A field-based estimate of the zircon fission-track closure temperature is proposed from 13 zircon fission-track cooling ages of the Gold Butte block, SE Nevada. Using previously published and new ...thermochronological data, the thermal history of the Gold Butte block is re-evaluated, resulting in a geothermal-gradient estimate of 20.3 °C/km and a slow cooling rate of 0.55
±
0.02 °C/m.y. from the Late Jurassic to the early Miocene before onset of rapid Miocene cooling. The rapidly cooled part of the Gold Butte block provides a slip rate of 10.5 km/m.y. of the hanging wall that caused the Miocene exhumation of this crustal section. Assuming these thermal conditions are correct, the closure temperature of the zircon fission-track system is determined at 205
±
18 °C, which is in good agreement with previous field-based estimates. Because of the variation in zircon fission-track annealing behavior with radiation damage, field studies are a suitable way to calibrate the closure temperature of the zircon fission-track system.
How and when the northwestern Tibetan Plateau originated and developed upon pre-existing crustal and topographic features is not well understood. To address this question, we present an integrated ...analysis of detrital zircon U–Pb and fission-track double dating of Cenozoic synorogenic sediments from the Kekeya and Sanju sections in the southwestern Tarim Basin. These data help establishing a new chronostratigraphic framework for the Sanju section and confirm a recent revision of the chronostratigraphy at Kekeya. Detrital zircon fission-track ages present prominent Triassic–Early Jurassic (∼250–170 Ma) and Early Cretaceous (∼130–100 Ma) static age peaks, and Paleocene–Early Miocene (∼60–21 Ma) to Eocene–Late Miocene (∼39–7 Ma) moving age peaks, representing source exhumation. Triassic–Early Jurassic static peak ages document unroofing of the Kunlun terrane, probably related to the subduction of Paleotethys oceanic lithosphere. In combination with the occurrence of synorogenic sediments on both flanks of the Kunlun terrane, these data suggest that an ancient West Kunlun range had emerged above sea level by Triassic–Early Jurassic times. Early Cretaceous fission-track peak ages are interpreted to document exhumation related to thrusting along the Tam Karaul fault, kinematically correlated to the Main Pamir thrust further west. Widespread Middle–Late Mesozoic crustal shortening and thickening likely enhanced the Early Mesozoic topography. Paleocene–Early Eocene fission-track peak ages are presumably partially reset. Limited regional exhumation indicates that the Early Cenozoic topographic and crustal pattern of the West Kunlun may be largely preserved from the Middle–Late Mesozoic. The Main Pamir–Tam Karaul thrust belt could be a first-order tectonic feature bounding the northwestern margin of the Middle–Late Mesozoic to Early Cenozoic Tibetan Plateau. Toward the Tarim basin, Late Oligocene–Early Miocene steady exhumation at a rate of ∼0.9 km/Myr is likely related to initial thrusting of the Tiklik fault and reactivation of the Tam Karaul thrust. Thrusting together with upper crustal shortening in the mountain front indicates basinward expansion of the West Kunlun orogen at this time. This episode of exhumation and uplift, associated with magmatism across western Tibet, is compatible with a double-sided lithospheric wedge model, primarily driven by breakoff of the Indian crustal slab. Accelerated exhumation of the mountain front at a rate of ∼1.1 km/Myr since ∼15 Ma supports active compressional deformation at the margins of the northwestern Tibetan Plateau. We thus propose that the West Kunlun Mountains are a long-lived topographic unit, dating back to Triassic–Early Jurassic times, and have experienced Middle–Late Mesozoic to Early Cenozoic rejuvenation and Late Oligocene–Miocene expansion.
•Zircon U–Pb/FT double dating provides new ages for the sediments in southwestern Tarim Basin.•The data show episodic exhumation and magmatism in the West Kunlun Mountains.•The orogen has emerged since the Triassic–Early Jurassic and was rejuvenated in the Meso-Cenozoic.•A double-sided lithospheric wedge model is proposed to explain Neogene tectonism in western Tibet.
