Denudation History Research Articles

Weathering history and landscape evolution of Western Ghats (India) from 40 Ar/ 39 Ar dating of supergene K–Mn oxides

Laterites preserved on both sides of the Western Ghats Escarpment of Peninsular India have formed by long-term lateritic weathering essentially after India–Seychelles continental break-up following Deccan Traps emplacement ( c. 63 myr ago). Supergene manganese ores of the Western Ghats were formed on Late Archean manganese protores. Among Mn oxides composing the ores, cryptomelane (K-rich Mn oxide) was characterized and dated by 40 Ar/ 39 Ar geochronology. Measured ages complement those previously obtained in other South Indian manganese ores from the hinterland plateau and further document three major weathering periods, c. 53–44, c. 39–22 and c. 14–10 Ma, the last being documented for the first time in India. These periods coincide with global palaeoclimatic proxies and date the lateritic weathering of three successive palaeolandscapes of the Western Ghats that evolved under slow denudation ( c. 8 m Ma −1 ) over the last 44 myr and were mostly incised during the Neogene (<22 Ma). This indicates that the Western Ghats are a relict of a South Indian plateau preserved at the headwaters of very long east-flowing river systems and above the Western Ghats Escarpment. Topography and denudation history of this landscape do not require Neogene tilt of the Peninsula as recently proposed. Supplementary material: Full details of field and sample description, methods and analytical data including electron probe microanalyses of cryptomelane, and isotopic analyses and degassing spectra of irradiated cryptomelane grains are available at https://doi.org/10.6084/m9.figshare.c.4726661

Climate control on Early Cenozoic denudation of the Namibian margin as deduced from new thermochronological constraints

The processes that control long term landscape evolution in continental interiors and, in particular, along passive margins such as in southern Africa, are still the subject of much debate (e.g. Braun, 2018). Although today the Namibian margin is characterized by an arid climate, it has experienced climatic fluctuations during the Cenozoic and, yet, to date no study has documented the potential role of climate on its erosion history. In western Namibia, the Brandberg Massif, an erosional remnant or inselberg, provides a good opportunity to document the Cenozoic denudation history of the margin using the relationship between rock cooling or exhumation ages and their elevation. Here we provide new apatite (U–Th–Sm)/He dates on the Brandberg Inselberg that range from 151 ± 12 to 30 ± 2 Ma. Combined with existing apatite fission track data, they yield new constraints on the denudation history of the margin. These data document two main cooling phases since continental break-up 130 Myr ago, a rapid one (∼10°C/Myr) following break-up and a slower one (∼1–2°C/Myr) between 65 and 35 Ma. We interpret them respectively to be related to escarpment erosion following rifting and continental break-up and as a phase of enhanced denudation during the Early Eocene Climatic Optimum. We propose that during the Early Eocene Climatic Optimum chemical weathering was important and contributed significantly to the denudation of the Namibian margin and the formation of a pediplain around the Brandberg and enhanced valley incision within the massif. Additionally, aridification of the region since 35 Ma has resulted in negligible denudation rates since that time.

Last Glacial Maximum and Younger Dryas piedmont glaciations in Blidinje, the Dinaric Mountains (Bosnia and Herzegovina): insights from 36Cl cosmogenic dating

The highest parts of the Dinaric Mountains along the eastern Adriatic coast of the southern Europe, known for their typical Mediterranean karst-dominated landscape and very humid climate, were glaciated during the Late Pleistocene. Palaeo-piedmont type glaciers that originated from Cvrsnica Mountain (2226 m a.s.l.; above sea level) in Bosnia and Herzegovina deposited hummocky, lateral and terminal moraines into the Blidinje Polje. We constrained the timing of the largest recognized glacier extent on Svinjaca and Glavice piedmont glaciers by applying the cosmogenic 36Cl surface exposure dating method on twelve boulder samples collected from lateral, terminal and hummocky moraines. Using 40 mm ka–1 bedrock erosion rate due to high precipitation rates, we obtained 36Cl ages of Last Glacial Maximum (LGM; 22.7 ± 3.8 ka) from the hummocky moraines, and Younger Dryas (13.2 ± 1.8 ka) from the lateral moraine in Svinjaca area. The amphitheater shaped terminal moraine in Glavice area also yielded a Younger Dryas (13.5 ± 1.8 ka) age within the error margins. Our results provide a new dataset, and present a relevant contribution towards a better understanding of the glacial chronologies of the Dinaric Mountains. Because our boulder ages reflect complex exhumation and denudation histories, future work is needed to better understand these processes and their influence on the cosmogenic exposure dating approach in a karstic landscape.

