Low-temperature Thermochronology Research Articles

Cenozoic faulting leading to petroleum escape in SW Ordos Basin, China: evidence from fault-related calcite in situ U-Pb dating, rare earth elements and fluid inclusions

Finding an effective way to link the fault movement to petroleum escape is key to understand the potential of petroleum exploration in the basin. The Ordos Basin is an important petroliferous basin in China, which encompasses a world-class uncompartmentalized Jingbian natural gas field in the Ordovician marine carbonate reservoir. However, it is not clear whether the unique exhumation history and the Cenozoic faulting are responsible for the formation of the large-scale oil-gas fields within Ordovician carbonate strata in the SW basin. The combination of fault-related calcite U-Pb dating and fluid inclusions analysis offers a unique opportunity for tracking petroleum leakage along the brittle fault zone within the carbonate strata. The calcite samples were collected in the SW Ordos Basin from the carbonate fault zone and cross the Ordovician carbonate, which show clear positive Eu, slight positive Y anomalies, non-positive La and Gd anomalies, lack of negative Ce. The ratios of Y/Ho range from 29 to 36 and the average value is 32. These calcites originated in a hydrothermal environment during fault activation and yielded U-Pb ages of 32.8±3.3 Ma and 23.7±7.4 Ma. The Raman spectroscopy reveals existence of CH4 gas within the fluid inclusions coeval with the fault-related calcite. The homogenization temperatures (Th) of aqueous inclusions coeval with CH4 inclusion from two calcite veins range from 140.0-172.4°C (average Th= 157.8°C, n=16) and 127.7-154.3°C (average Th= 142.2°C, n=18). Low temperature thermochronology suggest for a rapid uplift since 40 Ma that could be associated with the activity along these faults. The Cenozoic erosion rate was 0.06 mm/y during the ∼9 Myr period from 32.8 to 23.7 Ma in the SW Ordos Basin. These Cenozoic faulting might provide a permeable leakage pathway for petroleum release into the atmosphere. This work provided an explanation for the temporal association between Cenozoic uplift and faulting, potentially leading to petroleum losses in SW Ordos Basin.

Meso—Cenozoic Exhumation of the Altai-Sayan Region: Constrained by Available Low-Temperature Thermochronology

Meso—Cenozoic Exhumation of the Altai-Sayan Region: Constrained by Available Low-Temperature Thermochronology

Constraints of geomorphic indices on the expansion mode of the southeastern margin of the Tibetan plateau

The growth and expansion of the southeastern Tibetan Plateau remain contentious. Positioned as one of the regions characterized by the most robust tectonic activities on the plateau, the southeastern edge provides a distinctive setting for investigating plateau uplift and landform evolution. This study focuses on the southeastern margin of the plateau in the Three Rivers Region, conducting comprehensive analyses of slope, relief, hypsometric integral (HI), and channel steepness index (ksn). We use this new dataset to highlight the more significant role of tectonic activities in shaping the landform compared to climate and lithology. By examining the spatiotemporal characteristics of long-term and short-term rock exhumation rates, derived from low-temperature thermochronology and cosmogenic nuclide 10Be analysis, we establish a correlation between erosion rates and ksn, slope, and terrain undulation. Integrating this information with geophysical evidence and GPS data, we support the model for the expansion of the southeastern edge—the steady-state terrain crustal flow model. According to this model, there is an equilibrium achieved between rock uplift and surface erosion on the southeastern edge of the Tibetan Plateau. Despite ongoing southeastward extrusion of plateau material, the overall plateau morphology remains unaltered due to intense erosion along the plateau’s edge. Consequently, the large-scale topographic expansion of the southeastern Tibetan Plateau has effectively halted.

Anti-phase variation of long eccentricity and precipitation in inland Asia during the Middle Miocene Climatic Optimum

