Thermotectonic History Research Articles

Late Miocene to present synchronous extension and contraction in the eastern Pamir: Insights from inversion of thermochronologic data across the southern Muztaghata dome

Late Cenozoic gneiss domes cover ∼30% of the surface of the Pamir salient in the northwestern end of the India−Asia collision zone. The highest peaks of the Pamir are in the east, where the ∼250-km-long, ∼N−S-trending Kongur Shan extensional system controls the topography. We combined 115 new apatite (U-Th-Sm)/He and zircon (U-Th)/He single-grain dates from 18 samples and previous thermochronologic data with three-dimensional thermokinematic models to constrain the thermo-tectonic history of the southern portion of the Muztaghata dome, one of the largest gneiss domes in the eastern Pamir. The new cooling dates from the western boundary of the southern Muztaghata dome generally increase with distance from the southern Kongur Shan fault and are related to normal faulting along the fault at near-surface levels over the last 6.5 m.y. The new dates across the central−eastern portion of the dome outline the previously recorded U-shaped date pattern at a higher spatial resolution. The modeling indicates that this pattern is most likely the result of uplift and erosion above a flat-ramp-flat thrust fault at depth over the last 7 m.y. Modeling does not resolve how topographic changes may have affected the observed distribution of cooling dates, but it indicates a faster thrust-slip rate associated with an increase in relief and a slower one associated with steady-state topography. Our results suggest that the modern topography along the southern Muztaghata dome, similar to the rest of the eastern Pamir salient, is shaped by normal faulting at shallow depth, but its growth may still be governed by contraction and crustal thickening at depth.

Extrusion tectonism of Indochina reassessed: constraints from 40Ar/39Ar geochronology from the Day Nui Con Voi metamorphic massif, Vietnam

The extrusion tectonic model for the southeastern margin of the Himalayan orogeny links the crustal shear activity along the Red River Shear Zone (RRSZ) to the opening of the South China Sea (SCS). The Day Nui Con Voi (DNCV) metamorphic massif in northern Vietnam strikes NW-SE, is bounded by the RRSZ to the south and continues along the strike where it meets the SCS. The DNCV is thus a critical area to document thermotectonic history in order to advance our understanding of the tectonic evolution of Indochina extrusion and its relationship to the opening of the SCS. Our new 40Ar/39Ar data combined with microstructural and petrological analyses constrained the timing of the left-lateral shearing of the RRSZ and revealed the thermal evolution of the DNCV metamorphic massif. Three ductile deformation events were observed. D1 formed NNW-SSE striking upright folds under granulite to upper amphibolite facies conditions. D2 was a horizontal to sub-horizontal folding event that occurred at amphibolite facies conditions. D3 was a doming event that formed NW-SE striking up-right folds bounded by left-lateral shearing mylonite belts along the two limbs. The S/C fabrics were defined by muscovite fish, quartz + albite + K-feldspar aggregates, and muscovite folia. The D3 doming event exhumed the DNCV metamorphic massif from amphibolite facies conditions to the lower greenschist facies conditions. The 40Ar/39Ar ages obtained from amphibole (∼26 Ma), phlogopite (∼25 Ma), muscovites (∼24-23 Ma), biotite (∼25-23 Ma), and K-feldspars (∼25-22 Ma) from different structural domains of the DNCV metamorphic massif indicated a rapid exhumation ∼26–22 Ma. We interpreted this as the time period for the D3 event, with the onset of left-lateral shearing occurring around 24 Ma based on ages obtained from syn-kinematic muscovites. This age was much younger than the initiation of sea-floor spreading of the SCS (since 32 Ma) but coincided with the age for the ridge jump event in the SCS. Based on these new data, we proposed that extrusion tectonism cannot be the cause for the initial opening of the SCS. Rather, the extrusion of the Indochina block was temporally correlative with the southward ridge jump event of the already opened SCS.

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.

Thermochronology constraints on the Cretaceous-Cenozoic thermo-tectonic evolution in the Gaize region, central-western Tibetan Plateau: Implications for the westward extension of the proto-Tibetan Plateau

