Differential Exhumation Research Articles

Deciphering differential exhumation in the Gangdese orogen in southern Tibet using exposed porphyry alteration systems and geomorphic analysis

Topography and exhumation vary strongly in the Tibetan Plateau, reflecting different geodynamics and surface processes. The Gangdese orogen in southern Tibet is characterized by west-to-east variations in topography and occurrences of the Miocene porphyry copper deposits. We integrated remote sensing based hydrothermal alteration mapping and geomorphological analysis to detect patterns of differential exhumation since the Miocene. High abundances of propylitic and potassic alteration of the eastern Miocene granitoids are identified, indicating >2 km of exhumation since the Miocene. The western Gangdese has intensive phyllic and argillic alteration representing ∼1 km of exhumation. Geomorphic analyses also show E-W changes that most likely resulted from differential rock uplift histories. Channel steepness index values indicate the eastern Gangdese has channel gradients between 211 m1.02 and 457 m1.02, compared to values between 30 m1.02 and 160 m1.02 in the west. Linear inversion of tributaries of the Yarlung river shows a pulse of rock uplift between 25 Ma and 7 Ma with a maximum rate of 110 m/ m.y. in the east. In contrast, the western Gangdese exhibits slower and persistent rock uplift rates between 20 m/m.y. and 40 m/m.y. since 20 Ma. The integrated results record differential exhumation and rock uplift since the Miocene. We invoke the geometric variations of the subducted Indian lithosphere to interpret the E-W differential exhumation since the Miocene. Steeper subduction of the Indian lithosphere beneath the eastern Gangdese induced mantle upwelling, triggering rapid rock uplift and deep exhumation. Conversely, the shallower subduction of the Indian slab in the west generated slow and prolonged rock uplift with less exhumation. Our study refines the exhumation process of the Gangdese since the Miocene.

Exhumation of the Cuonadong Sn–W–Be polymetallic deposit, Tethyan Himalaya: Implications for exploration

The Cuonadong Sn–W–Be polymetallic ore deposit is the first rare-metal deposit related to leucogranites with giant mineralization potential to be discovered in the Himalayan Orogen. However, the post-mineralization exhumation and preservation processes of this deposit have not yet been studied in detail, although these factors are key to the exploration and evaluation of rare-metal deposits in the Himalaya. Geophysical data have revealed that a hidden fault (i.e., the Jisong secondary fault) cuts the southern part of the Cuonadong ore deposit. In order to determine the effects of the Jisong secondary fault on the exhumation of the Cuonadong deposit, we undertook zircon and apatite (U–Th)/He dating, apatite fission-track dating, and forward and inverse thermal history modeling of the footwall and hanging wall of the Jisong secondary fault. Our results show that the Cuonadong deposit experienced two stages of rapid, post-mineralization exhumation at ca. 10–9 and ca. 5–4 Ma, separated by a period of differential exhumation at ca. 9–5 Ma. These exhumation events were likely caused successively by the arc-shaped Nading Fault, normal faulting on the Jisong secondary fault, and thrusting on the Main Himalayan Thrust, although climate-related erosion may have also had a role in the exhumation. Owing to normal displacement on the Jisong secondary fault, the Cuonadong ore deposit underwent differential exhumation of 300–700 m. This implies that the eastern part of the deposit is more favorable for exploration than its western part if the deposit has the same mineralization depth. This study demonstrates that low-temperature thermochronological methods can be useful in the exploration for rare-metal deposits in the Himalayan Orogen.

The influence of lithospheric inheritance and Cenozoic magmatism on Phanerozoic rock cooling in the São Francisco Craton and adjacent orogens