The mechanisms and pace of orbital forcing on precipitation in inland Asia during the Cenozoic remain poorly understood. Many previous studies using magnetic proxies for precipitation have shown a consistent signal of long eccentricity (405 kyr) in hydrological records of central China that are younger than ca. 11 Ma. Most studies suggest that variations in rainfall amount were controlled by Northern Hemisphere summer insolation, and the peak of precipitation is associated with eccentricity maxima. Here, we report multiple magnetic records dating back to the Middle Miocene Climatic Optimum (MMCO, ∼14−17 m.y. ago), including a detailed record from a new section in the Qaidam Basin, which was dated using magnetostratigraphy, U-Pb geochronology, and apatite low-temperature thermochronology. Our records show the exact opposite: 405 kyr wet-dry cycles dominated, but the wetter intervals correspond to eccentricity minima and ice-volume maxima during the MMCO. Taken at face value, these results question the origin—monsoonal or westerly-derived—of the precipitation that reached central China during the middle Miocene and the mechanisms that enhanced monsoonal penetration of inland Asia. We also suggest that this anti-phase relationship could also reflect biases in magnetic proxies for precipitation during the wettest climatic phases, which can result in the dissolution of magnetic minerals and a significant underestimation of past rainfall.

Low-Temperature Thermochronology Records the Convergence between the Anatolide–Tauride Block and the Arabian Platform along the Southeast Anatolian Orogenic Belt

SE Anatolia is witnessing the final stage of the Wilson Cycle, where a continental collision between the Tauride–Anatolide block and Arabian platform occurred, and a 1.5 km Eastern Tauride mountain chain formed. We present new low-temperature thermochronology (LTT) ages, including eight apatite fission track (AFT) and seven apatite and zircon U-Th-Sm/He (AHe, ZHe) ages, for the metamorphic rocks from the Nappe Zone of the Southeast Anatolian Orogenic Belt. The ZHe ages vary from 51.2 ± 0.7 Ma to 30.4 ± 0.6 Ma, the AFT ages range from 33.1 ± 1.6 Ma to 18.1 ± 0.9 Ma, and the AHe ages range from 23.6 ± 2.5 Ma to 6 ± 1.9 Ma. The LTT data show a continuous slow uplift of the region. However, the thermal modeling results suggest an Eocene and middle–late Miocene fast uplift of the region. Similar to our results, the LTT studies along the SAOB show that the vertical movements initiated during the Eocene period have continued in a steady-state regime to recent times. The Eocene epoch is identified by arc–back-arc setting in the region, whereas the Miocene epoch is marked by the continental collision. Within this tectonic framework, vertical movements on the overriding plate are controlled by both extensional and compressional tectonics. The LTT data obtained along the SAOB show fingerprints of thrust propagation from north to south.

Deep-seated crustal faults and their role in the thermo-tectonic evolution of an active mountain belt: New evidence from the Northern Andes

Deep-seated structures can exhume deep crustal rocks (>20 km), transmitting the signal of geodynamic processes from the subduction zone to the interiors of the continents. The role of deep-seated structures can be analyzed with low-temperature thermochronological dating techniques. However, studies coupling low-temperature thermochronology with structural geological analyses of the deformational style are not common in the Northern Andes. In this contribution, we present new apatite (AFT) and zircon (ZFT) fission-track data coupled with meso- and microstructural analyses to reveal the deformational and exhumation history of the Santander Massif (SM; Northern Andes) and the related cortical Bucaramanga strike-slip fault (BF). Samples for thermochronological analyses were collected along an elevation profile with a significant elevation difference of 2.4 km across the western flank of the SM, crossing the BF. The time-temperature history modeling of ZFT data reveals phases of prolonged residence in the zircon partial annealing zone from ∼125 to 94 Ma and a cooling phase related to an exhumation episode at around 25 Ma based on samples collected near the BF. Inverse modeling of AFT data reveals structurally-controlled Pliocene exhumation rates of 0.6–0.7 km/Myr mediated by the action of secondary faults. A shift in the deformation style resulting from the oblique interaction of the SM and Mérida Andes domain is interpreted as the main driver of the Pliocene exhumation. This deformation phase is observed in the fault damage zone, where evidence of brittle-ductile deformation was exhumed. Finally, we discuss the geodynamic implications of our thermochronological and structural analyses, contrasting local and more regional competing hypotheses (Pamplona Indenter vs. slab break-off of the Caribbean plate), which may explain the tectonic evolution of the northern part of the Eastern Cordillera and the SM in the Colombian Northern Andes.

