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Late Triassic–Jurassic orogenic and Early Cretaceous epithermal Au deposits are significant producers of Au, Ag, and potentially critical elements (e.g., Te, Se and Sb) in the North Heilongjiang Belt in the Xing'an Block, NE China. However, the preservation mechanism of these Au deposits associated with tectonic evolution is unclear. Here, we conducted zircon U–Pb, sericite Ar–Ar, zircon and apatite (U–Th)/He dating as well as whole‐rock geochemistry in the Xing'an Block. Zircon U–Pb dating shows the ages of 174.1 ± 2.4 Ma for the granodiorite, 169.9 ± 1.6 Ma for the tonalite, 154.0 ± 2.0 Ma for the monzogranite and ca.122 Ma for the diorite. Sericite Ar–Ar dating presents plateau and isochron ages of 163.2 ± 1.8 Ma and 163.4 ± 2.8 Ma. The average apatite (U–Th)/He (AHe) and zircon (U–Th)/He (ZHe) ages from the Jurassic rocks have the ranges of ca. 146–89 Ma and ca. 150–116 Ma and from the Cretaceous are ca. 109–76 Ma and ca. 117–111 Ma, respectively. The Early‐Middle Jurassic intrusions are featured by the tonalite‐trondhjemite‐granodiorite (TTG) rock type. Late Jurassic monzogranite has the geochemical signature of adakitic rocks. The Early Cretaceous granitoids are classified as volcanic arc granites with a part of the Early Cretaceous granodiorite featured by adakitic. These new results reveal five group ages associated with tectonic evolution, Au mineralization and the preservation of the Au deposits. (i) Magmatic events were related to the subduction of the Mongolia‐Okhotsk Ocean during the Early Jurassic (ca. 177–170 Ma) and then the compressional settings with regional deformation (ca. 167–163 Ma). (ii) Thickening crust and orogenic Au mineralization were related to the closure of the Mongolia‐Okhotsk Ocean (ca. 154–145 Ma). (iii) The transformation was from compressional to extensional settings followed by exhumation during the Early Cretaceous (ca. 145–120 Ma), which is the factor of the exhumation of the orogenic Au deposits formed from the Late Triassic to Late Jurassic. (iv) Epithermal Au–Ag mineralization was associated with an extension related to the subduction of the Palaeo‐Pacific Plate (ca. 120–100 Ma). (v) Thermal history shows one thermal event during the Late Cretaceous (ca. 89–76 Ma). The Au deposits have been preserved since the Late Cretaceous. [ABSTRACT FROM AUTHOR]

The fast‐slipping Alpine (∼30 mm/yr), Hope (∼10–20 mm/yr) and Kelly (∼6 mm/yr) faults in the South Island of New Zealand form a complex intersection zone that accommodates tectonic strain along the Australian‐Pacific plate boundary. Analysis of digital topography reveals evidence for stream capture, drainage divide migration, landscape responses to incipient fault development, and preserved enclaves of relic topography that collectively reflect complex interplays between active faulting and landscape evolution. (U‐Th)/He thermochronology of zircon (ZHe) and apatite (AHe) is used to investigate the low‐temperature thermal evolution of rocks in the intersection zone. Weighted mean sample ages for ZHe single grain ages (n = 13 samples) range from ∼9 to 2 Ma, and AHe multi‐grain and single grain aliquot ages (n = 9 samples) range from ∼1.5 to 0.5 Ma. Inverse and forward thermal history modeling reveals distinct spatiotemporal variations in thermal histories. Late Miocene exhumation rates (∼0.6–3.5 km/Myr, assuming geothermal gradients of 33–40 °C/km) through crustal depths of approximately 5–6 km, are interpreted to be controlled by proximity to the Alpine fault, with rocks proximal to the fault recording faster exhumation rates relative to distal samples. Establishment of the Hope‐Kelly fault system in the Quaternary structurally juxtaposed rocks with discordant cooling histories. Rocks throughout the study region record increased cooling rates from ∼2 Ma. Possible causal mechanisms include, spatial changes in rock uplift associated with transport toward the Alpine Fault, increased erosion rates associated with Quaternary climate change, or increased rock mass erodibility associated with development of the Hope‐Kelly fault system. Plain Language Summary: The Alpine, Hope, and Kelly faults are tectonic plate‐boundary faults on New Zealand's South Island. We use topography analysis to show that the landscape in the area where these faults intersect was affected by the formation of the Hope and Kelly faults approximately 2 million years ago (Ma). These faults affect the paths of rivers, height of mountains, and the location of the main drainage divide. We use thermochronology of apatite and zircon crystals, which measures how quickly rocks have cooled as they progressed from depth to the Earth's surface. This analysis shows that rock cooling between 9 and 2 Ma was controlled primarily by the uplift of rocks along the Alpine Fault. At approximately 2 Ma, the rock cooling rate increased in the east, so the entire study area has the same cooling rate from 2 Ma to the present. This could have been caused by changes in rock uplift rates toward the Alpine Fault, which brought rocks more rapidly toward the surface, and/or increases in erosion associated with climate change and rock mass weakening. Key Points: Low temperature (<200°C) thermochronology indicates Late Miocene cooling rates decrease with increasing distance from the Alpine faultSpatially invariant Quaternary cooling rates caused by orogen structure or increased erosion rate due to climate or Hope‐Kelly fault systemThe landscape around the Hope‐Kelly‐Alpine fault intersection is undergoing geomorphic adjustment to incipient faulting [ABSTRACT FROM AUTHOR]

[Display omitted] • Amorgos is a Pelagonian-derived unit, situated above the Cycladic Blueschist Unit. • Variscan-Cadomian and Paleozoic DZ input for Kapsala and metaflysch, respectively. • Oligocene NW-ward retro -wedge thrusting vs Early–Mid Miocene zHe exhumation ages. In the Attic-Cycladic Crystalline Complex (Aegean Sea, Greece), following early syn -convergence exhumation processes, the extensional tectonics resulted in the extreme denudation of the upper plate, preserved today in a few places. The Cycladic Blueschist Unit (CBU) and the underlying Cycladic Basement and the Basal Units have been exhumed in the footwall of detachment systems, juxtaposed against the Pelagonian-derived hanging wall fragments. Traditional views accept that Amorgos Unit occupies a structurally lower position, correlated to the Basal Unit. This study presents lithostratigraphic and structural data, integrated with detrital zircon MDA, provenance analyses, and (U-Th)/He ages, showing a new investigation of the paleogeographic and structural position of Amorgos in the Cycladic archipelago. The low-grade metamorphosed Amorgos Unit presents a tripartite lithostratigraphy: a basal metaconglomerate, a middle carbonate sequence with shallow-water to pelagic facies, and an Eocene (meta)flysch. An HP/LT metabasite huge block is incorporated within the metaconglomerate either by gravitational movements as an isolated olistolith or tectonic processes as a slice during the early deformation stage. Detrital zircon U-Pb analysis on the meta -siliciclastic deposits revealed that the basal metaconglomerate shows a dominant Ediacaran input with Mid-Permian and Precambrian MDAs for the matrix and the high-grade clasts, respectively. The metaflysch shows Paleozoic affinity (e.g., mainly Pelagonian-sourced) and Triassic-Jurassic MDAs. The deformation history of Amorgos includes an early-stage top-to-NW thrusting in the retro -wedge setting of the Late Eocene–Oligocene subduction zone and a late-stage top-to-SE extensional low- and high-angle normal faulting. Zircon (U-Th)/He ages reveal an Early–Mid Miocene (18–14 Ma) exhumation below ∼ 200 °C. Similarities on lithostratigraphy, structural inventory, exhumation history, and structural position of Amorgos Unit with the Santorini Detachment System Pelagonian hanging wall imply their close spatial relationship. From all the above, we propose that Amorgos belongs to the upper plate of the CBU and is paleogeographically located at the southern Pelagonian margin. [ABSTRACT FROM AUTHOR]