The South American Platform encompasses the São Francisco Craton (SFC) and the Araçuaí-Ribeira orogenic system (AROS) located in the eastern Brazil. These geologic domains hold records of differential exhumation, sedimentation, volcanic activity, and post-rift reactivation of faults and shear zones. Therefore, these terranes provide outstanding opportunities for studying the dynamics of lithospheric processes, particularly in their interaction zones, characterized by the transition from cratonic to orogenic lithosphere. To investigate the processes involved in the contrasting behavior of the upper crust, we provide 23 new apatite fission track (AFT) ages and thermal histories from the northern segment of the AROS and from the eastern area of the SFC. The AFT ages range from 154.4 ± 20.1 and 37.1 ± 3.0 Ma and the mean track lengths range from 10.9 and 13.2 μm. We compiled thermal information from previous thermochronological analysis from 357 sites and constructed inverse distance weighted maps that depict the spatial distribution of AFT ages and the temperature evolution from 360 to 30 Ma. The results indicate that the SFC experienced its final exhumation within the apatite partial annealing zone (APAZ) at temperatures ranging from 110 °C to 60 °C during the late Paleozoic. In contrast, the AROS went through its last cooling within the APAZ during the Mesozoic or even in the Cenozoic. This suggests that reactivation and reheating, possibly associated with the South Atlantic rift, influenced the orogenic basement of the passive margin. We highlight that the reheating associated to the Abrolhos magmatic province in the northern segment of the AROS caused the youngest AFT ages of the study area. Our work demonstrates the importance of considering contrasting rheology when analyzing regional exhumation patterns, the structural fabric of orogens through reactivation of crustal discontinuities generating heating and exhumation, and how volcanism can disrupt the thermal record, inducing crustal reheating.

Incision history of the Mekong River valley revealed by spatially differential exhumation

The evolution of the Mekong River valley offers a unique record of the rock uplift and climate history of southeastern Tibet. Faster erosion rates along the valley than those on the flanks caused valley incision and local incision rates may reflect a mix of driving mechanisms, migrating knickpoints linked to a change in base level, and large-scale surface uplift. The thermochronometric-constrained erosion rates in the 2–3 km deep river channel compared to rates outside of the channels provide unique constraints on the driving mechanisms of the river incision. In particular, the onset of river incision at various points along the Mekong River helps identify whether exhumation signals are the result of knickpoint migration that would generate a younger incision upstream, or the outgrowth of the plateau, which would produce younger incision downstream. We analyze new and published apatite (UTh)/He ages collected along two elevation transects in the upper Mekong River: downstream at Tu'Er and upstream at Deqin. The data and thermokinematic modeling predict that the exhumation rates of the valley near Tu'Er and Deqin increased more rapidly than those of adjacent high-elevation, low-relief surfaces at ~11 Ma and ~ 4 Ma, respectively. Since then, exhumation variations have caused an increase of >2 km in the depth of the valley, indicating that the major incision of the Mekong River valley began at ~11 Ma near Tu'Er and approximately 4 Ma near Deqin. The results indicate that a major phase of the Mekong River valley incision may have developed and progressed upstream since the Miocene.

From Tethyan subduction to Arabia-Eurasia continental collision: Multiple geo-thermochronological signals from granitoids in NW Iran

NW Iran, situated between the Arabian and Eurasian plates, carries a record of both Paleo-Tethyan and Neo-Tethyan tectonic evolution. During the Wilson Cycle of Tethys Ocean opening and closing, several episodes of magmatism from Late Paleozoic to latest Cenozoic generated a massive volume of intrusive rocks. These intrusives, which record cooling histories from high-temperatures to final exhumation, are ideal for multiple geo-thermochronological studies. Our new zircon and apatite U-Pb results suggest three regional magmatic events in the Late Carboniferous, mid-Cretaceous and middle Eocene, which could be related to Paleo-Tethys subduction, Neo-Tethys subduction and Neo-Tethyan ridge subduction, respectively. New apatite fission track and (U-Th)/He data reveal post-magmatic cooling and differential exhumation related to subduction and collision. By integrating published regional thermochronological data from northeastern part of the Middle East, a broader tectono-thermal framework is outlined as follows: 1) Cretaceous cooling signals are most pronounced in the Alborz and Caucasus, and reflect back-arc extension during Neo-Tethyan subduction; 2) diachronous Neo-Tethyan evolution led to the Paleocene assemblage of Anatolia in the west, and subduction associated with a late Paleocene-Eocene magmatic flare-up in Iran. Subsequent westward escape of Anatolia and extensive surface uplift were driven by propagation of Arabia-Eurasia collision in the Miocene; 3) Continuous northward indentation of Arabia into Eurasia triggered late Miocene-Pliocene fast exhumation of the Zagros, Alborz and the Caucasus.