Uplift and denudation history of the Ellsworth Mountains: insights from low-temperature thermochronology

Abstract. While thermochronological studies have constrained the landscape evolution of several of the crustal blocks of West and East Antarctica, the tectono-thermal evolution of the Ellsworth Mountains remains relatively poorly constrained. These mountains are among the crustal blocks that comprise West Antarctica and exhibit an exceptionally well-preserved Palaeozoic sedimentary sequence. Despite the seminal contribution of Fitzgerald and Stump (1991), who suggested an Early Cretaceous uplift event for the Ellsworth Mountains, further thermochronological studies are required to improve the current understanding of the landscape evolution of this mountain chain. We present new zircon (U–Th) / He (ZHe) ages, which provide insights into the landscape evolution of the Ellsworth Mountains. The ZHe ages collected from near the base and the top of the sequence suggest that these rocks underwent burial reheating after deposition. A cooling event is recorded during the Jurassic–Early Cretaceous, which we interpret as representing exhumation in response to rock uplift of the Ellsworth Mountains. Moreover, our results show that while ZHe ages at the base of the sequence are fully reset, towards the top ZHe ages are partially reset. Uplift and exhumation of the Ellsworth Mountains during the Jurassic–Early Cretaceous was contemporaneous with the rotation and translation of this crustal block with respect to East Antarctica and possibly the Antarctic Peninsula. Furthermore, this period is characterized by widespread extension associated with the disassembly and breakup of Gondwana, with the Ellsworth Mountains playing a key role in the opening of the far southern Atlantic. Based on these results, we suggest that uplift of the Ellsworth Mountains during the disassembly of Gondwana provides additional evidence for major rearrangement of the crustal blocks between the South American, African, Australian and Antarctic plates. Finally, uplift of the Ellsworth Mountains commenced during the Jurassic, which predates the Early Cretaceous uplift of the Transantarctic Mountains. We suggest that the rift-related exhumation of the Ellsworth Mountains occurred throughout two events: (i) a Jurassic uplift associated with the disassembly of southwestern Gondwana and (ii) an Early Cretaceous uplift related with the separation between Antarctica and Australia, which is also recorded in the Transantarctic Mountains.

Fracture analysis and low-temperature thermochronology of faulted Jurassic igneous rocks in the Southern Colombian Andes: Reservoir and tectonic implications

Fractured basement hydrocarbon reservoirs are widely distributed worldwide in more than 30 basins, where volcanic and plutonic rocks have produced significant quantities of oil and gas. The Upper Magdalena Valley Basin (UMVB) is a mature and productive hydrocarbon basin located in the Colombian Andes. In this basin, plutonic and volcaniclastic Jurassic rocks are thrusted on top of Cretaceous to Cenozoic sedimentary rocks, which constitute the petroleum system. Multi-scale fracture analysis together with petrography, petrophysics, and low-temperature thermochronology were conducted in and outcrop analogue of this basement to assess the structural evolution and investigate the main factors controlling the development of fracture properties in igneous basements. Thermochronological data indicate the occurrence of three exhumation events between the Early Cretaceous and Miocene, suggesting that most of the fracture networks within the Agrado-Betania hanging-wall were likely formed before hydrocarbon migration. Structural analysis has identified a fault damage zone with a width of approximately 746 m. Volcanic breccias and ash tuffs exhibit slightly higher areal fracture intensities (P21 > 30 m/m2) compared to plutonic and clastic rocks (P21 < 20 m/m2). Furthermore, the fracture networks exhibit good connectivity, with connection per branch (CB) values exceeding the 1.5 percolation threshold. Petrophysical calculations of matrix-fracture properties indicate high permeabilities (ranging from 1000mD to 10000000mD) and low porosities (<10%). The structural position and the diagenetic transformation of the volcanic rocks are the primary factors controlling fracture intensity in the igneous rocks within the Agrado-Betania fault. Results from this outcrop analogue also show that polyphasic structural histories and the burial history positively influence the quality of fractured basement reservoirs.

Quartz chemical composition and apatite thermochronology trace leucogranite evolution and thermal history in the Koktokay No. 3 rare metal deposit, Chinese Altai