Using thermochronological data and thermokinematic modeling, we constrain the timing of late Miocene exhumation of the northern portion of the Gongga batholith, located in Southeast Tibet along the ...Xianshuihe Fault (XF). We show that rapid exhumation started in the north of the Gongga batholith at ∼9 Ma at a rate of ∼1.85 km/Myr and slowed down since ∼4 Ma. A magmatic pulse occurring during the early Pliocene (∼4 Ma) has overprinted the rapid Miocene exhumation phase in some parts of the batholith, which record mainly early Pliocene post-magmatic cooling. Slow exhumation since ∼4 Ma is consistent with the present-day lower relief observed in the centre of the batholith, which contrasts with the rugged high peaks located to the south. We propose that the northern segment of the XF, the Yalahe fault, which is not active at present, was active between 9 and 4 Ma, forming a restraining bend that focused exhumation south of it. Since ∼4 Ma, the Selaha and the Zheduotang faults form the present-day restraining bend south of which the highest part of the massif is located, including the Gongga Shan that rises more than 3000 m above the mean elevation of the plateau. In the north of the batholith, similar peaks have been removed since the Miocene by local relief reduction at high elevations. Considering that the onset of motion along the XF is contemporaneous with the onset of rapid exhumation recorded along the Kangding transect at ∼9 Ma and a total offset of ∼62 km documented for the XF, the average slip rate of the XF is ∼7 mm/yr since 9 Ma.
•Miocene cooling of the Gongga batholith, SE Tibet.•Phase of rapid cooling starting at ∼9 Ma at a rate of ∼1.85 km/Myr.•Slowing down of cooling since ∼4 Ma.•Onset of left-lateral Xianshuihe fault at ∼9 Ma.•Total offset of ∼62 km and average slip rate ∼7 mm/yr since 9 Ma.
The Colombian island of San Andrés is a popular tourist destination located about 195 km offshore of the east coast of Nicaragua in the southwestern Caribbean Sea. Together with Providencia and Santa ...Catalina, San Andrés is part of the UNESCO Seaflower Biosphere Reserve. With a 26 km2 surface area and 78,000 inhabitants, San Andrés is one of the most densely populated islands in the Caribbean with on average ∼ 3000 inhabitants/km2. The majority of the population and the mass tourism are concentrated in the low-elevation (0.5-6 m) areas, particularly in the north and along the east coast of the island. These areas are prone to flooding during storm events such as hurricanes Eta and Iota in 2020. A review of the geological, environmental and the socio-economic situation of the island, and the record of tropical cyclones since 1911, shows why the local population has become increasingly vulnerable to storm events and rising sea level. Tropical cyclones may form locally in the southwestern Caribbean or originate in the eastern Caribbean/Atlantic Ocean. The latter tend to be stronger and cause more damage when they reach San Andrés. The HURDAT2 dataset shows that the frequency of storm events affecting San Andrés has increased in recent decades, with six storms over the past 20 years, including three category 4-5 hurricanes since 2007. Increasing storm frequency and intensity may be linked to increasing sea surface temperatures caused by anthropogenic global warming, although the changes described here may be limited to a relatively small geographical region, as opposed to representing basin wide tropical cyclone behavior. The growing population density since the 1950s has augmented the potential for disaster.
We report a new interlaboratory exercise to evaluate the reproducibility of apatite fission‐track (AFT) and (U‐Th)/He (AHe) data and thermal history analysis. Twelve laboratory groups participated, ...analyzing apatite separates from two previously studied localities. Ten groups returned AFT data from 13 analysts, five groups returned AHe data, one contributed apatite U/Pb data, and nine contributed thermal history models. Submitted AFT age data were generally consistent with the original studies and each other to within uncertainties, although there were departures, particularly among results obtained using laser ablation inductively coupled plasma mass spectrometry for uranium determination. AFT‐confined track‐length data showed more variation, which correlated between samples, suggesting that they may reflect analyst‐specific factors. Accounting for anisotropy using c axis projection reduced the variation and correlation. AHe ages showed more dispersion than observed in the previous studies, with one sample showing many ages consistent with prior work but also many significantly older ages, and the other roughly matching prior work but showing symmetrical scatter suggesting a 1SE uncertainty of 17–21%. Thermal history models generally agreed in their major features but showed considerable variation in detail, due to differences in data and data entry, model setup, and modeling software approach. Addressing pitfalls in data entry and model setup improved congruence, as would greater emphasis on AFT length and etch figure calibration. Because of scatter, AHe data had to be entered selectively into the models to achieve reasonable results. Although cautionary in several respects, study results point to promising avenues for improving the reproducibility of thermal history modeling.