The growth mechanisms of the southeastern Tibetan Plateau are debated between models of Oligocene shortening and lateral extrusion of coherent crustal blocks versus Late Miocene flow of low-viscosity lower crust. To test these models, we examine brittle deformation of the north-striking Anninghe fault, which has been acting as a left-lateral strike-slip fault since Late Miocene time, using structural and bedrock low-temperature thermochronologic methods. Different from previous interpretations of Late Miocene strike-slip motion, our structural observations indicate westward contractional dip-slip along the southern segment of the fault. New zircon and apatite (U-Th)/He thermochronologic data along a vertical profile of Precambrian volcanoclastic cover both sides of the Anninghe fault. The age-elevation relationships and inverse thermal modelling suggest a phase of Oligocene-Early Miocene (~24-18 Ma) differential rock exhumation and cooling across the fault, with a mean erosion rate of ~0.30 ± 0.12 km/m.y. and ~0.007 ± 0.007 km/m.y. in the hanging wall and footwall, respectively. Consistent with the structural observations, the higher rate of rock exhumation in the hanging wall indicates an Oligocene-Early Miocene phase of west-verging reverse faulting. Combined with previously published data from adjacent sites, we suggest that the Anninghe fault has experienced a tectonic transition from Oligocene-Early Miocene east-west contraction to Late Miocene strike-slip motion. The early to Mid-Cenozoic crustal shortening contributed to the uplift of the southeastern Tibetan Plateau, supporting the crustal shortening and extrusion model. [ABSTRACT FROM AUTHOR]

The western North China Craton (NCC) entered a stage of craton thinning concentrated on its margin in the Cenozoic, but its Late‐Cretaceous conditions were previously deduced to be relatively quiescent. Therefore, whether the Late‐Cretaceous tectonic reactivation existed on the margin of this block is critical to understanding how the craton evolved into a thinned one. To investigate this possible margin reactivation in the Late Cretaceous, we apply zircon (U‐Th)/He thermochronology to Taibai Mountain on the southern margin of the western NCC. From an ∼3‐km‐high vertical profile with ages decreasing from 98 ± 5 Ma at the peak to 52 ± 7 Ma at the foot, the age‐elevation relationship suggests the rapid exhumation at ca. 78–71 Ma bracketed by two slow exhumation phases. This interpretation is confirmed by 1D half‐space modeling and QTQt inverse modeling, with the rapid exhumation stage having an exhumation rate of 0.1–0.6 km/Myr and a cooling rate of ∼10°C/Myr. Together with previously reported thermochronological data from the margin of the western NCC, the rapid exhumation at ca. 78–71 Ma implies a reactivated margin in the Late Cretaceous before widespread Cenozoic thinning of the craton margin. This Late‐Cretaceous reactivation likely resulted from WNW‐ESE extension expressed by thermo‐tectonic events, basin subsidence, and volcanism in East Asia. Excluding impacts from climate change, lithospheric delamination, and India subduction beneath Eurasia, we infer that the Late‐Cretaceous reactivation on the margin of the western NCC was driven by the far‐field effect of Izanagi Plate subduction beneath the Eurasian Plate during slab rollback of the subducted plate. Key Points: Rapid exhumation of Mt. Taibai at ca. 78–71 Ma is confirmed by the age‐elevation relationship, 1D half‐space modeling, and QTQt modelingSynchronous Late‐Cretaceous rapid exhumation suggests a reactivated margin of the western North China Craton before Cenozoic thinningThis reactivation was triggered by the far‐field effect of Izanagi Plate subduction beneath the Eurasian Plate [ABSTRACT FROM AUTHOR]

The ~1,500‐km‐long, north trending Eastern Flanking Belt of the Himalayan‐Tibetan orogenic system is located along the eastern margin of the Indian subcontinent. Although the belt is a key element of the Cenozoic India‐Asia collisional zone, its tectonic evolution remains poorly understood. This lack of knowledge has impacted our ability to differentiate between competing hypotheses for the evolution of the India‐Asia collision. To address this problem, we integrate constraints on the structural framework and magnitude of Cenozoic shortening strain with thermochronology of the northernmost segment of the belt located directly southeast of the eastern Himalayan syntaxis (i.e., the northern Indo‐Burma Ranges). The study area exposes a southwest directed thrust belt that is bounded by the Indian craton in the west and the right‐slip Jiali fault zone in the east. New and existing (U‐Th)/He and 40Ar/39Ar thermochronologic data indicate that thrust‐related cooling occurred from ~36 Ma in the northeast to ~5.6 Ma in the southwest. Episodes of out‐of‐sequence thrusting occurred at ~30–20, ~14–12, and ~11–6 Ma within the thrust belt. Restoration of the thrust belt yields a minimum horizontal shortening of ~280 km (~86%). These results combined with (1) the recorded local absence of several major Himalayan‐Tibetan lithologic units (i.e., Tethyan Himalayan Sequence, Greater Himalayan Sequence, and southern Gangdese batholith) and (2) the southward decrease in the thrust‐belt width (33–5 km) suggest a complex history of thrusting in the northern Indo‐Burma Ranges and an spatial increase in Cenozoic crustal shortening and/or continental underthrusting from west to east across the eastern Himalayan syntaxis. Key Points: The northern Indo‐Burma Ranges expose a Cenozoic southwest to west directed thrust belt that is bounded by two active right‐slip faultsThrusting since ~36 Ma accommodated >280 km (86%) shortening during clockwise crustal flow around the eastern Himalayan syntaxisOur findings support an increase in Cenozoic shortening and/or continental underthrusting along the easternmost India‐Asia plate boundary [ABSTRACT FROM AUTHOR]

The Taihangshan Mountain Belt, in the central North China Craton, represents an important crustal and tectonic boundary. To explore the complex tectonic evolution of this area during the Mesozoic–Cenozoic, we gathered zircon and apatite (U–Th)/He thermochronology data along a vertical transect (elevation of 630−1584 m) of the northern part of the Taihang Mountain Belt. From our data, we observed three separate rapid cooling phases that occurred at 100 Ma, 50−40 Ma and 27 Ma. Combined with previously published geochronological ages, we suggest that the uplift of the Taihang Mountain Belt initiated during the Jurassic and experienced multiphase rapid uplift from the Cretaceous to the Cenozoic. The early Cretaceous rapid cooling/uplifting events are widespread in the North China Craton and are caused by the collision between the Okhotomorsk Block and the East Asian continental margin. The Eocene and Oligocene rapid cooling events correspond to the initial rifting and thermal subsidence of the Bohai Bay Basin, indicating a coupling between the creation of basins and mountains. [ABSTRACT FROM AUTHOR]

