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[Abstract The uplift and associated exhumation of the Tibetan Plateau has been widely considered a key control of Cenozoic global cooling. The south‐central parts of this plateau experienced rapid exhumation during the Cretaceous–Palaeocene periods. When and how the northern part was exhumed, however, remains controversial. The Hoh Xil Basin (HXB) is the largest late Cretaceous–Cenozoic sedimentary basin in the northern part, and it preserves the archives of the exhumation history. We present detrital apatite and zircon (U‐Th)/He data from late Cretaceous–Cenozoic sedimentary rocks of the western and eastern HXB. These data, combined with regional geological constraints and interpreted with inverse and forward model of sediment deposition and burial reheating, suggest that the occurrence of ca. 4–2.7 km and ca. 4–2.3 km of vertical exhumation initiated at ca. 30–25 Ma and 40–35 Ma in the eastern and western HXB respectively. The initial differential exhumation of the eastern HXB and the western HXB might be controlled by the oblique subduction of the Qaidam block beneath the HXB. The initial exhumation timing in the northern Tibetan Plateau is younger than that in the south‐central parts. This reveals an episodic exhumation of the Tibetan Plateau compared to models of synchronous Miocene exhumation of the entire plateau and the early Eocene exhumation of the northern Tibetan Plateau shortly after the India–Asia collision. One possible mechanism to account for outward growth is crustal shortening. A simple model of uplift and exhumation would predict a maximum of 0.8 km of surface uplift after upper crustal shortening during 30–27 Ma, which is insufficient to explain the high elevations currently observed. One way to increase elevation without changing exhumation rates and to decouple uplift from upper crustal shortening is through the combined effects of continental subduction, mantle lithosphere removal and magmatic inflation., We present detrital apatite and zircon (U‐Th)/He data from late Cretaceous–Cenozoic sedimentary rocks of the Hoh Xil Basin (HXB). These data, combined with regional geological constraints and interpreted with inverse and forward model of sediment deposition and burial reheating, suggest that ~4–2.7 km vertical exhumation initiated at 30 Ma in the eastern HXB. A simple model of uplift and exhumation would predict a maximum of 0.8 km of surface uplift after upper crustal shortening during 30–27 Ma, which is insufficient to explain the high elevations currently observed. One way to increase elevation without changing exhumation rates and to decouple uplift from upper crustal shortening is through the combined effects of continental subduction, mantle lithosphere removal and magmatic inflation. ]

Water isotopes are an important tool for reconstructing the amount of atmospheric lifting related to high topography in the geologic past. However, our capacity for meaningful interpretation requires understanding the climatic setting and isolating the influence of orography on water isotopes. Patagonia9s simple, steady climatology and location within the Southern Westerlies makes it an ideal setting for successful application of water isotopes to measuring topography through time. Here we use hydrated volcanic glass to construct a new record of the size of the Patagonian Andes during the Cenozoic. We also utilize a novel method for identifying the contribution of orography in regional climate records. Our results show that variation in the observed record can largely be explained by variations in climate. Thus we conclude that the mountain range has maintained a size similar to modern since at least Paleocene. This result is in agreement with geologic data, which constrain the bulk of the surface uplift of the Andes to the Cretaceous. The reconstruction of the Patagonian Andes, which grew in the Cretaceous and remained high through the Cenozoic, is markedly different from the widely held view of Miocene formation of this mountain range. In particular, the topography appears to remain stable during the northward propagation and collision of offshore spreading centers.

Sedimentary provenance studies have come to be overwhelmingly based upon U–Pb geochronologic measurements performed with detrital zircon while alternative and potentially complementary approaches such as conglomerate clast studies and heavy mineral analysis have faded in importance. Measurement of Pb isotopic compositions in detrital K-feldspar is among the under-utilized approaches available to ascertain sedimentary source regions. While it has been long recognized that common Pb isotope compositions recorded by K-feldspar vary widely and reflect the crustal provinces from which the host basement rocks crystallized, use of the approach has suffered due to a lack of appropriate statistical models and ground truth compositional data from source regions. In this paper, we: (1) present high-throughput LA-ICPMS analysis protocols needed to generate statistically meaningful detrital K-feldspar Pb isotope data sets; (2) develop an interpretative approach based upon 208Pb/206Pb vs. 207Pb/206Pb that incorporate information from the U- and Th-decay systems into one two-dimensional plot that is amenable to analysis using two-dimensional Kolmogorov–Smirnoff statistical tests; (3) generate new Pb isotopic data from basement rocks from southwestern North America to improve knowledge of the Pb isotopic properties of potential source regions; and (4) generate new Pb isotopic data from Lower Eocene to Lower Miocene sedimentary rocks to evaluate changes in drainage patterns that occurred in response to deformation that affected the southern California margin. Through this case study, we demonstrate how our new analytical and interpretative methods could be profitably applied to future geochemical and provenance studies and tectonically driven re-organization of drainage patterns.