• The Gaize region has experienced three exhumation events of ∼100-70 Ma, ∼50-38 Ma and since early Miocene. • The central Tibetan Plateau has undergone five-stage thermo-tectonic evolution since the late Jurassic. • Late Cretaceous exhumation associated with surface uplift and topography growth in the Gaize region represented the westward extending of proto-Plateau. • Low-relief high-elevation topography of the central Tibetan Plateau has established by the early Oligocene. The temporal and spatial variations of exhumation in the central Tibetan Plateau (TP) contain information about timing of the initial rise and growth of the TP. Here, we present multiple system thermochronology data (zircon U-Pb, biotite 40 Ar/ 39 Ar, zircon and apatite fission track, and apatite (U-Th)/He ages) from the Gaize region, central-western TP, to reveal its exhumation and thermo-tectonic history since the Cretaceous. Zircon and apatite fission track and apatite (U-Th)/He analyses in combination with thermal history modeling depicted a three-phase of rapid exhumation scenario in the study area: a phase of Late Cretaceous rapid exhumation (∼10 °C/Ma) followed by an accelerated Eocene-early Oligocene exhumation event (∼ 12 °C/Ma) and a limitedly rapid exhumation episode (∼3 °C/Ma) since the early Miocene. Our study reveals that the Gaize region initially underwent a Late Cretaceous intense exhumation event associated with surface uplift and topography growth which represented the westward extending of proto-Plateau. Our results integrated with previous tectonic, sedimentology, magmatism and low-temperature thermochronology studies throughout the central TP enable us to reappraise a five-phase thermo-tectonic evolution since the Late Jurassic. The Central-Southern Qiangtang terrane experienced the earliest exhumation related to the initial Lhasa-Qiangtang collision during the late Jurassic-Cretaceous (∼150-125 Ma). This process propagated southwards to the southernmost Qiangtang and central Lhasa terranes by the late Early Cretaceous (∼125-100 Ma). Subsequently, most central TP underwent significant cooling and exhumation event during the Late Cretaceous (∼100-70 Ma) in response to the crustal thickening and subsequently lithospheric foundering beneath the Central-Northern Lhasa and southernmost Qiangtang terranes. A phase of rapid exhumation event was also extended to the central TP during ∼55 Ma to ∼30 Ma which was likely triggered by the combination of India-Asia hard collision and southward intracontinental subduction of Jinsha suture zone. Finally, the central TP experienced a limited exhumation with a slow erosion rate since the early Oligocene, suggestive of the establishment of low-relief, high-elevation topography of the proto-TP. Such five-stage thermo-tectonic evolution of the central TP supports an outward growth process of the TP that nucleated in the central Qiangtang core since the Late Jurassic.

Structure and thermochronology of basement/cover relations along the Defiance uplift (AZ and NM), and implications regarding Laramide tectonic evolution of the Colorado Plateau

Interpretation of the late Cretaceous to Eocene Laramide tectonic evolution of the Colorado Plateau is hampered by the difficulty of placing precise temporal constraints on fault-induced basement uplift, for there is a paucity of exposed basement from which thermochronologic ages might be obtained. The Defiance and Zuni uplifts, located on the southeasternmost Colorado Plateau, offer rare basement exposure that provide additional temporal insights. The Zuni uplift exposes abundant Precambrian basement rock, which has been the subject of previous apatite thermochronologic study to interpret low-temperature tectonic/exhumation history. In the Defiance uplift region, which is the main focus of this study, there are two outcrop areas of Precambrian-basement rock along the trace of the East Defiance monocline. Both sites are quarries. Uplift/erosion consequences of Pennsylvanian-Permian Ancestral Rocky Mountains (ARM) deformation are explicit in the geology of these quarries, for the contact between the Supai Group (Permian) and underlying basement (1,703 ± 1.3 Ma, zircon U-Pb) is a nonconformity. Here, we apply a combination of structural analysis of Laramide fold/fault relations and multi-method thermochronology to the exposed granitic basement of both the Defiance and Zuni uplifts. Zircon U-Pb, zircon (U-Th)/He, apatite fission-track, apatite (U-Th-Sm)/He, and hematite (U-Th)/He reveal a poly-phase thermo-tectonic history. Initially, the Paleo-Proterozoic 1.7 Ga basement cooled to ∼400 °C by at least 1.4 Ga, followed by 1.4–1.0 Ga unroofing to depths of ∼8 km. Following cooling, the Defiance-Zuni granitic basement experienced protracted residence at temperatures ≤200 °C (∼8 km) between <i>ca.</i> 900 and 600 Ma. Sedimentary evidence and hematite (U-Th)/He dates bracket the ARM event (400–200 Ma), which may suggest fluid-rock interaction or near-surface exposure associated with the ARM. Following the ARM, the Defiance uplift experienced heating (&gt;120 °C) associated with burial consistent with the stratigraphic overburden, until approximately 80 Ma. Finally, the Defiance-Zuni region experienced initial cooling at &lt;70 Ma, with the main phase of exhumation to the upper crust (&lt;2 km) at <i>ca.</i> 60–40 Ma. Detailed structural modeling along 15 normal-profile cross-sections across the east margin of the Defiance uplift reveals that Laramide trishear monoclinal folding was generated by an oblique-slip master fault that partitioned ∼8 km of strike-slip and ∼1.5 km of reverse-slip displacement. Inferred strike-slip compartmental faulting in the Zuni uplift appears to fit coherently within this overall kinematic model in relation to Laramide loading direction. In the context of geodynamic models for flat-slab subduction during the Laramide tectonic event, consideration of new data from the Defiance uplift (along with other recently reported thermochronology data) provides support for models that bring the flat slab beneath North America along an east-northeastward trajectory, rather than along a more northward trajectory.

