Low-temperature Thermochronological Data Research Articles

The daughter–parent plot: a tool for analyzing thermochronological data

Abstract. Data plots of daughter against parent concentration (D–P plots) are a potential tool for analyzing low-temperature thermochronology, similar to isochron plots in radioisotopic geochronology. Their purposes are to visualize the main term of the radiometric age equation – the daughter–parent ratio – and to inspect the daughter–parent relationship for anomalies indicating influences of geological processes or analytical bias. The main advantages of the D–P plot over other data analysis tools are (1) its ability to detect systematic offsets in D and P concentrations, (2) its unambiguous representation of radiation-damage-dependent daughter retention, and (3) the possibility to analyze potential age outliers. Despite these benefits, the D–P plot is currently not used for analyzing low-temperature thermochronology data, e.g., from fission-track, (U–Th) / He, or zircon Raman dating. We present a simple, decision-tree-based classification for daughter–parent relationships based on the D–P plot that places a dataset into one of seven classes: linear relationship with zero intercept, cluster, linear relationship with systematic offset, nonlinear relationship, several age populations, scattered data, and inverse relationship. Assigning a class to a dataset enables choosing further data analysis steps and how to report a sample age, e.g., as a pooled, central, or isochron age or a range of ages. This classification scheme aims at facilitating thermochronological data analysis and making decisions more transparent. We demonstrate the proposed procedure by analyzing published datasets from a variety of geological settings and thermochronometers and introduce Incaplot, which is graphical user interface software that we developed to facilitate D–P plotting of thermochronology data.

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.

Constraining the exhumation history of the northwestern margin of Tibet with a comparison to the adjacent Pamir

Regional variations in the evolution of the Tibetan Plateau have important implications for our understanding of crustal deformation processes. There have been few studies of the evolution of the NW margin of the plateau and its transition to the Pamir Mountains to the west. We focus on this region with a multi-technique detrital study of two sedimentary sections in the Tarim Basin. Our provenance data show that an appreciable component of the detrital material in the sedimentary sections was derived from the Songpan-Ganzi–Tianshuihai composite terrane, with some contribution from the Karakoram and/or West Qiangtang. Given the proximity of the West Kunlun terrane to the sedimentary sections under study, and its long history of exhumation, this terrane in all likelihood also contributed to the studied successions. Our thermochronological data record phases of exhumation in the hinterland in the Triassic, Early Cretaceous and Oligo-Miocene. Similar to the Pamir Mountains, the Triassic and Oligo-Miocene periods of exhumation are attributed to the Cimmerian and Himalayan orogenies, respectively. The Early Cretaceous signal may reflect the distal effects of the Lhasa–Qiangtang collision. Coevality with deformation in the Pamir Mountains suggests a coupled geodynamic system, with retro-arc deformation associated with Neotethyan subduction in the west and terrane accretion in the east. Supplementary material: Detailed analytical method, sample information, petrographic, geochronological and low-temperature thermochronological data are available at https://doi.org/10.6084/m9.figshare.c.7040686

Characteristics of geothermal field and tectono-thermal evolution in Baiyun Sag, Pearl River Mouth Basin, China

Baiyun Sag has become the primary focus of deepwater exploration in the Pearl River Mouth Basin. However, its complex and high-variate geothermal characteristics have severely constrained further oil and gas exploration and resource evaluation. In this study, the present-day geothermal field and tectono-thermal evolution histories of Baiyun Sag were systematically studied based on measured rock thermal conductivity and heat generation data, borehole temperatures, low-temperature thermochronometer analyses, and geodynamic methodologies. The thermal conductivity of 251 core samples ranges from 1.131 to 4.478 W/(m·K), with an average of 2.258 W/(m·K), while the heat generation rate of 106 samples ranges from 0.868 to 1.735 μW/m³, averaging 1.499 μW/m³. The thermal conductivity in Baiyun Sag exhibits a gradual decrease from the Wenchang Formation to the Hanjiang Formation, whereas the heat generation rate decreases with depth. The present-day heat flow in Baiyun Sag ranges from 66.6 to 139.1 mW/m2, with an average of 89.7 ± 14.7 mW/m2, showing a gradual increasing trend from northwest to southeast. Formation temperature at depths of 1–5 km increases proportionally with depth. Thermal inversion, as inferred from low-temperature thermochronological data of six basement samples, reveals distinct temperature paths for each tectonic unit in Baiyun Sag. These paths are primarily linked to regional tectonic uplift-subsidence and basement heat flow variation. Geodynamic simulations further indicate two extensional events in Baiyun Sag during the Eocene and Middle Miocene, leading to a rapid increase in basement heat flow. This study systematically elucidates the present-day geothermal field characteristics and tectono-thermal evolution history of Baiyun Sag, bearing significant implications for regional tectonic evolution and future deepwater oil and gas explorations.

