Detrital Fission-track Thermochronology Research Articles

Linking orogeny and orography in the Southern Alps of New Zealand: New observations from detrital fission-track thermochronology of the Waiho-1 borehole

Numerical modeling coupling erosion with crustal deformation predicts that development of an orographic rain shadow may explain the asymmetric exhumation of convergent plate boundary orogens. This prediction is consistent with observations from the Southern Alps of New Zealand, where bedrock thermochronology indicates crustal exhumation has been concentrated along the wet, windward side of the mountains. While the spatial correspondence of exhumation and precipitation patterns is compelling, a robust evaluation of the link between orographic and orogenic processes further requires a temporal comparison between exhumation history, plate reconstructions and paleoclimatic records. We present a detailed exhumation history of the Southern Alps from detrital apatite and zircon fission-track thermochronology of the Waiho-1 borehole, a 3.6 km-thick sequence of proximal foreland basin sediments. Inverse thermal modeling of a 2062-grain dataset predicts two periods of rapid exhumation in the Early and Late Miocene. Rapid exhumation in the Early Miocene was synchronous with the development of transpression along the Alpine Fault and a ca. 20–22 Ma pulse of exhumation may reflect cooling during inversion of preexisting extensional basins. Rapid exhumation in the Late Miocene was not synchronous with a discrete change in plate convergence but increased exhumation rates after 7.4 Ma may instead reflect localization of plate boundary deformation along the Alpine Fault as orographic precipitation concentrated exhumation in the Alpine Fault hanging wall. We propose that, similar to prior interpretations from bedrock thermochronology, detrital thermochronology of the Southern Alps foreland basin is consistent with numerical model predictions linking asymmetric exhumation of the orogen to the growth of an orographic rain shadow.

Cenozoic exhumation in the Qilian Shan, northeastern Tibetan Plateau: Evidence from detrital fission track thermochronology in the Jiuquan Basin

AbstractThe India‐Asia collision resulted in the Cenozoic framework of faults, ranges, and tectonic basins and the high topography of the northeastern Tibetan Plateau, but how and when these features formed remains poorly understood, leading to conflicting tectonic models. However, information on the tectonic evolution of these active orogenic belts is well preserved in synorogenic basin sediments. In this study, we carefully analyze the detrital apatite fission track ages of Cenozoic synorogenic sediments from the Jiuquan Basin to decipher the entire exhumation process of the adjacent Qilian Shan throughout the Cenozoic. Our data indicate that initially rapid Cenozoic exhumation occurred in the Qilian Shan during the late Paleocene‐early Eocene (~60–50 Ma), almost synchronous with the India‐Asia collision. The Qilian Shan subsequently experienced long‐lived exhumation that continued until at least the middle Miocene (~45–10 Ma). During this period of exhumation in the Qilian Shan, tectonic deformation occurred throughout the northeastern Tibetan Plateau. The early Cenozoic deformation in the northeastern Tibetan Plateau may have been caused by the transfer of tectonic stress from the distant India‐Asia collision boundary through the complex lithospheric environment of the Tibetan Plateau. The present tectonic configuration and topography of the Qilian Shan and the northeastern Tibetan Plateau likely became established since the middle Miocene and after the long‐lived deformation began in the early Cenozoic.

Source to sink evaluation of sediment routing in the Gulf of Alaska and Southeast Alaska: A thermochronometric perspective

AbstractIn this study, we present a source to sink evaluation of sediment routing at the glaciated convergent margin in Southeast Alaska. We investigate the efficacy of thermochronology to record spatial and temporal exhumation patterns in synorogenic sediment using Neogene strata drilled by Integrated Ocean Drilling Program Expedition 341 in the Gulf of Alaska. We present 1641 and 529 new detrital zircon and apatite fission track ages, respectively, from strata deposited on the continental shelf, slope, and deep‐sea fans. These data are compared to results from the proposed source terrains, including the St. Elias Mountains and new data from the Alsek River. We find that the offshore Bagley‐Bering sediment contains grains recording cooling ages much older (80–35 Ma) than those reported from the St. Elias syntaxis (3–2 Ma), indicating that extreme rapid exhumation does not extend west of the Seward‐Bagley divide. Data from the sediment on the continental shelf, slope, and proximal deep sea all yield similar results, suggesting the same general source region since 1.2 Ma and limited sediment mixing along this glaciated margin. Data from sediment in the distal deep sea show that extreme, rapid, and deep‐seated exhumation was ongoing at ~11–8 Ma. Overall, this study demonstrates the strengths and limitations of using detrital fission track thermochronology to understand sediment routing on a glaciated convergent margin and to record changes in exhumation rates over geologic time scales.

Structure and provenance of Late Cretaceous–Miocene sediments located near the NE Dinarides margin: Inferences from kinematics of orogenic building and subsequent extensional collapse

The NE part of the Dinarides Mountain chain, located near their junction with the Carpatho-Balkanides, is an area where sedimentary basins associated with the Neotethys subduction and collision are still exposed. We performed a provenance study, based on detrital fission track thermochronology combined with zircon UPb magmatic geochronology, and existing studies of kinematics and exhumation. Our study shows rapid sedimentation in the trench and forearc basin overlying the upper European tectonic plate. A number of latest Cretaceous–Early Paleocene igneous provenance ages show a dominant magmatic source area, derived from a Late Cretaceous subduction-related arc. This arc shed short time lag sediments in the forearc and the trench system, possibly associated with focused exhumation in the Serbo-Macedonian margin. This was followed by burial of the trench sediments and a novel stage of Middle–Late Eocene exhumation driven by continued continental collision that had larger effects than previously thought. The collision was followed by Late Oligocene–Miocene exhumation of the former lower Adriatic plate along extensional detachments that reactivated the inherited collisional contact along the entire Dinarides margin. This event re-distributed sediments at short distances in the neighboring Miocene basins. Our study demonstrates that the Dinarides orogenic system is characterized by short lag times between exhumation and re-deposition, whereas the upper tectonic plate is significantly exhumed only during the final stages of collision. Such an exhumation pattern is not directly obvious from observing the overall geometry of the orogen.