Thermo-tectonic history of coastal NW South China Sea: A low-temperature thermochronology study

Coastal NW South China Sea is a critical region for evaluating the contrasting thermo-tectonic histories between the onshore and offshore regions, and the possible surface response to a deep-seated mantle anomaly. To further elucidate the regional post-late Mesozoic tectonic cooling history, low temperature thermochronological data are reported from 16 onshore granite samples. These new data, together with previously reported data, are used to constrain the thermo-tectonic evolution of the onshore southern margin of the South China Block (SCB). Results show that the area has mostly experienced a similar three-stage cooling pattern, characterized by a ~3–8 °C/Myr Early Cretaceous to early Late Cretaceous (~130- ~80 Ma) cooling phase, followed by a period of relative thermal quiescence, and then a further cooling episode initiated in the early Eocene and for most samples continuing until the present day. The early cooling phase is recorded extensively along the southern SCB margin and is probably a combined response to several alternating compressional and extensional tectonic events during the Late Jurassic to early Late Cretaceous (~150- ~80 Ma). The second phase of relative thermal quiescence suggests, in contrast to the offshore and the eastern coast, that the onshore southern SCB margin was not affected markedly by compressional tectonics during the latest Cretaceous. Post-Eocene enhanced cooling and exhumation are probably related to widespread Eocene to Early Oligocene extension, and subsequent uplift due to convergence between the Indo-Australian, Eurasian and Pacific Plates in the onshore southern SCB margin. Southeastward extrusion due to Indo-Asia collision resulted in a decrease in uplift amplitude from NW to SE, but is not recorded in the offshore region. Different tectonic effects result in spatial relief variation from the onshore to the offshore southern SCB margin in the latest Cretaceous obviously different from in the late Cenozoic. NE Hainan Island, which was most likely mountainous during the Late Cretaceous to Paleocene, but became an area of low elevation and relief with gradual exhumation, particularly following significant Eocene–Early Oligocene exhumation. Neogene thermal histories in coastal NW South China Sea do not record any marked cooling rate changes which could be related to significant recent surface uplift and erosion, indicating that the deep anomalous body beneath the Leiqiong Depression might be just a branch of a much larger low-velocity anomalous structure. Our results suggest that the thermo-tectonic evolution of the onshore southern SCB margin (Guangdong) was mainly controlled by Cretaceous NE-trending subduction of the Palaeo-Pacific plate beneath the southeastern SCB, whilst during the Late Cenozoic it was mainly affected by the convergence of adjacent plates, particularly by the Indo-Asia collision.

Meso-Cenozoic thermo-tectonic evolution of the Yili block within the Central Asian Orogenic Belt (NW China): Insights from apatite fission track thermochronology

The Yili block in the Central Asian Orogenic Belt (CAOB), forms the easternmost part of the Kazakhstan collage system. Exploring its thermo-tectonic history is important to reconstruct the intra-continental evolution of the Tianshan belt. In this contribution, we report new apatite fission track (AFT) data from the basement rocks from the northern (i.e. the Wenquan complex) and southern (i.e. the Dahalajunshan - Nalati range) margins of the Yili block. Thermal history modeling reveals that the Wenquan complex underwent moderate basement cooling in the Cretaceous, possibly due to far-field effects of the Tethys-deformation and the following Lhasa-Qiangtang collision. These events at the southern Eurasian margin propagated tectonic stress to the northern Yili and triggered localized deformation. Early Triassic-middle Jurassic moderate cooling is also identified in the Dahalajunshan - Nalati range, and is interpreted to be related to the post-orogenic strike-slip motion along the major shear zones and the effects of the Qiangtang and Kunlun-Qaidam collision. Combined with the published thermochronological data, it is suggested that the northern and southern parts of the Yili block experienced different Mesozoic thermo-tectonic evolution. Basement cooling of the northern Yili block generally took place before the Cretaceous, exhuming shallower crustal levels as compared with the southern one. The intermontane Yili basin may have accommodated substantial propagated contraction induced by the Cretaceous collisional events. Based on our new results and the previously published thermochronological data, it is suggested that the intra-continental reactivation of the North Tianshan and Nalati faults probably did not invoke significant regional exhumation during the Meso-Cenozoic. Instead, small-scale brittle faults controlled localized enhanced denudation.

