Evolution Of Thrust Belt Research Articles

The Manantiales Basin, Southern Central Andes (∼32°S), Preserves a Record of Late Eocene–Miocene Episodic Growth of an East‐Vergent Orogenic Wedge

AbstractThe Manantiales basin contains >4 km of nonmarine sedimentary strata that accumulated at 31.75–32.5°S during construction of the High Andes. We report field and analytical data from the underexplored northern portion of this basin. The basin contains upper Eocene–middle Miocene strata that accumulated in back‐bulge or distal foredeep through inner‐wedge‐top depozones of the Andean foreland basin as it migrated through this region. A revised accumulation history for the basin‐filling Río de los Patos and Chinches Formations supports a regional pattern of flexure in front of an east‐vergent orogenic wedge. The former formation consists of eolian and localized fluviolacustrine deposits which accumulated between ca. 38 Ma and ≤34 Ma during thrust belt development in Chile. A subsequent ≤12 Myr hiatus may reflect passage of the flexural forebulge or cessation of subsidence during orogenic quiescence. The overlying Chinches Formation records a transition from the foredeep to wedge‐top depozones. Foredeep deposits of east‐flowing, meandering streams were incised prior to ca. 18 Ma, after which deposits of axial rivers, playas, and perennial lakes ponded in a depression behind orogenic topography to the east. After ca. 15 Ma, alluvial‐fan deposits were syndepositionally deformed adjacent to growing thrust‐belt structures along the western basin margin. Although the basin record supports a westward step in the locus of deformation during Early–Middle Miocene time, it conflicts with models involving west‐vergence of the orogenic wedge. Rather, this pattern can be explained as out‐of‐sequence deformation alternating with wedge forward propagation, consistent with Coulomb wedge models incorporating syntectonic sedimentation.

Whitehorse Trough records Late Triassic–Cretaceous accretionary orogenesis in the Northern Canadian Cordillera via detrital mineral thermochronometry

The Whitehorse Trough formed during early Mesozoic accretion of the Intermontane terranes to northwestern North America. Here we investigate its thermal history using detrital mineral thermochronology, including 171 single-crystal (U–Th)/He zircon (ZHe) ages from 35 samples, 158 single-crystal (U–Th)/He apatite (AHe) ages from 33 samples, and apatite fission track (AFT) ages from 12 samples. ZHe single crystal ages range from 222 to 42 Ma and define Triassic–Early Jurassic, Late Jurassic, and Cretaceous–Paleogene age groups. AFT central ages range from 95 to 30 Ma with a dominant age peak at ∼50 Ma, and AHe single crystal ages range from 228 to 13 Ma with a dominant age peak between 50 and 40 Ma. Forward and inverse models of thermochronological data are compatible with two regional burial/heating stages that variably reset He in zircon. Maximum temperatures of the Whitehorse Trough strata locally exceeded 150 °C during Early Jurassic burial and shortening into a fold and thrust belt. Following Middle to Late Jurassic exhumation-related cooling and development of a prominent unconformity, Whitehorse Trough strata were buried again. Temperatures locally exceeded 150 °C during the Cretaceous, suggesting maximum burial of between ∼4 and 7.5 km. Heating and cooling rates during the Early–Middle Jurassic were ∼10 °C/myr, coinciding with deposition, fold and thrust belt development, and regional crustal thickening during the final stages of Intermontane terrane accretion. Maximum heating rates during the Cretaceous were ∼4–7 °C/myr and likely correspond to regional crustal thickening of the northern Cordillera hinterland and establishment of an outboard, Andean-type continental arc system.

Emplacement and accumulation of magmatic products in contractional structures: How does it occur? Insights from Central Andes of northern Chile

Structural and stratigraphic data demonstrate that the magmatism in northern Chile was accompanied by shortening related to the development of fold and thrust belts. However, how magmatic products were emplaced and accumulated in the contractional structures is an unresolved question. We, therefore, integrated field and seismic data from the regions of the Pampa del Tamarugal, Salar de Punta Negra Basin, and the Hornitos Fold and Thrust Belt to determine the main structures that facilitated the magma accumulation. The syn-kinematic granitic intrusions in the Hornitos Fold and Thrust Belt were preferably emplaced along fold-related thrusts. In this region, magma migrated along thrust ramps and finally accumulated into the core of the anticlines and broken synclines. Subsidiary and vertical tensional fractures controlled the magma accumulation in the hinge zone and at the axis of the folds. The seismic data from the Pampa del Tamarugal and Salar de Punta Negra Basin present evidence of buried volcanoes on inversion anticlines. During the tectonic inversion of the pre-existing Late Paleozoic to Mesozoic half-graben structures in the regions, magma migrated along the master faults and finally accumulated into the core of the inversion anticlines as sills or was expulsed to the surface as volcanoes, as evidenced by the Punta Negra Monogenetic Volcano.

