Apatite Fission Track Data Research Articles

História termotectônica da margem continental brasileira a partir de dados de traços de fissão em apatita

A margem continental brasileira denota estruturas geomorfológicas moldadas durante vários episódios de atividade tectônica iniciados no Neoproterozoico. Com o objetivo de estabelecer um modelo de história termotectônica para a margem continental brasileira, foi realizada a integração e reinterpretação dos dados traços de fissão em apatita (TFA) disponíveis ao longo de toda a margem continental. As idades TFA variam de ~385-10 Ma. Os dados TFA revelam que a margem continental foi caracterizada por pelo menos três eventos térmicos após o Ciclo Brasiliano: Cretaceo Inferior, Cretaceo Superior e Paleógeno-Neógeno. Os eventos são relacionados aos processos de abertura do Oceano Atlântico Sul e às fases rifte e pós-rifte, com reativações tectônicas ao longo da margem. A Província Mantiqueira e o Cráton São Francisco registram os eventos mais antigos, desde o Ordoviciano e o Permiano, respectivamente, que afetaram de modo variado diferentes partes dessas províncias como reflexo das orogenias Famatiniana e Gondwanide.

Constraining quantitatively the timing and process of continent-continent collision using magmatic record: Method and examples

Based on the main driving force of plate motion (the slab pull force generated by the descent of the oceanic plate in subduction zones) and the three primary mechanisms for magma generation (adding fluid, increasing temperature, and decreasing pressure), the continent-continent collisional process has been divided into three stages, including initial collision, ongoing collision, and tectonic transition. These stages are characterized by normal calc-alkaline andesitic magma (dehydration of the oceanic crust to release fluids), the migration of calc-alkaline magma toward the trench (dehydration of the oceanic crust or an increase in temperature) or small-scale crust-derived peraluminous magma (heat from intra-crustal shearing), and extensive magmatism with compositional diversity induced by slab break-off (increasing temperature and decreasing pressure), respectively. On the basis of the obtained age of slab break-off, the timing of the initial continent-continent collision can be quantitatively back-dated using the convergence rate, depth of slab break-off, and subduction angle. The spatio-temporal migration of the magmatic activity of the Gangdese Batholith, the onset of magmatic flare-up, and the increase of magma temperature at 52–51 Ma documented by the volcanic rocks of the Linzizong Pana Formation were most likely the result of the break-off of the Yarlung-Zangbo Neo-Tethyan oceanic lithosphere at approximately 53 Ma. This proposed age of slab break-off suggests that the initial India-Asia collision likely occurred at approximately 55–54 Ma, which is consistent with the collision ages constrained by other abundant geological data (60–55 Ma). This magmatic method has been applied to the Bitlis orogenic belt in southern Turkey in the Arabia-Eurasia continental collision zone, yielding an age range of approximately 29–22 Ma for the initial Arabia-Asia continental collision that is close to the collision ages recently obtained by apatite fission-track dating (approximately 20 Ma) and regional tectonic shortening (approximately 27 Ma). The intense folding of the Upper Cretaceous and the angular unconformity between the overlying Linzizong volcanic rocks in the southern Lhasa Terrane (90−69 Ma) are not related to the initial continental collision between India and Asia, but can be interpreted as the consequences of the strong coupling between the hot and young subducting oceanic crust immediately south of the spreading ridge and the overriding lithosphere or the subduction of the Neo-Tethys oceanic plateaux or seamounts. The tectonic event documented by the angular unconformity between the Linzizong Dianzhong Formation and the Nianbo Formation lasted approximately 3 Ma and likely marks the initial India-Asia collision. The significant deceleration of the Indian continent at approximately 51 Ma can be attributed to the disappearance of the slab pull force in the subduction zone due to the break-off of the Yarlung-Zangbo Neo-Tethyan oceanic lithosphere. The descent of the eclogitized lower crust of the northern Indian continent provides the main driving force for the current northward motion of Indian plate. The weak deformation of the lithospheric plate in the overriding plate of the India-Asia collisional zone between 60 and 40 Ma can be attributed to the high-angle subduction related to the rollback of the Yarlung-Zangbo Neo-Tethyan oceanic lithosphere after the initial India-Asia continental collision, the presence of the thick crust and high elevation on the southern margin of the Lhasa Terrane, and the decoupling between the mid-upper and lower crust and between the lower crust and lithospheric mantle of the Indian continent.