Stepwise growth of the southeastern Tibetan Plateau: Structural and thermochronological evidence from the Panxi tectonic belt

The Panxi tectonic belt is located in the transition zone between the Tibetan Plateau and the Yangtze Block and is characterised by ~N–S-trending faults and active earthquakes, which have long been considered to be a result of the growth (expansion and uplift) of the Tibetan Plateau. However, the mismatch between the ~N–S-trending faults and top-to-the-SE arcuate thrust faults is problematic for understanding the mechanism of growth of the southeastern Tibetan Plateau. In this study, we integrate the results of structural analysis with new apatite fission track and (UTh)/He thermochronological data to constrain the cooling, exhumation, and uplift history of the Panxi tectonic belt. Thermochronological data reveal that widespread and rapid cooling was initiated during the late Eocene–Oligocene (36–26 Ma), with a change in cooling/exhumation rate (either increase or decrease, dependent on location) occurring at 13–8 Ma (Middle–Late Miocene). These two periods of cooling are attributed to two major tectonic deformation episodes, D1 and D2. The D1 deformation is characterised by top-to-the-east/southeast thrusting with back-thrusting along N–S-trending faults. The Middle–Late Miocene spatially differential exhumation was associated with D2 deformation involving strike-slip and local normal faulting that overprinted D1 and potentially accommodated accumulated strain. Integration of the new results with previous records of uplift and exhumation, sedimentation, magmatism, and fault activity, supports a diachronous staged uplift process of the southeastern Tibetan Plateau, with episodes during the late Eocene–Early Miocene and since the Middle–Late Miocene. Crustal deformation has played a significant role in promoting uplift through the generation of new faults and reactivation of pre-existing faults, whereas lower-crustal ductile channel flow might have driven the Middle–Late Miocene tectonic transformation in the upper crust.

Fault‐Driven Differential Exhumation in a Transpressional Tectonic Setting: A Combined Microstructural and Thermochronologic Approach From the Liquiñe‐Ofqui Fault System, Southern Andes (39°S)

AbstractCrustal deformation in transpressive tectonic settings is partitioned across fault‐bounded tectonic blocks whose borders may represent ideal loci for enhanced rock exhumation. Field and petrographic analysis, geothermobarometry, zircon U‐Pb geochronology, and zircon and apatite (U‐Th)/He thermochronology were applied to intrusive and metamorphic rocks to investigate exhumation patterns of fault blocks delimited by the Liquiñe‐Ofqui Fault System (LOFS), Southern Andes (39°S). Our integrated analyses document the relative influences of magmatism, fault‐driven differential exhumation, and fault‐controlled geothermal flow along the LOFS. Magmatism was concentrated in the Early to Late Jurassic (∼182–151 Ma), Early Cretaceous (∼116–104 Ma), and Miocene (∼17–6 Ma). Dextral mylonitic deformation was most likely coeval with the Miocene pulse of magmatism. Tectonic exhumation occurred across a positive flower structure during the Late Miocene to Early Pleistocene (∼6–2 Ma), and affected kilometric‐scale tectonic blocks bound by N‐striking, steeply dipping faults of the LOFS. Fault‐controlled geothermal flow occurred from the Early Pleistocene to the present‐day (∼1.5 Ma‐present). Our results suggest that individual faults not only facilitate exhumation of tectonic blocks but also act as pathways for long‐term hydrothermal fluid flow.

Partial melting of subducted continental crust during the exhumation: Insights from Palaeozoic granitic rocks in South Altyn, western China