Late Cenozoic tectonic evolution of the northwestern Tien Shan: New age estimates for the initiation of mountain building

The Tien Shan are the quintessential intracontinental range, situated more than 1000 km north of the suture between India and Asia. Their initiation and growth in the Cenozoic, however, remain poorly understood. In this study we present stratigraphic, detrital fission-track, and magnetostratigraphic results that provide a basis for reconstructing the Cenozoic tectonic evolution of the Kyrgyz Range and adjacent Chu basin in the northwestern Tien Shan. Detrital fission-track thermochronology indicates that the northwestern Tien Shan was tectonically quiescent for much of the Cenozoic. Prior to uplift and exhumation in the late Miocene, the Kyrgyz Range was buried by sediments shed from highlands to the south and/or east. Paired bedrock fission-track and [U-Th]/He ages from a sampling transect of 2.4 km relief demonstrate that rapid exhumation commenced at ca. 11 Ma. Initial thrusting in the hinterland was followed by evaporite accumulation (;0.4 km/m.y.), which coincided with erosion of the pre‐11 Ma strata that mantled the Kyrgyz Range. Between 10 and 3 Ma, bedrockexhumation rates decreased to ,0.3 km/ m.y., while sedimentation rates decelerated initially to ;0.25 km/m.y. before accelerating to ;0.4 km/m.y. at 4‐5 Ma. Detrital fission-track results indicate that by 4.5 Ma,

Detrital fission track thermochronology of Upper Cretaceous syn‐orogenic sediments in the South Carpathians (Romania): inferences on the tectonic evolution of a collisional hinterland

ABSTRACT The tectonic evolution of a collisional hinterland sourcing the Ha?eg Basin, a Late Cretaceous syn‐orogenic sedimentary basin in the South Carpathians (Romania), is revealed through fission track thermochronology of detrital apatite and zircon grains. This basin formed on the upper plate (Getic unit) in response to Late Cretaceous collision with the lower plate (Danubian unit), an allochtonous continental block of the Moesian Platform, upon closure of a narrow oceanic basin (Severin Basin). The fission track results suggest that Turonian to lower Maastrichtian sediments of the Ha?eg Basin have been dominantly derived from pre‐Late Cretaceous sources. The age components they contain relate to pre‐Cretaceous tectonothermal events such as the Variscan orogenic cycle, Jurassic rifting and Severin Basin formation, and to Early Cretaceous compressional tectonics. These results are compatible with the tectonic evolution of the upper plate that is identified as the primary source. From the onset of sedimentation (late Albian) until the early Campanian the Ha?eg Basin resembles a piggy‐back basin formed on the upper plate concomitant with underthrusting and internal stacking of the lower plate. In contrast, important tectonic subsidence during the late Campanian and early Maastrichtian reflects a shift to extensional tectonics causing the unroofing of the collision zone and the exhumation of lower plate rocks back to the surface. Our fission track data place important constraints on the timing of lower plate erosion that must have commenced during the late Maastrichtian, as documented by the completely reset Late Cretaceous age component within upper Maastrichtian sediments (Sînpetru Formation). Late Maastrichtian uplift of the basin and the formation of positive relief at the site of the collision zone is an expression of continuous convergence. The mismatch between the amount of denudation and the amount of sediments trapped in the Ha?eg Basin underlines the importance of concomitant extensional unroofing.

Exhumation history of orogenic highlands determined by detrital fission-track thermochronology

Abstract A relatively new field in provenance analysis is detrital fission-track thermochronology which utilizes grain ages from sediment shed off an orogen to elucidate its exhumational history. Four examples highlight the approach and usefulness of the technique. (1) Fission-track grain age (FTGA) distribution of apatite from modern sediment of the Bergell region of the Italian Alps corresponds to ages obtained from bedrock studies. Two distinct peak-age populations at 14.8 Ma and 19.8 Ma give calculated erosion rates identical to in situ bedrock. (2) Zircon FTGA distribution from the modern Indus River in Pakistan is used to estimate the mean erosion rate for the Indus River drainage basin to be about 560 m Ma −1 , but locally it is in excess of 1000 m Ma −1 . (3) FTGA distribution of detrital apatite and zircon from the Tofino basin records exhumation of the Coast Mountains in the Canadian Cordillera. Comparison of detrital zircon and apatite FT ages gives exhumation rates of c. 200 m Ma −1 during the interval between c. 34 and 54 Ma, but higher rates ( c. 1500 m Ma −1 ) at c. 56 Ma. (4) FTGA analysis of apatite grain ages from a young basin flanking Fiordland in New Zealand indicates that removal of cover strata was followed by profound exhumation at c. 30 Ma, which corresponds to plate reorganization at this time. Exhumation rates at the onset of exhumation were c. 2000–5000 m Ma −1 . These studies outline the technique of detrital FTGA applied to exhumation studies and highlight practical considerations: (1) well-dated, stratigraphically coordinated suites of samples that span the exhumation event provide the best long-term record; (2) strata from the basin perimeter are the most likely to retain unreset detrital ages; (3) the removal of ‘cover rocks’ precedes exhumation of deeply buried rocks, which retain a thermal signal of the exhumation event; (4) steady-state exhumation produces peak ages that progressively young with time and have a constant lag time; (5) same-sample comparison of zircon and apatite peak ages is best in sequences with high-uranium apatite grains (>50 ppm), and peak-ages statistics can be improved by counting numerous apatite grains (>100).