Low‐temperature thermochronological database of bedrock in the Japanese Islands

AbstractTo provide better access to thermochronological data and understand the long‐term denudation history of the Japanese Islands, we compiled a low‐temperature thermochronological dataset of fission‐track (FT) and (U–Th–Sm)/He (He) ages for apatite and zircon in bedrocks. These thermochronometric ages are compiled from 90 literature sources and 1,096 localities, and include 418 apatite FT ages, 851 zircon FT ages, 42 apatite He ages, and 30 zircon He ages. Many FT ages have been reported previously; however, the number of He ages is limited in the Japanese Islands. The compiled data are spatially biased; for instance, more data are reported for the Chubu and Kinki districts and the Pacific coast of the Shikoku Island, whereas less data were available for the Tohoku and Chugoku districts. For better understanding arc‐scale uplift‐denudation history, further thermochronological research in the lesser‐studied regions and more He thermochronometric measurements are desired. This compilation will be updated and provided on the website of the Fission‐Track Research Group in Japan (http://ftrgj.org/index.html).

First 36Cl cosmogenic moraine geochronology of the Dinaric mountain karst: Velež and Crvanj Mountains of Bosnia and Herzegovina

This article presents the first attempt to date moraines in the Dinaric mountain karst using cosmogenic 36Cl surface exposure dating technique. Twenty samples were collected from moraine boulders from two sets of the lowest and largest lateral moraines on the Velež (1965 m asl) and Crvanj mountains (1920 m asl) in Bosnia and Herzegovina. The dated lateral-terminal moraine complexes, spanning elevations from ∼980 to 1350 m asl, are up to 2.7 km long and rise more than 100 m above the valley floor. The moraine boulders yielded 36Cl ages spanning from Oldest Dryas for Velež (14.9 ± 1.1 ka) to Younger Dryas for Crvanj (11.9 ± 0.9 ka), considering the average age of the two oldest samples from each lateral moraine as the most representative time of moraine emplacement. The dated moraines mark the largest extent of glaciers in both study areas, which have been reconstructed to ∼28 km2 for Velež and ∼24 km2 for Crvanj, having a mean equilibrium line altitude at 1388 m and 1541 m, respectively. Under modern precipitation values, which account for ∼2000 mm, the temperature depression between 8 and 10 °C is required to sustain the palaeoglaciers with reconstructed equilibrium line altitudes. Glaciers of similar size with such low equilibrium line altitudes during the Lateglacial have not been reported until now for the Balkan Peninsula. It is very likely that the boulder ages reflect complex exhumation and denudation histories, which at this point do not allow obtaining more precise moraine chronologies for the study areas. Nevertheless, this article delivers new data on the extent and timing of Quaternary glaciations in the Mediterranean mountains, where records of glacier fluctuations seem to be asynchronous amongst different areas. It is clear that dating moraines with cosmogenic 36Cl surface exposure dating in carbonate lithologies in areas of high precipitation like the Dinaric karst, remains challenging.

Thermal history analysis of granitic rocks in an arc-trench system based on apatite fission-track thermochronology: A case study of the Northeast Japan Arc

We applied apatite fission-track (AFT) thermochronometry to the Cretaceous-Paleogene granitic rocks across the southern part of the Northeast (NE) Japan Arc in order to elucidate the denudation history. As the results, AFT ages were estimated at 79.5–66.0 Ma on the fore-arc side, 29.8–5.5 Ma in the Ou Backbone range (OBR) and 19.1–4.6 Ma on the back-arc side. Thermal inverse modeling with HeFTy offered high-resolution thermal histories, which were converted into denudation rates under the assumption of appropriate geothermal gradients. On the fore-arc side, stable and slow denudation setting (denudation rates < 0.05 mm/yr) was deduced through the Paleogene. On the contrary, in the OBR and on back-arc side, rapid denudation rates from 1 to a few mm/yr were estimated at some localities reflecting the uplift event after 3–2 Ma. Besides, the uplifting style of OBR was constrained from the thermochronometric data; the doming uplift is more plausible than the tilted pop-up style, which was previously suggested based on geological observations. The Iide and Asahi mountains on the back-arc side probably have started to uplift at 3–1 Ma, coeval with the uplift of the OBR. This observation disagrees with the previous tectonic models in which the deformation on the back-arc side initiated at 5–3.5 Ma, prior to the deformation in the OBR. This disagreement possibly suggests a heterogenous tectonic history on the back-arc side.