Koktokay No. 3 pegmatite is a globally renowned rare metal deposit. Recently, rare metal-enriched leucogranite was identified within this deposit. The leucogranite is locally cut by No. 3 pegmatite and scattered as fragments among the pegmatite in some outcrops. In this study, we aimed to investigate the emplacement depth, thermal history, and evolution process of leucogranite based on quartz chemical composition and apatite thermochronology. Li, Al, P, Ge are the higher content elements in leucogranite quartz, and Ti is the lower content element (approximately 38.7, 178, 23.9, 2.7, and 2.0 ppm, respectively). The Al, Ti, and Li contents decreased from the core to the rim of the quartz. The leucogranite quartz compositions have a high Ge/Ti ratio, similar to that of the quartz in the Li-Cs-Ta pegmatites, particularly the Koktokay No. 3 pegmatite. This similarity indicates that the leucogranite was formed by a highly evolved melt. Using laser ablation-inductively coupled plasma-mass spectrometry, the U–Pb age of leucogranite apatite was determined as 189.4 ± 6.8 Ma, which is substantially younger than the previous columbite U–Pb age of No. 3 pegmatite, suggesting that the magmatic-thermal activity of No. 3 pegmatite had interfered with the apatite U–Pb closure system. The apatite low-temperature thermochronology results showed that the thermal history of leucogranite can be divided into two cooling stages: rapid cooling stage (180–155 Ma, 9.6–10.6 ℃/m.y.) and slow cooling stage (from 155 Ma to the present day, 0.8–1.0 ℃/m.y.). According to the thermal history, the exhumation and erosion of the Koktokay No. 3 rare-metal deposit is at least 5–6 km long. Leucogranite formation pressure is approximately 2.5 kbar (1.8–3.7 kbar), and the emplacement depth approximately 9.5 km (7–14 km).

Formation of the Great Bend and Enhanced Quaternary Incision of the Upper Yangtze River: New Insights from Low-Temperature Thermochronology and Tributary Morphology

Abstract The occurrence of a sharp turn along the upper course of the Yangtze River is referred to as the “Great Bend” and represents a large-scale drainage reorganization in response to the surface rise of the Tibetan Plateau. However, the timing and mechanism of the formation of the Great Bend remain disputed. In this paper, we report new (U–Th)/He and apatite fission track thermochronological data from the deep river valley in the Great Bend area of the southeastern margin of the Tibetan Plateau. Compared with the adjacent Jianchuan Basin, two phases of younger rapid cooling for the Great Bend area are identified based on thermal-history modeling, namely, Miocene (ca. 17 to 11–8 Ma) and Quaternary, with the former phase being contemporaneous with the formation of the anticline in the Tiger Leaping Gorge. Progressive increases in the normalized channel steepness (ksn) and the degree of river-valley incision with increasing distance downstream for tributaries of the Yangtze River in the Tiger Leaping Gorge indicate that river rerouting and formation of the Great Bend occurred during the Miocene. Samples located at the bottom of the Tiger Leaping Gorge also reveal a phase of rapid cooling since ca. 1.9 Ma, with an exhumation rate of 1.5 ± 0.2 mm/year. We hypothesize that enhanced Quaternary exhumation in the southeastern margin of the Tibetan Plateau occurred mainly within the narrow region between the Sichuan Basin and the Eastern Himalayan Syntaxis, corresponding to an episode of widespread extensional deformation superimposed above middle- to upper-crustal flexure in this region.

Prolonged exhumation and preservation of the Yuku molybdenum ore field, East Qinling, China: Constraints from medium- to low-temperature thermochronology

Molybdenum (Mo) is an important globally strategic metal and mostly occurs as molybdenite (MoS2) in diverse Mo deposits. The Yuku ore field includes multiple porphyry-skarn Mo deposits and forms a significant world-class Mo cluster in the Qinling molybdenum belt, central China. Previous studies on the ore field were largely related to its genesis, and did not highlight the post-mineralization modifications that are important to formulate prospecting strategies. The exhumation and preservation processes of the ore field through multiple tectonic events also remain poorly understood. Here, we conducted multi-method apatite U-Pb, fission-track and (U-Th)/He and zircon (U-Th)/He medium- to low-temperature thermochronology and related thermal history modelling on granitoids from the ore-hosting Shibaogou and Yuku plutons in the Yuku ore field, and integrated published studies to unravel the post-mineralization exhumation and preservation of Mo deposits. The newly determined apatite U-Pb (158.3–104.9 Ma), zircon (U-Th)/He (158.2–115.0 Ma), apatite fission-track (90.8–63.1 Ma), and apatite (U-Th)/He (67.8–35.3 Ma) ages in this study document multiple cooling pulses during post-magma emplacement. The low-temperature thermochronological ages of 158.2–35.3 Ma also record the post-mineralization cooling and exhumation history. The thermal history modelling indicates an Early Cretaceous (132–125 Ma) rapid cooling pulse, two enhanced (or accelerated) cooling pulses at ca. 125–59 Ma and post-10 Ma, together with a slow cooling or reheating pulse at ca. 59–10 Ma in the Yuku ore field. The Early Cretaceous rapid cooling is related to the coeval collisional tectonics of the East Qinling Orogen. The enhanced cooling at ca. 125–59 Ma is triggered by the post-collisional assembly of the North China and Yangtze Blocks, the subduction of Paleo-Pacific Plate, and the sinistral strike-slip motion of the nearby Tan-Lu Fault Zone. The slow cooling during ca. 59–10 Ma and the post-10 Ma enhanced cooling are correlated with the extensional tectonics derived by the subduction of Pacific Plate and the far-field effects from India-Eurasia collision. The Yuku area underwent lower exhumation in comparison to the nearby Shibaoguo and Huangbeiling areas in the Yuku ore field, which thus is helpful to the preservation of Mo deposits. The un-exhumated areas within 1.0 km at the inner and outer contact zones between the Yuku pluton and its wall rocks are postulated to be favorable sites for Mo prospecting. In addition, the un-exhumated areas surrounding other Late Mesozoic plutons in the Luanchuan region are also suggested to have high potential for Mo exploration.