The Jurassic–Cretaceous Great Artesian Basin is the most extensive, and largest volume, sedimentary feature of continental Australia. The source of its mud-dominated Cretaceous infill is attributed largely to contemporary magmatism along the continental margin to the east, but the source of its Jurassic infill, dominated by quartz sandstone, remains unconstrained. This paper investigates the question of a Jurassic sediment source for the northern part of the basin. Jurassic uplift and exhumation of the continental margin crustal sector to the east provided the primary Jurassic sediment source. (U–Th)/He data are presented for zircon and apatite from Pennsylvanian to mid Permian granitoids of the Kennedy Igneous Association distributed within the northern Tasmanides between the Townsville and Cairns regions and for coeval granites of the Urannha batholith from the Mount Carlton district (N Bowen Basin), also within the northern Tasmanides. The data from zircon indicate widespread Jurassic exhumation of a crustal tract located to the east of the northern Great Artesian Basin and largely occupied by rocks of the Tasmanides. Detrital zircon age spectra for samples of the Jurassic Hutton and Blantyre sandstones from the northeastern margin of the Great Artesian Basin show their derivation to be largely from rocks of the northern Tasmanides. In combination, the detrital age spectra and (U–Th)/He data from zircon indicate exhumation owing to uplift generating appreciable physiographic relief along the north Queensland continental margin during the Jurassic, shedding sediment westward into the Great Artesian Basin during its early development. A portion of (U–Th)/He data for zircon are consistent with late Permian–mid Triassic exhumation within the Tasmanides, attributable to the influence of the Hunter--Bowen Orogeny. Evidence of Cretaceous and Paleocene exhumation episodes is also indicated for some samples, mainly by apatite (U–Th)/He analysis, consistent with data previously published from fission track studies. Overall, new data from the present study reveal that the exhumation related to Jurassic regional uplift and the subsequent erosional reworking of the northeast Australian continental margin is critical for the evolution and development of the northern side of the Great Artesian Basin in eastern Australia. Apart from this, another two previously suggested Permian–Triassic and Cretaceous exhumation and uplift episodes along the northeast Australian continental margin are also confirmed by the dataset of this study. U–Pb detrital zircon ages of sandstone samples from the northeastern Eromanga Basin reveal Paleozoic (480–280 Ma) and Proterozoic (1800–1400 Ma) age clusters. (U–Th)/He zircon and apatite dating results of granitoids samples from Cairns, Townsville and the Mount Carlton districts are dominated by Jurassic (198–164 Ma) and Permian–Triassic (272–238 Ma) age clusters. Combination of above two datasets proves the regional uplift-driving Jurassic exhumation episode in the northeast Australian continental is vital for the development of the northern Great Artesian Basin. [ABSTRACT FROM AUTHOR]

The abrupt boundary between accreted terranes and cratonic North America is well exposed along the Salmon River suture zone in western Idaho and eastern Oregon. To constrain the post-suturing deformation of this boundary, we assess the cooling history using zircon and apatite (U-Th)/He thermochronology. Pre-Miocene granitic rocks, along a regional transect, were sampled from accreted terranes of the Blue Mountains Province to cratonic North America (Idaho batholith). Each sample was taken from a known structural position relative to a paleotopographic surface represented by the basal unit of the Miocene Columbia River basalts. An isopach map constructed for the Imnaha Basalt, the basal member of the Columbia River Basalt Group (CRBG), confirms the presence of a Miocene paleocanyon parallel to the northern part of Hells Canyon. The (U-Th)/He zircon dates indicate mostly Cretaceous cooling below 200°C, with the ages getting generally younger from west to east. The (U-Th)/He apatite dates indicate Late Cretaceous-Paleogene cooling, which post-dates tectonism associated with the western Idaho shear zone (WISZ). However, (U-Th)/He apatite dates younger than the Imnaha Basalt, with one date of 3.4 ± 0.6 Ma, occur at the bottom of Hells Canyon. These young (U-Th)/He apatite dates occur along the trend of the Miocene paleocanyon, and cannot be attributed to local exhumation related to faults. We propose that burial ofMesozoic basement rocks by the Columbia River basalts occurred regionally. However, the only samples currently exposed at the Earth's surface that were thermally reset by this burial were at the bottom of the Miocene paleocanyon. If so, exhumation of these samples must have occurred by river incision in the last 4 million years. Thus, the low-temperature thermochronology data record a combination of Late Cretaceous- Paleogene cooling after deformation along the WISZ that structurally overprinted the suture zone and Neogene cooling associated with rapid river incision. [ABSTRACT FROM AUTHOR]

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

Exhumation 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. Key Points: Thermochronometry documents ~100-Myr thermotectonic history of the eastern Denali fault zone (EDFZ)‐bounded Kluane Ranges, southwest YukonData show ~95‐Ma uplift and exhumation, ~70‐ to 30‐Ma relief degradation, and ~30‐Ma uplift and exhumation associated with an evolving EDFZPost‐30‐Ma surface uplift and exhumation is focused <2 km from the EDFZ but less in magnitude than elsewhere along the Denali fault system [ABSTRACT FROM AUTHOR]

The Suez Rift is the northern extension of the Red Sea Rift and is an ideal location to study young continental breakup tectonics. Yet, despite much effort to constrain the timing of rift flank uplift and extensional exhumation in this region, the emerging picture remains uncertain. Here we present new thermochronologic constraints including apatite (U–Th)/He and fission track data from a transect across the eastern flank of the Suez Rift in SW Sinai. The use of two different thermochronometers in conjunction with thermal history modeling and well constrained kinetic parameters delineates a pronounced episode of relatively rapid cooling at 25-18 Ma followed by subdued post ∼18 Ma cooling. In contrast to previous estimates, this cooling pattern suggests that the most rapid uplift and exhumation phase along the Gulf of Suez took place during the early stage of rift formation, prior to the middle Miocene, with over 2.4 km of exhumation occurring during this stage. Uplift and exhumation along the Suez Rift flank slowed substantially post ∼18 Ma, as deformation migrated to the newly formed plate boundary along the Dead Sea Transform. This finding complements and strengthens previous indications for the initiation timing of the Dead Sea Transform plate boundary. The inferred late Oligocene–early Miocene timing of rapid exhumation, associated with tectonic extension and rift flank uplift coincides with the onset of regional alkali-basalt magmatism, suggesting lithospheric heating prior to the rift formation. This observation, along with the elevated topography around the Sinai triple junction and indications for some pre-rifting uplift, supports a more active mantle plume role in the rifting process. • First apatite (U–Th)/He data reported for the Gulf of Suez Rift flanks. • Thermal modeling of (U–Th)/He and Fission Track data including kinetic parameters. • More than 2.4 km of flank uplift is coeval with early volcanism at 25-18 Ma. • Post 18 Ma cessation of exhumation constrains the onset of the Dead Sea Transform. • Intense early uplift supports an active asthenospheric role in the rifting process. [ABSTRACT FROM AUTHOR]

• ZHe dates cluster at intervals of 341.08 ± 14.63 – 262.60 ± 29.10 Ma and 154.74 ± 11.54 Ma in the Jinchuan deposit. • The inverse modeling results support a rapid denudation at the interval of ∼ 340 – 310 Ma in the Jinchuan deposit. • Denudation of ∼ 340 – 310 Ma likely responded to the southward subduction of the Paleo-Asian Ocean. The Proterozoic Jinchuan Ni-Cu-PGE sulfide deposit is one of the three largest magmatic sulfide deposits on the earth which was formed in either the Mesoproterozoic or Neoproterozoic. After mineralization of the giant Jinchuan Ni-Cu-PGE orebody, orogenic movements occurred frequently and strongly in a large-scale area. However, less is known on how the deposit denudated after mineralization yet. In this study, we report a new finding of the rapid uplift and denudation event during Late Paleozoic which is supported by single-grain zircon (U-Th)/He dating of 7 samples with elevations ranging between 1453 m and 2180 m collected from a vertical profile in the Jinchuan area. The numerical dating results cluster within 341.08 ± 14.63 – 262.60 ± 29.10 Ma for 7 samples with elevations ranging between 2180 and 1453 m, and 154.74 ± 11.54 Ma for the lherzolite with elevation of 1220 m. Confined with the published 40Ar-39Ar data, the inverse modelling results support that the Jinchuan deposit underwent a rapid cooling at ∼320 Ma. The numerical dating and inverse modelling results obtained in this study support that the Jinchuan deposit and adjacent area experienced a rapid uplift during 341 – 262 Ma (Late Paleozoic). The rapid denudation during the Late Paleozoic is likely a response to the southward subduction of the Paleo-Asian Ocean, inferred from the regional orogenic movements and magmatism in the adjacent areas. Besides, the zircon (U-Th)/He age of 154.74 ± 11.54 Ma obtained from lherzolite supports a cooling event which is to be further studied. [ABSTRACT FROM AUTHOR]

