Fold Belt Research Articles

Structures in the active Western Foothills of Southwestern Taiwan: Fault-related folding versus shale tectonics

Taiwan is an active orogen where a west-verging fold-and-thrust belt deforms a Plio-Pleistocene foreland basin sequence. In southwestern Taiwan, the 3–4 km thick Gutingkeng mudstone, Late Miocene to Early Pleistocene in age, has characteristics similar to mobile shales, such as overpressure conditions and sourcing mud volcanoes. Present uplift rates as fast as 2 cm/year are observed mainly on the footwall of steep thrusts, including the Gutingkeng Fault, which features several mud volcanoes. We integrate surface observations near this fault with regional subsurface data to construct an upper crustal cross section and evaluate the roles of the competing models of fault-related folding and shale tectonics in deforming the region. Field observations indicate steep and well-preserved bedding on the hanging wall and footwall and a wide reverse fault zone with penetrative shearing corresponding to the Gutingkeng Fault. No distinct structure explaining footwall uplift is found in the outcrops. At the cross-section scale, surface geology and subsurface data point to a structural style with fairly narrow anticlines with steep limbs growing above a relatively deep detachment. This geometry is not easily explained using classical fault-related fold models. We infer that folding on the Gutingkeng Fault footwall and in the core of a frontal anticline occurs through layer thickening (pure shear) facilitated by weak mudstone rheology. The increase in pore-fluid pressure under burial and tectonic compression within the fold cores can lead the mudstone to mobilize and undergo plastic flow, causing the inflation of the fold cores. Fold growth, possibly aided by shale tectonics, will have progressively increased the dip of the Gutingkeng thrust, eventually leading to thrust inactivity and uplift mainly occurring on the footwall. Our study area offers a unique opportunity to study an active shale-dominated fold-thrust belt exposed on-land and highlights the importance of combining geodetic observations to investigate ongoing deformations in these settings.

Significance of c . 1 Ga granites from the South Delhi Fold Belt, NW India: implications for palaeogeographical reconstructions of Rodinia

In northwestern India, the South Delhi Fold Belt (SDFB) is a NE–SW-trending Proterozoic fold belt. The Phulad Shear Zone (PSZ), characterized by mylonites, marks its western margin, formed around c . 820 Ma in a ductile transpressional regime with a top-to-the-NNW reverse movement. Reports of isolated c . 1 Ga granites within the SDFB correlate in time with the Rodinia supercontinent assembly. These pink, foliated, equigranular granites, named Foliated pink granite, occur in a 6–12 km wide, 200 km long linear belt. Detailed investigations reveal synchronous deformation in both granites and PSZ mylonites. Geochemically, these granites are ferroan, calc-alkalic and dominantly metaluminous. Tectonic discrimination diagrams confirm A-type within-plate granite characteristics, indicating emplacement in an extensional regime. U–Pb zircon dating of the granites yields a magmatic concordia age of 970.7 ± 2.9 Ma, overprinted by a metamorphic age of 826.3 ± 6.9 Ma. This study documents similar magmatic and post-magmatic features across all c . 1 Ga granites. Field, petrological, geochemical and geochronological data suggest that Foliated pink granites originated from lower crustal melting during crustal thinning at c . 970 Ma, followed by thrusting and deformation at 820–810 Ma, coinciding with PSZ formation. Our study concludes that NW India lacks any geological evidence of Rodinia assembly, which is crucial for accurately reconstructing Rodinia's palaeogeography and understanding the role of India within Rodinia.

Timing of syn-orogenic extension in the Western Alps revealed by calcite U-Pb and hematite (U-Th)/He dating

Timing of syn-orogenic extension in the Western Alps revealed by calcite U-Pb and hematite (U-Th)/He dating

The Infiernillo fault, Malargüe fold and thrust belt (Andes of Mendoza), is a Miocene reverse fault: Implications for the tectonic history of the region

The Infiernillo fault, Malargüe fold and thrust belt (Andes of Mendoza), is a Miocene reverse fault: Implications for the tectonic history of the region

Crustal resistivity architecture beneath the Sikkim Himalaya and Foreland Basin, NE India: Constraint from magnetotellurics data

Crustal resistivity architecture beneath the Sikkim Himalaya and Foreland Basin, NE India: Constraint from magnetotellurics data

Evolution of the West African fold belts: review, new geochronological data, new correlations and new geodynamic hypothesis.