Interaction of surface processes and crustal flow in the Eastern Himalayan Syntaxis

The syntaxes at the eastern and western ends of the Himalaya located in the Tsangpo and Indus gorge regions provide examples of the interplay between tectonics and erosion. A previous borehole study along the Yarlung River in the Eastern Himalayan Syntaxis (EHS) revealed an ∼1 km thick sedimentary wedge upstream of the Tsangpo gorge with a &gt;2.5 Ma depositional age. However, the mechanism of formation of this sedimentary wedge remains under debate. Here, we combine low-temperature thermochronology data and thermomechanical modelling to discuss how a sedimentary wedge formed at the highly eroded EHS. Our low-temperature thermochronology results show late Miocene fast cooling episodes focused at the Gyaca and Tsangpo gorges, which are interpreted to be related to coeval rifting at the former and rapid erosion and hot-crust upwelling at the latter. Constrained by the geological and geophysical observations, we apply thermomechanical models to illustrate the mechanism of formation of the sedimentary wedge and present high relief of the EHS. The numerical geodynamic model shows that localized erosion triggers middle ‘crust extrusion’ and regional topographic adjustment at the EHS. Supplementary material : Supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.7008098 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

Integrated multi-proxy source-to-sink analysis of Late Barremian (Lower Cretaceous) clastic systems in the Essaouira-Agadir Basin

This study investigates the provenance of the continental and marine Late Barremian clastics of the Bouzergoun Formation, exposed in the Essaouira-Agadir Basin (EAB). Thin section petrography, Scanning Electron Micrography, heavy minerals analysis, and detrital zircon dating were conducted and integrated with a large dataset of published Low-Temperature Thermochronology (LTT) studies to reconstruct the associated source-to-sink system(s). The results constrain the source and size of the system, and composition of deposited clastics, and investigate the mechanism for delivery of coarse clastics into the offshore domain, a key target for hydrocarbon exploration.The homogeneity of rock composition fingerprints throughout the basin indicates a common provenance for both the northern and southern studied transects. Hinterland analysis based on LTT data identifies the Western Meseta and Massif Ancien de Marrakech (MAM) regions as the only possible source candidates exhuming during the Late Barremian, confirmed by detrital zircon geochronology. Heavy mineral populations reveal partly recycled sediment including a probable igneous source. Rock fragment populations comprise limestones, sandstones, and volcanic composition, which correlate with lithologies of the MAM.The integration of all data suggests a best-fit model for the Late Barremian of a source-to-sink system of moderate size (200–300 km long), dominantly sourced from the MAM (western High Atlas). This provided a sand-rich mix of sediment resulting from the erosion of exhuming Triassic continental basins, with associated clays from the weathering of basalts and Triassic/Jurassic mudstones.Late Barremian eustatic sea level fall, together with regional uplift in the hinterland, is interpreted to have resulted in a forced regression that allowed the system to prograde towards the slope margin, offering enhanced potential for sand delivery into the deep offshore domain. Seismic imaging offshore provides tentative interpretation of synchronous high reflectivity deepwater channels located in structural lows controlled by diapiric salt movement.The Mesetian domain was likely undergoing denudation at the same time and shedding clastic-rich sediments to the northern part of the EAB, beyond the studied region. Sediment supply from the MAM may be mixed with the Mesetian sands to the northern part of the EAB and tentatively in the offshore Essaouira.

