High Exhumation Rates Research Articles

Age, origin and tectonic controls on rapid recent exhumation of the Sibela Mountains, Bacan, Indonesia

The Sibela Mountains of the island of Bacan in eastern Indonesia contain one of the Earth’s youngest metamorphic complexes that is now exposed at elevations up to 2000 m. New mica 40Ar/39Ar and apatite (U–Th–Sm)/He data from metamorphic and igneous rocks indicate that these rocks were rapidly exhumed in the Pleistocene (c. 0.7 Ma). Exhumation of the metamorphosed Permo-Triassic basement (c. 249–257 Ma) was accompanied by metamorphism (recorded by schists) as well as partial melting (recorded by c. 1.4 Ma granitic dykes). These processes must have occurred at extremely high cooling and exhumation rates. The rapid exhumation on land was associated with significant subsidence in adjacent basins offshore that reach depths up to 2.4 km. Neogene metamorphic core complexes and other metamorphic complexes are well-known from eastern Indonesia, but they usually record much higher exhumation rates than those reported from older classic metamorphic core complexes found in other parts of the world and require a different formation mechanism. Unlike classic metamorphic core complexes that are characterized by low-angle detachment faults, the Bacan metamorphic rocks were exhumed on steep bounding normal faults forming a rectilinear block pattern. We suggest such complexes are termed metamorphic block complexes (MBC). The Bacan MBC is exceptionally young and like the other east Indonesian complexes was rapidly exhumed during subduction rollback. A flexure formed during arc-arc collision as the Sangihe forearc loaded the Halmahera forearc which reactivated steeply-dipping faults in a rectilinear chocolate block pattern.Graphical abstractThe Sibela Mountains of the island of Bacan in eastern Indonesia are formed by one of the Earth’s youngest metamorphic complexes. a Dense rain forest cover and steep flanks of the Sibela Mountains which rise from sea level to more than 2000 m. b Quaternary collision between the Sangihe and Halmahera arcs. Loading of the Halmahera forearc formed a flexure that reactivated steeply-dipping faults, which exhumed the Sibela Mountains metamorphic block. c Rapid cooling paths during exhumation of the Sibela metamorphic complex

Reconstruction of the topographic evolution of the Nanling Range in South China and its implications for the East Asian Monsoon evolution

The East Asian monsoon is the largest periodic airflow on Earth and significantly affects the climate of East Asia. However, considerable controversy exists about the onset timing of the East Asian monsoon. As one of the southern barriers blocking the northward movement of the warm and humid airflow, the Nanling Range has likely recorded key topographic information related to the East Asian monsoon onset and development. We used apatite and zircon (UTh)/He data obtained from the Shaoguan–Guidong horizontal cross-section to reconstruct the two-dimensional (2-D) paleotopography of the Nanling Range on a long-term scale. Four vertical profiles in Shulouqiu, Erjian, Sanfenshi, and Leiwangdian were used to constrain the exhumation history of the Nanling Range. The result revealed the following: 1) The drainage divide began to move from south to north at 80 Ma. At 80 Ma, the south segment of the cross-section reached a peak elevation of ∼3.6 km. The asymmetric topography experienced a rapid elevation (and relief) decrease from 80 Ma to 40–30 Ma. The four vertical profiles also experienced increased cooling and high exhumation rates from 100 Ma to 40–30 Ma. 2) The south segment experienced more rapid exhumation than the north segment from 80 Ma to 40–30 Ma. The rapid exhumation of the south segment during the Late Cretaceous–Paleocene is probably related to the activity of the Nanxiong Fault, and the rapid exhumation of the south segment during the Eocene probably results from the onset of the East Asian Monsoon.