The Role of Isostasy in the Evolution and Architecture of Fold and Thrust Belts

Abstract Warmer conditions prevalent in the hinterland of orogenic systems facilitate local ductile flow underneath the surface load, making Airy-like local isostasy more prevalent in these domains. In contrast, flexural isostasy better describes the regional response to surface loading of more rigid lithospheres. Here, we explore how the interaction between horizontal tectonic mass transfer and vertical isostatic mass transfer, through either elastic flexure or viscous flow, impacts the overall architecture of fold and thrust belts. We compare numerical models of fold and thrust belts under either an Airy-like ductile isostasy boundary condition or a flexural-like regional isostasy boundary condition. Our experiments suggest that when ductile flow is involved in accommodating isostatic adjustment, subsidence is rather local, larger, and results in narrower, less elevated fold-thrust belts with a complex internal architecture consisting of prominent steeply dipping faults. When isostatic subsidence is controlled by lithospheric flexure, the tilting of the basement on 10 s of km scale facilitates the outward propagation of fold-thrust belts. The internal architecture is simpler and involves prominent basement-parallel décollements. The outcome is wider fold and thrust belts with higher topographies. A change in lithospheric elastic thickness does not significantly affect fold-thrust belt structural styles. Our results are compared to natural examples from the Subandean zone.

Carbonate rocks in northern of West Jiwo Hills Bayat: The indication of thrust belt development in southern Central Java

Bayat, Klaten, Central Java, is one of three locations in Java with complete types of rocks exposed at the earth’s surface. All those rocks are scattered over a short distance in Bayat, revealing past processes of rock deformation (folding, fracturing, and faulting) and present-day processes of rock weathering and erosion. In this study, we present how clastic carbonate rock of the Oyo Formation at northern Jiwo Hills could be separated about ±15 km northern from its platforms as an indication of thrust fault growth. This study uses aerial photography for photogrammetry (drones) combined with structural geology and microfossil analyses (to know the exact formation) from the outcrop observation. Recent studies have certified that drones are one reliable observation tool in various aspects with better resolution, especially in structural geology studies. Aerial photogrammetry is very well done to see the exact condition of a wide area combined with high resolution on an outcrop scale. The result shows that the carbonate rocks are from Oyo Formation (N9–N11) with the Middle Neritic bathymetric zone. The structural geology phenomenon kinematically indicates the impact of the transpressional movement called flower structure. Based on subsurface interpretation, the authors hypothesize this area was the product of an imbrication thrust stack uplifted basement as the result of the thrust fault rather than horst or paleo-basement high.

Foreland basin response to middle Cretaceous thrust belt evolution, southwestern Montana, USA

Abstract The middle Cretaceous Blackleaf Formation records the first major transgressionregression of the Western Interior Seaway into the southwestern Montana retroforeland basin. Although Blackleaf sedimentology is well documented, sediment provenance and potential linkages with regional tectonics are not. Recent characterization of hinterland tectonics, fold-thrust belt detrital zircon signatures, and advances in high-n detrital zircon analysis allow for significant provenance refinement. We present new detrital zircon ages (n = 5468) from ten samples from the upper Blackleaf Formation (Intervals C and D) in southwestern Montana. Based on maximum depositional ages, sedimentation spanned from 106 to 92 Ma. Jurassic and Cretaceous grains were primarily derived from the older portion of the Cordilleran magmatic arc in western Idaho. Triassic and older grains were recycled from older central Idaho sedimentary strata inboard of the arc. Three depositional stages are identified based on statistical modeling of detrital age distributions. Stage 1 (106–104 Ma) records sourcing from lower Paleozoic strata in central Idaho. Stage 2 (105–101 Ma) records initial unroofing of upper Paleozoic–Triassic strata via propagation of the fold-thrust belt into eastern Idaho, accommodating shortening of Mississippian and younger rocks above the Lemhi Arch. Stage 3 (102–100 Ma) records continued unroofing in central Idaho down to Cambrian stratigraphic levels and distal mixing of sources in the eastern part of the basin. Exhumation in the fold-thrust belt beginning at ca. 105 Ma is coincident with marginwide fault slip-rate increases. We infer that increased sedimentation rates and lowmagnitude flexural loading from shallow thrusting in eastern Idaho drove clastic wedge progradation across the basin.