The early Palaeozoic continental subduction–collisional belt in South Altyn (SA) western China distributes a large amount of (ultra)-high-pressure ((U)HP) metamorphic and granitic rocks associated with subduction, collision, and exhumation. In this study, four granitic rocks were collected from Bashenwake located in eastern SA. The ages of the garnet-bearing alkali-feldspar granite (GAFG), garnet-bearing granitic gneiss (GGG), alkali-feldspar granite (AFG), and syenogranite (SG) are 458.0 ± 4.1, 483.0 ± 4.1, 450.0 ± 2.4, and 482.0 ± 4.9 Ma, respectively. Whole-rock major and trace elements and Sr–Nd–Pb isotope, and zircon Hf isotope compositions for all samples exhibit characteristics of a continental crustal source. Based on partial melting modeling, the source temperature of the GGG, GAFG, AFG and SG was concluded as 750–780 °C, 730–760 °C, 730–770 °C and ca. 800 °C, respectively. The source pressure was estimated as ca. 0.8 GPa for the GGG, GAFG and AFG, and ca.1.2 GPa for SG. Combined with studies on (U)HP metamorphic rocks in SA, this study reveals that GGG is formed by metamorphism while SG is formed from partial melting of upper crustal rocks heated by upwelling mantle during the initial stage of exhumation (ca. 480 Ma) of subducted continental crust in SA. During further stage of exhumation of the subducted continental crust at ca. 450 Ma, the GAFG and AFG were formed from partial melting of GGG as a result of decreased pressure and further mantle upwelling. Consequently, the exhumation age of subducted continental crust in eastern SA is ca. 30 Myr earlier than that in western SA. Thus, the geochronology and petrogenesis of four granitic samples in this study exhibit one of very few evidence for partial melting of subducted continental crust during the exhumation and also provide magmatism exhibits evidence for the differential exhumation model of eastern SA in Palaeozoic.

Reconstruction of the Meso-Cenozoic tectono-geomorphological evolution of the Keguqin mountain in the Central Tian Shan based on geomorphological analysis and low-temperature thermochronology

Forming the northwestern branch of the Chinese Tian Shan, the Keguqin mountain located north of the Yili basin is characterized by Mesozoic relict landscapes and active faults, which recorded abundant information of long term tectono-geomorphologic evolution of the Tian Shan mountain range. However, the post-Jurassic deformation history of the Keguqin mountain is unclear. In this study, we applied apatite fission track, apatite (UTh)/He and geomorphologic analyses to reconstruct the landscape evolution of the Keguqin mountain and the northern Yili basin. Our results suggest that this region underwent three stages of accelerated cooling/exhumation in the Permian, Late Triassic-Jurassic and Cretaceous. The Permian cooling event likely reflects post magmatic cooling related to the Paleozoic orogeny of the Tian Shan. Late Triassic-Jurassic exhumation is possibly a far field response of the Qiangtang collision. The Cretaceous differential exhumation in the study area was controlled by activation of the Kashihe fault zone and secondary faults. As the Cretaceous cooling is widely observed in the vast Central Asia region, northern Tibet and Southern Pamir, and coeval with the Mongol-Okhotsk orogeny, Qiangtang collision and Karakorum collision. It is difficult to decipher the tectonic drive of the Cretaceous activation of the Kashihe fault zone. Relict landscapes in the Keguqin mountain were firstly established after the Paleozoic, slightly exhumed during the Cretaceous, and were uplifted and tilted by Late Cenozoic deformation. The latest uplift magnitude of the Keguqin mountain is estimated to be ∼250–500 m and ∼ 380–430 m of the hanging wall of the Kashihe fault zone and the Keguqin fault, respectively.

Contrasting thermal histories for the Indian passive margins during syn‐ and post‐Gondwana break‐up: Insights from apatite fission‐track thermochronology

AbstractNew and published apatite fission‐track data provides evidence for differential exhumation between the eastern and western passive margins of southern India. The eastern margin records significant Late Jurassic to Early Cretaceous rifting‐triggered exhumation in response to Gondwana break‐up and minor Cenozoic cooling. In contrast, Meso–Cenozoic rifting and posterior tectonic events did not deeply exhume the basement of the western margin. The anomalous thick crust of the Western Dharwar Craton might explain why Mesozoic deformation in this area was subdued. In addition, the Cenozoic eastward tilting of the Indian plate and the onset of Bengal Fan sedimentation ca. 23 Ma allowed the accumulation of thick sedimentary sequences in the eastern coastal basins, probably inducing a flexural response of fault reactivation on the eastern margin. More generally, we demonstrate the influence of lithospheric strength and post‐rifting sedimentation to the exhumation history of passive margins.