The exhumation history of the middle Hsuehshan Range, Taiwan, as revealed by zircon thermochronological modeling

The Taiwan orogenic belt has high precipitation and high exhumation rates (3–6 km/Myr), making it a natural laboratory for understanding how erosion, tectonics, and climate interact. Understanding how rock exhumation rates have evolved since the late Miocene is key to unraveling climate–tectonic interactions. In this study, we present 8 new zircon fission track (ZFT) and (UTh)/He (ZHe) cooling ages (including 2 unreset ages) from 5 samples from 1700 to over 3300 m elevation around the highly incised Dajia River in the core of the Hsuehshan Range (termed the mid-HR in this study) in central Taiwan. Two of the ZFT and ZHe ages (5.3 Ma and 2.6 Ma) are the oldest ages recorded in this region. These ages suggest that the cooling rate of the mid-HR is lower than that of the Backbone Range and Yushan. With these and previously published cooling ages, we modeled the exhumation and cooling history using a 2-D thermal diffusion equation with time-varying erosion. The ZFT and ZHe ages are best explained by a steadily increasing exhumation rate up to 3.4 + 0.5/−0.3 km/Myr from 7 to 1 Ma. The exhumation rate in the last million years is not as well constrained but appears to have increased at a slower rate. Our findings differ from those of previous studies that propose that the exhumation rate increased rapidly in the last 1–2 Myr. We propose that the steady increase in the exhumation rate in the mid-HR indicates increasing topographic relief, which is likely caused by progressive crustal thickening.

Testing erosional and kinematic drivers of exhumation in the central Himalaya

This study investigates the influence of fault geometry, kinematics, and displacement on the exhumation history of the central Himalaya using geologic mapping constraints, a new interpreted cross-section, and a suite of 176 thermochronometer ages through the Marsyangdi valley in central Nepal. Guided by the cross-section, we integrate a forward model of fold-thrust belt evolution with a 2D thermokinematic model. Model-predicted and measured thermochronometer ages were compared to evaluate the sensitivity of thermochronometer ages to the geometry and location of structures, and their rates of deformation. Results indicate 84% of the measured data can be reproduced with a largely in-sequence system of faulting where displacement occurs on the Main Central thrust (MCT) from 23-16 Ma, the Ramgarh-Munsiari thrust (RMT) from 16-7.5 Ma, the Trishuli thrust (TT) from 7.5-6 Ma and the Main Boundary thrust (MBT) from 6-3 Ma. Our cross-section solution shows the development of a duplex that initiates at 4 Ma with the TT and MBT as the roof thrust. The duplex is translated over the Main Himalayan thrust (MHT) ramp, concurrent with forward propagation of faulting in the synorogenic Siwaliks from 3 Ma to present. Notably, the 2-0.5 Ma apatite fission-track ages between the MCT and Tethyan strata 45 km north of the MCT are not reproduced by the wide range of in-sequence deformation scenarios we explored. Instead, these data are consistent with simulations that include significant displacement on two out-of-sequence (OOS) faults in the last ∼1 Ma: 10 km of OOS faulting near the MCT followed by 5 km of displacement on a fault 15 km south of the MCT. Modeled OOS thrusting both builds significant topography in the hinterland and flexurally suppresses topography in the foreland. Consequently, our preferred kinematic solution has ∼10 km of final fault motion in the Siwaliks to rebuild topography at the MBT and the active MFT from ∼0.5 Ma to the present.Modeled exhumation rates are highly variable through time, and are highest during translation of rocks over high (∼10 km) ramps and during significant changes in architecture, such as duplex formation and OOS faulting. Notably high exhumation rates include 10.5 mm/yr during the first 4 Myr of MCT motion, 4-6 mm/yr at ∼7 Ma, due to the translation over an ∼10 km high TT ramp, and 7-12 mm/yr from 4 Ma to present driven by the development of the duplex and its translation over the MHT ramp, followed by OOS thrusting. The high (7-12 mm/yr) exhumation rates documented here from 4 Ma, correlate with a time of distinct climate change, including strengthening of the monsoon, and northern hemisphere glaciation, lending support to potential climate-tectonic feedbacks.