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 >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.

Geological insights from the newly discovered granite of Sif Island between Thwaites and Pine Island glaciers

AbstractLarge-scale geological structures have controlled the long-term development of the bed and thus the flow of the West Antarctic Ice Sheet (WAIS). However, complete ice cover has obscured the age and exact positions of faults and geological boundaries beneath Thwaites Glacier and Pine Island Glacier, two major WAIS outlets in the Amundsen Sea sector. Here, we characterize the only rock outcrop between these two glaciers, which was exposed by the retreat of slow-flowing coastal ice in the early 2010s to form the new Sif Island. The island comprises granite, zircon U-Pb dated to ~177–174 Ma and characterized by initial ɛNd, 87Sr/86Sr and ɛHf isotope compositions of -2.3, 0.7061 and -1.3, respectively. These characteristics resemble Thurston Island/Antarctic Peninsula crustal block rocks, strongly suggesting that the Sif Island granite belongs to this province and placing the crustal block's boundary with the Marie Byrd Land province under Thwaites Glacier or its eastern shear margin. Low-temperature thermochronological data reveal that the granite underwent rapid cooling following emplacement, rapidly cooled again at ~100–90 Ma and then remained close to the Earth's surface until present. These data help date vertical displacement across the major tectonic structure beneath Pine Island Glacier to the Late Cretaceous.

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.

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 (> ~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.

Architecture and Evolution of the Southern Chotts‐Jeffara Basin, Tunisia

AbstractSouthern Tunisia is known to be less deformed and simpler than its neighboring Atlassic domain to the north. This area is complex and basin evolution in the Southern Chotts‐Jeffara (SCJ) basin is debated. In this paper we combined surface and subsurface data with low temperature thermochronology (LTT) to reinvestigate the tectono‐sedimentary evolution of the SCJ basin from Permian to Jurassic. We reconstruct the present‐day architecture of the SCJ basin along two regional sections. In these sections, we focused mainly on regional thickness variations and on internal reflections interpreted from seismic data. We observe three structural elements: (a) A Paleozoic culmination, oriented E‐W, capped by Mid‐Upper Triassic deposits; (b) the Tebaga of Medenine (ToM), a culmination also oriented E‐W but located ∼50 km north of the Paleozoic culmination; and (c) A Triassic culmination in the eastern part of the area, oriented NW‐SE. We note the absence of major normal faults along the sections. The LTT data we present are the first published in this area and allow to reconstruct the timing and magnitude of vertical movements. These data prove: (a) exhumation at ∼230 Ma of the Permian and Lower Triassic units associated with the onset of the ToM removing locally about 900 m of pre‐Cretaceous sediments; and (b) the development of the Triassic culmination ∼180 Ma removing 2000 m of pre‐Cretaceous sediments in the Jebel Rehach. This study demonstrates that vertical movements in the SCJ basin are controlled by long‐wavelength processes developed essentially in shortening regimes.

Late Cretaceous exhumation of the Little Belt Mountains and regional development of the Helena salient, west-central Montana, USA