Evolution of the West African fold belts: review, new geochronological data, new correlations and new geodynamic hypothesis.

An Alternative Hypothesis for Forming the Eurekan Fold and Thrust Belts of Spitsbergen and North Greenland

An Alternative Hypothesis for Forming the Eurekan Fold and Thrust Belts of Spitsbergen and North Greenland

Geometrical Analysis of the Asos and Dokan Anticlines in Imbricated and High Folded Zones of the Zagros Fold-Thrust Belt, Iraqi Kurdistan Region

The Asos and Dokan anticlines are situated in the Imbricated and High Folded zones, respectively, in the NW segment of Zagros Fold and Thrust Belt within the Kurdistan Region of Iraq. The balanced section across these structures was constructed manually on the graph-paper by employing the kink-band methods and restored to their pre-deformed shape, the constructed balanced cross-section was constrained by integrating intensive surface geological observations and available subsurface seismic sections. The study aims to understanding the geometry of the structures as well as fold and fault architecture at depth. The structures are slightly asymmetrical with steeper forelimb and wide crestal region. The average horizontal shortening values of the Dokan and Asos anticlines are (7.21 %) and (17.05 %) respectively, and the fault-related shortening decrease upsection. The Asos anticline exhibits greater fault-related shortening values compared to the Dokan structure due to higher deformation intensity via thrusting processes. The studied section implies that the structures representing thrust-related anticline and the Dokan anticline show pop-up geometry, while Asos exhibits imbricate fan thrust.

Deep-sea crustaceans (400–3600 m) biodiversity in the northwestern Gulf of Mexico

Between 2016 and 2017, four oceanographic cruises were carried out in the Perdido Fold Belt area, in the northeastern province of the Gulf of Mexico. Benthic fauna was collected by bottom trawling with a benthic sled at 27 sampling sites, ranging from shallow to abyssal depths. The results obtained with the group of crustaceans are presented, selecting only the trawls representative of the bathyal benthic provinces (200–2000 m) and the abyssal plains (2000–6000 m) for analysis. Thus, 31 trawls with depths of 470 to 3600 m were recorded. The group was represented by 35 families, 72 genera, and 95 species. The lowest abundance/biomass recorded at the sampling sites was 2 org·ha−1/17.67 g·ha−1, while the highest was 400 org·ha−1/5042.62 g·ha−1. The highest species richness (16 species) was found at depths of 470 m, and the lowest (1 species) at 950–1000 m. Consequently, the lowest diversity (0.0 bits·ind−1) was recorded at 950–1000 m and the highest (2.943 bits·ind−1) at 470 m. The dominance of the top 5 species on each cruise reaches more than 50% for each, with 3 species remaining in this classification across all 4 cruises. The similarity given by the Bray-Curtis index associates similar depths. The NMDS (Non-metric Multidimensional Scaling) was used for the species ordinations because it is suitable for non-normal data or data that is discontinuous in scale, and shows most of the species close to the origin of the axes, only the most abundant species or those with the greatest weight are separated at the first crossing, in the rest there is no defined pattern. The sea bottom, as it presents physical conditions of great stability, presents a reduced biodiversity where biotic variables, such as competitive exclusion, resource division, and predation, are essential factors that define the structure and functioning of the communities of mega crustaceans in this area.

New Prospect Delineation at Shallower Depth in a Producing Gas Field of Bangladesh Using 3D Seismic and Wireline Log Data

The Chittagong-Comilla-Sylhet regions of the Chittagong-Tripura Fold Belt host most of the gas fields in Bangladesh, primarily within the anticlinal structures. The Tertiary Bhuban and Boka Bil formations are the key hydrocarbon-bearing zones where hydrocarbon has been encountered at depths ranging from 1000 to 4000 m in various producing gas fields. The study aims to analyze the hydrocarbon prospects in the shallower stratigraphic successions, particularly the upper part of the Boka Bil Formation in a commercial gas field in Bangladesh where gas is being extracted from depths of 3000–4000 m. Utilizing 3D seismic and wireline log data, we assessed the shallower prospective zones above the conventional producing depth, extending up to 2000 m, which have not yet been explored for hydrocarbon potential in the field. In the study, a classical interpretation approach, precise horizon mapping, and application of various seismic attribute analysis techniques are used to highlight amplitude anomalies indicative of gas accumulation. Results suggest the existence of a new gas-bearing zone at with an estimated resource potential of approximately 23.75 billion cubic feet (BCF). Correlating the new prospective zone with the similar geologic features (channel bounded strata showing higher reflection) observed in deeper producing zone of the field enhances the confidence of our findings. This study may open new prospecting avenues for exploration in the studied field as well as the adjacent fields. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 13(2), 2024, P 1-16