Kinematic evolution of the central Andean retroarc thrust belt in northwestern Argentina and implications for coupling between shortening and crustal thickening

Abstract The Andes are the culmination of shortening and crustal thickening that commenced during Late Cretaceous time. First-order questions regarding the tectonic evolution of the central Andes include the magnitude and timing of shortening, and controls on the along-strike variability in observed styles of shortening and deformation. Along-strike differences in the time of surface uplift have spawned two contrasting hypotheses: (1) uplift is related to dynamic and isostatic processes accompanying lithospheric removal and is decoupled in space and time from crustal thickening and shortening, and (2) uplift is directly coupled with shortening and crustal thickening. Although considerable work has been done in Bolivia to address these hypotheses, work in northern Argentina has not yet produced a transorogenic balanced structural cross section from which the total amount and kinematic history of shortening can be evaluated. To help understand the evolution of the thrust belt in northernmost Argentina, we present a regional, retrodeformable cross section at 23°–24°S across the Puna and Eastern Cordillera. New apatite fission-track thermochronological data integrated with other geochronological, sedimentological, and structural data constrain incremental retrodeformation of the cross section between ca. 45 and 6.5 Ma. Regional shortening was facilitated by at least 12 major thrust systems, linked to a regional mid-crustal décollement. Deformation generally propagated eastward through time and involved two major episodes of eastward advance of the orogenic front, separated by periods of internal out-of-sequence shortening and kinematic stagnation of the orogenic front. A new minimum estimate of ∼271 km of total shortening from the Cordillera de Domeyko to the eastern orogenic front explains crustal thickening at northern Puna latitudes. Together with previously published paleoaltimetry data, our new structural and thermochronologic data indicate that regional uplift in the northern Argentine Puna and Eastern Cordillera was synchronous with, and thus directly linked to, crustal shortening and thickening.

Deformation–sedimentation feedback and the development of anomalously thick aggradational turbidite lobes: Outcrop and subsurface examples from the Hikurangi Margin, New Zealand

ABSTRACT Concepts of the interaction between autogenic (e.g., flow process) and allogenic (e.g., tectonics) controls on sedimentation have advanced to a state that allows the controlling forces to be distinguished. Here we examine outcropping and subsurface Neogene deep-marine clastic systems that traversed the Hikurangi subduction margin via thrust-bounded trench-slope basins, providing an opportunity to examine the interplay of structural deformation and deep-marine sedimentation. Sedimentary logging and mapping of Miocene outcrops from the exhumed portion of the subduction wedge record heavily amalgamated, sand-rich lobe complexes, up to 200 m thick, which accumulated behind NE–SW-oriented growth structures. There was no significant deposition from low-density parts of the gravity flows in the basin center, although lateral fringes demonstrate fining and thinning indicative of deposits from low-density flows. Seismic data from the offshore portion of the margin show analogous lobate reflector geometries. These deposits accumulate into complexes up to 5 km wide, 8 km long, and 300 m thick, comparable in scale with the outcropping lobes on this margin. Mapping reveals lobe complexes that are vertically stacked behind thrusts. These results illustrate repeated trapping of the sandier parts of turbidity currents to form aggradational lobe complexes, with the finer-grained suspended load bypassing to areas downstream. However, the repeated development of lobes characterized by partial bypass implies that a feedback mechanism operates to perpetuate a partial confinement condition, via rejuvenation of accommodation. The mechanism proposed is a coupling of sediment loading and deformation rate, such that load-driven subsidence focuses stress on basin-bounding faults and perpetuates generation of accommodation in the basin, hence modulating tectonic forcing. Recognition of such a mechanism has implications for understanding the tectono-stratigraphic evolution of deep-marine fold and thrust belts and the distribution of resources within them.