Provenance evolution of the San Juan Precordillera Silurian-Devonian basin (Argentina): Linking with other depocentres in Cuyania terrane

This paper explores the sedimentary provenance of the Silurian to Devonian siliciclastic successions in the Central region of the San Juan Precordillera, in central-western Argentina. The comprehensive provenance analysis of the Tambolar Formation (upper Silurian), Talacasto Formation (Lower Devonian) and Punta Negra Formation (Lower-Middle Devonian) from the San Juan River section is based on petrography, detrital zircon analyses and combined U–Pb and Lu–Hf isotopic data. Modal composition of the three units here studied shows an evolution trend from quartzose recycled, mixed, to transitional arc. Detrital zircon morphologies indicate derivation from dominantly plutonic and metamorphic sources with little evidence of transportation. The most representative detrital zircon U–Pb age populations are Famatinian (middle Cambrian - Devonian), Pampean–Brazilian (Tonian - lower Cambrian), and Grenvillian (Ectasian - Stenian) cycles derived rocks. Hf isotopes determined mainly in Mesoproterozoic detrital zircons reflect a juvenile mantle source during crystallization, with less significant inputs from those with a crustal and recycled crust origin. Results from this work are compared to data from outcrops of the same units developed in the North-Central region of the Precordillera, presented in previous works. Provenance proxies provide insights regarding the correlation of probably equivalent units deposited in other foreland basins within the Cuyania terrane, such as the Villavicencio Formation (Mendoza Precordillera), Río Seco de los Castaños and La Horqueta Formations (San Rafael Block). The K–S test suggests a low correlation between the units studied at the San Juan River and the equivalent outcrops exposed towards the central and northern parts of the San Juan Precordillera, as well as with the known records of the Río Seco de los Castaños and La Horqueta Formations of the San Rafael Block. In contrast, the samples from the Villavicencio Formation show a high correlation with the sample from the Punta Negra Formation, indicating a possible common sediment source. The broad variations of U–Pb detrital age pattern distributions observed between Silurian and Devonian successions throughout the Precordillera and the San Rafael Block point to provenance shifts linked to variability in east-to-west sediment dispersal patterns within an axial peripheral foreland basin. Fluctuations in the sedimentary composition are ascribed to the differential exhumation rate of source rocks and a progression from a convergent tectonic setting in the San Rafael block towards a coeval collisional environment in the Precordillera. The Silurian - Early Devonian foreland basin is tectonically linked to the Ocloyic Orogen that resulted from the collision of Cuyania terrane to the Western margin of Gondwana. Source rocks were most likely located within the Mesoproterozoic basement of Cuyania, exhumed during the Middle Devonian as a response to the approximation of Chilenia.

Apatite Fission Track Thermochronology of Granite from Duobaoshan Porphyry Cu (Mo) Deposit, Northeast China: Implications for Cooling History and Ore Preservation

The Duobaoshan Cu (Mo) deposit is one of the oldest super large porphyry deposits in the eastern part of the Central Asian orogenic belt. Although ore-forming processes have been extensively concerned, the post-mineralization ore preservation state was poorly focused on. In order to improve the ability of prospecting forecast, it is necessary to consider both deposit formation and deposit preservation. Here, we reported apatite fission track (AFT) data for the Duobaoshan porphyry copper deposits in the belt to reveal the cooling and exhumation history and evaluate ore preservation. The results show that the rapid cooling of the ore-hosting rock body occurred later than the surrounding rock body. The rapid cooling of the surrounding granodiorite occurred between 82 and 72 Ma, with the exhumation depth of 2.33–3.11 km and the exhumation rate of 0.25 mm/a, whereas the ore-hosting granodiorite porphyry was rapid cooling between 71.8 and 50.2 Ma, with the exhumation depth of 2.99–3.86 km and the exhumation rate of 0.22 mm/a. This differential exhumation and cooling event provide favorable geological conditions for the preservation of the ore body.

Differential exhumation of cratonic and non-cratonic lithosphere revealed by apatite fission-track thermochronology along the edge of the S\xe3o Francisco craton, eastern Brazil

Lithosphere of cratons and orogens generally reacts differently to tectonic events. Although these differences are mostly clear during the orogenic phases, understanding how they respond to tectonic reactivation is still challenging. Here, we report the first detailed apatite fission-track (AFT) study pinpointing the gradual transition between cratonic and orogenic lithosphere, using the case study of the São Francisco craton (SFC) and the adjacent Araçuaí-West Congo Orogen (AWCO), eastern Brazil. The collision that built the AWCO partially affected the inherited rift structures of the Paramirim Aulacogen, embedded in the São Francisco-Congo paleocontinent. Our data reveal a differential Phanerozoic exhumation between closely interspaced areas affected and not affected by the AWCO deformation. Samples from the SFC present slow and protracted basement cooling during the Phanerozoic, while samples from the orogen display rapid exhumation since the Eocene. An intermediate ~ N–S zone of c.40 km shows lower magnitude basement cooling during the Cenozoic, possibly because the propagation of AWCO deformation decreases towards the craton interior. Within the orogen, the Rio Pardo salient is the main reactive structure and probably results from the deformation of a master fault, inherited from its precursor rift. Here, we show how the magnitude of Phanerozoic denudation may be deeply associated with previous events of lithosphere weakening.