Petroleum Source Rock Evaluation in the Eastern Fold Belt, Bengal Basin, Bangladesh: An Integrated Study Using Seismic, Well Log, Field Investigation, and Laboratory Analysis Data

This study focuses on the source rock, a critical component of the petroleum system, within the Eastern Fold Belt (EFB) of Bangladesh. It aims to assess the occurrence and quality of source rocks by employing a comprehensive approach that includes fieldwork, laboratory analysis, seismic interpretation, and well data. The research was conducted in the Sylhet and Khagrachari regions, where prior source rock evaluations were inadequate. Organic carbon content evaluation using TOC analysis reveals a substantial presence of source rock in the EFB, which can produce hydrocarbon upon maturation. Depositional environment analysis suggests the source rocks were deposited in geological settings, including the continental shelf, prodeltaic, shallow marine, and deltaic sub-environments. Laboratory studies indicate the total organic carbon (TOC) content varied, ranging from 0.24% to 1.812%, with an average TOC of 0.65% to 0.7% in Sylhet and an average TOC of 0.28% to 0.33% in Khagrachari where the Kopili Shale of Sylhet exhibiting the highest amount of organic content. The samples from the northern part of the Bengal Basin were observed to be richer in organic content than those from the southern regions. Well-log data from Fenchuganj show that the source rocks are located at depths ranging from 3500 to 4200 m, which is correlated by seismic data. This depth suggests that the source rocks have undergone sufficient thermal maturation (in the temperature window of 105 -140℃) to generate hydrocarbons. Seismic sections further demonstrate the regional distribution of source rock, reinforcing the potential for gas-prone hydrocarbon prospects in the EFB. The integrated approach provides valuable insights into the petroleum potential, emphasizing the crucial role of source rocks in the EFB for future hydrocarbon exploration efforts in the Bengal Basin, offering hope for future discoveries. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 13(2), 2024, P 77-104

Provenance, Paleoweathering and Paleotectonics of Cobalt Bearing Metasedimentary Rocks of the Delhi Supergroup, North Delhi Fold Belt, NW India

Provenance, Paleoweathering and Paleotectonics of Cobalt Bearing Metasedimentary Rocks of the Delhi Supergroup, North Delhi Fold Belt, NW India

Regional exhumation of the Laramide Province

Western North America is the archetypical Cordilleran orogenic system that preserves a Mesozoic to Cenozoic record of oceanic Farallon plate subduction-related processes. After prolonged Late Jurassic through mid-Cretaceous normal-angle Farallon plate subduction that produced the western North American batholith belt and retroarc fold-thrust belt, a period of low-angle, flat-slab subduction during Late Cretaceous−Paleogene time caused upper plate deformation to migrate eastward in the form of the Laramide basement-involved uplifts, which partitioned the original regional foreland basin. Major questions persist about the mechanism and timing of flat-slab subduction, the trajectory of the flat-slab, inter-plate coupling mechanism(s), and the upper-plate deformational response to such processes. Critical for testing various flat-slab hypotheses are the timing, rate, and distribution of exhumation experienced by the Laramide uplifts as recorded by low-temperature thermochronology. In this contribution, we address the timing of regional exhumation of the Laramide uplifts by combining apatite fission-track (AFT) and (U-Th-Sm)/He (AHe) data from 29 new samples with 564 previously published AFT, AHe, and zircon (U-Th)/He ages from Laramide structures in Arizona, Utah, Wyoming, Colorado, Montana, and South Dakota, USA. We integrate our results with existing geological constraints and with new regional cross sections to reconstruct the spatial and temporal history of exhumation driven by Laramide deformation from the mid-Cretaceous to Paleogene. Our analysis suggests a two-stage exhumation of the Laramide province, with an early phase of localized exhumation occurring at ca. 100−80 Ma in Wyoming and Montana, followed by a more regional period of exhumation at ca. 70−50 Ma. Generally, the onset of enhanced exhumation occurs earlier in the northern Laramide province (ca. 90 Ma) and later in the southern Laramide province (ca. 80 Ma). Thermal history models of selected samples along regional cross sections through Utah−Arizona−New Mexico and Wyoming−South Dakota show that exhumation occurred contemporaneously with deformation, implying that Laramide basement block exhumation is coupled with regional deformation. These results have implications for testing proposed migration pathway models of Farallon flat-slab and for how upper-plate deformation is expressed in flat-slab subduction zones in general.

