimentary rocks, and associated plutonic rocks, and (vi) Late Paleoproterozoic metasedimentary rocks. Airborne magnetic data and textural features derived from remote sensing and fieldwork allow us to identify faults and shear zones that affect the whole studied terrane. Interpreted tectonic lines and foliation paths leads us to suggest a deformation model which involves two deformation pahses: an older N-S to NNE-SSW shortening D1 and a younger D2 defined by the N-S trend and a compressional character revealed in the Ahnet terrane and Camp Zohra Complex domain which is considered a continuum deformation split into three phases that affect and form structures of the whole Ahnet and the northwestern part of Tin Zaouatine terranes at the Pan-African orogeny. The most recent stress field recorded in this region is expressed as NE-SW strike-slip faults.

The ca. 1740–1710 Ma Leichhardt Event: Inversion of a continental rift and revision of the tectonic evolution of the North Australian Craton

Interpretation and modelling of high resolution regional geophysical data of the central Leichhardt River Fault Trough in the Mount Isa Inlier are used to determine the timing of a major basin inversion event following the development of the ca.1780–1740Ma Leichhardt Superbasin. Inversion of the Leichhardt Superbasin formed the regional north-south trending Leichhardt Anticline during east-west shortening. The limbs of the anticline are overprinted by several east-west trending wedge-shaped, non-magnetic sub-basins filled with ca.1710Ma Calvert and Isa superbasin successions. These relationships suggest inversion of the Leichhardt Superbasin occurred between ca.1740 and 1710Ma. The event is also known to have affected the northern and eastern North Australian Craton. The scale of the inversion suggests it was a significant event that we have defined as the Leichhardt Event. This event requires a major tectonic driver to the east of the North Australian Craton, possibly the accretion of a micro-continental ribbon to the east of the Mount Isa Inlier. The results of this study have implication for paleogeographic reconstruction of the Australian continent during the formation of Nuna because eastern North Australian Craton faced an ocean at ca.1740–1720Ma. The results also challenge the significance and intensity of crustal shortening associated with the ca.1600–1500Ma Isan Orogeny throughout the western Mount Isa Inlier.

Structural inversion of the Tamworth Belt: Insights into the development of orogenic curvature in the southern New England Orogen, Australia

The middle to late Permian Hunter Bowen Event is credited with the development of orogenic curvature in the southern New England Orogen, yet contention surrounds the structural dynamics responsible for the development of this curvature. Debate is largely centred on the roles of orogen parallel strike-slip and orogen normal extension and contraction to explain the development of curvature. To evaluate the dynamic history of the Hunter Bowen Event, we present new kinematic reconstructions of the Tamworth Belt. The Tamworth Belt formed as a Carboniferous forearc basin and was subsequently inverted during the Hunter Bowen Event. Kinematic reconstructions of the Tamworth Belt are based on new maps and cross-sections built from a synthesis of best-available mapping, chronostratigraphic data and new interpretations of depth-converted seismic data. The following conclusions are made from our study: (i) the Hunter Bowen Event was dominantly driven by margin normal contraction (east–west shortening; present-day coordinates), and; (ii) variations in structural style along the strike of the Tamworth Belt can be explained by orthogonal vs. oblique inversion, which reflects the angular relationship between the principal shortening vector and continental-arc margin. Given these conclusions, we suggest that curvature around the controversial Manning Bend was influenced by the presence of primary curvature in the continental margin, and that the Hastings Block was translated along a sinistral strike-slip fault system that formed along this oblique (with respect to the regional east–west extension and convergence direction) part of the margin. Given the available temporal data, the translation of the Hastings Block took place in the Early Permian (Asselian) and therefore preceded the Hunter Bowen Event. Accordingly, we suggest that the Hunter Bowen Event was dominantly associated with enhancing curvature that was either primary in origin, or associated with fault block translation during the Early Permian. This model differs to previously proposed reconstructions where curvature largely formed by orogen parallel strike-slip transportation during the Hunter Bowen Event.

Tectonic evolution of the European Variscan belt constrained by palaeomagnetic, structural and anisotropy of magnetic susceptibility data from the Northern Vosges magmatic arc (eastern France)

Geochronology, structural and anisotropy of magnetic susceptibility data from the northern Vosges batholith, which belongs to the Northern Vosges–Mid-German Crystalline Rise arc, show contrasting emplacement modes of southern granodiorites and northern granites. The ENE–WSW-trending fabrics of granodiorites (346–334 Ma) are parallel to the metamorphic cleavage affecting the host rocks developed during regional compression. The NNW–SSE-trending fabrics of younger granitoids ( c . 330 Ma) reveal an extensional emplacement mode, associated with a normal shear zone separating the two magmatic suites. Palaeomagnetism shows that the switch from a compressive to an extensional regime coincides with a regional counterclockwise rotation. The 330–325 Ma extension is further supported by palaeomagnetic and seismic data indicating southeastward tilt of the whole batholith. Finally the system is rotated clockwise without any structural overprint. Data from the Early Carboniferous northern Vosges magmatic arc and remote Bohemian Massif suggest that this evolution is valid for the whole eastern branch of the European Variscan belt, for which the following model is proposed: (1) Late Devonian–Early Carboniferous east–west shortening of the Variscides above the Rhenohercynian subduction zone; (2) axial NNW–SSE shortening of the assembled Variscan orogen associated with (3) ‘internal’ sinistral rotation of inherited Rhenohercynian transform faults and shortening of intervening blocks; (4) east–west extension and dextral ‘external’ rotation of blocks between dextrally reactivated transforms. Supplementary materials: Analytical procedures for geochronology, magnetism, anisotropy of magnetic susceptibility and palaeomagnetism are available at www.geolsoc.org.uk/SUP18635 .