The topography, climate, and geology of the central Patagonian Andes provide an auspicious natural laboratory to track long-term rates of erosion in a dynamic mountainous landscape. Herein, we report a mountain-scale record of erosion rates in the central Patagonian Andes from >10 million years (Ma) ago to present, which covers the transition from a fluvial to alpine glaciated landscape. Apatite (U-Th)/He ages of 72 granitic cobbles from alpine glacial deposits show slow erosion before ~6 Ma ago, followed by a two- to three-fold increase in the spatially averaged erosion rate of the source region after the onset of alpine glaciations and a 15-fold increase in the top 25% of the distribution. This transition is followed by a pronounced decrease in erosion rates over the past ~3 Ma. We ascribe the pulse of fast erosion to local deepening and widening of valleys, which are characteristic features of alpine glaciated landscapes. The subsequent decline in local erosion rates may represent a return toward a balance between rock uplift and erosion.

Early glaciations in the Patagonian Andes show that fast initial glacial erosion is transient and is not a steady condition., We report a mountain-scale record of erosion rates in the central Patagonian Andes from >10 million years (Ma) ago to present, which covers the transition from a fluvial to alpine glaciated landscape. Apatite (U-Th)/He ages of 72 granitic cobbles from alpine glacial deposits show slow erosion before ~6 Ma ago, followed by a two- to threefold increase in the spatially averaged erosion rate of the source region after the onset of alpine glaciations and a 15-fold increase in the top 25% of the distribution. This transition is followed by a pronounced decrease in erosion rates over the past ~3 Ma. We ascribe the pulse of fast erosion to local deepening and widening of valleys, which are characteristic features of alpine glaciated landscapes. The subsequent decline in local erosion rates may represent a return toward a balance between rock uplift and erosion.

The studied deep-seated plutonic rocks of the Malyi Ural Paleozoic island arc include Sob’ gabbroid, diorite, and plagiogranitoid and Kongor gabbroid, diorite, and monzonitoid, which formed under similar P–T conditions. U–Pb LA-ICP-MS zircon dating established similar concordant age values: 406 ± 2 Ma for hornblende gabbrodiorite of the major intrusive phase in the Sob’ complex and 396 ± 1 and 393 ± 2 Ma for bipyroxene gabbrodiorite of the early and major phases in the Kongor complex. Our age data have made it possible to determine the formation time of the Kongor complex as Late Emsian–Early Eifelian (399–393 Ma). The largest volumes of island-arc igneous rocks belonging to the calc-alkali gabbro–diorite–tonalite–plagiogranite series formed in the Praghian–Early Eifelian (410–393 Ma). The Late Emsian–Early Eifelian (399–393 Ma) was characterized by the development of much smaller bodies consisting of Kongor rocks pertaining to the calc-alkali and high-K calk-alkali range, gradually transitioning into shoshonite–latite. High-K rocks formed upon completion of calc-alkali magmatism, likely due to the gradual decay of Devonian suprasubduction magmatism and partial melting in magma generation or due to the involvement of a second magma source.

The information provided by detrital studies can be greatly enhanced by coupling geochronology and isotopic measurements from the same grains. While accessory minerals like zircon and apatite have been widely exploited in this regard, modal phases have been under-utilized. The benefits of using K-feldspar in detrital studies are twofold: K-feldspar 40Ar/39Ar has shown promise as a detrital thermochronometer and incorporation of common Pb into K-feldspar allows its Pb isotope composition to be used as a provenance tool. In this paper, we quantitatively investigate the effects of laser fusion during 40Ar/39Ar analyses of K-feldspar upon subsequent LA-ICP-MS measurement of Pb isotopic ratios. The results reveal that significant Pb volatilization occurs during laser fusion of K-feldspar. While Pb isotopes do not appear to be significantly fractionated, counting statistics suffer as Pb concentrations are lowered. Conversely, neutron irradiation appears to have a small though inconsequential impact upon Pb isotopic measurement of K-feldspar. Consequently, K-feldspar can be analyzed for Pb isotopes prior to total fusion 40Ar/39Ar analysis. Despite this artifact, coupled 40Ar/39Ar and Pb isotopic measurements constitute a promising approach for provenance studies that seek to constrain the geochemical nature and thermal evolution of basement source regions.

Outcrops within the Eocene Domengine Formation (central California) provide an exceptional opportunity to observe the relationship between depositional facies and submarine mass failure. The Domengine Formation is interpreted as an assemblage of heterolithic, shallow- to marginal-marine deposits that record progradation and aggradation prior to regional flooding and local collapse of the shelf. Structural analysis of soft-sediment folds and reverse faults within the informally named New Idria mass-transport deposit (MTD) suggests transport toward the west to southwest, which is consistent with paleoflow measurements from cross bedding within the MTD. Depositional facies have a strong influence on the character of soft-sediment deformation (e.g., style and scale of folding and faulting), and major layer-­parallel detachment surfaces within and below the New Idria MTD occur where mudstone-dominated or heterolithic units underlie sandstone-dominated units. Conditions favorable to gravitational instability and eventual collapse of the shelf include (1) high sedimentation rates within a rapidly aggrading system; (2) loading of under-compacted, mechanically weak, fine-grained ­layers by overlying, denser sand bodies; and (3) earthquake seismicity and/or over-steepening of slopes within a tectonically active, convergent margin setting. This study provides a rare detailed glimpse into the collapse of a deltaic stratigraphic sequence, yielding insight into the linkage between marginal marine facies and depositional architecture and the propensity for submarine mass failure of continental shelves.