Initial Cenozoic Exhumation of the Northern Chinese Tian Shan Deduced from Apatite (U-Th)/He Thermochronological Data

Abstract The present topography of Tian Shan is related to the India-Asia collision, whereas the mechanisms for the topographic growth of Tian Shan remain at the center of debate partly due to the poorly constrained onset timing of the Cenozoic tectonic deformation. Our new apatite (U-Th)/He (AHe) data in the northern Chinese Tian Shan suggest that rapid cooling commenced at 20.2±4.9 Ma along the northern margin, which is consistent with published fission-track data from the same area and confirms that the youngest component of fission-track has been totally annealed. Moreover, AHe data from the interior mountain suggest that enhanced cooling began at 28.0±2.3 Ma, which is slightly older than that from the northern edge of the mountain. Although thermochronological data suggest that both the interior and northern margin of the northern Chinese Tian Shan have undergone rapid cooling since the late Oligocene-early Miocene, well preservation of relict low-relief surfaces along the northern rim of the northern Chinese Tian Shan and published thermochronological data indicate that the northern Chinese Tian Shan may have experienced differential exhumation in the Cenozoic. Combining the thermochronological and geomorphological evidence, we propose a progressive northward growth model for the northern Chinese Tian Shan. During the late Oligocene and early Miocene, compressive deformation derived from the India-Asia collision have arrived at the northern Tian Shan to reactivate both the interior mountain and its northern margin, while intense exhumation was concentrated in the interior mountain range. Then, deformation extended northward into the foreland basin that may be initiated in the middle-late Miocene.

Low‐temperaturethermochronological insights into the Mesozoic–Cenozoic exhumation history of the Taihang–Lvliangshan region: A review

The Taihang–Lvliangshan region is located in the central part of the North China Craton (NCC), which has undergone significant reactivation and reconstruction during the Mesozoic–Cenozoic period. Documenting its long‐term uplift and exhumation history is critical for accurately characterizing the reformation extent of the NCC. In order to further reveal the Mesozoic and Cenozoic exhumation stages and spatial exhumation pattern of the Taihang–Lvliangshan, we present a comprehensive low‐temperature thermochronometric datasets from the region. The compilation revealed five distinct rapid exhumation episodes within the Taihang–Lvliangshan, including the Middle‐Late Jurassic (~160–150 Ma), Early Cretaceous (~120–110 Ma), Late Cretaceous (~100–60 Ma), Eocene (~50–40 Ma), and Late Oligocene–Early Miocene (~30–20 Ma). During the Middle–Late Jurassic, the Taihang–Lvliangshan underwent a strong thrusting deformation caused by the synthesis of northwestward subduction of the Palaeo‐Pacific Plate and southward subduction/collision of the Mongol–Okhotsk suture zone. Subsequently, rapid exhumation under an extensional tectonic environment occurred during the Early Cretaceous primarily owing to the subduction of the Palaeo‐Pacific Plate. During the Late Cretaceous, the collision between the Okhotomorsk Block and East Asia resulted in the regional northwest–southeast shortening and uplift of the Taihang–Lvliangshan. During the Eocene, normal fault activations were occurring throughout the range, likely owing to the change in the convergence rate and direction between the Palaeo‐Pacific Plate and East Asia. Another important exhumation event occurred during the Late Oligocene–Early Miocene period, which was likely attributed to the result of combined effects from both the India–Eurasia collision and Pacific Plate subduction. Furthermore, differential exhumation of the Taihang–Lvliangshan were clearly revealed according to the five separate E–W elevation–distance profiles of the Taihang–Lvliangshan. They displayed greater exhumation thicknesses at the southern regions than those along the northern regions, which can be explained by the development of the Shanxi Rift that began to form following the Oligocene–Miocene period.