The 2018 Mw 7.5 Highlands Earthquake in Papua New Guinea: Implications for Structural Style in an Active Fold and Thrust Belt

AbstractThe Papuan Fold and Thrust Belt (PFTB) in Papua New Guinea is actively forming within a complex tectonic setting at the boundary of the obliquely converging Australian and Pacific plates. The tectonic setting and inaccessibility of the PFTB make it one of the least well‐understood fold and thrust belts on Earth. On February 25, 2018, a Mw 7.5 earthquake occurred within the PFTB, triggering an aftershock sequence which included five events ≥Mw 6. In this study, we combine seismological, GPS and remote sensing observations to investigate the spatiotemporal distribution of crustal deformation during these events. All earthquakes ≥Mw 6 were related to reverse offset on northeast‐dipping fault planes and five out of the six, including the mainshock, were associated with midcrustal focal depths (∼15–30 km). During the sequence, the PFTB underwent up to 1.2 m of uplift and ground deformation occurred over 7,500 km2. Combining these observations with our geological knowledge of this convergent margin highlights the primary control of the northern Australian passive margin on PFTB structural style. We propose that the earthquake sequence was related to tectonic inversion on a hidden extensional fault system beneath the PFTB and lateral variations along this fault zone had significant influence on the complex distribution of ground deformation. It follows that this fault system has had an important control on the evolution of variable structural styles within the PFTB. This study highlights the complexity that can characterize the evolution and structural style of fold and thrust belts.

Late Mesozoic–Cenozoic cooling history of the northeastern Tibetan Plateau and its foreland derived from low-temperature thermochronology

AbstractThe growth history and formation mechanisms of the Cenozoic Tibetan Plateau are the subject of an intense debate with important implications for understanding the kinematics and dynamics of large-scale intracontinental deformation. Better constraints on the uplift and deformation history across the northern plateau are necessary to address how the Tibetan Plateau was constructed. To this end, we present updated field observations coupled with low-temperature thermochronology from the Qaidam basin in the south to the Qilian Shan foreland in the north. Our results show that the region experienced a late Mesozoic cooling event that is interpreted as a result of tectonic deformation prior to the India-Asia collision. Our results also reveal the onset of renewed cooling in the Eocene in the Qilian Shan region along the northern margin of the Tibetan Plateau, which we interpret to indicate the timing of initial thrusting and plateau formation along the plateau margin. The interpreted Eocene thrusting in the Qilian Shan predates Cenozoic thrust belts to the south (e.g., the Eastern Kunlun Range), which supports out-of-sequence rather than northward-migrating thrust belt development. The early Cenozoic deformation exploited the south-dipping early Paleozoic Qilian suture zone as indicated by our field mapping and the existing geophysical data. In the Miocene, strike-slip faulting was initiated along segments of the older Paleozoic suture zones in northern Tibet, which led to the development of the Kunlun and Haiyuan left-slip transpressional systems. Late Miocene deformation and uplift of the Hexi corridor and Longshou Shan directly north of the Qilian Shan thrust belt represent the most recent phase of outward plateau growth.

Multiple thermochronometers applied to the quantitative analysis of compressive systems: The southern sub-Andean fold and thrust belt of Bolivia. From source rock to trap

The evolution of fold and thrust belts requires time data restrictions to determine the rates related to the interaction of surface and subsurface processes and to quantify the time relationship between the components of the petroleum system: reservoir, seal, source rock and trap. The sub-Andean fold-and-thrust belt in the Bolivian territory in general, and the regional transect that links the structures of Curuyuqui-Carohuaicho-Tatarenda-Borebigua-Charagua and Mandeyapecua in particular, constitutes a complex multi-variable system in which the definition of time-Temperature (t-T) trajectories has led to new suitable structural and stratigraphic conclusions.The integration of multiple thermochronological-geochronological systems (Apatite Fission Track, Apatite (U-Th-Sm)/He and UPb SHRIMP on zircon) and the existing surface and subsurface geological constraints made it possible to develop a chrono-kinematic characterization of fault-related anticlines, defining their formation chronology, structural growth rate and link between them in the study area. Furthermore, it was also possible to perform a quantitative analysis of the subsidence-burial and exhumation-erosion phenomena that occurred from the deposition of Silurian-Devonian source rocks to the present time, providing relevant determinations to the modeling of the Oil & Gas system.