Application of multi‐kinetic apatite fission track and (U‐Th)/He thermochronology to source rock thermal history: a case study from the Mackenzie Plain, NWT, Canada

AbstractShale of the Upper Cretaceous Slater River Formation extends across the Mackenzie Plain of the Canadian Northwest Territories and has potential as a regional source rock because of the high organic content and presence of both oil‐ and gas‐prone kerogen. An understanding of the thermal history experienced by the shale is required to predict any potential petroleum systems. Our study integrates multi‐kinetic apatite fission track (AFT) and apatite (U‐Th)/He (AHe) thermochronometers from a basal bentonite unit to understand the timing and magnitude of Late Cretaceous burial experienced by the Slater River Formation along the Imperial River. We use LA‐ICP‐MS and EPMA methods to assess the chemistry of apatite, and use these values to derive the AFT kinetic parameter rmr0. Our AFT dates and track lengths, respectively, range from 201.5 ± 36.9 Ma to 47.1 ± 12.3 Ma, and 16.8 to 10.2 μm, and single crystal AHe dates are between 57.9 ± 3.5 and 42.0 ± 2.5 Ma with effective uranium concentrations from 17 ppm to 36 ppm. The fission track data show no relationship with the kinetic parameter Dpar and fail the χ2‐test indicating that the data do not comprise a single statistically significant population. However, when plotted against their rmr0 value, the data are separated into two statistically significant kinetic populations with distinct track length distributions. Inverse thermal history modelling of both the multi‐kinetic AFT and AHe datasets, reveal that the Slater River Formation reached maximum burial temperatures of ~65–90 °C between the Turonian and Paleocene, indicating that the source rock matured to the early stages of hydrocarbon generation, at best. Ultimately, our data highlight the importance of kinetic parameter choice for AFT and AHe thermochronology, as slight variations in apatite chemistry may have significant implications on fission track and radiation damage annealing in apatite with protracted thermal histories through the uppermost crust.

Tracking the multi-stage exhumation history of the western Chinese Tianshan by apatite fission track (AFT) dating: Implication for the preservation of epithermal deposits in the ancient orogenic belt

The western Chinese Tianshan, located in the southern domain of the Central Asian Orogenic Belt (CAOB), was originally established by multiple accretion-collision processes in the Paleozoic, and was modified by complicated intracontinental tectonic evolution in the Mesozoic to Cenozoic. Understanding the timing and mechanism of the latter geological processes is critical to unravel the preservation conditions of the epithermal deposits in the western Chinese Tianshan. This work presents new apatite fission track (AFT) data for three mountain ranges (Keguqinshan, Wusunshan and Nalatishan) of the western Chinese Tianshan to track their exhumation history. Our AFT data gave a wide range of ages from 76.8±5.5Ma to 182.3±9.9Ma, and the mean confined fission track lengths are between 9.8±0.5μm and 12.3±0.2μm. The new data, in combination with the thermal history modeling results, allow us to summary three main episodes of exhumation in the western Chinese Tianshan, including the Early Permian (300–280Ma), Late Triassic–Late Jurassic (230–140Ma), and Late Oligocene–Early Miocene (30–20Ma). The first episode may have been caused by terrane accretion-collision in the late Paleozoic, leading to uplift of the Keguqinshan that supplied abundant sediments to form a critical cover of ca. 4km thick on these epithermal deposits. The second episode was likely related to closure of the Mongol-Okhotsk Ocean in the Mesozoic, and an extremely slow exhumation rate (ca. 0.0083mm/y) as well as a moderate erosion of ca. 0.8km thick are estimated. The last episode is regarded to be the result of collision between the Indian Plate and the Eurasia Plate in the Cenozoic, and this significant tectonic event triggered rapid exhumation (up to ca. 0.1mm/y) of the whole region in the western Chinese Tianshan, which removed more than ca. 3.2km pre-Cenozoic sedimentary cover and sent the epithermal deposits to the subsurface level.