The Arctic Alaska terrane of northern Alaska and Yukon is one of several exotic terranes in the North American Cordillera with putative early Paleozoic connections to the northern Caledonian-Appalachian orogen. The U-Pb and 40 Ar/ 39 Ar isotopic data from detrital minerals in pre-Mississippian sedimentary units of the northeastern Brooks Range are presented here to investigate the consequences of Caledonian orogenesis on sediment dispersal trends and the paleogeography of northern Laurentia. Neoproterozoic–Cambrian siliciclastic rocks of the informal Firth River group and the Neruokpuk Formation were most likely deposited along a passive margin that sourced Archean and Paleoproterozoic basement rocks of the Canadian shield and reworked Mesoproterozoic and younger sedimentary units. These strata are overlain by a Lower Ordovician–Lower Devonian succession of fine-grained siliciclastic turbidites, herein referred to as the Clarence River group, which records a prominent shift in provenance most likely associated with the onset of the Caledonian-Appalachian orogeny in northeast Laurentia. U-Pb detrital zircon age populations of ca. 470–420 and 990–820 Ma, along with 40 Ar/ 39 Ar detrital muscovite ages of ca. 470–430 Ma, support provenance connections with the East Greenland Caledonides, Pearya, and Svalbard. Partially reset 40 Ar/ 39 Ar ages in these sedimentary successions are linked to low-grade metamorphism associated with the Early–Middle Devonian Romanzof orogeny, a poorly understood tectonic event in the Brooks Range that is possibly associated with the emplacement of an allochthonous oceanic assemblage, herein named the Whale Mountain allochthon.

In the central Klamath Mountains, the English Peak plutonic complex (EPC) invaded the faulted contact between the outboard Eastern Hayfork and inboard North Fork terranes of the Western Paleozoic and Triassic Belt (WTrPz). This calc-alkaline igneous complex is composed of two small, ~1–2-km-diame­ter, relatively mafic satellitic plutons peripheral to the younger, much larger, ~10–15-km-diameter English Peak zoned granitic pluton. The EPC magmas were mantle derived and reflect temporary residence and mixing at various depths in the overlying crust, with initial storage and modification near the Moho, and uppermost crustal emplacement at 5–10 km depths. Phase assemblages suggest pre-emplacement magma storage at a depth of ~20–25 km for the early satellitic plutons, versus ~15–20 km for samples from the larger zoned granitic pluton. We obtained zircon U-Pb geochronologic results (reported as internal and external weighted-mean 207 Pb-corrected 206 Pb/ 238 U ages, 95% confidence level) from seven samples in the complex via laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS). The 172.3 ± 2.0 [3.7] Ma Uncles Creek and 166.9 ± 1.6 [3.4] Ma Heiney Bar satellitic plutons range from gabbro–quartz diorite to granodiorite in bulk-rock composition. The main English Peak pluton consists of an early stage of gabbro-tonalite (three samples: 160.4 ± 1.1 [3.1] Ma, 158.1 ± 1.1 [3.1] Ma, and 158.0 ± 1.2 [3.1] Ma) and a late stage (two samples: 156.3 ± 1.3 [3.1] Ma and 155.3 ± 1.2 [3.0] Ma) passing inward from tonalite through granodiorite to a central zone of granite. The 172 Ma age of the Uncles Creek pluton makes it coeval with Middle Jurassic Western Hayfork arc magmatism. In contrast, Heiney Bar and the main English Peak igneous ages overlap some of the oldest and youngest components, respectively, of the Middle to Late Jurassic Wooley Creek plutonic suite. Study of this multiple-intrusion complex provides an illuminating example of the gradual intermediate-to-felsic modification of the upper crust in the central Klamath Mountains. Inherited zircon ages of ca. 172 Ma in two other EPC samples indicate potential Middle Jurassic crustal sources or contaminants. Geochronologic correlation of the EPC with geologic histories of other Klamath terranes provides fresh insights for understanding spatial and temporal elements of Middle to Late Jurassic arc magmatism in the Klamath Mountains sector of the Cordilleran margin. This igneous activity illuminates some petrotectonic processes whereby accreted ophiolitic basement terranes were modified and incorporated into the evolving Jurassic continental crust. It took place prior to the earliest Cretaceous onset of westward transport of the stack of Klamath allochthons relative to the active Jura-Cretaceous Sierran calc-alkaline arc.