Petroleum tectonic comparison of fold and thrust belts: the Zagros of Iraq and Iran, the Pyrenees of Spain, the Sevier of Western USA and the Beni Sub-Andean of Bolivia

Abstract The genetic analysis of fold and thrust belts is facilitated by tracking the evolution of their organic endowment (petroleum tectonics). Petroleum tectonic analysis of convergent orogenic systems provides an audit of the processes that control the deformation and kinematics of orogenic belts. The distribution and deformation paths of the organic endowment intervals are key factors in determining the petroleum system evolution of fold and thrust belts. This comparison of orogenic systems illustrates the importance of flexural v. dynamic processes, orogenic wedge taper, mechanical stratigraphy and inherited architecture on the creation, preservation and destruction of petroleum accumulations. The Zagros, Pyrenees, Sevier and Beni Sub-Andean convergent systems share key characteristics of fold and thrust belts, with major differences in scale, degree of incorporation of organic endowment in evolution of the fold and thrust belt and its foreland, and preservation of fold and thrust belt wedge-top deposits. The Zagros is an orogen dominated by flexural processes that is a perfect storm for hydrocarbon generation and preservation. Its multiple stacked sources ensure continuous hydrocarbon generation while stacked detachments foster a low taper and thick wedge-top basins. The Pyrenees is also a flexurally dominated orogen, but the early consumption of its source rocks led to minimal survival of hydrocarbon accumulations during exhumation in a long lasting, high-taper orogenic wedge. The Sevier was initially a flexural orogen that was later dominated by dynamic uplift of the fold and thrust belt and distal foreland subsidence with foreland deformation. The consumption of its pre-orogenic sources during the early low-taper phase indicates a probable robust petroleum system at that time. However, the late high-taper phase exhumed and destroyed much of the early petroleum system. The addition of syntectonic foreland sources to be matured by both local and dynamic subsidence created an additional later set of petroleum systems. Post-orogenic events have left only remnants of world-class petroleum systems. The Beni segment of the Sub-Andean Orogen is a flexural system with probable dynamic overprints. Its most robust petroleum system probably occurred during its early low-taper flexural phase, with dynamic subsidence enhancement. Its late high-taper phase with possible dynamic uplift shuts down and stresses the petroleum systems. Comparison of these orogenic systems illustrates the importance of flexural v. dynamic processes, orogenic wedge taper kinematics, mechanical stratigraphy, distribution of source rocks relative to shortening and inherited architecture on the creation, preservation and destruction of petroleum accumulations in fold and thrust belts.

Surface fluids in the evolving Sevier fold–thrust belt of ID–WY indicated by hydrogen isotopes in dated, authigenic clay minerals

Hydrogen isotopic composition (δD) and 40Ar/39Ar geochronological data of neomineralized clay minerals from fault rocks and cleavage seams in the Sevier belt record primary involvement of surface-sourced fluids during Cretaceous–Paleogene mountain building events. δD values of authigenic clays range from −78.8±1.7‰ to −97.2±3.2‰. Given temperature constraints of mineral formation, we calculate δD values of mineralizing fluids as ∼−63 to −96‰, which fall within the range of δD values of Cretaceous–Paleogene surface waters in the region. The potential infiltration and presence of surface fluids at depths of several kilometers during deformation implies that pore spaces and fractures acted as conduits for surface water. Uplift of thrust sheets generated topography that favored meteoric recharge and flow of fluids into margins of the foreland basin, which were subsequently incorporated into the propagating thrust wedge. This is in contrast to the hypothesis that the release of overpressured metamorphic fluids dominates during fold–thrust belt evolution. As a result of shortening and tectonic uplift, fluid flows through basin sediments toward the foreland basin as meteoric waters recharge sediments at the basin margins. This study shows that stable isotopic compositions of shallow, deformation-related clay minerals are robust and may be used alongside other surface fluid proxies to probe the origin and composition of ancient fluids in orogenic systems.