The timing of deformation within and adjacent to the Helena salient of west-central Montana is poorly constrained relative to other segments of the Sevier fold-and-thrust belt. This study presents low-temperature thermochronology data from the Little Belt Mountains, a basement-cored Laramide uplift that is juxtaposed with the leading edge of the salient. We analyzed eight samples of Paleoproterozoic basement for apatite fission-track (AFT) and zircon (U-Th)/He (ZHe) thermochronology. Four samples yielded AFT ages ranging from ca. 80 Ma to 73 Ma and associated long, unimodal confined track lengths, indicating rapid cooling and exhumation of Little Belt Mountains basement during the Late Cretaceous. The other four samples are characterized by younger AFT ages (ca. 55 Ma), which suggest a combination of prolonged residence in the apatite partial annealing zone and postexhumation magmatic reheating. In total, 20 new ZHe dates range from ca. 236 Ma to 28 Ma and show a correlation between date and effective uranium. Forward model results for ZHe data are consistent with upper-crustal residence during the Proterozoic followed by Phanerozoic burial and rapid Late Cretaceous cooling. Cross sections across the Little Belt Mountains display the geometry of the Volcano Valley fault zone, an array of down-to-the-south Proterozoic normal faults that profoundly influenced the development of the Cordilleran thrust belt. Our new constraints from the Little Belt Mountains when integrated with published kinematic constraints from the Helena salient reveal significant out-of-sequence deformation in this portion of the thrust belt between ca. 80 Ma and 55 Ma. A kinematic model is proposed that involves Late Cretaceous (ca. 80 Ma) exploitation of rheologically incompetent units at the base of the Belt Supergroup within the Helena Embayment, facilitating early exhumation in the Little Belt Mountains. Our new data and synthesis are consistent with previous interpretations in which an inherited stratigraphic and structural architecture of Proterozoic ancestry was the predominant control on the development of the Helena salient during Cretaceous−early Eocene time.

Tectono-geomorphological evolution of the Eastern Pyrenees: Insights from thermo-kinematic modeling

Constraining the tectono-geomorphological evolution of the Pyrenees is still a major challenge, especially in the Eastern Pyrenees where late Neogene exhumation history and topographic evolution appear contrasted and have been debated. In this study, we performed thermo-kinematic (Pecube) modeling using a relatively dense spatial compilation of previously-published low-temperature thermochronological data for the Eastern Pyrenees, and quantified the late-Neogene exhumation history based on different topographic evolution models reconstructed from literature constraints. Our modeling outcomes suggest a major decrease in the regional exhumation rate between 37 and 35 Ma, associated to an early-end contractional tectonics for the Eastern Pyrenees. Two main periods of the Têt fault normal activity have been characterized, with the existence of pluri-kilometric (2–3 km) post- Oligocene-Miocene displacement along the western segment of the Têt fault. The different topographic evolution models show relatively similar results for the regional exhumation since ca. 35 Ma and for the most recent (mid to late-Miocene) tectonic event recorded along the Têt fault. Conversely, inversion results obtained for pre-35 Ma regional exhumation rates, and more importantly for the Oligocene-Miocene activity of the Têt fault appear contrasted between the investigated topographic scenarios. Overall, this study confirmed a mid to late Miocene significant extensional tectonic event for the Eastern Pyrenees, which may have had a non-negligible role in late-stage relief evolution for this part of the orogen. However, deciphering the long-term evolution of topographic relief through thermo-kinematic modeling appears still challenging for slowly-exhuming mountain ranges given the limited resolution of low-temperature thermochronological data to topographic changes.

Extent and significance of the Racklan–Forward Orogen in Canada: far-field interior reactivation during Nuna assembly

Abstract Mesoproterozoic orogenesis is well established on the western and southern flanks of Laurentia in the well-known Racklan–Forward and Mazatzal orogens, but its significance within the previously assembled interior of the supercontinent Nuna has not been established. We examine regional isotopic and structural evidence for Mesoproterozoic deformation in the c. 1.7–1.63 Ga Hornby Bay, Elu, Thelon and Athabasca intracontinental basins, and present evidence for Mesoproterozoic reactivation of Paleoproterozoic structures in the Wopmay and Trans-Hudson orogens. The Racklan–Forward Orogeny in the interior of north Laurentia comprises north–south-trending, high-angle, east-vergent folds and thrusts that occur across a region 1660 km wide and over 1000 km long, stretching from the Yukon to near Hudson Bay and from Banks Island to below the Western Canada Sedimentary Basin. The structures progress from ductile amphibolite and greenschist facies in the Racklan type area to sub-greenschist facies and ultimately brittle or brittle-ductile in the far foreland, showing a predominant thick-skinned style typical of many intracontinental orogens. We present compiled low-temperature thermochronological data, including ages of spatially associated uraninite mineralization, to characterize the scope of reactivation of basement structures in the Archean Rae craton in Nuna's interior. We compare the nature of widespread far-field reactivation in the Racklan–Forward Orogen with other orogens of Nuna's assembly to show it is unusual for Nuna's peripheral margin. We suggest that c. 1.6 Ga continent–continent collision of North Australia with NW Laurentia propagated stresses far into the interior as a result of combined favourable pre-existing structural grain and a weak subcontinental lithospheric mantle in the Rae craton due to repeated episodes of refertilization across 500 Ma of accretion and intrusion. Cratons that experience the complex, two-sided collision and protracted upper plate setting during supercontinent assembly noted herein may be particularly susceptible to extensive foreland propagation of peripheral orogens.