Mesozoic building of the Eastern Tianshan and East Junggar (NW China) revealed by low-temperature thermochronology

The Eastern Tianshan and East Junggar orogenic belts are major constituents of the southwestern Central Asian Orogenic Belt. This study applies low-temperature thermochronology to constrain the thermo-tectonic history of these two domains. Apatite fission track (AFT) dating of Paleozoic basement samples from the Eastern Tianshan and East Junggar dominantly yield Cretaceous (∼126–70 Ma) AFT ages, except for two granitic samples from the East Junggar with older ages of ∼239 and ∼157 Ma, respectively. Thermal history modeling reveals that the Eastern Tianshan and southern part of the East Junggar experienced moderate to rapid basement cooling throughout the Cretaceous. We interpret it as a far-field effect of accretion and collision along the south Eurasia margin since the Early Cretaceous. Major faults were reactivated and thus may have played an important role in controlling localized fast uplift and cooling. We also dated seven Mesozoic sandstone samples collected from the eastern margin of the Junggar Basin. The detrital AFT age peaks, together with inverse thermal history modeling of the basement, reveal that the East Junggar underwent late Permian to Early Jurassic cooling episodes. These cooling events are thought to be related to post-orogenic transpression along major faults and distal effect of Qiangtang-Eurasia collision. Combined with already published evidence, our new data suggest that the Eastern Tianshan and East Junggar did not undergo significant exhumation during the Cenozoic.

Combined Zircon/Apatite U-Pb and Fission-Track Dating by LA-ICP-MS and Its Geological Applications: An Example from the Egyptian Younger Granites

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) is classically used in U-Pb dating to measure U and Pb isotopic concentrations. Recently, it has become frequently used in fission-track (FT) chronometry too. As an advantage, the U-Pb and FT double dating will enable efficiently determining the crystallization ages and the thermo-tectonic history concurrently as samples volume, analytical time, efforts, and cost will be greatly reduced. To demonstrate the validity of this approach, a Younger granite (Ediacaran age) sample from North Eastern Desert (NED), Egypt was analyzed for U-Pb and FT double dating. The integration of multiple geochronologic data yielded a zircon U-Pb crystallization age of 599 ± 30 Ma, after emplacement, the rock cooled /uplifted rapidly to depths of 9–14 km as response to the post-Pan African Orogeny erosional event as indicated by apatite U-Pb age of 474 ± 9 Ma. Afterwards, the area experienced a slow cooling/exhumation for a short period, most-likely as response to denudation effect. During the Devonian, the area was rapidly exhumed to reach depths of 1.5–3 km as response to the Hercynian tectonic event, as indicated by a zircon FT age of 347 ± 16 Ma. Then the studied sample has experienced a relatively long period of thermal stability between the Carboniferous and the Eocene. During the Oligocene-Miocene, the Gulf of Suez opening event affected the area by crustal uplift to its current elevation. This integration of Orogenic and thermo-tectonic information reveals the validity, efficiency, and importance of double dating of U-Pb and FT techniques using LA-ICP-MS methodology.

Episodic burial and exhumation in North-East Greenland before and after opening of the North-East Atlantic