The 3D Geophysical Investigation of a Middle Cretaceous to Paleocene Regional Décollement in the Cordillera of Northern Canada and Alaska

AbstractA new approach to the 3D inversion and interpretation of gravity data is applied to the crustal architecture of the northern Cordillera of Canada and Alaska. The technique models the distribution and depth extent of rocks with systematic density contrasts, such as sedimentary or intrusive rocks. In the northern Cordillera, the geometry of low‐density zones, primarily associated with middle to Late Cretaceous granitic intrusions, and Neoproterozoic and Cretaceous sedimentary rocks, is defined. Variation in the depth extent of these zones delimits a surface, interpreted herein as a regional décollement syntectonic with, or postdating, middle Cretaceous intrusions, but predating and displaced ~430 km by the Eocene‐aged Tintina fault. The décollement trends N35°E and shallows from a depth of ~15–20 km beneath Selwyn basin to ~11 km beneath the Mackenzie Mountains. Here surface faults echo the décollement geometry, linked to fold and thrust belt development between the middle Cretaceous and Paleocene. The décollement continues southward for an unknown distance into northern British Columbia, but the Liard line represents a structural discontinuity between the fold and thrust belts of the Mackenzie Mountains and northern Rocky Mountains. The décollement's northwestern extent is broadly defined by surface faults in the northern Ogilvie Mountains. However, prior to Tintina fault displacement, the décollement was likely connected to a fold and thrust belt and related décollement in east‐central Alaska. Estimates of post‐middle Cretaceous exhumation suggest regional tectonic modification of the décollement, possibly including the presently active detachment inferred for the weak lower crust.

Metavolcanic rocks and orthogneisses from Porongos and Várzea do Capivarita complexes: A case for identification of tectonic interleaving at different crustal levels from structural and geochemical data in southernmost Brazil

The Dom Feliciano Belt (DFB), part of the Mantiqueira Province in southern Brazil and Uruguay, results from multiple Neoproterozoic collisions leading to the construction of the Gondwana supercontinent. Therefore, complex structural relations are expected, as it is the case for the Porongos Metamorphic Complex (PMC) and Várzea do Capivarita Complex (VCC). Several papers have described structural features from both complexes, and some evolution models were proposed for them. However, very few papers have tried to correlate them, and recent geochronological and provenance studies carried out in both complexes pointed out some inconsistencies in these models. Such studies demonstrate that part of the protoliths of metasedimentary and metaigneous rocks of PMC and VCC, of different metamorphic grades, could have been deposited in the same sedimentary environment. The geological meaning of such data is still poorly explained and requires a better understanding of the original geometrical relations between PMC and VCC. This paper focuses on the metavolcanic rocks from two subareas near the northeastern tip of the Porongos Metamorphic Complex area, and on the previously published data for the VCC. In order to investigate the structural and kinematic history of this part of PMC, detailed structural mapping, petrography, whole-rock and mineral chemistry studies were carried out in selected subareas. Metavolcanic rocks from Subarea 1 and Subarea 2 are metadacites and metarhyolites bearing a geochemical imprint of arc magmatism at ca. 790 Ma. Structural investigation of the area reveals that the main deformation phase D1 is mostly compressive and reached the metamorphic peak at amphibolite facies conditions. D2 and D3 are late deformation phases which develop open folds and axial plane cleavages. The most conspicuous D1 structure is an alternation of non-mylonitic S1 and mylonitic-S1, developed over an originally horizontal foliation, which suggests strain concentration in sub-horizontal shear zones interpreted as related to a fold and thrust belt evolution. The scattering of stretching lineation (L1) measurements along a great circle in stereoplots is interpreted to result from shearing along S1 planes, similar to what is described for the progressive deformation of VCC nearby. The present dataset supports the interpretation that PMC and VCC have shared a single volcano-sedimentary basin which subsequently achieved different crustal levels. A W-directed collisional event at 650 Ma metamorphosed the rocks and generated thrust-folds in both complexes. As indicated by recent studies in the local literature, deformed metavolcanics rocks of ca. 578 Ma magmatic age form concordant sheets in the PMC. Such data suggest a metamorphic-deformational event younger than ca. 578 Ma, which, in our view, is probably related to the reactivation of the contractional structures generated at ca. 650 Ma. This younger event must have folded the eastern part of the PMC generating shallow-level folds, and thrusted the rocks onto the eastern side to place them on top of the PMC western-side rocks. Thus, it is possible that PMC rocks register two thrusting episodes, one during peak metamorphic conditions (ca. 650 Ma) and one under retrograde metamorphic conditions (ca. 578 Ma).