The first U‒Pb dates are obtained for detrital zircons from Upper Precambrian deposits of the Sredni (Zemlepakhtinskaya and Kuyakan formations) and Rybachi (Lonskii Formation) peninsulas. The spectra of ages of detrital zircons in sandstone samples from the Zemlepakhtinskaya and Kuyakan formations are similar to a significant extent to each other, which implies the dominant role of the same provenances. Most zircon grains are the Paleoproterozoic and Mesoproterozoic in age; some of them are characterized by Mesoarchean and Neoarchean ages. Zircons dated back to 1.0‒2.0 Ga with maxima at approximately 1.8, 1.5, 1.3, and 1.1 Ga are the most abundant. The youngest zircon grains are the Mesoproterozoic in age: 1050 ± 21Ma (i.e., close to the Mesoproterozoic‒Neoproterozoic boundary) and 1028 ± 21 Ma from the Zemlepakhtinskaya and Kuyakan formations, respectively. The distribution spectrum of ages obtained for zircons from sandstones of the Lonskii Formation significantly differs from that characteristic of zircons from sandstones of the Zemlepakhtinskaya and Kuyakan formations. The zircon population from the Lonskii Formation is dominated by detrital zircons with Neoarchean and Paleoproterozoic ages (2.8‒1.6 Ga); Paleoarchean and Mesoarchean grains are scarce. Their age maxima are registered at levels of approximately 2.7 and 1.8 Ga. The minimum age obtained for zircons from sandstones of the Lonskii Formation (1349 ± 35 Ma) allows the Rybachi block to be considered as being older as compared with the Sredni bock. Crystalline complexes of the Baltic Shield served as a main provenance for the Upper Precambrian deposits of the peninsulas under consideration. The dates obtained for detrital zircons from the Upper Precambrian deposits of the Sredni and Rybachi peninsulas are compared with similar data on the Upper Precambrian sequences of the Timan and Varanger Peninsula areas to reveal differences and similarities in the distribution of ages.

A major limitation in the accuracy of zircon (U–Th)/He thermochronometry (ZHe) is the alpha-ejection correction. The standard alpha-ejection correction (F T ) assumes a homogeneous U–Th distribution in the host crystal. Here, two approaches are used to address parent nuclide heterogeneity often observed in natural zircons: 1) a new methodology where offending zonation is mechanically removed, and 2) custom alpha-ejection corrections informed by a LA-ICP-MS depth-profile (F ZAC ). We present an empirical test of these methodologies on a suite of bedrock zircons from Variscan orthogneisses of the central Aegean, which display marked parent nuclide zonation, which has impacted the ability to obtain accurate and precise thermochronometric data. During the progressive mechanical abrasion of enriched U, Th, and He zones, the change in grain diameter exhibits a parabolic relationship with respect to the apparent age, where the youngest age should represent the true age of the sample. The abrasion-corrected weighted mean age for sample 08PA01 is 8.8 ± 0.7 Ma (F T = 1), a “too young” age possibly the result of parent nuclide enriched cores. The findings also show that using F ZAC instead of F T may change single sample ZHe aliquots up to ~ 29%. Using F ZAC increases the weighted mean age ~ 17% for sample 08PA01, from 9.2 ± 0.7 Ma (F T ) to 10.8 ± 0.9 Ma (F ZAC ), and ~ 6% for sample 08PA71, from 10.9 ± 0.8 (F T ) Ma to 11.5 ± 0.9 Ma (F ZAC ). In this case, the F ZAC correction improves the overall accuracy of the ZHe data, but does not impact the problem of over-dispersed ages, suggesting they may be separate issues. The increase in ZHe age brings the dataset into agreement with previous thermochronometric studies, indicating that cooling of the Paros footwall below 180 °C may have occurred earlier than hitherto thought.

Excimer laser technologies enable a rapid and effective approach to simultaneous U/Pb geochronology and (U–Th)/He thermochronology of a wide range of detrital accessory minerals. Here we describe the ‘laser ablation double dating’ (LADD) method and demonstrate its viability by applying it to zircon and titanite crystals from the well-characterized Fish Canyon tuff. We found that LADD dates for Fish Canyon zircon (206Pb/238U – 28.63 ± 0.11 Ma; (U–Th)/He – 28.38 ± 0.73 Ma) are statistically indistinguishable from those obtained through established, traditional methods of single-crystal dating. The same is true for Fish Canyon titanite LADD dates: 206Pb/238U – 28.08 ± 0.90 Ma; (U–Th)/He – 27.98 ± 0.86 Ma. As anticipated, given that LADD involves the analysis of smaller amounts of material than traditional methods, it yields dates with higher analytical uncertainty. However, this does not substantially reduce the utility of the results for most applications to detrital datasets. An important characteristic of LADD is that it encourages the chemical characterization of crystals by backscattered electron, cathodoluminescence, and/or Raman mapping prior to dating. In addition, by permitting the rapid and robust dating of crystals regardless of the degree of their abrasion during sedimentary transport, the method theoretically should yield dates that are more broadly representative of those of the entire population of detrital crystals in a natural sample.