The geology of North-East Greenland (70–78°N) exposes unique evidence of the basin development between the Devonian collapse of the Caledonian Orogen and the extrusion of volcanics at the Paleocene–Eocene transition during break-up of the North-East Atlantic. Here we pay special attention to unconformities in the stratigraphic record – do they represent periods of stability and non-deposition or periods of subsidence and accumulation of rocks followed by episodes of uplift and erosion? To answer that and other questions, we used apatite fission-track analysis and vitrinite reflectance data together with stratigraphic landscape analysis and observations from the stratigraphic record to study the thermo-tectonic history of North-East Greenland. Our analysis reveals eight regional stages of post-Caledonian development: (1) Late Carboniferous uplift and erosion led to formation of a sub-Permian peneplain covered by coarse siliciclastic deposits. (2) Middle Triassic exhumation led to removal of a thick cover including a considerable thickness of upper Carboniferous – Middle Triassic rocks and produced thick siliciclastic deposits in the rift system. (3) Denudation at the transition between the Early and Middle Jurassic affected most of the study area outside the Jameson Land Basin and produced a weathered surface above which Middle–Upper Jurassic sediments accumulated. (4) Earliest Cretaceous uplift and erosion along the rifted margin and further inland accompanied the Mesozoic rift climax and produced coarse-grained sedimentary infill of the rift basins. (5) Mid-Cretaceous uplift and erosion initiated removal of Cretaceous post-rift sediments that had accumulated above the Mesozoic rifts and their hinterland, leading to cooling of Mesozoic sediments from maximum palaeotemperatures. (6) End-Eocene uplift was accompanied by faulting and intrusion of magmatic bodies and resulted in extensive mass wasting on the East Greenland shelf. This event initiated the removal of a thick post-rift succession that had accumulated after break-up and produced a peneplain near sea level, the Upper Planation Surface. (7) Late Miocene uplift and erosion, evidenced by massive progradation on the shelf, resulted in the formation of the Lower Planation Surface by incision below the uplifted Upper Planation Surface. (8) Early Pliocene uplift raised the Upper and the Lower Planation Surfaces to their present elevations of about 2 and 1 km above sea level, respectively, and initiated the formation of the present-day landscape through fluvial and glacial erosion. Additional cooling episodes of more local extent, related to igneous activity in the early Eocene and in the early Miocene, primarily affected parts of northern Jameson Land. The three earliest episodes had a profound impact beyond Greenland and accompanied the fragmentation of Pangaea. Younger episodes were controlled by plate-tectonic processes, possibly including dynamic support from the Iceland Plume. Our results emphasise that gaps in the stratigraphic record often reflect episodes of kilometre-scale vertical movements that may result from both lithospheric and sub-lithospheric processes.

Lithospheric evolution, thermo-tectonic history and source-rock maturation in the Gippsland Basin, Victoria, southeastern Australia

A fully integrated 3D basin model was built to study the lithospheric structural evolution and the thermal history of the offshore part of the Gippsland Basin to investigate the type, timing and magnitude of its initial opening mechanism and their effects on source rocks. The applied workflow included seismic interpretation of major faults and magmatic features, seismic reinterpretation of existing main stratigraphic boundaries and adjustment of the basement topography. Different scenarios for a McKenzie-type basal heat flow evolution were tested based on a two-step inversion approach, which translates the thickness changes of lithospheric layers into basal heat flow. Finally, a crustal layer model was assigned to the existing 3D numerical basin model and the effects on thermal maturation of petroleum source rocks were investigated. The results of the calibrated inversion model suggest intense lithospheric stretching and mantle upwelling during the Early Cretaceous caused initial breakup and subsidence of the Gippsland Basin. This syn-rift phase was accompanied by increasing basal heat flow from initially ∼50 mW/m2 to a maximum of 80–90 mW/m2. The resulting upwelled Moho with an associated crustal thickness of locally only 8 km agrees with geophysical observations. Elevated paleogeothermal gradients between 50 and 60 °C/km prevailed from ca 120 to 80 Ma. Episodes of compression, uplift, erosion, and thermal subsidence resulted in fast and continuous cooling during the early post-rift and a constant basal heat flow of 45–50 mW/m2 since the Eocene. Two main pulses of petroleum generation were identified in the Paleocene and in the Miocene–Pliocene. This novel two-step crustal layer inversion method allows a detailed reconstruction of the thermal history of rift basins and can provide useful information about the maturation of petroleum source rocks. KEY POINTS A temperature history reconstruction of the Gippsland Basin is given based on a large-scale numerical 3D model. Tectonically induced strong variability in paleoheat flows is recognised. Strong maturation and petroleum generation developed during the Paleogene and Neogene.

Inherited structure as a control on late Paleozoic and Mesozoic exhumation of the Tarbagatai Mountains, southeastern Kazakhstan