Out of sequence faulting in the backbone range, Taiwan: Implications for thickening and exhumation processes

The Taiwan orogenic belt results from convergence between the Philippine Sea plate and Eurasia plate since the late Cenozoic. An extremely high exhumation rate has been observed in the Backbone Range, which has motivated interpretive models that show underplating as the primary process in driving uplift and thickening. Here we integrate new (U-Th)/He and fission-track dates of detrital zircons with previously published thermochronology to document a significant out-of-sequence thrust in the core of Taiwan orogen. The thrust, informally named the Tayulin fault system, is identified by structural kinematics and offset metamorphic temperature trends, low-temperature thermochronometric dates, and seismic tomography. The OOST appears to be composed of three segments that crop out along the western flank of the Backbone Range. The apparent age-elevation profiles suggest a relatively slow exhumation rate, <1.0 mm/yr, in the early stages from 8 Ma to 2 Ma followed by a stage of significantly higher exhumation rates, ranging from 2.3 to 6.5 mm/yr after 2 Ma. The early slow exhumation stage is related to regional folding and foliation development. In contrast, we suggest the younger rapid exhumation stage is related to slip on the out-of-sequence thrust.

Tectonothermal evolution of the Lohit Valley, Eastern Himalaya: New low‐temperature thermochronological constraints

The present contribution provides the first low‐temperature thermochronological record from the Lohit Valley, Eastern Himalaya, presenting eight ZHe and two AHe cooling ages across the major tectonic boundaries. The ZHe cooling ages range from 6.94 ± 1.17 Ma to 12.51 ± 2.84 Ma, whereas AHe ages vary between 1.73 ± 0.15 Ma and 3.56 ± 0.42 Ma. The ZHe cooling ages suggest that the Mishmi Crystallines exposed at the southwestern mountain front are the slowest exhuming domain since ~12 Ma. The ZHe ages are youngest in the Demwe Thrust (DT) zone, and the contact between the frontal low‐grade metamorphic rocks of Mishmi Crystalline and high‐grade gneissic rocks of the Mayodia Group. The rapid exhumation in the DT zone as obtained from the ZHe cooling ages suggests an out‐of‐sequence thrusting at ~7 Ma. The QTQt thermal history modelling of the co‐genetic pairs of ZHe and AHe cooling ages of the northeasternmost Lohit Plutonic Complex suggests that the exhumation rates in this region were as high as ~3.7 mm/year during the Pliocene‐Quaternary. These high exhumation rates are in good correlation with the local topographic relief, hill slopes, and channel steepness, which suggests the establishment of the present‐day topography of the Lohit valley region at the latest by Pliocene‐Quaternary. Variation in exhumation rates does not correlate with the present‐day precipitation pattern. Tectonics appears to be the prime driver for exhumation rates of the Lohit valley region of the easternmost Himalaya.

Central Pyrenees Mountain Building: Constraints From New LT Thermochronological Data From the Axial Zone

AbstractEarly phases of mountain building are usually poorly constrained although they may provide insights into both the wedge rheology and the role of inheritance. In the central Pyrenean Axial Zone, a main exhumation peak at 35–30 Ma is particularly well constrained but the previous exhumation stages are much less constrained. In this study, we present new low‐temperature thermochronological zircon fission‐track and (U‐Th)/He data and structural observations to constrain the thermal history of the Axial Zone and its shortening sequence during the whole Alpine collision. The dataset collected along the ECORS profile suggests two main collisional cooling phases. An early stage of Alpine shortening (from 70 to 40 Ma) is characterized by low rates of cooling/exhumation in the whole Axial Zone around 5–10°C/Myr and 200 ± 50 m/Myr. During this phase, deformation was distributed within the whole Axial Zone. This result questions the occurrence of a quiescence phase in the Axial Zone. Between 40 and 20 Ma, a more localized second phase with cooling rates around 30°C/Myr and high exhumation rates &gt;800 m/Myr is only recorded in the Maladeta massif. During this second phase, much lower denudation rates are recorded further north and south, thus suggesting rather symmetrical exhumation in the Axial Zone, controlled by underplating of the youngest crustal ramp, the Rialp thrust. This sequence of shortening, from distributed to localized deformation, appears to be characteristic in other collisional wedges as well.