Late to post-Variscan basement segmentation and differential exhumation along the SW Bohemian Massif, central Europe

Abstract. The exposed Variscan basement in central Europe is well-known for its complex structural and lithological architecture resulting from multiple deformation phases. We studied the southwestern margin of the Bohemian Massif, which is characterized by major and long-lived shear zones, such as the Pfahl and Danube shear zones, extending over > 100 km and initiated during Variscan tectonics. We integrated Bouguer gravity anomaly and lidar topographic data analyses and combined our results with available data and observations from low-temperature thermochronology, metamorphic grades, and the exposed granite inventory to detect patterns of basement block segmentation and differential exhumation. Three NW–SE-striking basement blocks are bordered by the Runding, Pfahl, and Danube shear zones from the northeast to the southwest. Basement block boundaries are indicated by abrupt changes in measured gravity patterns and metamorphic grades. By applying high-pass filters to gravity data in combination with lineament analysis, we identified a new NNW–SSE-striking tectonic structure (Cham Fault), which further segments known basement blocks. Basement blocks that are segmented by the Cham Fault differ in the abundance and spatial distribution of exposed late Variscan granites and are further characterized by variations in apparent thermochronological age data. Based on our observations and analyses, a differential exhumation and tectonic tilt model is proposed to explain the juxtaposition of different crustal levels. Block segmentation along the NW–SE-striking Pfahl and Runding shear zones most likely occurred prior, during, and after late orogenic granite emplacement at ca. 320 ± 10 Ma, as some of the granites are cross-cut by the shear zones, while others utilized these structures during magma ascent and emplacement. In contrast, activity and block segmentation along the Cham Fault occurred after granite emplacement as the fault sharply truncates the granite inventory. Our study provides evidence of intense and continuous fault activities during late and post-orogenic times and highlights the importance of tectonic structures in the exhumation and juxtaposition of different crustal levels and the creation of complex lithological patterns in orogenic terrains.

Long-term topographic evolution of the Central Tianshan (NW China) constrained by low-temperature thermochronology

The Tianshan belt forms the southwestern part of the Central Asian Orogenic Belt, and its current topography is a product of punctuated Meso-Cenozoic intra-continental deformation that is still active today. This study provides new apatite fission track data on the Paleozoic rocks in and adjacent to the Chinese Central Tianshan, including two age-elevation profiles in the Alagou and Gangou areas. Inverse thermal history modelling reveals that the Central Tianshan experienced regional slow to moderate cooling during most of the Mesozoic, and that the present-day topography was mainly built by Cenozoic uplift and erosion. Geomorphological observation reveals several fragments of flat, low-relief surfaces within the Central Tianshan, which were likely to have formed in the Mesozoic as evidenced by thermal history modelling of the Alagou age-elevation profile. Furthermore, our data suggest that the Chinese Central Tianshan and its adjacent terranes did not undergo intensive relief building during its long-term Mesozoic evolution, as several pre-Mesozoic deep-rooted regional faults did not record evidence for a strong Mesozoic reactivation. Finally, differential exhumation in the Western Chinese Tianshan and Junggar is discussed, and we propose that the development of regional brittle faults could significantly influence the processes of intra-continental deformation.

Mesozoic exhumation of the Jueluotage area, Eastern Tianshan, NW China: constraints from (U–Th)/He and fission-track thermochronology

AbstractThe Jueluotage area, which is located in the southern branch of the Eastern Tianshan and northeast of the Tarim Basin, represents a vital locality for investigating intracontinental reactivation induced by the tectonic events at the Eurasian plate margin. This study applies zircon and apatite (U–Th)/He and apatite fission-track thermochronology to the Jueluotage area in the Eastern Tianshan. Our data and thermal history modelling show that the Jueluotage area experienced Triassic–Early Jurassic (˜240–180 Ma) cooling, reflecting the closure of the North Tianshan Ocean and subsequent far-field effects of collision/accretion of the Qiangtang Block and Kunlun terrane. Following this period of fast cooling, a differential exhumation process occurred between the various tectonic belts in the Jueluotage area. The Aqishan–Yamansu belt was exposed at the surface during the Triassic–Early Jurassic cooling phase and experienced subsequent burial, which continued until Early Cretaceous time when a pulse of exhumation occurred. However, the major fault zones (Kanggurtag ductile shear zone and Aqikkuduk Fault) and Central Tianshan arc have remained tectonically stable since Early Jurassic time. No Cenozoic rapid cooling was recorded by the low-temperature thermochronology results in this study, indicating that much of the Jueluotage area was exhumed to the upper crust in the late Mesozoic period.