Central Asia hosts the Tianshan, the largest intracontinental mountain belt in the world, which experienced major reactivation and uplift since the Oligocene in response to the collision of India with Asia. This reactivation was focused around pre-existing structures inherited from the Paleozoic tectonic history of the region. The significant Cenozoic tectonic reworking of Central Asia complicates efforts to understand earlier phases of intracontinental tectonics during the late Paleozoic and Mesozoic. The Tarbagatai Mountains of eastern Kazakhstan record a thermotectonic history that provides insight into the timing and distribution of intracontinental tectonic activity in Central Asia prior to the India–Eurasia collision. Apatite fission-track and (U–Th–Sm)/He analysis of igneous samples from the Tarbagatai Mountains reveals two episodes of cooling as a result of exhumation following Paleozoic amalgamation. Initial intracontinental deformation during the Late Permian drove exhumation synchronous with activity along newly formed strike-slip faults spanning the Central Asian Orogenic Belt. The major Chingiz–Tarbagatai Fault was reactivated during the Early Cretaceous, driving localized exhumation along the fault. The relative lack of Cenozoic tectonic activity in the Tarbagatai Mountains means that they provide unique insight into the broader thermotectonic evolution of Central Asia during the late Paleozoic and Mesozoic. Supplementary material: Detailed thermochronological data, including plots and tables, are available at https://doi.org/10.6084/m9.figshare.c.5414555

South Atlantic passive margin evolution: A thermochronology case study from the Rio de Janeiro-Três Rios section, SE Brazil

The southeastern Brazilian passive margin records a complex post-rift evolution, with two parallel high-elevation features formed after the opening of the South Atlantic. We applied apatite fission track (AFT) and U–Th/He (AHe) low temperature thermochronology to constrain the thermo-tectonic history of the Serra do Mar escarpment in the area of Rio de Janeiro state. New AFT central ages for basement areas collected from a N–S transect orthogonal to the shoreline between the cities of Rio de Janeiro and Três Rios, range between 98.5 ± 5.3 and 54.1 ± 4.2 Ma, with mean track lengths between 12.34 ± 0.40 and 14.63 ± 0.17 μm. Uncorrected AHe ages lie between 68.1 ± 5.9 and 60.2 ± 7.3 Ma and are consistent with AFT results. Inverse thermal history models constrained by AFT and AHe data imply the earliest cooling onset from the Barremian (Early Cretaceous), with steady rates more common for samples closer to coastal areas. Maximum depths of denudation are between 2.5 and 4.5 km. Published thermochronological data from adjacent areas combined with the new results show a seemingly simpler post-rift evolution for the area, although suggesting structural control of age distribution and exhumation.

Thermochronology of South America passive margin between Uruguay and southern Brazil: A lengthy and complex cooling history based on (U–Th)/He and fission tracks

Thermochronology studies carried out in crystalline rocks on the South America passive margin reveal distinct cooling patterns along the coast. While most of the margin presents syn-to post-rift final exhumation, the region between parallels 29° and 35° S presents primarily pre-rift exhumation. This stretch of the coast corresponds to Uruguay and southern Brazil, where the Rio de La Plata Craton and the Dom Feliciano Belt occur. Previous studies in the area suggest temperatures below 200 °C since the early Paleozoic, and a complex thermotectonic history during the Phanerozoic. Here we present the first zircon fission track ages for both craton and belt; they range between 562 and 280 Ma and corroborate an early Paleozoic cooling of the basement, likely related to regional exhumation after the Brasiliano/Pan-African Cycle (Neoproterozoic-Cambrian) and the formation of West Gondwana. The thermal history after this cooling phase is a matter of debate. Therefore, we compiled all thermochronometry ages available for the region to evaluate the current hypotheses for the basement exhumation. We suggest that this region went through protracted and continuous cooling during the Paleozoic-Mesozoic, until South Atlantic opening in the Jurassic-Cretaceous. The basement was exposed to near surface conditions (T ≤ 60 °C) in the Mesozoic, and the magmatism associated with the breakup likely caused a geothermal disturbance, which may be responsible for the highly dispersed apatite (U–Th)/He ages observed in previous studies. Basement exhumation after South Atlantic opening was minimal in the region. The key to constrain the low temperature thermotectonic history of both craton and belt appears to be a better comprehension of the long-term effects of accumulation of radiation damage within thermochronometers, and to quantify the effects of protracted cooling and minor reheating events on apatites and zircons with variable uranium content.

Late Mesozoic and Cenozoic thermotectonic history of eastern, central and southern Mexico as determined through integrated thermochronology, with implications for sediment delivery to the Gulf of Mexico