Key Points
An interlaboratory exercise examined the reproducibility of apatite fission‐track and (U‐Th)/He data and thermal history analysis
Thermal history models agreed on major features but varied on detail, due to differences in data, data entry, model setup, and software
Although cautionary in many respects, study results point to promising avenues to improve the reproducibility of thermal history modeling
A new data set combining thermobarometry, geo‐thermochronology, chronostratigraphic, and structural analyses highlights the tectono‐thermal evolution of the St. Martin granodiorite from its ...emplacement to its surface exposure. The described vertical motions in this part of the upper plate of the Lesser Antilles subduction zone since 30 Myrs are linked to the migration of the Lesser Antilles volcanic arc toward the plate interior. Results suggest that the St. Martin granodioritic pluton emplaced at 4–5 km depth and underwent a four‐step history: (a) 30–27 Ma, emplacement along N20–40° transtensive structures oblique to the trench followed by, (b) 27–24 Ma, rapid post‐emplacement cooling and exhumation (∼0.6 mm/yr) controlled by perpendicular to the trench N45° trending structures, (c) 24–9 Ma, slow subsidence (0.01 mm/yr) and development of carbonate platforms associated to tectonic quiescence, westward migration of the arc, and subsequent cooling of the crust, (d) 9 Ma to present‐day, exhumation (∼0.25 mm/yr) and uplift of Neogene carbonate platforms mainly along N45° faults that likely accommodate the progressive trench curvature since 30 Ma. Pecube forward modeling using this scenario reproduces both the observed present‐day geometry and thermochronometric ages. A similar sequence of events is observed in the Virgin Islands. Along with our new data, this suggests a southward migration of the deformation associated with the opening of the Anegada Trough.
Key Points
The tectono‐thermal history of the St. Martin Oligocene granodiorite is reconstructed
Exhumation occurred during two periods: between 27 and 24 Ma and since 9 Ma, along N45° trending normal faults
Regionally, exhumation rates suggest a southward migration of the deformation associated with the opening of the Anegada Trough
Apatite and zircon fission track thermochronology studies are applied to basement and sedimentary rocks from the Sul-Rio-Grandense Shield to unravel the tectonic history of the onshore southernmost ...Brazilian margin. The Sul-Rio-Grandense Shield is a major geotectonic feature of southernmost Brazil that includes Paleoproterozoic basement areas and Neoproterozoic fold belts linked to the Brasiliano/Pan-African orogeny. Crustal reworking and juvenile accretion events related to this cycle were dated in the region between 900 and 500Ma and were responsible for the assembly of southwestern Gondwana in southeastern South America. Apatite fission track (AFT) ages range from 340±33 to 77±6Ma and zircon fission track (ZFT) ages range from ca. 386 to 210Ma. Based on thermal history modeling, the most part of the samples record an early cooling event during the Carboniferous, which reflect the main tectonic activity of the final stages of the Gondwanides at the Pacific margin of West Gondwana. Subsequently, the Permo-Triassic cooling event is related to the last stages of the Gondwanides, with convergence along the southern border of Western Gondwana and consequent reactivation of N-S and NE-SW trending basement structures. The onset of initial breakup of southwestern Gondwana with opening of the South Atlantic Ocean is mostly recorded in the eastern terrain and ZFT ages show that the temperature during this period was high enough for total or at least partial resetting of fission tracks in zircon. The last cooling event of the Sul-Rio-Grandense Shield records the final breakup between South America and Africa, which began during the Late Cretaceous. However, the Cenozoic rapid cooling episode probably is a result of plate adjustment after breakup and neotectonic reactivation of faults associated with South Atlantic rift evolution.