Extensional exhumation of cratons: insights from the Early Cretaceous Rio Negro–Juruena belt (Amazonian Craton, Colombia)

Abstract. This study presents results from apatite fission track (AFT) thermochronology to investigate the thermal history and exhumation dynamics of the Rio Negro–Juruena basement, situated within the western Guiana Shield of the Amazonian Craton. AFT dating and associated thermal history modeling in South America has largely been restricted to the plate's margins (e.g., Andean active margin, Brazilian passive margin, and others). Our paper reports on low-temperature thermochronological data from the internal part of the western Guiana Shield for the first time. This area is part of a vast cratonic lithosphere that is generally thought to be stable and little influenced by Mesozoic and Cenozoic tectonics. Our data, however, show AFT central ages ranging from 79.1 ± 3.2 to 177.1 ± 14.8 Ma, with mean confined track lengths of ca. 12 µm. Contrary to what might be expected of stable cratonic shields, inverse thermal history modeling indicates a rapid basement cooling event in the early Cretaceous. This cooling is interpreted as a significant exhumation event of the basement that was likely driven by the coeval extensional tectonics associated with back-arc rifts in the Llanos and Putumayo–Oriente–Maranon basins. The extensional tectonics facilitated both basement uplift and subsidence of the adjoining basins, increasing erosional dynamics and consequent exhumation of the basement rocks. The tectonic setting shifted in the late Cretaceous from extensional to contractional, resulting in reduced subsidence of the basins and consequential diminishing cooling rates of the Guiana Shield basement. Throughout the Cenozoic, only gradual, slow subsidence occurred in the study area due to regional flexure linked to the Andean orogeny. Comparative analysis with low-temperature thermochronology data from other west Gondwana cratonic segments highlights that exhumation episodes are highly controlled by tectonic inheritance, lithospheric strength, and proximity to rift zones. This study underscores the complex interplay between tectonic events and the response of cratonic lithosphere over geological timescales and highlights extensional settings as an important geological context for craton exhumation.

Low temperature thermochronology reveals tilting of crystalline bodies, Halilaga porphyry Cu-Au deposit, NW Anatolia: Implications for exploration of porphyry copper deposits and interpretation of low-temperature thermochronology data for regional tectonics

Because most crystalline bodies lack intrinsic paleo-horizontal information, their tilting cannot be measured directly. Their vertical movement, however, may be tracked by low-T thermochronology (LTT) tools. Because tilting is caused by differential vertical movements, it can be understood if the rate of differential movements is determined. In this regard, here we apply a new LTT-based approach to calculate the orientation of a tilted crystalline body, the Halilaga Cu-Au deposit, in NW Anatolia. Orientation is consistent with the one calculated from a drillhole-based 3D model of the deposit. This reveals the significance of tilting calculations for the exploration of porphyry Cu deposits. On the other hand, and more importantly, it emphasizes the importance of tilting calculations for geological applications such as LTT-based exhumation histories of samples taken from vertical profiles, and paleomagnetic studies. AHe data from the Halilaga deposit reveals the earliest response to the Aegean back-arc extension at ∼ 24 Ma in the north of Western Anatolia. Lastly, thermal models, the new complementary datasets for the tectonic evolution of the region, show that the Halilaga deposit was exhumed to the surface by the coupling effects of Aegean extension and westward propagation of the North Anatolian Fault, which occurred not earlier than 2 Ma.

Reconstructing the thermal history of the Morondava Basin, Madagascar, after Gondwanan breakup as resolved through detrital zircon (U–Th)/He and U–Pb geochronology