The southern Moroccan passive continental margin: An example of differentiated long-term landscape evolution in Gondwana

The ENE-trending Anti-Atlas mountain belt reveals variation in recent topography with elevations of >3km indicating a differentiated long-term landscape evolution. To unravel the subsidence and exhumation history, low-temperature thermochronology has been applied on 21 samples from the Precambrian basement of the Irherm, Kerdous, Ifni, and Bas Drâa inlier. Thermochronological data suggest a common geological evolution of the western Anti-Atlas. Zircon fission-track ages from 287 (±23) to 331 (±24)Ma point to a main exhumation in the Late Carboniferous–Early Permian assigned to the Variscan folding and post-folding erosion. Zircon (U-Th)/He (205–287Ma) and apatite fission-track (120–219Ma) data are related to the Central Atlantic rift and drift stage, as the Anti-Atlas formed the exhumation shoulder of the rift system. The rock uplift and exhumation phase lasted up to the Early Cretaceous, whereby 9km of Precambrian–Palaeozoic overburden has been eroded. Thermal modelling reveals a minor sedimentary burial (1.5–2.5km) throughout the Cretaceous, in accordance with the widespread transgression across the northern Africa in the Cenomanian–Turonian. Apatite (U-Th-Sm)/He ages between 49 (±3) and 164 (±10)Ma confirm recent minor exhumation in the western Anti-Atlas with an increasing impact of the Atlasian orogeny and potentially a mantle plume anomaly from southwest to northeast reflecting the differentiated topography in the area.

“Inverted” zircon and apatite (U–Th)/He dates from the Front Range, Colorado: High-damage zircon as a low-temperature (

Zircon (U–Th)/He (ZHe) data were acquired for 23 Proterozoic basement samples from an E–W transect through the Colorado Front Range to evaluate whether metamict zircons yield sensible (U–Th)/He data patterns and useful thermal history information. The 112 ZHe dates vary from 147 to 7 Ma, define positive and negative date–eU correlations, and are younger than titanite (U–Th)/He dates that range from 976 to 614 Ma. At moderate to high alpha dose of 1018–1019α/g, zircons from the range core yield Laramide (52.5±9.6 Ma) dates, whereas those within ∼15 km of the range front yield Miocene (21.6±7.7 Ma) results. The He dates for the high alpha dose zircons are reproducible within each sample suite despite their visibly metamict character. The ∼20 Ma range front ZHe dates are younger than apatite (U–Th)/He (AHe) dates (66.5±9.6 Ma) and published apatite fission-track data (65–45 Ma) for the same and nearby samples. Thermal history simulations can reproduce the first-order range front date–eU patterns and ZHe–AHe date inversion, but the high-damage zircons are more He retentive than predicted by the zircon damage He kinetic model. The ∼20 Ma ZHe dates may be explained by reheating from hydrothermal fluids along range front faults. The results demonstrate the promise of using He data for high-damage zircons to detect low-temperature (<50 °C) events within and below the temperature sensitivity of the AHe system.

Unravelling basin shoulder dynamics through detrital apatite fission-track signature: the case of the Quaternary Mugello Basin, Italy

AbstractDetrital apatite fission-track (AFT) thermochronology has been applied to lower Pleistocene lacustrine fan-delta sediments of the NE shoulder of the Mugello Basin, the youngest and closest to the main watershed among the Northern Apennines intermontane basins. The aim was to decode the shoulder uplift dynamics during the development of the basin through the analysis of the Quaternary fluvio-lacustrine deposits. Bedrock shoulder analysis, performed to match the detrital AFT data with their source, revealed the presence of a unexpected only partially annealed portion of a turbidite foredeep unit (AFT ages &gt;7–5 Ma) belonging to the structural complex that constitutes the shoulder bedrock. These data disagree with the AFT age distribution pattern of the well-studied Northern Apennines chain, suggesting a segmentation of the foredeep basin. The latter may have been related to the presence of a tectonically induced topographic high (pre-late Langhian) in the area limiting the thickness of the overriding Ligurian lid. On the other hand, detrital AFT data provided arguments for understanding the dynamics of Mugello Basin shoulder uplift and rotation. The proportion in the different stratigraphic units of the fan-delta sediments of single grains showing young (reset) and old (non-reset) ages points to late Early Pleistocene timing of the development of the SW-verging backthrust that characterizes the study area. These data confirm and detail the picture of an early Quaternary development of the Mugello Basin under a compressional setting, only later (middle Pleistocene to present) superimposed by normal faultings.