Multiproxy Isotopic and Geochemical Analysis of the Siwalik Sediments in NW India: Implication for the Late Cenozoic Tectonic Evolution of the Himalaya

AbstractProvenance analysis of the Sub‐Himalayan Late Miocene‐Pleistocene foreland basin deposits (Siwaliks) from the Dehradun reentrant area provides a 10‐Myr long record of the denudation history and tectonic evolution of the northwestern Indian Himalaya. We studied Siwalik sediments exposed along the Mohand‐Rao and Haripur‐Khol sections, using detrital zircon U‐Pb geochronology, major and trace elements, and Sr‐Nd isotope geochemistry. Results suggest that the erosion pattern has been relatively stable since the Late Miocene with sediments derived from the Tethyan Himalayan (THS), Greater Himalayan (GHS), and outer‐ (oLHS) and inner‐Lesser Himalayan (iLHS) sequences. Provenance data indicate that erosional unroofing of the Lesser Himalayan Crystalline sequences (LHCS) initiated around 6 Ma, possibly related to out‐of‐sequence movement of the Ramgarh‐Munsiari Thrust. Our data also suggest erosional recycling of older foreland basin deposits into younger Siwaliks since ~5.5 Ma, which may indicate the time of thrust propagation from the Lesser Himalaya into the foreland basin. While the iLHS has been exposed to erosion since at least ~10 Ma, the Siwaliks were dominated by materials derived from the GHS and THS sources. We interpret these results as an indication that tectonic uplift and erosion of the orogenic wedge occurred in response to duplexing of the iLHS and concomitant high topography and rock uplift rate in the Greater and Tethyan Himalaya. Comparing the provenance of the Siwalik sediments with that of the modern Ganga and Yamuna river sediments further indicates that deposition during the Late Cenozoic was most likely accomplished by southward flowing transverse Himalayan rivers, analogous to the modern ones.

Episodic erosion in West Antarctica inferred from cosmogenic 3He and 10Be in olivine from Mount Hampton

The polar climate of Antarctica results in the lowest erosion rates on Earth. The low long-term erosion history of high elevation mountain tops that are exposed above the ice preserve a record of climate change that can be accessed using cosmogenic nuclides. However, unravelling the complexity of the long-term denudation histories of Antarctic summits is frequently hampered by intermittent ice cover. The aim of this work is to identify denudation rate changes in a surface that has been continuously exposed since the middle Miocene. We have measured stable (3He) and radioactive (10Be) cosmogenic nuclides in olivine from lherzolite xenoliths from the summit of the Mount Hampton shield volcano within the West Antarctic Ice Sheet. The peak (3200 m) has never been covered by the current ice sheet and local ice caps, consequently the data record the subaerial erosion history of a mountain top within the Antarctic interior. The 10Be concentrations in the olivines yield minimum exposure ages (33 to 501 ka) that are significantly younger than those derived from the cosmogenic 3He (90 to 1101 ka). The data reveal a complex exposure history that provide an integrated long-term erosion rate of between 0.2 and 0.7 m/My that is most likely caused by mechanical weathering. Inverse modelling shows that the data are readily explained by episodic erosion, consisting of one to five erosion pulses that may record major regional climatic changes.