Geologic mapping, supported by 40 Ar/ 39 Ar and U-Pb geochronology and geochemistry of sedimentary and volcanic rocks, reveals the details of the Cenozoic depositional and tectonic history of the eastern Pinon Range and central Huntington Valley in the north-central Basin and Range Province, Nevada (USA). Cretaceous to Miocene supracrustal successions were studied in detail in order to compare the geologic evolution of the upper crust near the Ruby Mountains-East Humboldt Range (RMEH) metamorphic core complex (MCC) with the magmatic, metamorphic, and deformational history of the deep crust in the developing MCC. During the well-documented Late Cretaceous–Oligocene history of partial melting and infrastructure development within the RMEH, surface deposits in Huntington Valley reflect general tectonic quiescence, with evidence for the development of the shallow Elko Basin, minor extension, and eruption of southward-younging ignimbrite flare-up volcanism. Thin, discontinuous successions of Cretaceous–early Cenozoic sedimentary strata were locally blanketed by rhyodacite ignimbrites, domes, and subvolcanic intrusions of the Robinson Mountain volcanic field between 38.5 and 36.8 Ma. This magmatic event represents the first local expression of Cenozoic volcanism linked to the ignimbrite flare-up, and its onset occurred slightly after a renewal of partial melting in the RMEH beginning ca. 42 Ma. The volcanic section was subsequently tilted ∼10°–15° west before ca. 33.9 ± 0.4 Ma. Although melting continued at depth in the RMEH until after 30 Ma, there was no eruption of volcanic rocks after Robinson Mountain volcanism. An additional ≥10°–15° of westward tilting occurred between 31.1 ± 0.3 Ma and ca. 24.4 Ma, as bracketed by the 31 Ma tuff of Hackwood Ranch (which was probably erupted from a distant caldera) and an angular unconformity beneath the overlying Miocene Humboldt Formation. Neither of these tilting events and unconformities appears to represent significant (>∼1 km each) extension, but they could be surface expressions of magmatism, metamorphism, and crustal flow at depth. The Humboldt Formation includes >2000 m of sediment deposited mostly between ca. 16 and 12 Ma, with deposition lasting until at least ca. 8.2 Ma. Humboldt Formation sediments thicken eastward, toward the west-dipping fault that bounds the RMEH, and are interpreted as a basin that developed in the hanging wall of this fault system. Motion on this normal fault system led to the exhumation of metamorphic and igneous rocks of the core complex ∼10 m.y. after the documented cessation of partial melting, high-temperature metamorphism, and intrusion of granitoids into the deep crust ca. 29 Ma. Metamorphic clasts and a detrital zircon signature thought to represent RMEH provenance are first detected in 14.2 Ma or younger sediments.

Upper Cretaceous sandstones from 17 localities from California to southeastern Alaska (United States) contain unexpectedly large populations of detrital zircons with Proterozoic U-Pb ages, with age peaks at 1800–1650 and 1380 Ma. These peaks are indicative of a sediment source region in the southern part of the Proterozoic Belt Supergoup basin in central Idaho, which hosts 1800–1650 Ma detrital zircons and which was intruded by rift-related 1380 Ma bimodal plutons and sills. Belt rocks were strongly uplifted and eroded during Late Cretaceous Sevier shortening and fed four paleoriver systems. The Lemhi Pass–Hawley Creek river system flowed east and sourced the Beaverhead-Harebell-Pinyon nonmarine megafan in the Cordilleran foreland basin. The Kione River flowed southwest to northern California, where it sourced a very large, ca. 82–80 Ma, ∼600-m-thick delta and submarine fan complex within the northern Great Valley forearc basin. Considerable Kione detritus also transited the forearc basin to reach the Franciscan trench, sourcing a pulse of deposition and subduction accretion in central California and even part of southern California. The Swakane River flowed northwest out of Idaho into Washington, sourcing the protolith for the high-grade Swakane gneiss. More speculatively, a Yakutat River may have flowed northwest and deposited Yakutat strata in a trench off Washington or British Columbia, before those rocks were translated north to southeastern Alaska. Recognition of a major source area in central Idaho for zircons with an uncommon age of 1380 Ma helps constrain the ca. 85–65 Ma paleogeography and paleotectonics of major sectors of the North American convergent margin orogen.