Analysis of exhumation history in Misho Mountains, NW Iran: Insights from structural and apatite fission track data

Analysis of exhumation history in Misho Mountains, NW Iran: Insights from structural and apatite fission track data

Where is my sink? Reconstruction of landscape development in southwestern Africa since the Late Jurassic

Quantifying the rates and timing of landscape denudation provides a means to constrain sediment flux through time to offshore sedimentary basins. The Late Mesozoic evolution of drainage basins in southern Africa is poorly constrained despite the presence of several onshore and offshore sedimentary basins. A novel approach has been developed to calculate the volume of material eroded since the Late Jurassic at different time steps by constructing structural cross-sections and extrapolating thicknesses of eroded material. Using different assumptions, the calculated volumes of material eroded from southwestern Africa range from 2.52×106km3 (11.3km of vertical thickness removed) to 8.87×105km3 (4.0km of vertical thickness removed). For the southward draining systems alone, the calculated removal of 7.81×105–2.60×105km3 of material is far greater than the volumes of sediment recorded in offshore sedimentary basins (268500km3). Reconstruction of the drainage systems using geomorphic indicators and clast provenance of the Uitenhage Group, as well as extrapolated surface exposure ages, indicate the southern draining systems were active from the Late Jurassic with coeval activity in axial and transverse drainage systems. The calculated volumes are tied to published apatite fission track (AFT) dates to constrain the changes in exhumation rate through time (using multiple scenarios), which indicate a significant amount of Early Cretaceous exhumation (up to 1.26×106km3, equivalent to 5.70km of vertical thickness). For the first time, this has permitted long-term landscape evolution to be used to support the interpretation that some of the ‘missing’ sediment was deposited in sedimentary basins on the Falkland Plateau as it moved past southern Africa during the Early Cretaceous. This implies that in this instance, the sinks are separated from their source areas by ~6000km.

EXHUMATION OF THE HELLENIC ACCRETIONARY PRISM – EVIDENCE FROM FISSION-TRACK THERMOCHRONOLOGY

Below the Potamos extensional detachment fault exposed in northern Kythera, the phyllite-quartzite unit (PQU) shows very consistent zircon FT cooling ages of c.11 Ma reflecting the time just after the rapid exhumation through the brittle-ductile transition. In contrast, a wide range of Mesozoic and some Paleozoic zircon FT cooling ages from Eocene-Oligocene Tripolis and Pindos flysch sandstones from above the detachment reflect sedimentary source ages. Early Miocene apatite fissiontrack cooling ages characterize the flysch sandstones, and show that early Miocene exhumation affected rocks above the detachment. The thermotectonic evolution of the flysch of Tripolis and Pindos units within the rocks above the Potamos detachment on Kythera is reconstructed using zircon and apatite fission-track (FT) thermochronology. The apatite FT data provide evidence for a burial depth of at least 6km for the samples, which were reset. Burial was not deeper than 11km, since the zircon fission-track system in the same rocks was not reset. The exposed rocks of Tripolis and Pindos flysch on Kythera represent part of an accretionary wedge with a burial shortly after deposition in or near the subduction trench, and a cooling history due to exhumation of the flysch in the early Miocene. The subsequent Mid-Late Miocene exhumation of the PQU unit follows from beneath the (mostly carbonate) Tripolis and Pindos sedimentary rocks.

Preservation and exhumation history of the Harizha-Halongxiuma mining area in the East Kunlun Range, Northeastern Tibetan Plateau, China