Provenance of the Surveyor Fan and Precursor Sediments in the Gulf of Alaska—Implications of a Combined U-Pb, (U-Th)/He, Hf, and Rare Earth Element Study of Detrital Zircons

The history of exhumation and denudation of the Cenozoic St. Elias orogen is stored in the sediments of the Miocene to Holocene Surveyor Fan, Gulf of Alaska. The orogeny of the mountain belt coincides with major climatic events leading to varying degrees of glaciation that are considered to have strongly interacted with mountain-building processes. In order to assess the relative influence of climate and tectonics on erosion patterns and to reconstruct sediment routing to the ocean, we combine zircon U-Pb dating and (U-Th)/He thermochronology with analysis of rare earth elements and Hf isotopes of zircons of sands and silts from Integrated Ocean Drilling Program expedition 341 sites U1417 and U1418 in the Surveyor Fan. All Miocene to Pleistocene sediments show similar U-Pb age spectra, indicating that the main source areas remained the same during different stages of glaciation. A prominent age component at 50–60 Ma can be linked to the Chugach Metamorphic Complex and the Sanak-Baranof plutonic belt in the mountain range. Older grains can be referred to low-grade metamorphic sources within the Chugach, Prince William, and Yakutat terranes. A decrease in 50–60 Ma igneous and metamorphic zircons implies a reduction of input from the Chugach Metamorphic Complex and the Sanak-Baranof plutonic belt. This indicates that the southward advance of glaciers toward the ocean, together with tectonic changes from the Miocene to the Pliocene, triggered a higher contribution from the newly glaciated areas. During times of increased glaciation in the Pleistocene, glaciers appear to have been nested in the same area as before. Our data do not give evidence of a general change in the drainage systems or the tectonic setting during the Pleistocene but also do not prove the absence of such.

Episodic Meso-Cenozoic denudation of Chinese Tianshan: evidence from detrital apatite fission track and zircon U–Pb data, southern Junggar Basin margin, NW China

It is generally accepted that the Tianshan was reactivated repeatedly throughout Meso-Cenozoic time. However, the extent of these episodes has not been fully understood. Using a previous magnetostratigraphic baseline, this study reports a detrital zircon U–Pb and apatite fission track dating study along the ~4 km thick Cenozoic Jingou River section at the southern margin of the Junggar Basin. Our results provide direct insight into the denudation history of the bordering Tianshan Mountains and suggest that they experienced two phases of rapid cooling in the Jurassic and Cretaceous. These cooling phases are attributed to tectonic events at distant plate margins such as the Late Triassic-Cretaceous accretion of peri-Gondwanan blocks (e.g. Qiangtang and Lhasa). The detrital zircon U–Pb ages range widely from ∼58 to 3055 Ma with a majority falling between ∼58 and 600 Ma. They can be statistically separated into two primary age peaks at 300–290 Ma and 450–410 Ma, as well as two secondary peaks at 170 Ma and 850 Ma. Detrital zircon U–Pb dating results suggest that the Central Tianshan may have still shed detritus into the Junggar Basin during the Early Palaeogene. In the Late Oligocene-Early Miocene, the modern North Tianshan started to form a topographic barrier that blocked all northward rivers flowing from the Central Tianshan to the Junggar Basin. Progressive northward indentation of India into Eurasia, caused a final intense phase of cooling and denudation of the Tianshan between ∼11 and 3 Ma, leading to deposition of the Xiyu Formation, a widely distributed thick conglomerate.

High-resolution 3D seismic study of pockmarks and shallow fluid flow systems at the Snøhvit hydrocarbon field in the SW Barents Sea

The Barents Sea is an epicontinental shelf sea with a fragmented structure consisting of long fault complexes, basins and basement highs. Fluid leakage from deep-seated hydrocarbon accumulations is a widespread phenomenon and mostly related to its denudation history during the glacial/interglacial cycles. In this study, we aimed to better understand shallow fluid flow processes that have led to the formation of numerous pockmarks observed at the seabed, in this area. To achieve this goal, we acquired and interpreted high-resolution 3D seismic and multibeam swath bathymetry data from the Snøhvit area in the Hammerfest Basin, SW Barents Sea. The high-resolution 3D seismic data were obtained using the P-Cable system, which consists of 14 streamers and allows for a vertical resolution of ~1.5 m and a bin size of 6.25 × 6.25 m to be obtained. The frequency bandwidth of this type of acquisition configuration is approximately 50–300 Hz. Seismic surfaces and volume attributes, such as variance and amplitude, have been used to identify potential fluid accumulations and fluid flow pathways. Several small fluid accumulations occur at the Upper Regional Unconformity separating the glacial and pre-glacial sedimentary formations. Together, these subsurface structures and fluid accumulations control the presence of pockmarks in the Snøhvit study area. Two different types of pockmarks occur at the seabed: a few pockmarks with elliptical shape, up to a few hundred meters wide and with depths up to 12 m, and numerous circular, small, “unit pockmarks” that are only up to 20 m wide and up to 1 m deep. Both types of pockmarks are found within glacial ploughmarks, suggesting that they likely formed during deglaciation or afterwards. Some of the larger normal pockmarks show columnar leakage zones beneath them. Pressure and temperature conditions were favourable for the formation of gas hydrates. During deglaciation, gases may have been released from dissociating gas hydrates prolonging the period over which active seepage occurred. At present, there is no evidence from the 3D seismic data of active gas seepage in the Snøhvit area. Low sedimentation rates or the influence of strong deep ocean currents may explain why these pockmarks can still be identified on the contemporary seabed.