Palaeozoic and Pliocene tectonic evolution of the Salt Range constrained by low‐temperature thermochronology

AbstractThe Salt Range in Pakistan exposes Precambrian to Pleistocene strata outcropping along the Salt Range Thrust (SRT). To better understand the in‐situ Cambrian and Pliocene tectonic evolution of the Pakistan Subhimalaya, we have conducted low‐temperature thermochronological analysis using apatite (U‐Th‐Sm)/He and fission track dating. We combine cooling ages from different samples located along the thrust front of the SRT into a thermal model that shows two major cooling events associated with rifting and regional erosion in the Late Palaeozoic and SRT activity since the Pliocene. Our results suggest that the SRT maintained a long‐term average shortening rate of ~5–6 mm/yr and a high exhumation rate above the SRT ramp since ~4 Ma.

Low‐temperature thermochronology as a control on vertical movements for semi‐quantitative source‐to‐sink analysis: A case study for the Permian to Neogene of Morocco and surroundings

AbstractContinental passive margins and their hinterlands in the Atlantic realm have been the locus of many Low Temperature Thermochronology (LTT) and time‐Temperature (t‐T) modelling studies that evidence pre‐, syn‐ and post‐rift episodic km‐scale exhumation and burial episodes. In this study, we integrate data from over 30 published LTT and t‐T modelling studies from Morocco and its surroundings using a three‐step workflow to obtain: (a) exhumation/burial rates, (b) erosion rates and (c) palaeoreconstructions of source‐to‐sink domains, between the Permian and the Present. Our synthesis of available t‐T modelling results predicts high exhumation rates in the Anti‐Atlas (0.1 km/Myr) during the Early to Middle Jurassic, and in the High Atlas (0.1 km/Myr) and Rif (up to 0.5 km/Myr) during the Neogene. These rates are comparable to values typical of rift flank, domal or structural uplifts settings. During the other investigated periods, exhumation rates in the Meseta, High‐Atlas, Anti‐Atlas and Reguibat shield are around 0.04 ± 0.02 km/Myr. Interpolation of the exhumation rates at the regional scale allow calculation of the volume of rocks eroded. Estimates of erosion rates are between 0.2 x 103 and 7.5 x 103 km3 (in the Meseta and the Reguibat Shield respectively). Ten erosional (quantitative, from interpolation results) and depositional (qualitative, from data synthesis) “source‐and‐sink” maps have been constructed, with emphasis on the Jurassic and Cretaceous periods. The maps integrate the extent of exhumed domains, using information from geological maps, lithofacies and biostratigraphic data from new geological fieldwork and well data from onshore and offshore basins. The results illustrate changes in the source‐to‐sink systems and allow for a better understanding of the Central Atlantic margin hinterlands evolution.

Deep subduction of felsic rocks hosting UHP lenses in the central Saxonian Erzgebirge: Implications for UHP terrane exhumation

Contrasting metamorphic conditions determined by chemical geothermobarometric investigations of ultrahigh-pressure (UHP) lenses surrounded by high-pressure (HP) and medium-pressure (MP) felsic country rocks are an enigmatic feature of UHP terranes. One of the major questions arising is whether the UHP lenses and the country rocks are a product of different peak metamorphic conditions corresponding to different maximum depth or whether country rocks also experienced UHP conditions but equilibrated and/or re-equilibrated at a different metamorphic stage. Here we address this question to the central Saxonian Erzgebirge in the northwestern Bohemian Massif, Germany. In order to screen the variety of garnet from lithologies occurring in the study area, we analyzed the detrital garnet record from seven modern stream sands. In addition to 700 inclusion-bearing garnet grains previously studied from the 125–250 μm grain-size fraction, we analyzed the 63–125 and 250–500 μm fractions and extended the dataset to overall 2100 inclusion-bearing grains. The new findings of coesite and diamond inclusions in several garnet grains, which are in compositional contrast to garnet of the known UHP lenses but match with those of the felsic country rocks, show that considerable parts of the country rocks underwent UHP metamorphism. Melt inclusions containing cristobalite, kokchetavite, and kumdykolite in garnet derived from the country rocks point to partial melting and re-equilibration during exhumation at HP/HT conditions. Although an amalgamation of rocks which reached different maximum depth may be responsible for some of the contrasting peak metamorphic conditions, the mineralogical evidence for UHP conditions in the felsic country rocks surrounding the UHP lenses proves a largely coherent slab subducted to UHP conditions. Furthermore, the presence of coesite in the subducting voluminous felsic crust and its transformation to quartz during exhumation have great implications for buoyancy development during the metamorphic cycle, which may explain the high exhumation rates of UHP terranes.