Formation of the Phanerozoic basins of Madagascar coincided with the initial stages of Permian break-up of Gondwana. The largest of these, the Morondava Basin, records the tectonic history of rifting, drifting, and uplift of the Malagasy terrane over the last 300 Myr. Herein, we have applied detrital zircon U–Pb geochronology and (U–Th)/He low-temperature thermochronology to resolve the thermal history of the basin as Madagascar separated from Africa and subsequently India. Coarse-grained siliciclastic samples were taken along two transects parallel to the Morondava River in the central basin, including from the Permo-Triassic failed rift basin and from post-Jurassic passive margin sequences. Detrital zircon U–Pb age distributions are defined by common Neoarchean and Neoproterozoic populations which suggests input from the basement terranes of the Malagasy Central Highlands (Antananarivo domain). Samples also contain Paleo-to Mesoarchean and Cambrian populations likely associated with metamorphic terranes amalgamated during the Pan-African orogeny. Single crystal zircon (U–Th)/He dates are 503 ± 17 Ma to 40 ± 1 Ma with effective uranium (eU) values ranging from 35 to 1760 ppm, which exhibit a strong negative date-eU relationship that indicates partial resetting of the He systematics in zircon throughout the basin. Inverse and forward thermal history models from the data reveal separate thermal histories for strata on either side of basin-dividing Illovo Fault. Under an elevated geothermal gradient, temperatures did not exceed 180 °C either during post-Gondwanan burial of Jurassic rift strata or during Late Cretaceous burial of Early Cretaceous passive margin strata. Intrusion of Turonian-age dikes and sills related to the Marion hot spot likely promoted subtle yet widespread heating. The time of latest cooling during the Paleogene recorded in the basin is poorly constrained by the detrital zircon thermochronology.

Late Cenozoic Cooling History of the Xigaze Fore-Arc Basin along the Yarlung–Zangbo Suture Zone (Southern Tibet): New Insights from Low-Temperature Thermochronology

Abstract The Tibetan Plateau is currently the widest and highest elevation orogenic plateau on Earth. It formed as a response to the Cenozoic and is still ongoing collision between the Indian and Eurasian plates. The Xigaze fore-arc basin distributed along the Indus–Yarlung suture zone in southern Tibet preserves important information related to the late Cenozoic tectonic and topographic evolution of the plateau. In this study, apatite fission track (AFT) thermochronology was carried out on twelve sandstone samples from the middle segment of the Xigaze basin and additionally on four sedimentary rocks from the neighboring Dazhuka (Kailas) and Liuqu Formations. Inverse thermal history modeling results reveal that the fore-arc basin rocks experienced episodic late Oligocene to Miocene enhanced cooling. Taking into account regional geological data, it is suggested that the late Oligocene-early Miocene (~27–18 Ma) cooling recognized in the northern part of the basin was promoted by fault activity along the Great Counter thrust, while mid-to-late Miocene-accelerated exhumation was facilitated by strong incision of the Yarlung and Buqu rivers, which probably resulted from enhanced East Asian summer monsoon precipitation. Sandstone and conglomerate samples from the Dazhuka and Liuqu Formations yielded comparable Miocene AFT apparent ages to those of the Xigaze basin sediments, indicative of (mid-to-late Miocene) exhumation soon after their early Miocene burial (&amp;gt; ~3–4 km). Additionally, our new and published low-temperature thermochronological data indicate that enhanced basement cooling during the Miocene prevailed in vast areas of central southern Tibet when regional exhumation was triggered by both tectonic and climatic contributing factors. This recent and widespread regional exhumation also led to the formation of the high-relief topography of the external drainage area in southern Tibet, including the Xigaze fore-arc basin.

Assessing the Activity of Eastern Himalayan Extensional Structures: Evidence from Low-Temperature Thermochronology of Granitic Rocks from Yadong

The east–west-trending South Tibetan Detachment System (STDS) and north–south-trending rifts (NSTRs) are the two main types of extensional structures that have developed within the Tibetan Plateau during continent–continent collision since the early Cenozoic. They have played significant roles in the evolution of the plateau, but it is unclear how they are related genetically. In the Yadong area of the eastern Himalaya, the NSTRs cross-cut the STDS. Apatite and zircon fission track ages of a leucogranite pluton in the footwall of the two extensional faults can be used to reconstruct the cooling and exhumation history and thereby constrain the activity of extensional structures. The new AFT ages range from 10.96 ± 0.70 to 5.68 ± 0.37 Ma, and the ZFT age is 13.57 ± 0.61 Ma. Track length distributions are unimodal, albeit negatively skewed, with standard deviations between 1.4 and 2.1 µm and mean track lengths between 11.6 and 13.4 µm. In conjunction with previously published datasets, the thermal history of the region is best explained by three distinct pulses of exhumation in the last 16 Ma. The first pulse (16–12 Ma) records a brittle slip on the STDS. The two subsequent pulses are attributed to the movement on the Yadong normal fault. The normal fault initiated at ~12 Ma and experienced a pulse of accelerated exhumation between 6.2 and 4.7 Ma, probably reflecting the occurrence of two distinct phases of fault activity within the NSTRs, which were primarily instigated by slab tear of the subducting Indian plate.