Apatite fission track evidence for Miocene denudation history in the Gangdese conglomerate belt and Yarlung Tsangpo River: Implications for the evolution of Southern Tibet

Low-temperature thermochronology is used widely in the Tibet plateau uplift. Some researches, however, have defined the time of rapid denudation as simply rock uplift and have neglected the fact that the rock denudation recorded by fission track (FT) data was controlled by both surface incision and rock uplift. The incision of the Yarlung Zangbo River had a significant influence on uplift history inversion in Southern Tibet. This paper simulated the bedrock denudation and river incision histories using apatite fission track (AFT) data sampled from the Gangdese conglomerate belt, which is located in the middle of Southern Tibet, and analyzed the geological meaning of the AFT age of each sample. The results showed the following: (1) In the early Miocene (22–16 Ma), both the value of the denudation rate and the incision rate were high (0.56 mm/yr and 0.24 mm/yr). (2) In the middle-late Miocene, the incision rate (0.12 mm/yr) was similar to the denudation rate (0.09–0.11 mm/yr). (3) The historical model between river incision and bedrock denudation revealed a significant difference in the denudation rate during the period ca. 8–6 Ma. Combining these data with previously published thermochronological ages and synthesizing these ages with regional geological, we arrived at the following conclusions: (1) In the early Miocene, the denudation event probably was caused by a combined result of Indian plate rollback and the incision of the Yarlung Zangbo River. (2) In the middle-late Miocene, the denudation rate was consistent with the incision rate, which suggested that the denudation episode was caused by climate change associated with Asian monsoon intensification. (3) After 8 Ma, the stable and slow incision rate indicated that regional drastic uplift had ceased. The paleo-elevation of the research area had approached, and even exceeded, the present-day elevation in the late Miocene.

Estimates of late Cenozoic climate change relevant to Earth surface processes in tectonically active orogens

Abstract. The denudation history of active orogens is often interpreted in the context of modern climate gradients. Here we address the validity of this approach and ask what are the spatial and temporal variations in palaeoclimate for a latitudinally diverse range of active orogens? We do this using high-resolution (T159, ca. 80 × 80 km at the Equator) palaeoclimate simulations from the ECHAM5 global atmospheric general circulation model and a statistical cluster analysis of climate over different orogens (Andes, Himalayas, SE Alaska, Pacific NW USA). Time periods and boundary conditions considered include the Pliocene (PLIO, ∼ 3 Ma), the Last Glacial Maximum (LGM, ∼ 21 ka), mid-Holocene (MH, ∼ 6 ka), and pre-industrial (PI, reference year 1850). The regional simulated climates of each orogen are described by means of cluster analyses based on the variability in precipitation, 2 m air temperature, the intra-annual amplitude of these values, and monsoonal wind speeds where appropriate. Results indicate the largest differences in the PI climate existed for the LGM and PLIO climates in the form of widespread cooling and reduced precipitation in the LGM and warming and enhanced precipitation during the PLIO. The LGM climate shows the largest deviation in annual precipitation from the PI climate and shows enhanced precipitation in the temperate Andes and coastal regions for both SE Alaska and the US Pacific Northwest. Furthermore, LGM precipitation is reduced in the western Himalayas and enhanced in the eastern Himalayas, resulting in a shift of the wettest regional climates eastward along the orogen. The cluster-analysis results also suggest more climatic variability across latitudes east of the Andes in the PLIO climate than in other time slice experiments conducted here. Taken together, these results highlight significant changes in late Cenozoic regional climatology over the last ∼ 3 Myr. Comparison of simulated climate with proxy-based reconstructions for the MH and LGM reveal satisfactory to good performance of the model in reproducing precipitation changes, although in some cases discrepancies between neighbouring proxy observations highlight contradictions between proxy observations themselves. Finally, we document regions where the largest magnitudes of late Cenozoic changes in precipitation and temperature occur and offer the highest potential for future observational studies that quantify the impact of climate change on denudation and weathering rates.