Establishing of Soil Loss Tolerance Limit and Sediment Yield in Zagros Fold Thrust Belt: A case study in the Kanarwe river basin, Iraq-Iran

Establishing of Soil Loss Tolerance Limit and Sediment Yield in Zagros Fold Thrust Belt: A case study in the Kanarwe river basin, Iraq-Iran

Wholesale flat subduction of the Indian slab and northward mantle convective flow: Plateau growth and driving force of the India–Asia collision

The tectonic evolution of the Tibetan Plateau has been influenced by continental collision and postcollisional convergence of Indian and Eurasian plates, both of which have undoubtedly imposed their imprints on the lithosphere and upper-mantle structures beneath the collision zone. However, the mode by which the Indian Plate has subducted beneath Tibet, and its driving forces, have been highly uncertain. Here, we present seismic evidence from a full-waveform tomographic model that reveals flat subduction of the Indian Plate beneath nearly the entire plateau at [Formula: see text]300 km depth, implying that the slab may have transitioned to positive/neutral buoyancy and is no longer capable of supporting steep-angle deep subduction. The horizontal distance over which the flat slab slides northward increases from west (where it collides with the Tarim lithospheric keel) to east (where it has resided approximately north of the Songpan-Ganzi Fold Belt beyond the Qiangtang Block). The Asian lithosphere is subducting beneath northeastern Tibet without colliding with the Indian slab. The low-velocity zone, with a thickness of 50 to 110 km, sandwiched between the Tibetan crust and Indian slab, is positively correlated with the high-elevation, low-relief topography of Tibet, suggesting partial melting of the uppermost mantle that has facilitated the growth and flatness of the plateau by adding buoyant material to its base. We propose that deep mantle convective currents, traced to the Réunion plume and imaged as large-scale low-velocity anomalies from the upper mantle under the Indian Plate downward toward the uppermost lower mantle under the Baikal-Mongolia Plateau, are the primary force driving the ongoing India-Asia postcollisional convergence.

Triassic contractional deformation and sedimentary response in the Helanshan fold–thrust belt, Northwest China: evidence from growth strata

ABSTRACT The Helanshan fold – thrust belt is located between the Alxa and Ordos blocks and has been a deformation area of tectonic activity since the Mesozoic. During the Mesozoic tectonic deformation, the Jurassic WNW – ESE-trending contraction transformed the Triassic NNE – SSW shortening. Field mapping and structural analysis reveal that the Middle Triassic Zhifang Formation in the northern wing of the Rujigou overturned anticline is characteristic of a growth strata, which is in response to SSW-NNE contraction. Detrital zircon U – Pb age spectra of the Middle Triassic Zhifang Formation show that the Triassic sedimentary materials originated from the North China Craton to the north, the Alxa block to the north, the Qilian orogenic belt to the south, and the Qinling orogenic belt to the south. The youngest age at the bottom of the growth strata is 282 ± 11 Ma, and the youngest age at the top is 291 ± 12 Ma, indicating that the strata maximum depositional age was later than the Permian, revealing that the youngest detrital zircon of the Middle Triassic Zhifang Formation is derived from the Rujigou overturned anticline, reflecting the characteristics of the reverse sedimentary sequence of detrital zircon and suggesting an interaction between structure and deposition. We propose that with the closure of the Paleo-Tethys Ocean, under the far-field response to the collision between the North China Craton and South China Craton, the Helanshan fold – thrust belt expanded northward and formed a northward protruding tectonic node that controlled the sedimentary process of the Triassic foreland basin.