Differential exhumation of ultrahigh-pressure metamorphic terranes: A case study from South Altyn Tagh, western China

South Altyn Tagh contains ultrahigh-pressure (UHP) terranes that have been exhumed from ~300 km mantle depth. Previous zircon U–Pb geochronology has yielded an eclogite-facies age of ca. 500 Ma and a high-pressure (HP) granulite-facies retrograde age of ca. 450 Ma in the Jianggalesayi area in the western segment of South Altyn Tagh. However, in the eastern segment (Yinggelisayi and Danshuiquan localities), an age range of 500–480 Ma has been determined, and it remains uncertain as to whether this age range represents the timing of the peak metamorphic stage or the retrograde overprint. Our study of newly discovered retrograde eclogite in the Danshuiquan locality shows that it underwent three stages of metamorphism, under eclogite-facies, HP granulite-facies and amphibolite-facies P–T conditions of 2.5–4.0 GPa and 870–1050 °C, 2.0–1.4 GPa and 830–940 °C, and 0.7–1.3 GPa and 704–880 °C, respectively. The decompression-dominated P–T path evolved mainly after crossing the solidus, indicating marked retrograde modification under melt-bearing conditions. LA–ICP–MS and SIMS zircon U–Pb dating yielded ca. 500 Ma eclogite-facies and ca. 484 Ma granulite-facies retrograde ages and a later retrograde age of ca. 452 Ma. The clockwise P–T–t path indicates rapid exhumation from eclogite-facies to granulite-facies within around 16 Myr, which is faster than that of the UHP rocks in the western segment. Thus, the HP–UHP rocks in South Altyn Tagh suggest a differential exhumation process for the eastern and western segments. The distinct HP–UHT metamorphism and rapid exhumation of (U)HP rocks in the eastern segment likely resulted from local mantle heating. The continuing P–T evolution of the (U)HP rocks under UHT conditions during exhumation led to a pervasive granulite-facies overprint in the eastern segment of the South Altyn Tagh. The rapid exhumation recorded in the eastern segment provides valuable insights into the exhumation mechanism of ultra-deep subducted UHP terranes.

Differential Exhumation of the Eastern Cordillera in the Central Andes: Evidence for South‐Verging Backthrusting (Abancay Deflection, Peru)

AbstractLocated at the northern tip of the Altiplano, the Abancay Deflection marks abruptly the latitudinal segmentation of the Central Andes spreading over the Altiplano to the south and the Eastern Cordillera northward. The striking morphological contrast between the low‐relief Altiplano and the high‐relief Eastern Cordillera makes this area a well‐suited place to determine spatiotemporal variations in surface and/or rock uplift and discuss the latest phase of the formation of the Central Andes. Here, we aim to quantify exhumation and uplift patterns in the Abancay Deflection since 40 Ma and present new apatite (U–Th)/He and fission track data from four altitudinal profiles and additional individual samples. Age–elevation relationships and thermal modeling both document that the Abancay Deflection experienced a moderate, spatially uniform, and steady exhumation at 0.2 ± 0.1 km/Myr between 40 and ∼5 Ma implying common large‐scale exhumation mechanism(s). From ∼5 Ma, while the northern part of the Eastern Cordillera and the Altiplano registered similar ongoing slow exhumation, the southern part of the Eastern Cordillera experienced one order‐of‐magnitude of exhumation acceleration (1.2 ± 0.4 km/Myr). This differential exhumation since ∼5 Ma implies active tectonics, river capture, and incision affecting the southern Eastern Cordillera. 3D thermokinematic modeling favors a tectonic decoupling between the Altiplano and the Eastern Cordillera through backthrusting activity of the Apurimac fault. We speculate that the Abancay Deflection, with its “bulls‐eye” structure and significant exhumation rate since 5 Ma, may represent an Andean protosyntaxis, similar to the syntaxes described in the Himalaya or Alaska.