Kovadúsulásos és alumíniumdúsulásos mállási és üledékképződési folyamatok a kora-albai folyamán a Csehbányai-medencében

The tectonically controlled uplift affecting various sectors of the Csehbanya Basin in early Aptian times seems to have been very inhomogeneous. As a result, individual, tectonically controlled blocks show very different denudation histories reflected by the basal layers of the Albian cover sequence (Tes Clay-Marl Formation) postdating the uplift-cumerosion event. At places where the Tes Fm is underlain by Jurasssic to Aptian formations these basal layers developed in the form of the clastic.Kepekő Member rich in chert fragments. At other places where the immediate bedrock of the Tes Fm is Late Triassic limestone or limestone with intercalated dolomitic layers, at the unconformity surface there are often bauxites or Al-rich clays belonging to the Alsopere Bauxite Formation. This suggests that the pre-Tes Fm. relief must have been highly variegated. Therefore both the depositional and the early diagenetic environments of the Alsopere Bauxite Fm and the clastic, cherty Kepekő Member could have been quite different. The differences may reflect different climates and/or different paleoenvironmental conditions. On the other hand since they both belong to one and the same major regional unconformity they have also some characters in common. These are: (1) the mostly local source material,(2) the predominantly oxidized nature of the sediment, (3) the abundance of “slack-water” microfacies, (4) sphericity, roundness and sorting of the coarse detrital material. However, unlike the bauxite, the material of the Kepekő Member is obviously of local origin. It is essentially an in situ dissolution residue without any signs of transport-related concentration/separation of even the chert fragments. Limestone-fragments in the bauxite on the other hand must have been added to the fine-grained sediment in the course of some transport/redeposition, to the distance of which we have no clue. The original source of the prebauxitic material is not known, either. Had it been of local origin it could not have been of the same age as the cherty Kepekő Member since the climatic and/or hydrologic conditions favourable for bauxitisation are substantially different from those favouring the accumulation of the silica-rich sediments, particularly because the latter show even some degree of silica mobilization and reprecipitation.

Sphene and Zircon Fission Track Analysis of Syenite Rocks of the Sushina Hills, Purulia-Bankura Shear Zone (TPSZ)

Sushina hills are situated in the Purulia-Bankura Shear Zone. This is tectonically disturbed narrow zone nearly 100 Km long having WNW-ESE trend. Two different rock assemblages namely Chhotanagpur Gneissic Complex and rocks of Singhbhum Group occur on the two sides of this shear zone. In this paper, I have used fission track ages of two cogenetic minerals and their corresponding closure temperatures to describe the denudation history. The difference of their fission track ages provides the rate of denudation 4 m/Ma during the period 970Ma-1458Ma due to tectonic activity. The youngest age of zircon of 970Ma represents the timing of the initiation of denudation.

Uplift and denudation history of the Akaishi Range, a thrust block formed by arc‐arc collision in central Japan: Insights from low‐temperature thermochronometry and thermokinematic modeling

AbstractFission track (FT), (U‐Th)/He (He), and U‐Pb data were used to identify the denudation history of the Akaishi Range, central Japan. The northern Akaishi Range is bounded on the east by the Itoigawa‐Shizuoka Tectonic Line Fault Zone (ISTL‐FZ). The thermochronometric ages progressively decrease with the decreasing distance to the ISTL‐FZ. Thermokinematic calculations suggest that the age pattern observed can be explained by 5–7.5 mm/yr reverse slip on the ISTL‐FZ that dips 34–45° west and soles onto detachment at 20–22.5 km depth. By assuming the same geometry and slip rate of the fault, the bedrock uplift rates and denudation rates are estimated at ~4 mm/yr. Thus, the uplift and denudation style of the northern Akaishi Range is well explained as a simple tilted thrust block that has been exhumed along the listric ISTL‐FZ. On the other hand, considering both the difference in apatite FT age and the active fault distribution, the southern Akaishi Range might be different in uplift origin and timing, although the difference in apatite FT ages between them may be attributable to the chlorine content variation in apatite. The inferred total denudation is larger than several kilometers and likely exceeds 10 km since the beginning of the northern Akaishi Range uplift, suggesting that the low‐relief surfaces on the ridges and the relatively constant elevations of the summits reflect postuplift denudation rather than preexisting low‐relief landforms.