Display omitted
•Southern Brazilian Shield record an early cooling event during the Ordovician.•Precambrian structures were reactivated during breakup of southwestern Gondwana.•The Cenozoic cooling episode is associated with South Atlantic rift evolution.
The Isère River system drains parts of the Western Alps in south-eastern France. Zircon fission-track data of the Isère River and its tributaries show a range of apparent cooling ages from about 7 to ...150 Ma. Zircons with Jurassic to early Tertiary cooling ages are derived from partially reset or non-reset sedimentary cover units of the internal and external Alps, while grains belonging to the minimum age fraction are derived from areas of active river incision in the external crystalline massifs or from the Penninic front. With the absence of major normal faults, upper crustal exhumation in the Western Alps is driven by erosion. First-order long-term exhumation rate estimates based on minimum ages are about 0.5–0.6 km/Myr for the fastest exhuming areas, while drainage basin average rates based on central ages are about 0.2–0.4 km/Myr. These rates are slower than published short-term erosion rates determined from detrital quartz 10Be analyses in the Pelvoux massif. While present-day erosion is faster than the long-term average exhumation rates, the Isère River drainage zircon fission-track data do not show evidence for increasing erosion rates at 5 Ma. Exhumation has not been sufficient in this area to expose rocks with <5 Ma cooling ages today. The increase in erosion may have happened only in glaciated areas between 1 and 2 Ma.
Whereas a straightforward link between crustal thinning and geothermal gradients during rifting is now well established, the thermal structure of sedimentary basins within hyperextended domains ...remains poorly documented. For this purpose, we investigate the spatial distribution of rift-related High-Temperature Low-Pressure (H
T
/L
P
) metamorphism recorded in the preserved hyperextended rift basins inverted and integrated in the Pyrenean-Cantabrian belt. Based on Vitrinite Reflectance (R
o
) data measured in 169 boreholes and more than 200 peak-metamorphic temperatures (
T
max
) data obtained by Raman Spectroscopy of Carbonaceous Material (RSCM) added to ∼425 previously published
T
max
data, we propose a new map depicting the spatial distribution of the H
T
/L
P
metamorphism of the Pyrenean-Cantabrian belt. We also provide three regional-scale geological cross-sections associated with R
o
and
T
max
data to constrain the distribution of paleo-isograds at depth. Based on these results, we show that the impact of rift-related metamorphism is restricted to the pre- and syn-rift sequence suggested by the depth profiles of R
o
values measured in different tectonostratigraphic intervals (pre-, syn- and post-rift and syn-convergence sediments). However, a small strip of early orogenic sediments (Santonian in age) appears also affected by high temperatures along the North Pyrenean Frontal Thrust and above the Grand Rieu ridge, which we attribute to the percolation of hot hydrothermal fluids sourced from the dehydration of underthrust basement and/or sedimentary rocks at depth during the early orogenic stage. The map shows that the H
T
/L
P
metamorphism (reaching ∼500 °C) is recorded with similar intensity along the Pyrenean-Cantabrian belt from the west in the Basque-Cantabrian Basin to the east in the Boucheville and Bas-Agly basins, for similar burial and rift-related structural settings. This thermal peak is also recorded underneath the northern border of the Mauléon Basin (calibrated by wells). It suggests that the high temperatures were recorded at the basement-sediment interface underneath the most distal part of the hyperextended domain. At basin-scale, we observe in the Basque-Cantabrian, Mauléon-Arzacq and Tarascon rift segments an asymmetry of the thermal structure revealed by different horizontal thermal gradients, supporting an asymmetry of the former hyperextended rift system. Using our results, we compare the Pyrénées to the Alps that also recorded hyperextension but no H
T
/L
P
metamorphic event and suggest that the high-temperature record within the basins depends on high sedimentation rate promoting a thermal blanketing effect and circulation of hydrothermal fluids.