Constraints on late cenozoic tectonics in the Southern Longmen Shan: evidence from low-temperature thermochronology

ABSTRACT The NE-trending Longmen Shan (LMS) thrust belt, located between the Songpan-Garze terrane and the Yangtze craton, is one of the steepest topographic margins around the Tibetan Plateau. However, the exhumation history and the fault activity of the southern segment of the LMS have remained poorly constrained, particularly in the range front, where little thermochronology ages have been reported. Herein, we report 17 apatites (U-Th)/He (AHe) ages from the southern LMS along the Qingyi River across the Dachuan–Shuangshi Fault (DSF), the Yanjing–Wulong Fault (YWF), and the Gengda–Longdong Fault (GLF). The AHe ages in the hanging-wall of the DSF are ca. 6–11 Ma, which increase to ca.19–23 Ma in the footwall of the DSF. New AHe ages reveal that exhumation rates across the DSF increased significantly from 0.05 to 0.1 km/Myr in the footwall to 0.2–0.4 km/Myr in the hanging-wall since the Late Miocene. The width of the high exhumation rate (0.4–0.6 km/Myr) belt concentrated between the DSF and the GLF, and towards DSF eastward and GLF westward, the exhumation rates decrease rapidly. The results show that continuous crustal shortening along the DSF. Our results support the upper crustal thrusting model that emphasizes crustal shortening deformation along the eastern Tibetan Plateau margin.

Response of a Rheologically Stratified Lithosphere to Subduction of an Indenter‐Shaped Plate: Insights Into Localized Exhumation at Orogen Syntaxes

AbstractThis study investigates the influence of the 3‐D geometry of a down‐going plate, the rheological structure of the upper plate, and the migration of the overriding plate toward the trench in relation to the overall subduction velocity on the exhumation pattern in orogen syntaxes. Using a thermomechanical numerical code (DOUAR), we analyze the strain localization, rock uplift, and exhumation response of a rheologically stratified continental lithosphere to subduction of a convex‐upward‐shaped indenter. The models consider three thermorheological lithospheric profiles that determine the degree of mechanical coupling between the upper crust and lithospheric mantle. These models include a strong, cratonic lithosphere; a weaker, younger (and hotter) continental plate; and an intermediate case. The strongly coupled case predicts a localization of high rock uplift rates along narrow linear bands crossing the entire model domain parallel to the trench. In contrast, in a weakly coupled lithosphere, rock uplift is concentrated within a curved ellipse region of anomalously high exhumation rates located above the indenter apex. The aspect ratio of the localized area of rapid rock uplift is controlled by the initial width of the rigid indenter and the relationship between boundary velocities. In particular, the combination of little or no upper plate migration with a narrow indenter causes a nearly circular region (~100‐km diameter) of rapid exhumation that resembles the pattern of thermochronometer ages observed in orogen syntaxes such as the Southeast Alaska and the Olympic Mountains of the Cascadia subduction zone (western USA).

Thermochronology and exhumation rates of granitic intrusions at Mesa Central, Mexico