The early onset of deformation following the India-Asia collision, Neogene expanse of uplift, and complex systems that comprise strike-slip faults, thrust faults, and intermontane basins characterize the Cenozoic tectonism of Northern Tibetan Plateau and raise two prominent questions in orogenic geodynamics: 1) What mechanism(s) control(s) the transfer of stress related to the India-Asia collision across the distance of >2000 km; and 2) Why the development of high topography was delayed in the Northern Tibetan Plateau and what does it reveal about how the internal forces and external boundary conditions evolved. To address these two questions, we reconstruct a holistic spatial-temporal deformation history of the Northern Tibetan Plateau by using a range of thermochronometers, with closure temperature spanning from 350 degrees C to-60-70 degrees C. This multi-thermochronometer study reveals three stages of faulting related cooling, in the early Cretaceous, in Paleocene-Eocene and in middle-late Miocene. We observe that Paleocene-Eocene deformation was spatially restricted and mostly occurred on reactivated Cretaceous structures, indicating a control of pre-existing weakness on early Cenozoic deformation. Extensive Neogene deformation contrasts with restricted Paleocene-Eocene deformation and relatively quiescent shortening during the Oligocene-early Miocene, which implies a change in the regional tectonics regime. Global plate reconstructions show that this tectonic reorganization is coeval with an increase in Pacific-Asia plate convergence rates. We argue that this change in regional tectonics is a result of increasing constrictive environment of the eastern plate boundary, which changed the behavior of the Altyn Tagh fault the boundary fault of Northern Tibetan Plateau, causing it to change from feeding slip into structures out of the plateau to feeding slip into structures at plateau margins.

Mid-Palaeozoic assembly models for the Arctic Alaska–Chukotka microplate predict the presence of cryptic crustal sutures, the exact locations and deformational histories of which have not been identified in the field. This study presents data on the provenance of polydeformed and metamorphosed strata in the southern Brooks Range Schist Belt and Central Belt of presumed Proterozoic–Devonian depositional age, as well as for the structurally overlying strata, to help elucidate terrane boundaries within the Arctic Alaska–Chukotka microplate and to add new constraints to the palaeogeographical evolution of its constituent parts. The protoliths identified support correlations with metasedimentary strata in the Ruby terrane and Seward Peninsula and suggest a (peri-) Baltican origin in late Neoproterozoic–early Palaeozoic time. Proximity to Laurentia is only evident in what are inferred to be post-early Devonian age strata. By contrast, the North Slope and Apoon terranes originated proximal to Laurentia. The mid-Palaeozoic boundary between these (peri-) Baltican and (peri-) Laurentian terranes once lay between rocks of the Schist/Central belts and those of the Apoon terrane, but is obscured by severe Mesozoic–Cenozoic deformation. Whether this boundary represents a convergent or transform suture, when exactly it formed and how it relates to broader Caledonian convergence in the North Atlantic are still unresolved questions.

The Yukon-Koyukuk Basin is a large depression that covers ∼118,000 km2 in western interior Alaska and is divided into two subbasins by a volcanic arc assemblage. Interpretations of the depositional setting of the northern Kobuk Koyukuk subbasin vary from a syncollisional forearc basin to a postorogenic successor basin formed by lithospheric extension. New results from sandstones and conglomerates collected from the Kobuk Koyukuk subbasin provide evidence for the timing of basin development, insight into the provenance of coarse siliciclastic sediments, and understanding of the nature of Cretaceous paleogeography and paleodrainage of Arctic Alaska. Early sedimentary rocks of the Kobuk Koyukuk subbasin contain abundant mafic to ultramafic volcanic and plutonic lithic fragments and mafic heavy minerals (e.g., spinel, clinopyroxene, and amphibole). They also contain abundant Middle Triassic to early Late Jurassic zircons (240−160 Ma; peak maximum ca. 200 Ma) that yield highly juvenile Hf isotopic compositions. Geochemistry of chromium spinels (Cr# = 0.17−0.86) suggests crystallization in an immature arc setting that likely developed over mid-ocean-ridge basalt−type crust. These early sediments originated from the mafic and ultramafic rocks of the Angayucham terrane, which was once much more extensive. These results suggest that the Angayucham terrane consists of an obducted Middle Triassic to early Late Jurassic oceanic arc complex that was coeval with oceanic- to continental-margin mafic arc magmatism in the Canadian Cordillera. Our generalized stratigraphy, along with U-Pb ages and Lu-Hf isotope analyses of zircons from sedimentary rocks of the Kobuk Koyukuk subbasin, reflects the tectonic and/or erosional unroofing of the adjacent southern Brooks Range and Ruby terrane. U-Pb ages of detrital zircons collected from the stratigraphically lowest mafic- to ultramafic-rich strata yield maximum depositional ages (107 Ma) that reflect initial erosion of the structurally highest Angayucham terrane and initiation of basin formation and deposition in the late Early Cretaceous. Continued uplift and erosion exposed structurally deeper metamorphic rocks, as revealed by incorporation of low-grade phyllites and eventually higher-grade metamorphic schistose lithic detritus and intermediate-composition (e.g., biotite) to metamorphic (e.g., chloritoid and xenotime) heavy mineral suites into the basin sediments. Differences in detrital zircon signatures between similar-age strata in the Colville foreland basin to the north of the Brooks Range and the Kobuk Koyukuk subbasin indicate that the sediments within the two basins were derived from two different sources, and the Brooks Range orogen acted as a drainage divide during late Early Cretaceous deposition.