Soft collision and polyphasic tectonic evolution of Wuxia foreland thrust belt: Evidence from geochemistry and geophysics at the northwestern margin of the Junggar Basin

A key unit of the Paleozoic Central Asian Orogenic Belt (CAOB), the northwestern margin of the Junggar Basin is located between the Kazakhstan, Siberian and Tarim plates with widespread late Paleozoic volcanic rocks and molasse deposits. In recent years, there has been intense debate about how the Carboniferous-Permian soft-collision geodynamic setting was developed and how long-distance detachment nappes were formed. In this study, on the basis of seismic reflection data, magnetotelluric profiles, and geochronological and geochemical data, we established the superimposed tectonic framework of the Wuxia thrust belt and Hala’alat Mountain and reconstructed the polyphasic tectonic evolution since the Late Carboniferous period. The petrographic and geochemical data suggest that the basaltic rocks of the Late Carboniferous were derived from a metasomatized depleted mantle source in a subduction-related island arc setting, while the Early Permian magmas derived from subduction-modified lithosphere mantle sources in a post-collision intraplate environment. Analysis of the Rittmann Index, Gottini Index and DI frequency curve suggested that the study area had experienced a key tectonic transition from a Late Carboniferous (i.e. end of Carboniferous) subduction-orogen setting to an Early Permian post-collisional extension setting. The Hala’alat Mountain and Zhayier Mountain exhibited a similar tectonostratigraphic framework and structure in space, such as double-layer nappes, long-distance slab detachment and unilateral transection by the northern Darbut fault. Both of these mountain ranges could be called soft-collision foreland thrust belts. On the basis of described four regional unconformities, the tectonic evolution of the soft-collision Wuxia thrust belt and adjacent regions could be divided into four crucial tectonic stages. As a result, thick autochthonous Lower Permian strata are buried under long-distance Hala’alat nappe and extended to the northern Darbut fault, which showed the huge oil and gas exploration potential in the northwestern margin of the Junggar Basin.

Style and timing of tectonic deformation across the Bou Arada-El Fahs troughs system, Northeast Tunisia: integration in the structural evolution of Atlas fold and thrust belt

The Bou Arada-El Fahs troughs system is a particularly E-W trending collapsed structure with the manifestation of normal-to-strike-slip faults. A combined multi-source and multi-scalar structural and geophysical investigation provides important insights on the geometry and the kinematics evolution of trough systems in the Atlas of Tunisia. New data, as well as a reappraisal of available data show that the studied troughs system is established during three main successive events: the Oligocene-Miocene, the Tortonian, and the Plio-Quaternary events. The goal of this paper is to present the structural evolution of the study area, on a pre-structured substratum. The structural evolution progressed from an extensional event, manifested by the formation of grabens, passing by an episode of reactivation of faults related troughs in strike-slip motion during the Atlas compression accompanied by an en-echelon folding in foot wall and hanging wall. These results acquired and presented in the following order: We will initially present the geological context by integrating and correlating the lithostratigraphic data. We continue by examining the geometry and kinematics of structure-related troughs via the detailed geological mapping, the interpretation of available 2D seismic data, and the interpretation of processed fault slip data. This integrated geological and geophysical study allows a better understanding of the BETS, and makes it possible to propose a new geometrical and kinetic model of the establishment of trough structure in the Tunisian Atlas.

Changes in fluid regime in syn-orogenic sediments during the growth of the south Pyrenean fold and thrust belt