New zircon and apatite (U‐Th)/He data (AHe and ZHe) from the crystalline basement of the South American passive margin in southern Brazil present a wide distribution of Phanerozoic apparent ages, recording its prerift evolution. Its geological significance can be investigated by modeling the influence of the accumulated radiation damages on the measured crystals in its He ages during a long upper crust residence. Despite the presence of a significant fault in the studied area, the samples essentially constrain a uniform thermal history for the entire study area. Zircon helium ages spread from 472 to 26 Ma and correlate strongly with the radioactive element content of the crystals. Although the region was probably covered by Paleozoic sediments of the Paraná Basin, the ZHe system experienced a more intense thermal overprint, most likely the onset of the Paraná Large Igneous Province (LIP), causing its dispersion. The nearby intrusion of a feeding system of the LIP, the Florianópolis Dyke Swarm, may have contributed for keeping geothermal gradients elevated for a period long enough to promote the observed reset. After the extrusion of the volcanism, the study area was probably covered by up to 2 km of basalt floods, imprinting temperatures above the AHe partial retention zone on the crystalline basement. These were eroded during rapid cooling between 75 and 55 Ma, as indicated by thermal modeling. Additional analyses with Raman spectroscopy were used for calculating radiation damage ages in the zircon crystals measured for (U‐Th)/He, resulting in a comparable set of ages. Key Points: Zircon He ages influenced by accumulated radioactive damage of crystals were partially reset by Cretaceous Paraná LIPApatite He ages were completely reset and record a cooling event between 75 and 55 Ma by erosion of an up to 2‐km thick cover layerRaman spectroscopy‐based zircon radiation damage ages are comparable to He ages [ABSTRACT FROM AUTHOR]

New zircon, titanite, and apatite (U-Th)/He (ZHe, THe, AHe) data for four samples of the 524 Ma McClure Mountain syenite (MMS) in the Wet Mountains of Colorado constrain the <200 °C thermal history of this 40 Ar/ 39 Ar geochronology standard. ZHe dates vary from 420 to 567 Ma, do not correlate with their limited eU range (66–388 ppm), have dispersion attributable to eU zonation, and show no systematic variation between samples. THe dates are 488 to 515 Ma. AHe dates range from 70 to 211 Ma, with some inter-sample variability that could be due to modest post-70 Ma displacements along faults. Our dataset is consistent with recently published (U-Th)/He data for the MMS, although the published ZHe results extend to higher eU and define a negative date-eU correlation not captured by our lower eU zircons. Existing U-Pb and 40 Ar/ 39 Ar thermochronologic data, together with the THe and ZHe results, document rapid post-emplacement cooling of the MMS to ≤200 °C by ~500 Ma. A recent (U-Th)/He study inferred that the MMS subsequently underwent simple slow monotonic cooling until present-day. However, geologic relationships are incompatible with such a history, instead requiring that rocks in the vicinity of the MMS were at the surface at ~480 Ma, ~180 Ma, and ~60 Ma, with possible phases of burial and erosion of varying magnitude between these times. Inverse thermal history modeling can simultaneously satisfy the new and previously published ZHe and AHe data while honoring these geologic constraints. The outcomes of this work highlight that date-eU patterns can be generated by protracted cooling as well as by multiphase heating and cooling histories, and underscore the importance of integrating geologic data to help identify the most probable explanation for a (U-Th)/He dataset. [ABSTRACT FROM AUTHOR]

The timing of cooling and exhumation of mantle peridotites in oceanic and continental settings has been challenging to determine using traditional geo- and thermochronometric techniques. Hence, the timing of the exhumation of mantle rocks to the Earth's surface at mid-ocean ridges, rifted and passive continental margins, and within continental volcanic and orogenic systems has remained largely elusive or only loosely constrained by relative age bracketing. Magmatic spinel [(Mg, Fe)(Al,Cr) 2 O 4 ] is a ubiquitous primary mineral phase in mantle peridotites and is often the only primary mineral phase to survive surface weathering and serpentinization. This work explores spinel (U–Th)/He thermochronology as a novel tool to directly date the exhumation and cooling history of spinel-bearing mantle peridotite. Samples were chosen from a range of tectonic and petrologic settings, including a mid-ocean ridge abyssal peridotite (ODP Leg 209), an orogenic tectonic sliver of sub-continental mantle (Lherz massif, France), and a volcanic-rock hosted mantle xenolith (Green Knobs, NM). Spinel grains were selected based on grain size and morphology, screened for internal homogeneity using X-ray computed tomography, and air abraded to eliminate effects of alpha ejection/implantation. These case studies yield spinel He age results that are reproducible and generally in good agreement with independent age constraints. For ODP Leg 209, a spinel He age of 1.1 ± 0.3 Ma (2 SE) ( n = 8 ) is consistent with independent U–Pb and magnetic anomaly ages for the exhumation of oceanic crust by detachment faulting along this segment of the slow-spreading ridge. Spinel from the Lherz massif yield He ages from 60–70 Ma ( n = 3 ), which correspond well with independent thermochronometric constraints for cooling associated with Pyrenean collisional exhumation. Spinel from a mantle xenolith within a previously undated kimberlite diatreme at Green Knobs, New Mexico, generate a reproducible mean He age of 11.7 ± 1.8 Ma (2 SE) ( n = 6 ) that appears to record young volcanism in the area or age resetting by post-emplacement re-heating or alteration. The combined results of these case studies demonstrate the viability for spinel He thermochronometry to resolve cooling histories of peridotite exhumed through tectonic and volcanic processes. [ABSTRACT FROM AUTHOR]

Titanite is a common U-Th bearing accessory mineral that previous study suggested has a (U-Th)/He closure temperature ( T c ) of 210–175 °C. Although it has been recognized that radiation damage influences the He retentivity of apatite and zircon, this effect has not been documented in titanite. We acquired 51 THe analyses from 11 Archean basement samples across the Kaapvaal craton, South Africa. The THe dates range from ∼20 to 1200 Ma and are negatively correlated with their ∼10–970 ppm span of effective uranium concentration (eU). Raman spectra acquired for 4 of these samples display peak broadening with increasing eU. 4 He diffusion experiments on the same 4 samples suggest T c values that vary by ∼175 °C. Estimated alpha dose versus T c for our results and published THe diffusion data document T c values of ∼150–210 °C at alpha doses <50 × 10 16 α/g, with a sharp decrease in He retentivity above this threshold. This damage-diffusivity pattern is similar to zircon, but the damage level at which the reduction in retentivity occurs appears to be lower for titanite. Because titanite typically has substantially lower eU than zircon, for the same protracted thermal history THe dates are likely to record higher temperature portions of the history than zircon (U–Th)/He dates. The results demonstrate that THe dating can access a much larger temperature range and potentially be used to decipher more detailed time–temperature paths than previously thought. [ABSTRACT FROM AUTHOR]