This study was carried out to determine the initial age and time-span of interaction of two major crustal provinces of Asia: the Siberian craton and the Central Asian Orogenic Belt (CAOB). Single grain U–Pb ages of detrital zircon suites from the Neoproterozoic passive margin strata of the Siberian craton were used to determine the first appearance of extraregional source regions. Twelve Neoproterozoic clastic rocks from the Baikal-Patom margin of Siberia and one sample from the volcaniclastic Padrinsky Group that was deposited unconformably above accreted CAOB crust were analyzed. In total, 1152 grains were analyzed, 703 were used for provenance interpretation. Stratigraphically lower strata from the Siberian margin yield Archean – Paleoproterozoic detrital zircon ages, which are similar to, and probably derived from the Siberian Precambrian craton. A few extra-regional Mesoproterozoic grains are also present. The provenance shift happens in the upper portion of the section and is marked by the influx of extra-regional zircons. The youngest included zircons (610 Ma) constrain the age of deposition and provide evidence for the timing of initial interaction between CAOB and Siberia in this region. Neoproterozoic zircons also dominate the overlying sedimentary units of the CAOB, suggesting continuing convergence. Coeval volcaniclastic unit deposited across the accreted CAOB terrane has a similar U–Pb detrital zircon age distribution, strengthening the provenance links between the two sides of the orogen. Analysis of the local tectonics suggests that the beginning of accretion might have started even before the first appearance of Neoproterozoic zircon: during the development of a regional unconformity, capped by 635 Ma (?) “Snowball Earth” tillites of Dzhemkukan Formation. The absence of Neoproterozoic zircons in Dzhemkukan Formation is probably explained by the absence of development of an extremely thickened crust. Our data are in good agreement with data collected from other Neoproterozoic sedimentary basins of southern Siberian craton, including Cisbaikalia and Bodaibo Synclinorium.

Previous constraints on the timing and rate of exhumation of the footwall of the South Tibetan detachment system (STDS) north of Mount Everest suggest rapid Miocene cooling from ∼ 700°C to 120°C between ∼14–17 Ma. However, 25 new single grain zircon He ages from leucogranites intruding Greater Himalayan Sequence rocks in the footwall of the STDS are between 9.9 and 15 Ma, with weighted mean ages between 10 and 12 Ma. Zircon grains exhibit a positive correlation between age and effective uranium (eU). Laser ablation zircon U-Pb geochronology, detailed SEM observations, and laser ablation depth-profiling of these zircons reveal low-eU 0.5–2.5 Ga inherited cores overgrown by high-eU 17–22 Ma rims. This intragranular zonation produces ages as much as 32% too young when a standard alpha-ejection correction assuming uniform eU distribution is applied. Modeling of the effects of varying rim thickness and rim eU concentration on the bulk grain eU and alpha-ejection correction suggests that zonation also exerts the primary control on the form of the age-eU correlation observed. Application of grain-specific zonation-dependent age corrections to our data yields zircon He ages between 14 and 17 Ma, in agreement with AFT and 40Ar/39Ar ages. Growth of magmatic rims followed by cooling to

Morphological analysis and U/Pb LA-ICP-MS dating were carried out for detrital zircon (400 age determinations) from four core samples of Triassic rocks recovered by Well Severnaya (Graham Bell Island, Franz Josef Land Archipelago). It is shown that source areas were mainly composed of peraluminous granites. U/Pb LA-ICP-MS zircon data were used to decipher the provenance evolution in the northern Barents Sea region. The main source of clastic material in the North Barents sedimentary basin in the Middle-Late Triassic was the Uralian fold belt, with lesser contribution from the East European Craton (Baltica), Timanides, Taimyr, and rocks related to the Siberian plume. The clastic material was mainly transported from the south and southeast. From the beginning of the Middle to the terminal Late Triassic, influence of the Neoproterozoic sources systematically decreased, whereas contribution of Caledonian sources increased.

The new data obtained during thorough geological-structural, geochronological, petrographic, and petrochemical investigations of Late Cretaceous granitoids from the southern Sredinnyi Range in Kamchatka and zircon dating by the U-Pb SIMS and LA-ICPMS methods indicate that this region was characterized by intense granitoid magmatism in the Campanian (83.1 ± 2.0 to 76.2 ± 1.5 Ma). The Campanian granitoids mark initiation of the “newly formed” continental crust in Kamchatka. The composition of these Late Cretaceous rocks demonstrates similarity to peraluminous I-type granites. The data allow the Campanian stage of magmatic activity to be defined in southern Kamchatka.