The extent to which ore bodies are preserved in orogenic belts remains a poorly understood area of ore deposit research. Using zircon and apatite fission track analysis together with apatite (U-Th)/He dating we constrained the erosion history of the ore bodies in the Harizha–Halongxiuma mining area of the East Kunlun Range, Northern Tibetan Plateau, China. Apatite fission-track ages range from 114±8 to 87±6Ma, with mean track lengths varying from 11.4±1.9 to 12.9±2.0μm. Zircon fission-track ages vary from 205±14 to 142±7Ma. In addition, apatite (U–Th)/He dating yielded ages of 60–56Ma. The thermal history of Jiapigou was modelled based on the apatite fission-track data, including ages and track lengths, with constraints of zircon fission-track ages and (U-Th)/He ages. The exhumation history of the Harizha–Halongxiuma mining area was reconstructed with these age data, revealing that since the early Mesozoic the area has undergone three cooling stages: (1) rapid cooling from 175±30Ma to 100±10Ma with a cooling rate and inferred exhumation of 2.0±0.8°C/Myr and 4.3±1.7km, respectively; (2) a relatively stable stage from 100±10Ma to 40±10Ma with a cooling rate and inferred exhumation of 0.3±0.1°C/Myr and 0.5±0.2km, respectively; and (3) rapid cooling since 40±10Ma with a cooling rate and inferred exhumation of 1.2±0.6°C/Myr and 1.4±0.4km, respectively. This exhumation history is consistent with the subduction process of Pacific plate and the strike slip movements of Dunmi fault. The total exhumation after main mineralization is calculated to be 7.6±3.2km, suggesting that ore bodies in the Harizha–Halongxiuma mining area remain partially preserved.

Exhumation history of the Jiaodong and its adjacent areas since the Late Cretaceous: Constraints from low temperature thermochronology

The thermal history of the Jiaodong region and adjacent provinces (Shandong and northern Jiangsu) have been extensively studied, particularly by apatite fission track (AFT) dating. However, the AFT ages from surface outcrops range broadly and do not show an apparent relationship between age and elevation. This work provides a multiple low temperature thermochronological dataset including zircon and apatite (U-Th)/He ages (ZHe and AHe), and AFT ages from a 1000-m-deep borehole at the Jiaojia goldfield in the northwest of Jiaodong Peninsula. ZHe, AFT and AHe ages range from ~100–70, ~85–50 and ~65–50 Ma, respectively. These data conform to the principles of age vs. closure temperature and age vs. elevation and thus can be employed to estimate the exhumation history. Based on the density histogram of fission track length calculation, thermal history modeling, and previously published AFT ages from the Chinese Continental Science Drill program, this work concludes that compared to the AFT ages from surface outcrops, the low temperature thermochronological ages from the boreholes show a better relationship between age, elevation and closure temperature, and the age becomes younger with increasing depth. In addition, the exhumation history in the Jiaodong and adjacent areas can be divided into two distinct stages: a short, rapid tectonic exhumation (~100–95 Ma) and a long, slow exhumation since 95 Ma. The rate and amount of tectonic exhumation since 95 Ma are inferred as ~30 m Ma - 1 and ~3 km, respectively.

Late Miocene-Pleistocene evolution of India-Eurasia convergence partitioning between the Bhutan Himalaya and the Shillong Plateau: New evidences from foreland basin deposits along the Dungsam Chu section, eastern Bhutan

The Shillong Plateau is a unique basement-cored uplift in the foreland of the eastern Himalaya that accommodates part of the India-Eurasia convergence since the late Miocene. It was uplifted in the late Pliocene to 1600 m, potentially inducing regional climatic perturbations by orographically condensing part of the Indian Summer Monsoon (ISM) precipitations along its southern flank. As such, the eastern Himalaya-Shillong Plateau-ISM is suited to investigate effects of tectonics, climate, and erosion in a mountain range-broken foreland system. This study focuses on a 2200 m thick sedimentary section of the Siwalik Group strategically located in the lee of the Shillong Plateau along the Dungsam Chu at the front of the eastern Bhutan Himalaya. We have performed magnetostratigraphy constrained by vitrinite reflectance and detrital apatite fission track dating, combined with sedimentological and palynological analyses. We show that (1) the section was deposited between ~7 and 1 Ma in a marginal marine deltaic transitioning into continental environment after 5 Ma, (2) depositional environments and paleoclimate were humid with no major change during the depositional period indicating that the orographic effect of the Shillong Plateau had an unexpected limited impact on the paleoclimate of the Bhutanese foothills, and (3) the diminution of the flexural subsidence in the basin and/or of the detrital input from the range is attributable to a slowdown of the displacement rates along the Main Boundary Thrust in eastern Bhutan during the latest Miocene-Pleistocene, in response to increasing partitioning of the India-Eurasia convergence into the active faults bounding the Shillong Plateau.