Bien que l’association de l’amincissement crustal et de gradients géothermiques élevés lors du rifting continental soit largement reconnue, la structure thermique des bassins sédimentaires dans la partie distale des systèmes de rift reste mal documentée. Pour cela, nous étudions la distribution spatiale du métamorphisme Haute-Température/Basse Pression (H
T
/B
P
) enregistrée dans les bassins préservés du système de rift hyper-aminci, par la suite inversés et intégrés dans la chaîne Pyrénéo-Cantabrique. Basé sur la réflectance de la Vitrinite (R
o
) mesurée dans 169 puits et plus de 200 données de pic de température lié au métamorphisme (
T
max
) obtenues avec la méthode de Spectroscopie Raman de la Matière Carbonée (RSCM) ainsi que plus de 425
T
max
provenant d’études précédentes, nous proposons une nouvelle carte de la distribution spatiale du métamorphisme H
T
/B
P
de la chaîne Pyrénéo-Cantabrique. Nous proposons également trois coupes géologiques regionales, sur lesquelles nous avons placé les données de
T
max
et de R
o
afin de contraindre la distribution des paléo-isogrades en profondeur. Basé sur ces résultats, nous montrons que l’impact du métamorphisme lié au rifting est restreint aux sédiments pré- et syn-rift, ce qui est suggéré par la tendance des profils des valeurs de R
o
en profondeur mesurées dans les différents intervalles tectonostratigraphiques (sédiments pré-, syn- et post-rift ainsi que syn-convergence). Cependant, une fine bande de sédiments syn-orogéniques (d’âge Santonien) est affectée par des températures relativement élevées au-dessus de la ride de Grand Rieu et le long du Chevauchement Frontal Nord Pyrénéen, que nous attribuons à la percolation de fluides hydrothermaux chauds provenant de la déshydratation du socle chevauché et/ou des sédiments profonds, lors du stade d’inversion précoce. La carte présentée montre que le métamorphisme (atteignant ∼500 °C) est enregistré avec la même intensité du bassin Basque-Cantabrique à l’ouest, aux bassins de Boucheville et du Bas-Agly à l’est, pour un enfouissement et un positionnement lors du rifting équivalents. Le pic thermique est également enregistré sous la bordure nord du bassin de Mauléon (calibré par des puits). Cela suggère que les hautes températures ont été enregistrées à l’interface socle-sédiments au niveau de la partie la plus distale du domaine hyper-aminci. À l’échelle des bassins, nous observons dans les segments Basque-Cantabrique, Mauléon-Arzacq et Tarascon une asymétrie de la structure thermique, révélée par différents gradients thermiques horizontaux, supportant une asymétrie de l’ancien système de rift hyper-aminci. En utilisant nos résultats, nous comparons les Pyrénées avec les Alpes qui ont également enregistré l’hyper-extension mais pas d’évènement métamorphique H
T
/B
P
, ce qui suggère que l’enregistrement des hautes températures dans les bassins dépend de taux de sédimentation élevés, favorisant un effet de couverture thermique et de circulations de fluides hydrothermaux.
Here, we present seven new zircon (U-Th)/He (ZHe) ages and three new zircon fission track (ZFT) ages analyzed from an age-elevation profile (Machu Picchu, Peru). ZFT data present ages older than ...those obtained with other thermochronological data, whereas the ZHe data interestingly present ages similar to those obtained with apatite (U-Th)/He (AHe). It has been proposed that He retention in zircon is linked to the damage dose, with an evolution of the closure temperature from low values associated with a low α-dose (<1016 α/g), subsequently increasing before decreasing again at a very high α-dose (>1018 α/g). Studies have focused on He diffusion behavior at high α-dose, but little is known at low doses. We propose that the ZHe closure temperature at α-dose ranging from 6 × 1015 to 4 × 1016 α/g is in the range of ~60–80 °C. This value is lower than that proposed in the current damage model ZRDAAM and demonstrates that the ZHe and AHe methods could have similar closure temperatures at low α-dose (i.e., similar ages). These new data strengthen our previous geological conclusions and even highlight a cooling rate approximately twice as important as that deduced from AHe and apatite fission track data alone at Machu Picchu.
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