Monazite is a petrologically important and analytically promising target for (U–Th)/He thermochronology. Previous studies have reported highly variable He diffusion results from monazite from a single sample and demonstrated that composition can significantly affect He diffusion parameters. In this study, we performed incremental heating of single monazite grains to experimentally determine the 4He diffusion properties of reference monazite ‘554’ that occurs within a peraluminous two-mica granite from the Catnip Sill within the Catalina Core complex, Arizona. Assuming that the grain size defines the diffusion geometry, the six experiments yielded E a values of 212 to 238 ± 5 kJ mol − 1 (1σ) and D o values of 15.7 to 103 cm 2 s − 1 with one value of 784 cm 2 s − 1 . Monazite (U–Th)/He data from five grains yielded closure temperatures of 291 to 262 °C (± c. 15 °C) and ages of 23.8 – 20.3 ( ± ∼ 1.2 ; 2 σ ) Ma ; the weighted mean age is 21.8 ± 0.73 ( MSWD = 1.83 , n = 5 ) and the weighted mean closure temperature is 282 ± 6 ° C ( MSWD = 0.96 , n = 5 ; 1 σ ). We tested the accuracy of these results by comparing our monazite thermochronology data with monazite Th/Pb depth profiling results, the 40Ar/39Ar thermal history for the Catnip Sill constrained using coexisting muscovite, biotite, and K-feldspar, and published regional zircon and apatite fission track results. The monazite Th/Pb data indicate emplacement of the Catnip Sill at ∼ 45 Ma . The 40Ar/39Ar muscovite and biotite data indicate cooling from 460 to 350 °C from 27 to 26 Ma. K-feldspar MDD modeling suggests cooling from 360 to 240 °C from 26 to 24 Ma. Zircon fission track data indicate cooling through 250 °C between 29 and 20 Ma. Additional cooling through 110 °C is recorded by apatite fission track ages of 19–16 Ma. Because the monazite thermochronology results are reproducible and consistent with the thermal history constrained by the other chronometers, our results 1) confirm the accuracy of the 4He diffusion kinetics from monazite ‘554,’ and 2) demonstrate that monazite can be an effective (U–Th)/He thermochronometer, provided that He diffusion properties are either measured or reasonably assumed for each sample.

In the Bendeleben Mountains, Seward Peninsula, mid-Cretaceous granites are exposed in an uplifted block bounded on its south side by an E-W striking normal fault. The Bendeleben fault has well-preserved scarps 4–7 m in height that offset Holocene moraines. Seismic activity, young normal faulting, and Quaternary basaltic volcanism are all evidence of active extension. South of the Bendeleben fault, there is a 3–4 km deep basin. Fifteen apatite (U-Th)/He ages from granitic samples of the footwall yield an Eocene weighted mean age of 41.3±4.8 Ma. Biotite 40Ar/39Ar ages from the country rock of the Bendeleben pluton are 81–83 Ma. In spite of the young fault scarps, HeFTy and Pecube thermal modeling results illustrate that rapid exhumation of the Bendeleben Mountains occurred in the Late Cretaceous-Eocene and slowed since the Oligocene. A weak age-elevation relationship of apatite He ages and a lack of correlation between age and distance from the fault indicate that exhumation was accomplished with minimal block rotation on a steeply dipping, long-lived normal fault. Timing of extension in the Seward Peninsula can be correlated with deformation in the offshore Hope Basin where seismic reflection lines document Early Tertiary large-magnitude normal faulting followed by minor post-Miocene reactivation. The faulting observed in the Bendeleben Mountains is part of an extensional system that spans a large portion of the Bering Strait region. The tectonic model proposed in previous studies suggests that clockwise rotation of the Bering block relative to North America is the cause of extensional deformation in western Alaska.

The Patagonian Magallanes retroarc foreland basin affords an excellent case study of sediment burial recycling within a thrust belt setting. We report combined detrital zircon U–Pb geochronology and (U–Th)/He thermochronology data and thermal modelling results that confirm delivery of both rapidly cooled, first-cycle volcanogenic sediments from the Patagonian magmatic arc and recycled sediment from deeply buried and exhumed Cretaceous foredeep strata to the Cenozoic depocentre of the Patagonian Magallanes basin. We have quantified the magnitude of Eocene heating with thermal models that simultaneously forward model detrital zircon (U–Th)/He dates for best-fit thermal histories. Our results indicate that 54–45 Ma burial of the Maastrichtian Dorotea Formation produced 164–180 °C conditions and heating to within the zircon He partial retention zone. Such deep burial is unusual for Andean foreland basins and may have resulted from combined effects of high basal heat flow and high sediment accumulation within a rapidly subsiding foredeep that was floored by basement weakened by previous Late Jurassic rifting. In this interpretation, Cenozoic thrust-related deformation deeply eroded the Dorotea Formation from ca. 5 km burial depths and may be responsible for the development of a basin-wide Palaeogene unconformity. Results from the Cenozoic Rio Turbio and Santa Cruz formations confirm that they contain both Cenozoic first-cycle zircon from the Patagonian magmatic arc and highly outgassed zircon recycled from older basin strata that experienced burial histories similar to those of the Dorotea Formation.