Evidence for Eocene–Oligocene glaciation in the landscape of the East Greenland margin

Abstract Assessing the onset and extent of Northern Hemisphere glaciation is required to understand Cenozoic climate change and its impact on topography. While the onset of accelerated Cenozoic erosion is generally associated with the Quaternary at mid-latitudes, some high-latitude passive margins may have undergone earlier glaciation starting at 38–30 Ma or even 45 Ma. Here we document a rapid phase of exhumation in the East Greenland margin between 68°N and 76°N starting at 30 ± 5 Ma. The timing is coincident with the dramatic worldwide fall of surface temperature at the Eocene-Oligocene transition. Our inference is based on apatite fission track and apatite helium data. We suggest that a transition from an Eocene fluvial to an Oligocene glacial-dominated landscape triggered a period of enhanced erosion. This study provides the first onshore potential evidence of the onset of continental ice in East Greenland margin at the Eocene-Oligocene transition (ca. 34 Ma), contemporaneously with the onset of Antarctica glaciation and erosion. Our interpretation is consistent with that based on the oldest ice-rafted debris found in the sedimentary records offshore East Greenland and implies that East Greenland exhibits the oldest onshore record of Cenozoic glacial erosion on Earth.

Apatite fission track and (U-Th)/He thermochronology from the Archean Tanzania Craton: Contributions to cooling histories of Tanzanian basement rocks

Borehole and surface samples from the Archean Tanzania Craton were analysed for apatite fission track (AFT) and (U-Th)/He data with the aim of deciphering cooling histories of the basement rocks. Fission track dates from borehole and outcrop samples are Carboniferous–Permian (345 ± 33.3 Ma to 271 ± 31.7 Ma) whereas (U-Th)/He dates are Carboniferous–Triassic (336 ± 45.8 Ma to 213 ± 29 Ma) for outcrop grains and are consistently younger than corresponding AFT dates. Single grain (U-Th)/He dates from the borehole are likely to be flawed by excessive helium implantation due to their very low effective uranium contents, radiation damage and grain sizes. All AFT and (U-Th)/He dates are significantly younger than the stratigraphic ages of their host rocks, implying that the samples have experienced Phanerozoic elevated paleo-temperatures. Considerations of the data indicate removal of up to 9 km overburden since the Palaeozoic.Thermal modelling reveals a protracted rapid cooling event commencing during the early Carboniferous (ca. 350 Ma) at rates of 46 m/Ma ending in the Triassic (ca. 220 Ma). The model also suggests minor cooling during the Cretaceous of the samples to surface temperatures. The suggested later cooling event remains to be tested. The major cooling phase during the Carboniferous is interpreted to be associated with compressional tectonics during the Variscan Orogeny sensu far field induced stresses. Coeval sedimentation in the Karoo basins in the region suggests that most of the cooling of cratonic rocks during the Carboniferous was associated with denudation.

Proterozoic–Mesozoic history of the Central Asian orogenic belt in the Tajik and southwestern Kyrgyz Tian Shan: U-Pb,40Ar/39Ar, and fission-track geochronology and geochemistry of granitoids