New (U-Th)/He thermochronology data from the syn-extensional granitoids in the central part of the Menderes Massif in western Turkey reveal a minimum slip rate of 12.5 km/Myr along the Alasehir detachment (~ 14° dip angle) and denudation rates between 1.75 km/Myr and 3.25 km/Myr between 4 Ma and 2 Ma. These values suggest relatively fast exhumation of the Central sub-massif, associated with cooling rates between 53 °C/Myr and 128 °C/Myr, which are higher than the estimated footwall cooling rates (60 °C/Myr to 120 °C/Myr) from the Northern sub-massif. Based on the initial crystallization ages of the syn-extensional granitoid intrusions and their exhumation–related cooling ages, our thermochronological findings suggest that the Central sub-massif in Menderes underwent accelerated uplift and faster exhumation in the latest Cenozoic than the Northern and Southern sub-massifs. This latest doming and rapid extension of the Central sub-massif was associated with the asthenospheric upwelling beneath the region and the related Na-alkaline, Kula volcanism. Our results indicate that the Menderes Massif has had a diachronous uplift and cooling history during its extensional tectonic evolution in the late Cenozoic. Thermal weakening of the young orogenic crust in western Anatolia via both lithospheric and asthenospheric melting episodes and magmatism produced higher than normal geothermal gradients and played a significant role in core complex formation. [ABSTRACT FROM AUTHOR]

The Qinling–Dabie–Sulu orogen is the most prominent Phanerozoic orogenic belt in China. The discovery of ultra-high pressure (UHP) minerals in zircon inclusions suggests that the crust was subducted to deeper than 120 km into the mantle and then exhumed to shallow crustal. Recently, low temperature thermochronology has been applied to constrain the final exhumation of Dabie Shan, while there are few studies describing the Cenozoic exhumation history of the Sulu belt. Here we report some (U–Th)/He ages for various lithologies from Sulu Orogenic belt and its northern part-Jiaobei terrane. The single grain He ages range between 18 and 154 Ma, and most of the samples having large intra-sample age scattering. Several reasons such as invisible U/Th-rich inclusions, grain size effect, slow cooling rate, and zonation of parent nuclide or radiation damage effect may account for this dispersion. For all samples, the pattern of the single grain age data exhibits a peak at ~ 45 Ma which is consistent with the borehole fission-track age pattern in adjacent Hefei Basin. Both (U–Th)/He and fission track ages of the Sulu area suggest an enhanced exhumation/cooling in Early-Middle Eocene in the southern part of Tan-Lu fault zone. This enhanced cooling event coincides with rapid subsidence of North China Basin and rapid uplift of its surrounding reliefs, which indicates basin-mountain coupling. This Eocene event is widespread in central China and could be far-field consequence of India–Asia collision. The convergence rate between Pacific Plate and Eurasia decreased substantially during early Tertiary and reached a minimum in Eocene (~ 30–40 mm/yr) while at the same time the collision between India and Asia was completed. Therefore, the Cenozoic exhumation history of the Sulu Orogenic Belt was a combined result of far-field effect of India–Asia collision and declined subduction rate of the Pacific Plate under Eurasia. [ABSTRACT FROM AUTHOR]

The timing and mode of uplift of the Troodos ophiolite are constrained by low-temperature thermochronology combined with geomorphic analysis. Zircon (U-Th)/He and apatite fission track cooling ages in the Troodos plutonic sequence are all Cretaceous (83-106 Ma) and within error of published zircon U-Pb crystallization ages. This indicates early cooling of the oceanic crust and termination of spreading axis magmatism at ~90 Ma. Apatite (U-Th)/He ages decrease with reconstructed crustal depths from ~40 Ma near the top of the sheeted-dike complex to ~4 Ma within the mantle sequence. A prominent inflection point in the age versus depth curve defines the bottom of the exhumed helium partial retention zone and records the onset of rapid exhumation of the main Troodos massif at 6 ± 2 Ma. Inverse thermal modeling supports this conclusion, indicating that the timing of uplift is earlier than previously estimated. The boundaries of the mantle sequence exposed in the core of the Troodos structure closely overlap the boundaries of a concentric zone delineated by high local relief and higher channel steepness indices, indicating differential exhumation and uplift of this area relative to its surroundings. This zone also overlaps with a prominent negative Bouguer gravity anomaly. The timing and pattern of the Troodos ophiolite uplift suggest that it is driven by serpentinite diapirism, possibly triggered by Miocene reactivation of subduction along the Cyprean Arc. The worldwide ubiquity of suprasubduction zone ophiolites may thus reflect the importance of extensive serpentinization at the overthrusting mantle wedge in obduction processes. [ABSTRACT FROM AUTHOR]

The Tasmanides of eastern Australia record much of the Phanerozoic tectonic development of the retreating Pacific-Australia plate boundary and are an oft-cited example of an orogen that has undergone “tectonic mode switching.” To begin to constrain the timing of exhumation of basement rocks that are now exposed in portions of the NE Tasmanides, we measured apatite and zircon (U–Th)/He ages from the Thomson Orogen and overlying Paleozoic strata in the back-arc of the New England Orogen in NE Australia. Zircon (U–Th)/He ages from basement samples (including those recovered from boreholes at depths of up to 1.1 km) are characterized by large inter- and intra-sample variability and range from approximately 180 Ma (Early Jurassic) to 375 Ma (Late Devonian). (U–Th)/He zircon ages from several individual samples are negatively correlated with effective uranium (eU), a pattern that is also true of the dataset as a whole, suggesting that variations in U and Th zoning and radiation damage are partially responsible for the age variability. The oldest zircon (U–Th)/He cooling ages coincide with the formation of regionally extensive Late Devonian–early Carboniferous back-arc basins, suggesting that Late Devonian extension played a significant role in exhumation of parts of the northern Thomson Orogen. Apatite (U–Th)/He ages from a basement sample and a late Permian sandstone in the overlying Bowen Basin, which are also marked by intra-sample variability and age–eU correlations, span from the Early Cretaceous through Oligocene, in general agreement with previous apatite fission track data. In conjunction with observations of key geologic relationships and prior K–Ar and 40 Ar/ 39 Ar data, our results suggest four overall phases in the thermal history of the northern Thomson Orogen: (1) Cambrian–early Silurian metamorphism during the Delamerian and Benambran Orogenies; (2) protracted cooling during the Late Devonian through mid-Permian that likely resulted from extensional exhumation; (3) Permian–Triassic reheating during burial beneath thick sedimentary basins; and (4) Cretaceous and Paleogene cooling during uplift and erosion. [ABSTRACT FROM AUTHOR]

K-feldspar from the late Miocene Capoas Granite on Palawan in The Philippines appears to contain highly retentive diffusion domains that are closed to argon diffusion at near-solidus temperatures during cooling of this ∼7 km-diameter pluton. This is an important result, for K-feldspar is commonly considered not retentive in terms of its ability to retain argon. Closure temperatures for argon diffusion in K-feldspars are routinely claimed to be in the range ∼150–400°C but the release of39Ar from irradiated K-feldspar during furnace step-heating experimentsin vacuoyields Arrhenius data that imply the existence of highly retentive core domains, with inferred closure temperatures that can exceed ∼500–700°C. These high closure temperatures from the Capoas Granite K-feldspar are consistent with the coincidence of40Ar/39Ar ages with U–Pb zircon ages atca13.5 ± 0.2 Ma. The cooling rate then accelerated, but the rate of change had considerably slowed byca12 Ma. Low-temperature (U–Th)/He thermochronology shows that the cooling rate once again accelerated atca11 Ma, perhaps owing to renewed tectonic activity. [ABSTRACT FROM AUTHOR]