U-Pb ages of Gongga Shan granite, western Sichuan and its implication to the tectonic evolutions of eastern Tibet

The eastern margin of the Tibetan Plateau has given rise to much debate about mechanisms of plateau uplift and evolution and, in particular, the role of the lower crust in crustal thickening. Knowledge of the middle to lower crust conditions is critical for evaluating various models of crustal deformation, but data on crustal evolution through time are lacking. Here, we turn to the Gongga Shan granite, an intrusion along the Xianshuihe fault in easternmost Tibet that directly records local Cenozoic crustal conditions. We present 124 U-Pb samples from the Gongga Shan granite (GSG) that prove that the crust has been stepwise producing partial melt from 56 Ma to 4 Ma. According to the age distribution, the GSG can be separated into four major groups with ages of 4–10 Ma, 12–20 Ma, 25–40 Ma, and 43–56 Ma. Combining the timing information with geophysics and low-temperature thermochronology data, we suggest that events younger than 10 Ma may indicate the onset of recent crustal channel flow in the middle to lower crust. In contrast, the youngest 4 Ma ages indicate the ongoing partial melting of the middle crust. The 12–20 Ma events could be related to an earlier stage of crustal channel flow, consistent with the regional large-scale crustal channel flow in central Tibet.

Several Problems in Low-Temperature Thermal History Modeling

Thermal history modeling based on low-temperature thermochronological data is widely used in the study of geology. Despite its common applications, several problems remain easy to ignore yet should not be overlooked in the execution of such models. This paper describes four key problems of thermal history modeling, namely, (1) is the best-fit thermal history the best? (2) Is the date constraint box a suitable constraint? (3) Does the bimodal distribution of the apatite fission track confined track length absolutely correspond to the cooling reheating model? (4) Is the whole thermal history path credible? Counterexamples are then provided to stress the importance of accounting for these problems in the application of thermal history modeling. Acknowledging the uncertainty and considering the geological constraints are recommended to improve the accuracy of thermal history models. Moreover, thermal historical intervals with high credibility and strong constraint ability are recommended to interpret the selected geological phenomenon.

Cenozoic low temperature cooling history of the eastern Lhasa terrane: Implications for high-relief topography of external drainage area in the southern Tibetan Plateau

The Tibetan Plateau geographically contains internal and external drainage areas based on the distributions of river flows and catchments. The internal and external drainage areas display similar high-elevations, while their topographic reliefs are not comparable; the former shows a large low-relief surface, whereas the latter is characterized by relatively high relief. The eastern Lhasa terrane is a key tectonic component of the Tibetan Plateau. It is characterized by high topography and relief, but the thermal history of its basement remains relatively poorly constrained. In this study we report new apatite fission track data from the eastern part of the central Lhasa terrane to constrain the thermo-tectonic evolution of the external drainage area in the southern Tibetan Plateau. Twenty-one new AFT ages and associated thermal history models reveal that the basement underlying the external drainage area in southern Tibet experienced three main phases of rapid cooling in the Cenozoic. The Paleocene-early Eocene (∼60–48 Ma) cooling was likely induced by crustal shortening and associated rock exhumation, due to accelerated northward subduction of the NeoTethys oceanic lithosphere. A subsequent cooling pulse lasted from the late Eocene to early Oligocene (∼40–28 Ma), possibly due to the thickening and consequential erosion of the Lhasa lithosphere resulted from the continuous northward indentation of the India plate into Eurasia. The most recent rapid cooling event occurred in the middle Miocene-early Pliocene (∼16–4 Ma), likely induced by accelerated incision of the Lhasa River and local thrust faulting. Our AFT ages and published low-temperature thermochronological data reveal that the external drainage area experienced younger cooling events compared with the internal drainage area, and that the associated differentiated topographic evolution initiated at ca. 30 Ma. The contributing factors for the formation of the high-relief topography mainly contain active surface uplift, fault activity, and the enhanced incision of the Yarlung River.