Multimethod geochronology (U-Pb zircon; 40 Ar/ 39 Ar hornblende, biotite, feldspar; apatite fission track) on granitoids, gneisses, and Cenozoic intramontane basin clastics of the Gissar-Alai ranges, South Tian Shan collisional belt, west of the Talas-Fergana fault, elucidates a history of Neoproterozoic magmatism, late Paleozoic magmatism and metamorphism, and Mesozoic−Cenozoic thermal reactivation. Zircon-core and grain-interior U-Pb ages of ca. 2.7−2.4, 2.2−1.7, 1.1−0.85, and 0.85−0.74 Ga tie the early evolution of the Gissar-Alai ranges to that of the Tarim craton. At least part of the Gissar range crystalline basement—the Garm massif—shows U-Pb zircon crystallization ages of ca. 661‒552 Ma (median ca. 609 Ma), again suggesting a Tarim craton connection. Tarim collided with the Middle Tian Shan block at ca. 310‒305 Ma, completing the protracted formation of the South Tian Shan collisional belt. The massive Gissar range granitoids intruded later (ca. 305‒270 Ma), contemporaneous with peak Barrovian-type metamorphism in the Garm massif rocks. Major- and trace-element compositions suggest that the Gissar granitoid melts have continental arc affinity. Zircon e Hf and whole-rock e Nd values of −2.1 to −6.9 and −2.7 to −7.2, respectively. and Hf-isotope crustal model and Nd-isotope depleted mantle model ages of ca. 1.0‒1.2 and ca. 1.1‒2.2 Ga, respectively, suggest significant input of Precambrian crust in the Gissar granitoid and Garm orthogneiss melts, consistent with the U-Pb ages of inherited and detrital zircons. The distinct ca. 661‒552 Ma Garm gneiss crystallization ages and the ca. 1.0−2.2 Ga model ages (and the lack of 2.4−3.4 Ga model ages) tie the Garm gneisses and the reworked crust of the Gissar range to the northern rim—the Kuqa and Kolar sections—of the Tarim craton, suggesting a united Karakum-Tarim craton. Although about contemporaneous with widespread postcollisional magmatism in the entire Tian Shan, the large volume and short duration of the Gissar range magmatism, including crustal thickening and prograde metamorphism during Tarim craton‒Middle Tian Shan block collision, and formation and closure of an oceanic back-arc basin (the Gissar basin), indicate its origin in a distinct setting. Combined, this likely resulted in midcrustal melting and upper-crustal batholith emplacement. Mafic dikes and pipes intruded at ca. 256−238 Ma (median ca. 241 Ma); the source region of the parental melts was within the asthenospheric mantle. The simplest interpretation for these basanites is that they were part of the Tarim flood basalt province; this would extend this province westward from the Tarim craton into the southwestern Tian Shan and imply that the relatively short-lived flood basalt event (ca. 290‒270 Ma) was followed by much less voluminous but longer-lasting hotspot magmatism. The 40 Ar/ 39 Ar and detrital apatite fission-track dates outline post−Gissar-Alai range granitoid emplacement cooling, Cimmerian collision events at the southern margin of Asia, Late Cretaceous crustal extension and local magmatism, and early Cenozoic shortening and burial in the far field of the India-Asia collision.

Geothermal constraints on Emeishan mantle plume magmatism: paleotemperature reconstruction of the Sichuan Basin, SW China

The Middle–Late Permian Emeishan Large Igneous Province (ELIP) in southwestern China represents a classic example of a mantle plume origin. To constrain the thermal regime of the ELIP and contemporaneous magmatic activity in the northeastern Sichuan Basin, maximum paleotemperature profiles of deep boreholes were reconstructed using vitrinite reflectance (Ro) and apatite fission track data. Two heating patterns were identified: (1) heating of the overlying lithosphere by magma storage regions and/or magmatic activity related to the mantle plume, which resulted in a relatively strong geothermal field and (2) direct heating of country rock by stock or basalt. Borehole Ro data and reconstructed maximum paleotemperature profiles near the ELIP exhibit abrupt tectonothermal unconformities between the Middle and Late Permian. The profiles in the lower subsections (i.e., pre-Middle Permian) exhibited significantly higher gradients than those in the upper subsections. Distal to the basalt province, high paleo-geotemperatures (hereafter, paleotemperatures) were inferred, despite deformation of the paleogeothermal curve due to deep faults and igneous rocks within the boreholes. In contrast, Ro profiles from boreholes without igneous rocks (i.e., Late Permian) contained no break at the unconformity. Paleotemperature gradients of the upper and the lower subsections and erosion at the Middle/Late Permian unconformity revealed variations in the thermal regime. The inferred spatial distribution of the paleothermal regime and the erosion magnitudes record the magmatic and tectonic-thermal response to the Emeishan mantle plume.