Single-grain apatite (U–Th–Sm)/He ages (He ages) from non-detrital samples sometimes show larger dispersions than can be explained by known sources of age dispersion, such as grain size, radiation damage, parent zonation, fracturing, or intracrystalline inclusions. We present observations and model age bias effects of an additional source of apatite He age dispersion observed in some cases: U–Th-rich grain boundary phases (GBPs) precipitated on apatite crystal surfaces. Apatite grains from several samples with dispersed apatite He ages are coated or partially coated by reddish-orange GBPs rich in Fe, U, and Th. These GBPs are heterogeneous in thickness, grain coverage, and composition, and have effective U concentrations ([eU]) up to ~ 1000 ppm. These phases may have large effects on the bulk [eU] and 4 He compositions of apatite grains and can produce significant He age biases. The direction and magnitude of this age bias is primarily a function of four factors: 1) the host grain's size, 2) the GBPs' thickness and [eU] relative to the host grain, 3) the timing of GBP formation relative to the cooling age of the host grain, and 4) whether the GBPs are preserved and analyzed with the grain during He dating. Some of the most severe effects occur when GBPs formed before or near the time of the apatite cooling age but were lost just prior to analysis, for example during mineral separation. In this case, GBPs of commonly observed thicknesses (1–10 μm) with [eU] 2–10 times that of the host apatite grain implant enough 4 He into typical-sized apatite grains to produce hundreds of percent positive age biases. In contrast, when U–Th-rich GBPs are preserved and analyzed with apatite grains, the resulting He ages can be negatively biased. Though the heterogeneity, variable preservation, and ambiguous formation ages of GBPs preclude a general, quantitative, and practical solution to this problem, our model demonstrates that observed age dispersions in some samples are consistent with the effects of U–Th-rich grain boundary phases and illustrates the conditions under which, and by how much, they will bias He ages. [ABSTRACT FROM AUTHOR]

Extensional-type geothermal systems are complicated by the interrelation between footwall advection during exhumation, and the subsequent redistribution of heat by migrating hydrothermal fluids in the hanging wall. The southern Wassuk Range (WR) hanging wall hosts a moderate-temperature, extensional-type geothermal system and is ideal for studying this duality by analyzing a suite of apatite (AHe) and zircon (ZHe) helium samples from the footwall and hanging wall of the southern WR. Young (~3–4Ma) AHe ages along the WR front are concentrated along the SE corners of segmented footwall blocks, marking the location of focused Mio-Pliocene transtension, fracture dilation, and advection. Hydrothermally reset AHe ages along the footwall range front suggest that the Hawthorne geothermal system (85°–135°C) is long lived and has resided at a prominent structural boundary in the WR footwall marked by localized advection and range-front deformation. In contrast, the presence of both hydrothermally reset and non-reset AHe ages from a ~1.4km deep borehole in the hanging-wall basin probably indicate that the geothermal plumbing system and current manifestation as a thermal anomaly (~113°C) are juvenile and are controlled by the generation of newly formed faults in the hanging wall. AHe ages have been shown here to greatly enhance the focusing of regional-scale geothermal exploration efforts, and for the first time have been used to identify and estimate the temperature of unseen hydrothermal fluids. [ABSTRACT FROM AUTHOR]

The active north trending North Lunggar rift in west central southern Tibet exposes an extensional metamorphic core complex bounded by an east dipping low-angle normal fault. Apatite and zircon (U-Th)/He thermochronology and thermal modeling of the North Lunggar rift document a minimum timing for rift inception at >10 Ma and rapid footwall exhumation between 5 and 2 Ma. Miocene footwall cooling and exhumation rates were initially slow to moderate at <50°C Ma−1 and <1 mm a−1, followed by increased Pliocene rates as high as >400°C Ma−1 and 4-10 mm a−1. Footwall isotherms were significantly compressed during rapid exhumation resulting in an elevated transient geothermal gradient between 50 and 90°C km−1. The minimum magnitude of horizontal extension for the North Lunggar rift is 8.1-12.8 km; maximum is 15-20 km, less in the south at ~10 km. Mean Pliocene extension rate is 1.2-2.4 mm a−1 in the ~120° direction. Results for the North Lunggar rift are similar in magnitude, rate, and orientation of slip to the kinematically linked Lamu Co dextral strike-slip fault to the north. This suggests a state of constrictional strain during Pliocene time along this stretch of the Bangong-Nujiang suture from which the Lamu Co fault emanates. The onset of extension in this region may be explained by crustal thickening and gravitational orogenic collapse, followed by accelerated rifting resulting from localized crustal stretching and increased magmatic activity, potentially driven by the position and northward extent of underthrusting Indian lithosphere. [ABSTRACT FROM AUTHOR]

Abstract: The southern Patagonian Andes constitute the narrow, high-latitude end of the Andean orogen belt in South America, where inherited basin paleogeography, subduction processes, retroarc crustal thickening, and late Cenozoic glaciation have collectively influenced their unusual tectonic and physiographic evolution. New zircon and apatite (U–Th)/He thermochronology from the Patagonian Andes between 50°30′ and 51°30′S suggest concentrated exhumation across the retroarc (leeward) side of the orogen since early Miocene time. Zircon (U–Th)/He (ZHe) ages range from 44 to 10 Ma; oldest ages are recorded in the Patagonian batholith and along the far eastern frontal foreland monocline. Regionally-uniform ZHe ages between 22 and 18Ma, located across a ∼75km wide-zone of the Patagonian retroarc thrust-belt indicate widespread early Miocene cooling through the ZHe partial retention zone. Mesozoic sedimentary and volcanic rocks in this region have been exhumed from at least 5 to 6km depths. Early Miocene denudation of the thrust-belt, deformation, and increased foreland sedimentation rates coincided with opening of the Scotia Sea, suggesting a causal response of the foreland to changes in plate dynamics. The apatite (U–Th)/He (AHe) ages from a similar region range from 11 to 3Ma; the youngest ages (6–3Ma) are spatially clustered within the more deeply-exhumed central thrust domain. We interpret these AHe ages to record >1–2km of erosional denudation associated with late Cenozoic glaciation and fluvioglacial processes in Patagonia beginning ca. 7Ma. Zircon results indicate that since ca. 22Ma, long-term exhumation rates have been highest across the western and central thrust domains (0.22–0.37mmyr−1), and significantly lower along the eastern thrust front (0.10–0.17mmyr−1). Since ∼7Ma, apatite results from these same regions suggest comparable and slightly higher denudation rates (0.14–0.46mmyr−1), particularly within the eastern thrust domain, consistent with efficient erosional processes acting in the retroarc region. These results from the Patagonian retroarc region, particularly the predominance of <7–4Ma AHe ages, provide a new understanding for regional orogenic erosion models that are largely based on existing data from the windward regions. We suggest that retroarc denudation was enhanced by widespread Miocene structural uplift and unroofing of the fine-grained siliciclastic rocks of the marine Cretaceous Magallanes/Austral foreland basin. Furthermore, its location at the southern tip of the orogen, may have allowed additional moisture to reach the leeward side, leading to sustained late Cenozoic erosional denudation. [Copyright &y& Elsevier]

Movement within the Earth’s upper crust is commonly accommodated by faults or shear zones, ranging in scale from micro-displacements to regional tectonic lineaments. Since faults are active on different time scales and can be repeatedly reactivated, their displacement chronology is difficult to reconstruct. This study represents a multi-geochronological approach to unravel the evolution of an intracontinental fault zone locality along the Danube Fault, central Europe. At the investigated fault locality, ancient motion has produced a cataclastic deformation zone in which the cataclastic material was subjected to hydrothermal alteration and K-feldspar was almost completely replaced by illite and other phyllosilicates. Five different geochronological techniques (zircon Pb-evaporation, K–Ar and Rb–Sr illite, apatite fission track and fluorite (U-Th)/He) have been applied to explore the temporal fault activity. The upper time limit for initiation of faulting is constrained by the crystallization age of the primary rock type (known as “Kristallgranit”) at 325 ± 7 Ma, whereas the K–Ar and Rb–Sr ages of two illite fractions <2 μm (266–255 Ma) are interpreted to date fluid infiltration events during the final stage of the cataclastic deformation period. During this time, the “Kristallgranit” was already at or near the Earth’s surface as indicated by the sedimentary record and thermal modelling results of apatite fission track data. (U–Th)/He thermochronology of two single fluorite grains from a fluorite–quartz vein within the fault zone yield Cretaceous ages that clearly postdate their Late-Variscan mineralization age. We propose that later reactivation of the fault caused loss of helium in the fluorites. This assertion is supported by geological evidence, i.e. offsets of Jurassic and Cretaceous sediments along the fault and apatite fission track thermal modelling results are consistent with the prevalence of elevated temperatures (50–80°C) in the fault zone during the Cretaceous. [ABSTRACT FROM AUTHOR]