Abstract The eastern sector of the south Pyrenean fold and thrust belt developed during the Alpine compression and affected Upper Cretaceous to lower Oligocene foreland basin deposits. In this study, we determine the changes in fluid regime and fluid composition during the growth of this fold and thrust belt, integrating petrographic and geochemical data obtained from fracture-filling cements. Hydrothermal fluids at temperatures up to 154 °C, migrated from the Axial zone to the foreland basin and mixed with connate fluids in equilibrium with Eocene sea-water during lower and middle Eocene (underfilled foreland basin). As the thrust front progressively emerged, low-temperature meteoric waters migrated downwards the foreland basin and mixed at depth with the hydrothermal fluids from middle Eocene to lower Oligocene (overfilled non-marine foreland basin). The comparison of the fluid flow models from the Southern Pyrenees with other orogens worldwide, seems to indicate that the presence or absence of thick evaporitic units highly control fluid composition during the development of fold and thrust belts. Whereas in thrusts not detached along thick evaporite units, mixed fluids are progressively more depleted in δ18O and have a lower temperature and lower Fe and Sr contents as the thrust front emerges, in thrust detachments through thick evaporite units, the mixed fluids are enriched in δ18O.

Stratigraphic and provenance variations in the early evolution of the Magallanes-Austral foreland basin: Implications for the role of longitudinal versus transverse sediment dispersal during arc-continent collision

Resolving the role of longitudinal versus transverse sediment dispersal in ancient sedimentary basins is paramount for understanding filling history and the timing of source area exhumation. The southern Patagonian Andes provide a unique opportunity for constraining these relationships because Upper Cretaceous shallow- and deep-marine strata that record the longitudinal filling history of the Magallanes-Austral foreland basin are exposed along a 500+ km outcrop belt. New stratigraphic, sedimentologic, and facies analyses of the Cenomanian-aged Lago Viedma Formation indicate a protracted phase of a dominantly shoreface and foreshore depositional setting at the northern end of the basin (Austral basin sector), whereas 200 km to the south, age-equivalent strata of the Punta Barrosa Formation are characterized by southward-flowing deep-water fan systems. New sandstone compositional data from both formations are rich in intermediate volcanic grains and suggest an undissected to transitional volcanic arc source. However, detrital zircon populations from the shallow-marine Lago Viedma Formation are dominated by arc sources (126−75 Ma), whereas deep-water strata of the Punta Barrosa Formation contain much greater abundances of Jurassic (199−161 Ma) and pre-Jurassic (>200 Ma) ages. This indicates that deep-water fan systems were not linked to a shelfal sediment dispersal system by a simple northward point-source model, despite consistent southward-directed paleocurrents in deep-water strata. Time-transgressive provenance variations continue southward (along strike), where lithostratigraphic equivalents in the Ultima Esperanza and Fuegian sectors of the basin contain a mix of arc and pre-Jurassic metamorphic basement sources and a paucity of Jurassic ages. We interpret these along-strike provenance variations to be the result of significant local sediment contributions from transverse sources. The influence of transverse tributaries during the early history of the Magallanes-Austral foreland basin suggests that the diachronous onset of coarse clastic deposition in the basin was likely due to the progressive delivery (and initiation) of more locally derived coarse clastic sediment. We attribute this to southward-progressing thrust-belt development associated with progressive north to south collision (or suturing) of the parautochthonous Patagonian arc with attenuated continental crust of South America.

Palaeomagnetism in fold and thrust belts: use with caution

Abstract The application of palaeomagnetism in fold and thrust belts is a unique way to obtain kinematic information regarding the evolution of these systems. However, since many potential problems can affect the reliability of palaeomagnetic datasets and their interpretations, such data should be used with caution. In this paper, we thoroughly review the sources of error from palaeomagnetism with a particular focus on deciphering vertical-axis rotations and the assumptions behind the method. Recent investigations have demonstrated that the age of the magnetization and syn-folding results from the fold test must also be carefully examined: factors such as internal deformation, deficient isolation of components (i.e. overlapping) or incorrect restoration procedures may produce apparent syn-folding results. In fact, the restoration procedure used to return the palaeomagnetic signal to the palaeogeographic coordinate system may itself inhibit accurate estimations of vertical-axis rotations when complex deformation histories induce different, non-coaxial, deformation axes. We recommend the auxiliary use of the inclination v. dip diagram as an efficient tool for identifying many errors. Finally, to determine accurate vertical axis rotations, the reference direction should honour standard reliability criteria and would ideally be measured within the undeformed foreland of the thrust system. In this paper, we review five decades of palaeomagnetic research in fold and thrust belts by concentrating on maximizing standard reliability criteria procedures to reduce uncertainty and increase confidence when applying palaeomagnetic data to unravel the tectonic evolution of fold and thrust belts.