A Pleistocene origin of the strandflat coastal platform in southwestern Scandinavia

An impressively extensive shore platform, the strandflat, is cut 20–50 km into hard crystalline bedrock along most of the Norwegian coastline. Its age and origin have been debated for more than a century, including a model that it represents a weathered, buried and re-exposed Triassic surface. Resolving this issue requires integrated examination of the coastal area together with the offshore Mesozoic rift margin. Here I combine new 3D broadband seismic, bathymetric, and onshore elevation data along coastal West Norway and find that the near-horizontal strandflat postdates both the west-sloping onshore “paleic” surface and the offshore Jurassic denudation surface. It also postdates tilted North Sea Neogene sediments. Consistent with low-temperature thermochronologic data, this shows that the strandflat is a Pleistocene geomorphic feature formed through periods of varying climatic conditions, facilitated by preexisting fault and fracture zones. It is not part of an inherited Mesozoic landscape.

Exhumation and preservation of the Tianyu Cu-Ni deposit constrained by low-temperature thermochronology: Insights into the thermo-tectonic history of the Chinese Eastern Tianshan

The Chinese Eastern Tianshan is an important metallogenic region where major Cu-Ni ores are mined. Previous research in the region primarily focused on the ore genesis. Precise thermochronological data to constrain the exhumation history and preservation of the ore deposits are limited at best. Tianyu is one of these Cu-Ni deposits in the area. Here we present new low-temperature thermochronological data to contribute to the understanding of its exhumation and preservation history. Zircon (U-Th)/He ages of ∼ 134–69 Ma, apatite fission track ages of ∼ 100–75 Ma, and apatite (U-Th)/He ages of ∼ 117–38 Ma from five granodiorite samples of the ore wall rock at different depths of a borehole in the Tianyu deposit were obtained. Our thermochronological data and inverse thermal history modeling reveal a moderate to rapid and final basement cooling phase during the Cretaceous (∼115–85 Ma) with an averaged cooling rate of ∼ 3–4 ℃/Ma. It is envisaged that this phase eventually exposed the ore deposits and that posterior erosion was limited, contributing to the preservation of the deposit. Combined with previously published geochronological and thermochronological data, a multi-stage cooling history of the ore bearing host rocks can be established. After its late Permian (∼280–260 Ma) magmatic-hydrothermal formation, two phases of accelerated regional cooling (i.e., in the late Permian-Early Triassic, ∼260–240 Ma; and the mid-Cretaceous, ∼115–85 Ma) can be recognized. The more intense Cretaceous cooling is associated with the ore body finally being exhumed to the surface, and provides essential information for ore exploration in the region. Further, we propose that areas in the Eastern Tianshan with similar thermal histories to the Tianyu Cu-Ni deposit may be potential exploration targets.

Cretaceous−Cenozoic cooling history of the Qiangtang terrane and implications for Central Tibet formation

Reconstructing the growth process of the Qiangtang terrane in space and time is crucial for understanding the geological evolution of Central Tibet. However, its growth process and dynamic mechanism remain unclear. Here, we present new fission track data obtained along a N-S transect near the Puruo Kangri Mountain in the central zone of the Northern Qiangtang terrane. The completely reset apatite fission track ages of detrital samples range from 65.1 to 89.6 Ma, which show a northward younging trend. The thermal history modeling results indicate that this region underwent northward-propagating exhumation during the Late Cretaceous (ca. 92−65 Ma). Our data, combined with previously reported low-temperature thermochronology data for the Qiangtang terrane, suggest that the Qiangtang terrane experienced three main stages of cooling: ca. 120−65, ca. 55−35, and <25−0 Ma. The first stage (ca. 120−65 Ma) displays an outward-propagating cooling pattern from the Central Qiangtang terrane, which was related to the crustal shortening and thickening driven by the Lhasa-Qiangtang collision. The low exhumation rate, flat lavas, and paleoaltimetry studies imply that the central and southern zones of the Northern Qiangtang terrane and Central Qiangtang terrane may form plateau landscape by 65−55 Ma. The second stage (ca. 55−35 Ma) of cooling is mainly documented in the Southern Qiangtang terrane, and the northern zone of the Northern Qiangtang terrane. This cooling event was caused by the crustal deformation and shortening driven by intracontinental subduction related to ongoing convergence of the Indian and Asian plates. Subsequently, both the transition to low erosion rates (<0.05 mm/yr) and paleoaltimetry data indicate that the Qiangtang terrane became a primitive plateau by ca. 35 Ma. The final stage (<25−0 Ma) of cooling was linked to the E-W extension in the Qiangtang terrane.