Arctic Fold-and-Thrust Belts

The modern Arctic has been formed through a series of continent-continent collisions, accretion of terranes and phases of crustal extension. The Neoproterozoic Timanian, Paleozoic Caledonian and Uralian, and late Mesozoic Verkhoyansk-Kolyma, Chukotkan and Brookian orogenies formed several large fold-and-thrust belts (FTBs). The FTBs are exposed across vast areas of continents and continue offshore to form a complex tectonic basement for thick sedimentary basins, playing an important role in the history of accumulation and deformation of younger unmetamorphosed sedimentary successions that are the subject of this volume. Recognition of the importance of FTBs in the Arctic geological history and their role as a controlling factor of development of Arctic sedimentary basins resulted in this chapter, in which we review the current state-of-knowledge about Arctic FTBs and highlight questions that remain to be addressed. The Enclosure D, a Map showing boundaries of the FTB and their internal first-order structural fabric, is a part of the overview.

Relationship between hydrocarbon genration-expulsion and deformation in exhumated Lower Cretaceous kitchen of the Austral-Magallanes basin, Southern Patagonia

The thermal evolution of the hydrocarbon exhumated kitchen of the Rio Mayer Formation (Lower Cretaceous) in the Austral-Magallanes basin, was characterized in two profiles outcropping in the Southern Patagonian Andes. This study presents an integration of fluid inclusions, organic petrology, geochemistry, and apatite fission-track data incorporated into a one-dimensional (1D) basin and petroleum system modeling, to evaluate the timing of hydrocarbon generation and expulsion processes. In Ea. La Federica (internal fold-thrust belt domain), the lower organic-rich interval of Rio Mayer Formation is at present-day conditions in oil window, with development of natural fractures filled with fibrous calcite crystals. In Ea. Cristina, the unit is in dry gas window (basement domain), with natural fractures filled with granular calcite and quartz. The kitchens began the generation and expulsion processes from the west (Lower Cretaceous) to east (Upper Cretaceous - Eocene), i.e., from basement to internal and external fold-thrust belt domains. The advance of the orogenic wedge deactivated and exhumated those kitchens from west to east as well. The western kitchen was deactivated during the Late Cretaceous, while eastern kitchen, during the Eocene. These successive compressional pulses conditioned the eastward migration of the hydrocarbon generation front and would have favored the charge of reservoirs located in the westward (foreland region). The results of this study emphasize the importance to consider the temporal source kitchens activation related to Andean deformation, in order to a better comprehension of basin-scale controls related to source rock evolution and petroleum system development.

A geochemical and isotopic outline on the Alto Moxotó Terrane: a record of the best-preserved Paleoproterozoic crust in the Central Borborema Province, NE Brazil

The Alto Moxotó Terrane is one of the best-preserved Paleoproterozoic crustal segments of the Borborema Province and shows a close correlation with basement domains of the Central African Fold Belt. Here, we review geochemical and isotopic data of Neoarchean and Paleoproterozoic rocks within the terrane and their implications for the crustal evolution of western Gondwana. The lithospheric framework of the terrane consists of three main tectono-magmatic stages: i) Neoarchean (ca. 2.6 Ga) crustal accretion with TTG juvenile injections, consisting of calcic, magnesian, meta- to peraluminous magmas derived from a basaltic oceanic crust that likely experienced high-pressure conditions; ii) Rhyacian-Orosirian (ca. 2.1 – 1.9 Ga) tholeiitic mafic-ultramafic and calc-alkaline series Cordilleran-related granitic and gneissic rocks; and iii) Statherian-Calymmian within-plate magmatism (ca. 1.6 Ga), with granitic rocks that correspond to A-type ferroan magmas, generated via partial melting of a continental source. The presence of older events within the Alto Moxotó Terrane enables correlation with basement domains within the Borborema Province and other Neoproterozoic orogens of Gondwana. These correlations strengthen the role of the province Paleoproterozoic domains in sspaleogeographic reconstructions of the Nuna/Columbia supercontinents.

Structural style of the Guañacos Fold and Thrust Belt (southern Central Andes): A tectonic setting for the Cura Mallín Basin revisited

Structural style of the Guañacos Fold and Thrust Belt (southern Central Andes): A tectonic setting for the Cura Mallín Basin revisited