Abstract A database of 134 apatite fission track (AFT), and apatite and zircon (U–Th)/He analyses has been assembled for eastern Mexico. Most of these samples have reset ages and track lengths reflecting rapid cooling. Time–temperature histories were modelled for 99 localities, and were converted to depth using a constant gradient of 30°C km −1 . Maps of these results reveal smooth temperature patterns in space and time, indicating that heating was due to regional burial rather than hydrothermal circulation. Cooling began by 90 Ma in the west and 50 Ma along the eastern edge of the Sierra Madre Oriental. These ages mimic the duration of the Mexican Orogeny, which verifies that most of these AFT ages have event significance. The elongate Mayrán Basin, a part of the Mexican foreland basin system, formed and grew across and above the eastern toe of the active Sierra Madre Oriental. This basin subsided between at least 70 and c. 40 Ma, and reached a minimum depth of 6 km. It was a both a catchment and routing system for sediment from US and Mexican sources. The shape of the basin suggests that early outflow was directed through the Burgos Basin into the Gulf of Mexico (GoM). By 50 Ma, some outflow potentially routed southwards through the Tampico Misantla Basin area. The Mayrán Basin subsided until 40 Ma, and then began to uplift and erode. This inversion mobilized the stored sediment and redeposited it into the GoM, filling the offshore Bravo Trough. Volcanism swept eastwards between 90 and 40 Ma, driven by northeastward-directed flat-slab subduction, which may also have driven the contraction. Local subsidence during contraction suggests there was dynamic pull-down created by the underriding flat slab. Subsidence ceased at c. 40 Ma, as volcanism swept back westward and asthenosphere replaced the flat slab. The crust rebounded, creating an ensuing period of massive erosion which peaked around 20 Ma. Southern Mexico was relatively quiet until rapid uplift began in Oaxaca in late Oligocene–early Miocene time. Uplift progressed eastwards to the Chiapas Massif in the late Miocene, commensurate with the eastward translation of the Chortis Block.

Late Mesozoic and Cenozoic thermo-tectonic history of Eastern, Central and Southern Mexico as determined through integrated thermochronology, with implications for sediment delivery to the Gulf of Mexico

Late Mesozoic and Cenozoic thermo-tectonic history of Eastern, Central and Southern Mexico as determined through integrated thermochronology, with implications for sediment delivery to the Gulf of Mexico

Anatexis and metamorphic history of Permian pelitic granulites from the southern Chinese Altai: Constraints from petrology, melt inclusions and phase equilibria modelling

Pelitic granulites from the southern Chinese Altai record a prominent Permian high–temperature reworking event. The lack of solid constraints on anatexis and metamorphic P–T path of these rocks has hindered our understanding of the thermo–tectonic history of Chinese Altai orogen. Here, we present a detailed field and petrological study of the pelitic granulites cropping out at Wuqiagou area, Fuyun county. They occur as lenses or interlayers hosted within biotite–plagioclase gneisses, with a rutile–bearing assemblage composed of garnet ± orthopyroxene + cordierite + biotite ± K–feldspar + plagioclase + quartz ± spinel ± sillimanite + ilmenite. These pelitic granulites preserve diagnostic features of anatexis, such as small patches of leucosomes at macroscopic scale, melt inclusions in garnet porphyroblasts and highly cuspate quartz at microscopic scale. Melt inclusions (up to ~40 μm) are now crystallized into a cryptocrystalline aggregate of feldspars, quartz and biotite (i.e. they are nanogranitoids). Phase equilibria modelling in the NCKFMASHTO (Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3) 10–compositional model system suggests a possible clockwise P–T path involving a post–peak isobaric cooling (IBC) process from 800 to 850 °C to near solidus conditions (700–720 °C) at 5.0–6.0 kbar. SIMS zircon UPb geochronology indicates that the granulite–facies metamorphism took place at 284.1 ± 2.6 Ma, which is coeval with spatially associated mantle–derived mafic intrusions. Therefore, we propose that the Permian granulite–facies metamorphic event occurred in a post–orogenic extensional tectonic setting, which was associated with the input of external heat, related to underplating and intruding of mantle–derived magmas possibly as a result of the Tarim mantle plume activity.

Terrestrial heat flow in the baiyinchagan sag, erlian Basin, northern China

The Baiyinchagan Sag of the Erlian Basin is a Mesozoic continental rift basin located in the eastern part of the Central Asian Orogenic Belt between the North China Craton and the Siberian Craton. The sedimentary fill comprises mainly the Cretaceous sandstones and mudstones underlying Cenozoic succession. Knowledge regarding the factors affecting the tectonic evolution of the Baiyinchagan Sag is lacking. The objective of this study is to obtain new terrestrial heat flow measurements in the Baiyinchagan Sag for constraints on its thermotectonic history. We obtained continuous temperature logs from three boreholes, namely Xi24, Xi3-76 and Xi30 with depths of 1230, 1660 and 2160 m, respectively. Additionally, we gauged the thermal conductivity of the lithologic samples of the main sedimentary rocks. Our analysis indicates that subsurface temperatures are affected by the convection of groundwater and subsurface warming. After removing the influence of groundwater and climatic effects, the subsurface temperature gradients of the Cretaceous Duhongmu and Tenggeer Formations range from 40.4 to 42.1 ℃ km−1. We performed water saturation correction for the measured thermal conductivity data. The thermal conductivities of the Saihantala, the Duhongmu, the Tenggeer, and the Aershan Formations were found to be 1.15, 2.13, 1.99, and 2.15 W m-1 K−1, respectively. Vertical Peclet number analysis of the temperature-depth profile of Xi3-76 borehole with a Peclet number of 0.16 indicates that the conductive heat transfer dominates in the component of the vertical heat transfer. The three new heat flow values range from 80.8 to 89.7 mW m-2, with a mean of 84.9 ± 3.4 mW m-2, significantly higher than the global and regional average whereas consistent with its deep thermotectonic regime.