Abstract: This study presents new down-hole zircon (U–Th)/He (ZrHe) ages, laboratory He diffusion measurements, and numerical thermal modeling of ZrHe ages from the Continental Deep Drilling Project (KTB) in Germany to investigate He diffusion kinetics in zircon in nature over geologic timescales and to test to applicability of laboratory-derived He diffusion kinetics. Single-grain laser (U–Th)/He ages, calculated using standard alpha-ejection correction procedures assuming homogenous parent-nuclide distribution, display a systematic decrease in ZrHe ages from ∼112 to <1Ma with increasing depth. Down-hole ZrHe results display consistent ages of ∼85±15Ma down to ∼4.7km, in agreement with rapid Cretaceous cooling documented by previous thermochronometric studies from the KTB drill hole. Below ∼5km, ZrHe ages systematically decrease in age and are completely reset (<1Ma) below ∼7.2km. The temperature range (∼130–200°C) in which ZrHe ages systematically decrease defines a well-behaved zircon helium partial retention zone (HePRZ). In addition, this study presents new, cycled step-heating experiments on zircon samples from the KTB drill hole. Results from these new KTB zircon diffusion experiments indicate an activation energy (E a ) of 160kJ/mol and a frequency factory (Do) of 0.03cm2 s− 1 with an estimated closure temperature (T c) of 181°C, which are in excellent agreement with published He diffusion kinetics for zircon. To compare the ZrHe results and bulk diffusion kinetics, we modeled diffusion parameters using the well-established thermal history of the KTB drill hole. The computed zircon HePRZ for the KTB drill hole is consistent with observed down-hole ZrHe ages and published and KTB-specific laboratory-derived He diffusion kinetics. Our results from ZrHe analysis from the KTB drill hole suggest that He diffusion of zircon in nature may not be controlled by anisotropic diffusion behavior, but rather behaves in accordance with laboratory-derived diffusion kinetics. The observed ZrHe ages from the KTB drill hole are in excellent agreement with predicted ZrHe age data and underscore the validity and applicability of ZrHe dating as a reliable thermochronometer. [Copyright &y& Elsevier]

Most of the 150 km-long Owens Valley of east-central California, the westernmost graben of the Basin and Range Province and location of the active right-lateral Owens Valley Fault Zone, is filled with more than 2-3 km of Neogene sediments. Two prominent but structurally enigmatic basement blocks, the Alabama Hills and Poverty Hills, rise from the floor of the southern part of the valley. The late Cenozoic tectonic origin of these basement blocks is not known, but previously published hypotheses include: (1) transpressional uplifts; (2) down-dropped normal fault blocks; and (3) giant landslides from adjacent ranges. We measured apatite (U-Th)/He ages on 15 samples from the Alabama and Poverty Hills to understand the history of shallow crustal exhumation of these structures, and to potentially correlate them to rocks from adjacent ranges. Apatite He ages for the Alabama and Poverty Hills range from ∼63 to 52 and ∼61 to 39 Ma, respectively, with one sample from the Alabama Hills yielding an older weighted mean age of 79.3 ± 2.2 Ma (2σ). These ages are similar to those measured at elevations 1.5-3.0 km higher in both the adjacent Sierra Nevada and White/Inyo Mountains. Together with a lack of evidence for transpressional structures and the presence of extensive weathering of an ancient inherited surface on top of the Alabama Hills, these results are most consistent with an origin as a down-dropped normal fault block. A structural reconstruction using tilt-corrected southern Sierra Nevada age-elevation correlations requires 2.6 km of vertical and 1.5 km of eastward motion for the Alabama Hills along the Sierra Nevada Frontal Fault. Although we cannot conclusively rule out a landslide origin, our preferred explanation for the Poverty Hills data is that it is a down-dropped normal fault block that was transported from the Inyo Mountains along a right-lateral fault possessing a significant normal component. [ABSTRACT FROM AUTHOR]

Structural and thermochronologic studies of the western margin of the central Andean Plateau show changing styles of deformation through time that give insights into tectonic evolution. In southwest Peru, uplift of the plateau proceeded in several distinct phases. First, NW striking, NE dipping reverse faults accommodated uplift prior to ∼14-16 Ma. Subsequent uplift of the plateau relative to the piedmont (between the plateau and the Pacific Ocean) occurred between ∼14 and 2.2 Ma and was accommodated by NW striking, SW dipping normal faults and subparallel monoclinal folds. The youngest phase of uplift affected the piedmont region and the plateau margin as a coherent block. Although the uplift magnitude associated with phase 1 is unknown, phases 2 and 3 resulted in at least 2.4-3.0 km of uplift. Up to 1 km of this may have occurred during phase 3. Geodynamic processes occurring in both the continental interior and the subduction zone likely contributed to uplift. [ABSTRACT FROM AUTHOR]

Abstract: A practical issue in determining a (U–Th)/He age is the correction factor (F He) that accounts for potential He loss due to alpha ejection during the decay of U and Th located in the outer 20 µm of a mineral grain. An accurate determination of F He is affected by the accuracy of measurements made by individual observers and the need for a subjective assessment of crystal morphology relative to an ideal crystal shape. Other issues include the presence of latent mineral inclusions or fracture planes that are potential pathways for helium loss. These issues are potentially most important for detrital grains where grain shape and transparency have been affected by weathering. We used X-ray Micro-Computed Tomography (MicroCT) analysis to objectively and quantitatively address these problems. Using traditional microscopy, four workers with considerable experience in U–Th/He studies independently examined the same set of apatite and zircon grains and reported F He values that agree to within 4% and 9%, respectively. These same grains were then imaged and measured using MicroCT to obtain X–Y–Z dimension, surface area (S) and volume (V) data. F He values calculated using the MicroCT S/V differed by up to 24% as compared to microscope-based F He determinations. The largest discrepancies occurred in small grains with deviations from ideal hexagonal/tetragonal dipyramidal grain morphology. A significant advantage of MicroCT scans is the ability to computationally excise the outer 20 µm layer from the grain via a 3D-erosion procedure. The “effective” F He is proportional to (eroded V /original V) and objectively accounts for the daughterless parent component in each grain independent of morphology and without the need for microscopic measurements. The “effective” F He determined by triple erosion is up to 6% smaller than that derived using traditional microscopy methods. MicroCT can also be successfully used prior to analysis to reveal internal fractures, mineral and fluid inclusions to 1 µm resolution via density and elemental contrasts, and to provide accurate volume measurements for the calculation of U and Th concentrations in single grains. [Copyright &y& Elsevier]