Spatio-temporal trends in normal-fault segmentation recorded by low-temperature thermochronology: Livingstone fault scarp, Malawi Rift, East African Rift System

The evolution of through-going normal-fault arrays from initial nucleation to growth and subsequent interaction and mechanical linkage is well documented in many extensional provinces. Over time, these processes lead to predictable spatial and temporal variations in the amount and rate of displacement accumulated along strike of individual fault segments, which should be manifested in the patterns of footwall exhumation.Here, we investigate the along-strike and vertical distribution of low-temperature apatite (U–Th)/He (AHe) cooling ages along the bounding fault system, the Livingstone fault, of the Karonga Basin of the northern Malawi Rift. The fault evolution and linkage from rift initiation to the present day has been previously constrained through investigations of the hanging wall basin fill. The new cooling ages from the footwall of the Livingstone fault can be related to the adjacent depocentre evolution and across a relay zone between two palaeo-fault segments. Our data are complimented by published apatite fission-track (AFT) data and reveal significant variation in rock cooling history along-strike: the centre of the footwall yields younger cooling ages than the former tips of earlier fault segments that are now linked. This suggests that low-temperature thermochronology can detect fault interactions along strike. That these former segment boundaries are preserved within exhumed footwall rocks is a function of the relatively recent linkage of the system.Our study highlights that changes in AHe (and potentially AFT) ages associated with the along-strike displacement profile can occur over relatively short horizontal distances (of a few kilometres). This is fundamentally important in the assessment of the vertical cooling history of footwalls in extensional systems: temporal differences in the rate of tectonically driven exhumation at a given location along fault strike may be of greater importance in controlling changes in rates of vertical exhumation than commonly invoked climatic fluctuations.

Exhumation history of the Peake and Denison Inliers: insights from low-temperature thermochronology

ABSTRACTMulti-method thermochronology applied to the Peake and Denison Inliers (northern South Australia) reveals multiple low-temperature thermal events. Apatite fission track (AFT) data suggest two main time periods of basement cooling and/or reheating into AFT closure temperatures (∼60–120°C); at ca 470–440 Ma and ca 340–300 Ma. We interpret the Ordovician pulse of rapid basement cooling as a result of post-orogenic cooling after the Delamerian Orogeny, followed by deformation related to the start of the Alice Springs Orogeny and orocline formation relating to the Benambran Orogeny. This is supported by a titanite U/Pb age of 479 ± 7 Ma. Our thermal history models indicate that subsequent denudation and sedimentary burial during the Devonian brought the basement rocks back to zircon U–Th–Sm/He (ZHe) closure temperatures (∼200–150°C). This period was followed by a renewal of rapid cooling during the Carboniferous, likely as the result of the final pulses of the Alice Springs Orogeny, which exhumed the inlier to ambient surface temperatures. This thermal event is supported by the presence of the Mount Margaret erosion surface, which indicates that the inlier was exposed at the surface during the early Permian. During the Late Triassic–Early Jurassic, the inlier was subjected to minor reheating to AFT closure temperatures; however, the exact timing cannot be deduced from our dataset. Cretaceous apatite U–Th–Sm/He (AHe) ages coupled with the presence of contemporaneous coarse-grained terrigenous rocks suggest a temporally thermal perturbation related with shallow burial during this time, before late Cretaceous exhumation cooled the inliers back to ambient surface temperatures.

Paleogeothermal reconstruction and thermal evolution modeling of source rocks in the Puguang gas field, northeastern Sichuan Basin

The thermal history and organic matter maturity evolution of the source rocks of boreholes in the Puguang gas field were reconstructed. An integrated approach based on vitrinite reflectance and apatite fission track data was used in the reconstruction. Accordingly, the geothermal conditions of gas accumulation were discussed in terms of the geological features of reservoirs in the northeastern Sichuan Basin. The strata reached their maximum burial depth in the Late Cretaceous era and were then uplifted and denuded continuously to the present day. The geothermal gradient and heat flow in the Late Cretaceous era were approximately 30.0 °C/km and 66 mW/m2, respectively, which were both higher than those at present. The tectonothermal evolution from the Late Cretaceous era to the present is characterized by denudation and cooling processes with an erosion thickness of ~2.7 km. In addition to the Triassic era, the Jurassic era represents an important hydrocarbon generation period for both Silurian and Permian source rocks, and the organic matter maturity of these source rocks entered into a dry gas period after oil generation. The thermal conditions are advantageous to the accumulation of conventional and unconventional gas because the hydrocarbon generation process of the source rocks occurs after the formation of an effective reservoir cap. In particular, the high geothermal gradient and increasing temperature before the denudation in the Late Cretaceous era facilitated the generation of hydrocarbons, and the subsequent cooling process favored its storage.