Geochemistry of late miocene-pleistocene basalts in the Phu Quy island area (East Vietnam Sea): Implication for mantle source feature and melt generation

Geochemistry of late miocene-pleistocene basalts in the Phu Quy island area (East Vietnam Sea): Implication for mantle source feature and melt generation

First report of (U\u2013Th)/He thermochronometric data across Northeast Japan Arc: implications for the long-term inelastic deformation

(U–Th)/He thermochronometric analyses were performed across the southern part of the Northeast Japan Arc for reconstructing the long-term uplift and denudation history in the region. Apatite (U–Th–Sm)/He ages ranged from 64.3 to 1.5 Ma, while zircon (U–Th)/He ages ranged between 39.6 and 11.0 Ma. Apatite (U–Th–Sm)/He ages showed obvious contrast among the morphostructural provinces; older ages of 64.3–49.6 Ma were obtained in the Abukuma Mountains on the fore-arc side, whereas younger ages of 11.4–1.5 Ma were determined in the Ou Backbone Range (OBR) along the volcanic front and the Asahi Mountains on the back-arc side. The age contrasts are basically interpreted to reflect the differences in the uplift and the denudation histories of the provinces considering the thermal effects of magmatism and timing of the known uplift episodes. Denudation rates were calculated to be <0.1 mm/year in the Abukuma Mountains, ~0.1 to 1 mm/year in the Ou Backbone Range, and ~0.1 to 0.3 mm/year in the Asahi Mountains. The denudation rates tend to increase from the mountain base to the ridges in the OBR (and the Asahi Mountains). This relationship shows a contrast with the previous findings in fault-block mountains in the Southwest (SW) Japan Arc, where the highest denudation rates were estimated near fault(s) along the base(s). This observation might reflect a difference in mountain uplift mechanisms between the NE and the SW Japan Arcs and imply that thermochronometric approaches are useful for constraining uplift and denudation histories at the scale of an island arc, as well as continental orogens. However, careful discussion of magmatic thermal effects is required.Graphical abstract(U–Th)/He ages across NE Japan Arc, indicating different uplift/denudation histories among the morphostructural provinces.

Late Cenozoic exhumation history of the Luoji Shan in the southeastern Tibetan Plateau: insights from apatite fission-track thermochronology

Denudational history inferred from bedrock low-temperature thermochronological data provides significant constraint to tectonic models for explaining the growth of the Tibetan Plateau. Here, we present new apatite fission-track ages from the Luoji Shan, bounded by the Anninghe and Zemuhe faults in the southeastern Tibetan Plateau. Cooling ages vary from c. 5 to c. 13 Ma from the bottom to the top of a vertical profile. The age–elevation relationship can be interpreted as either (1) a phase of river incision at a rate of c. 0.16 km Ma −1 from c. 13 to c. 5 Ma or (2) a phase of denudation of c. 0.40 km Ma −1 between c. 13 and c. 10 Ma, followed by a phase of extremely slow denudation ( c. 0.03 km Ma −1 ). The results suggest that initiation of river incision started before c. 13 Ma in the study area. Combined with previously published data from adjacent sites, our results indicate that denudation in this region displayed substantial spatial variation. This finding does not support the existing lower crustal flow model for Tibetan Plateau growth, which predicts uniform denudation. We further speculate that the vertical component of slip along the southern extension of the Anninghe fault might have significantly declined since late Miocene time, explaining the decreased rate of erosion c. 10 Ma.

低温領域の熱年代学の発展と日本の山地の隆起・削剥史研究への応用( 内陸盆地の構造と形成プロセス)

低温領域の熱年代学の発展と日本の山地の隆起・削剥史研究への応用( 内陸盆地の構造と形成プロセス)