Thermotectonic History of the Kluane Ranges and Evolution of the Eastern Denali Fault Zone in Southwestern Yukon, Canada

AbstractExhumation and landscape evolution along strike‐slip fault systems reflect tectonic processes that accommodate and partition deformation in orogenic settings. We present 17 new apatite (U‐Th)/He (He), zircon He, apatite fission‐track (FT), and zircon FT dates from the eastern Denali fault zone (EDFZ) that bounds the Kluane Ranges in Yukon, Canada. The dates elucidate patterns of deformation along the EDFZ. Mean apatite He, apatite FT, zircon He, and zircon FT sample dates range within ~26–4, ~110–12, ~94–28, and ~137–83 Ma, respectively. A new zircon U‐Pb date of 113.9 ± 1.7 Ma (2σ) complements existing geochronology and aids in interpretation of low‐temperature thermochronometry data patterns. Samples ≤2 km southwest of the EDFZ trace yield the youngest thermochronometry dates. Multimethod thermochronometry, zircon He date‐effective U patterns, and thermal history modeling reveal rapid cooling ~95–75 Ma, slow cooling ~75–30 Ma, and renewed rapid cooling ~30 Ma to present. The magnitude of net surface uplift constrained by published paleobotanical data, exhumation, and total surface uplift from ~30 Ma to present are ~1, ~2–6, and ~1–7 km, respectively. Exhumation is highest closest to the EDFZ trace but substantially lower than reported for the central Denali fault zone. We infer exhumation and elevation changes associated with ~95–75 Ma terrane accretion and EDFZ activity, relief degradation from ~75–30 Ma, and ~30 Ma to present exhumation and surface uplift as a response to flat‐slab subduction and transpressional deformation. Integrated results reveal new constraints on landscape evolution within the Kluane Ranges directly tied to the EDFZ during the last ~100 Myr.

New insights from low-temperature thermochronology into the tectonic and geomorphologic evolution of the south-eastern Brazilian highlands and passive margin

The South Atlantic passive margin along the south-eastern Brazilian highlands exhibits a complex landscape, including a northern inselberg area and a southern elevated plateau, separated by the Doce River valley. This landscape is set on the Proterozoic to early Paleozoic rocks of the region that once was the hot core of the Araçuaí orogen, in Ediacaran to Ordovician times. Due to the break-up of Gondwana and consequently the opening of the South Atlantic during the Early Cretaceous, those rocks of the Araçuaí orogen became the basement of a portion of the South Atlantic passive margin and related south-eastern Brazilian highlands. Our goal is to provide a new set of constraints on the thermo-tectonic history of this portion of the south-eastern Brazilian margin and related surface processes, and to provide a hypothesis on the geodynamic context since break-up. To this end, we combine the apatite fission track (AFT) and apatite (U–Th)/He (AHe) methods as input for inverse thermal history modelling. All our AFT and AHe central ages are Late Cretaceous to early Paleogene. The AFT ages vary between 62 Ma and 90 Ma, with mean track lengths between 12.2 μm and 13.6 μm. AHe ages are found to be equivalent to AFT ages within uncertainty, albeit with the former exhibiting a lesser degree of confidence. We relate this Late Cretaceous–Paleocene basement cooling to uplift with accelerated denudation at this time. Spatial variation of the denudation time can be linked to differential reactivation of the Precambrian structural network and differential erosion due to a complex interplay with the drainage system. We argue that posterior large-scale sedimentation in the offshore basins may be a result of flexural isostasy combined with an expansion of the drainage network. We put forward the combined compression of the Mid-Atlantic ridge and the Peruvian phase of the Andean orogeny, potentially augmented through the thermal weakening of the lower crust by the Trindade thermal anomaly, as a probable cause for the uplift.