Abstract: Apatite fission-track (FT) and single grain (U–Th)/He ages from four vertical profiles in central Dronning Maud Land (East Antarctica) range from 312±20 Ma to 135±11 Ma and 304±28 Ma to 104±8 Ma, respectively. The combined age data allows to discriminate between undisturbed cooled (due to exhumation) and thermally overprinted crustal blocks. Profiles at the Zwieselhöhe and the Conradgebirge revealed unusual apatite FT vs. elevation relationships and (U–Th)/He ages older than the corresponding central apatite FT ages, possibly providing evidence for a Jurassic thermal overprint. Most probably Jurassic magmatism and associated advective heating led to total annealing of the apatite fission-tracks but helium only partially diffused. The model developed in this paper suggests that the (U–Th)/He ages from the Zwieselhöhe and Conradgebirge profiles are in part relicts of the pre-Jurassic cooling history. Two thermally undisturbed vertical profiles are used to record the long-term cooling history of central Dronning Maud Land. Time-temperature paths derived from modelled apatite FT data of these profiles revealed two phases of accelerated cooling during the Late Carboniferous and the Early Jurassic. Both phases are followed by slow cooling which is also documented by the spread in apatite (U–Th)/He single grain ages. The cooling at the end of the Carboniferous is most probably related to far field effects associated to the prevailing convergent tectonics. During the initial separation between East Antarctica and Mozambique erosion along an evolving rift shoulder caused the Jurassic cooling. Denudation of the basement was simultaneous with volcanism with both pre-dating (c. 20–10 Ma) sea-floor spreading in the Riser Larsen Sea (c. 155 Ma). Post Jurassic cooling was restricted to the lowest temperature sensitivity of both methods. Combined inverse modelled apatite FT data and forward modelled (U–Th)/He data suggest an Eocene/Oligocene cooling step, possibly related to the flexural-isostatic response to the development of ice-sheets. [Copyright &y& Elsevier]

Abstract: The use of (U–Th)/He thermochronometry in old slowly cooled terranes has long been debated. Hence, studies of natural setting are needed to verify the expected diffusivity behaviour of helium. Our results demonstrate that the (U–Th)/He method can be applicable to samples older than 200 Ma, and that available helium diffusion models can reproduce the results obtained from the age-vs.-depth trends. In addition, the results shed some light on the cross-validation with the apatite fission-track thermochronometer. (U–Th)/He thermochronometry on apatites has been applied to samples taken from drill cores in the Precambrian basement in southeast Sweden to unravel the time of exhumation of the uppermost 1–3 km of the crust. Much of the Phanerozoic exhumation history in Sweden is poorly constrained due to a large hiatus in the sediment record. Results from the drill cores yield He ages decreasing with increasing depth from ∼270 Ma at the surface down to ∼120 Ma at 1700 m depth. The age-vs.-depth trend shows an inflection point at ∼1400 m depth, which coincides with the upper boundary of the present Helium Partial Retention Zone. A period of slow exhumation (∼17 m/my), probably linked to the isostatic uplift of the Caledonian foreland basin, is revealed by the upper section of the trend in the data. The results demonstrate that the area has not been reheated since the mid-Permian. This argues against the existence of a thick Mesozoic sedimentary cover in this region, which, if present at all, cannot have exceeded 100 m in thickness. Furthermore, the age-vs.-depth trend below the inflection point allows dating the cessation of exhumation at approximately 100 Ma. The area has had no significant amount of sedimentation, erosion or uplift since this time. [Copyright &y& Elsevier]

Foreland basins associated with collisional mountain belts undergo postdepositional deformation in response to compressive stress exerted from the evolving orogen. The low thermal regime of such processes requires sensitive methods to unravel the structural evolution of such regions. In this study, we conducted apatite fission track (AFT) and (U-Th)/He thermochronology on the sedimentary succession of the Subathu basin in the Himalayan foreland of the Himachal Pradesh region in India, an area preserving the sedimentary record of the India-Asia collision since the late Paleocene-early Eocene. The results show that the Subathu basin exposes a fossilised apatite partial annealing zone (APAZ) depicted by incompletely reset AFT ages and shortened track lengths in the Paleocene-middle Miocene pre-Siwalik units and unreset ages in the Neogene Siwalik Group. We associate the partial annealing of the pre-Siwalik rocks with thickening due to internal imbrication and nappe stacking triggered by shearing along the Main Boundary Thrust and its splays since the middle Miocene. Thermal modelling of the Siwalik rocks projects a rapid heating up to approximately 90–100 °C reached between 4 and 1 Ma. Following the thermal peak, the Siwalik rocks cooled rapidly, as indicated by 2.6–1.2 Ma AHe ages. We associate this recent cooling event with SW-directed thrusting along the Main Frontal Thrust, which placed the foreland basin over the Gangetic Plains. Our results are similar to those obtained for the foreland basin in Nepal, indicating that the movement along the youngest major discontinuity of the Himalaya is synchronous along the orogen. • Foreland basin in the NW Himalaya exposes apatite partial annealing zone • Thermal climax achieved during nappe stacking linked to thrusting along the MBT • Rapid cooling of the Siwalik sediments records initiation of the MFT at 1 Ma [ABSTRACT FROM AUTHOR]

• Zhengguang has experienced at least two post-ore tectono-magmatic events. • The post-ore volcanic eruption and slow exhumation since ~ 100 Ma favor the preservation of Zhengguang. • There is exploration potential for pre-Mesozoic porphyry and epithermal deposits within eastern CAOB. The Zhengguang epithermal Au-Zn deposit, located in Heilongjiang Province, NE China, is an Early Paleozoic intermediate sulfidation epithermal deposit which is adjacent to the Duobaoshan and Tongshan porphyry Cu deposits in the Duobaoshan magmatic arc, eastern Central Asian Orogenic Belt (CAOB). Our new 40Ar/39Ar dating presents plateau ages of 276.9 ± 1.2 Ma (MSWD = 1.5) for adularia and 265.7 ± 1.2 Ma (MSWD = 3.5) for illite. These ages are clearly younger than the mineralization age of Zhengguang (~480 Ma) and therefore represent a post-ore event which reset the adularia and illite argon systems. The resetting event could be related to post-collision of Xing'an Block and Songliao-Xilinhot Block. The weighted mean of zircon (U–Th)/He ages (ZHe) and apatite (U–Th)/He ages (AHe) from the same dacite porphyry with illite dating sample are 192 ± 10 Ma (MSWD = 2.2) and 98.8 ± 5.3 Ma (MSWD = 2.1), respectively. The ZHe age (~190 Ma) indicates a tectonothermal resetting event, possibly related to the development of Tongshan fault whereas the AHe age (~100 Ma) likely reflects 3 km-deep burial at Zhengguang. The intra-sample variations of (U–Th)/He ages for zircon grains are mainly due to radiation damage, while those for apatite are unknown. We argue that the post-ore volcanic eruption and slow uplift and exhumation rate caused by rollback of the Paleo-Pacific plate could facilitate burial and preservation of the epithermal (and by inference porphyry) deposits in NE China. Considering the complex collisional and amalgamation history in this area, we believe that there is exploration potential for ancient porphyry and epithermal deposits within the eastern section of the CAOB. [ABSTRACT FROM AUTHOR]

The northeastern Tibetan Plateau is a key place to test several contrasting tectonic models regarding uplift of the plateau. However, our understanding of the Cenozoic deformation history of the northeastern Tibetan Plateau is incomplete, preventing a clear understanding of the uplift and deformation mechanisms of this plateau. Here, we present new apatite (U-Th)/He ages from the hanging wall of the Qaidam Shan fault, which lies on the southern margin of the Qilian Shan. Our results reveal a phase of rapid exhumation during 15–10 Ma driven by thrusting accompanied by southward growth of the Qilian Shan. A review of the literature reveals that this phase of tectonic deformation is widespread in the northeastern Tibetan Plateau and some recent studies suggest ~25–20 Ma onset of sediment accumulation in the northern Qaidam Basin bounding the Qilian Shan. These results challenge models arguing for early deformation of northeastern margin of the Tibetan Plateau. • We present apatite (U-Th)/He altitude transect ages from the southern Qilian Shan. • The data reveal rapid exhumation of the southern Qilian Shan during 15–10 Ma. • Regional deformation in the mid-late Miocene occurred in the NE Tibetan Plateau. [ABSTRACT FROM AUTHOR]