The Early Cretaceous hydrothermal sedimentation and its influence on sandstone-type uranium mineralization in the Xinniwusu Sag, Bayingobi Basin, NW China

The presence of Early Cretaceous hydrothermal sedimentation was initially observed in the Xinniwusu Sag, Eastern Bayingobi Basin, NW China. To gain deeper insights into the features of hydrothermal sedimentation in this region and its relationship with uranium mineralization, we conducted an analysis encompassing petrography, geochemistry, the electron microprobe, and low-temperature thermochronology of the hydrothermal sedimentary rocks. Petrographic analysis revealed that the predominant hydrothermal sedimentary rocks in the upper member of the Bayingobi Formation within the Xinniwusu Sag encompass dolomitic limestone and sinter, followed by clastic rocks mixing with hydrothermal sedimentation. Major and trace element analyses emphasized the enrichment of elements including Ca, Mg, P, U, REEs, Sr, Y, Mo, Sb, Cd, and Pb in the hydrothermal sedimentary rocks. Notably, a prominent positive correlation was identified between U and P, REEs, Sr, and Y. Electron microprobe analyses illuminated that uranium primarily exists within fluorapatite in the form of adsorption or isomorphism. Isotopic analyses, δ13CV-PDB and δ18OV-PDB, of carbonate cements in clastic rocks and limestone yielded values ranging from −3 to 2.1 ‰ and − 17 to −6.9 ‰, respectively. These findings suggest that the carbon in the hydrothermal fluids predominantly originates from marine strata, with some potential contribution from the mantle. The paleotemperatures based on the O isotope data range from 67 °C to 78 °C, with an average of 71 °C, implying that the hydrothermal sedimentation corresponds to the continental low temperature white smoker type. Furthermore, apatite fission-tracks of grayish-white gritstone within the upper member of the Bayingobi Formation were completely annealed at 116 ± 7 Ma, partially annealed at 112 ± 4 Ma, also indicating that there was a hydrothermal sedimentary environment for a long time. The hydrothermal sedimentation predominantly influenced the uranium preconcentration in the upper member of the Bayingobi Formation. The uranium source in the hydrothermal fluids is likely linked to the Mesoproterozoic Zhaertai Group within the southern basement of the basin. This revelation offers valuable insights into the distribution of uranium deposits and mineralization points in the Bayingobi Basin, primarily concentrated in the southern sector. Consequently, these areas characterized by well-developed faults connecting the basement and the Lower Cretaceous Formation in the south of Bayingobi Basin are favorable areas for uranium mineralization. This study bears immense significance in enhancing our understanding of the uranium metallogenic mechanisms in the Bayingobi Basin and hydrothermal sedimentation mineralization widely distributed in the world.

Geomorphological and geo/thermo-chronological responses of Indian plate’s deformation during neogene- quaternary time along the Eastern Himalayan Syntaxis: Formation of Manabhum anticline

India-Eurasia and India-Burma collision systems encircle Eastern Himalayan Syntaxis (EHS) in the north and the southeast. The main active structure responsible for the uplift of the Quaternary and Neogene rocks in the easternmost part of the EHS is the NW-SE trending Mishmi Thrust (MT). The spectacular antiformal Manabhum Hill developed during the Quaternary as a ramp antiform over a splay of Mishmi Thrust in its foreland region. The current work presents the deformation scenario, uplift rate, and landform development along the Mishmi Thrust from the Neogene to the Recent for the first time. The surface deformation and the rock and sediment deformation histories have been interpreted from the geomorphology, structure and petrology of the rocks and sediments. We use new (U + Th + Sm)/He low-temperature thermochronology (LTT) of zircon and apatite and Optically Stimulated Luminescence (OSL) dates to calculate the uplift rate for the Neogene to early Quaternary and late Quaternary time intervals, respectively. The Neogene uplift rate varies between 0.91 and 2.3 mm/yr, whereas the early Quaternary uplift rate is ∼3.1 mm/yr. The increased uplift rate during the Quaternary period with significant deformation of sediments indicates the non-rigid character of the Indian plate in this sector, which experienced compression and clockwise rotation.