ABSTRACTThe Mesa Central of Mexico (MC) is an elevated plateau located 2000 m above sea level in central Mexico, where intrusions outcrop that register the history of exhumation-erosion occurring during the Late Cretaceous-Paleogene. The tectonic history of the region records formation of the Late Cretaceous-Paleogene ‘Mexican orogen’; this was followed by extension of the entire region and several plutons were then exhumed. The age and magnitude of the crustal uplift and erosion occurring during exhumation has not been addressed to date. Therefore, this study reports the crystallization and cooling ages of two plutons, the Tesorera Granodiorite and the Comanja Granite, and estimates their emplacement depths. Based on these data, the exhumation age of the Tesorera Granodiorite is estimated to be between ~73 Ma and ~63 Ma at an exhumation rate of ~528 m/m. y. and that of the Comanja Granite is 52 Ma and 48 Ma at an exhumation rate of ~2500 m/m. y. Exhumation-erosion event of the Tesorera Granodiorite was located on the trace of the San Luis-Tepehuanes Fault System and that of the Comanja Granite on the a trace of the El Bajío Fault System. Furthermore, the high exhumation rate in the Comanja Granite suggests that gravitational collapse played an important role during exhumation.

Relics of a Paleoproterozoic orogen: New petrological, phase equilibria and geochronological studies on high-pressure pelitic granulites from the Pingdu-Laiyang areas, southwest of the Jiaobei terrane, North China Craton

High-pressure (HP) pelitic granulites have been used as important targets in evaluating ancient geodynamic processes similar to subduction, collision and exhumation operating in modern plate tectonics. In this contribution, relic HP pelitic granulites were identified from the Pingdu-Laiyang areas of the Jiaobei terrane that are dominated by low- to medium-pressure (LMP) pelitic granulites, suggesting their linear distribution and that at least some of LMP types should be retrograde products of the HP pelitic granulites. Their metamorphic P-T-t paths were traced by integrated methods of petrographic observation, mineral chemistry, P-T-X pseudosection modeling, Zr-in-rutile thermometry, and zircon and monazite geochronology. These HP pelitic granulites record consistent clockwise P-T-t paths that are manifested by similar peak metamorphism of high-pressure granulite-facies, with P-T conditions of P > 13 kbar, T > 850 °C possibly during 1950–1900 Ma, followed by near isothermal decompression (ITD) to mid-crustal level at 1900–1850 Ma and subsequent near isobaric cooling (IBC) to low temperature during 1850–1800 Ma. The consistent clockwise P-T-t paths and linear distribution of HP pelitic granulites explicitly indicate a sequence of geodynamic processes similar to modern-style plate tectonics must have operated during formation of the Paleoproterozoic Jiao-Liao-Ji belt (JLJB). These include a process similar to subduction that brought sedimentary precursors of HP pelitic granulites down, which was followed by continental orogeny during 1950–1900 Ma, leading to crustal thickening (40–50 km) and high-pressure granulite-facies metamorphism, and a post-orogenic collapse during 1900–1800 Ma that resulted in exhumation and cooling of HP granulites along ITD and IBC paths. Therefore, it is argued that ancient HP pelitic granulites can be regarded as relics of orogen and ascertain tectonic interpretation of the dominated LMP pelitic granulites in the same Precambrian metamorphic terranes. Notably, the apparent thermal gradients estimated from peak metamorphism are 15–20 °C/km, much higher than those of typical products in Phanerozoic plate tectonics, and the HP pelitic granulites that contain well-preserved kyanite probably require relatively high exhumation rates during ITD to middle crustal level. These seem to mark the differences in thermal regimes and tectonic mechanisms between Paleoproterozoic and Phanerozoic collisional orogenic systems.

Late Cenozoic Foreland‐to‐Hinterland Low‐Temperature Exhumation History of the Kashmir Himalaya

AbstractNew apatite and zircon (U‐Th)/He cooling ages quantify late Cenozoic exhumation patterns associated with fault activity across the Kashmir Himalaya. Apatite (U‐Th)/He (AHe) cooling ages of detrital grains from the Sub‐Himalayan foreland sediments indicate significant resetting. AHe data and thermal modeling reveal cooling and exhumation initiated by 4 Ma at the deformation front and by 2–4 Ma throughout other Sub‐Himalayan structures. Exhumation rates for Sub‐Himalayan structures are ≥1 mm/year. In the hinterland, thrust sheet samples from the Main Boundary thrust and Main Central thrust yield AHe cooling ages between 5.1 and 21.1 Ma. Published apatite fission track cooling ages (&lt;3 Ma) and high exhumation rates (3.6–3.2 mm/year) across the Kishtwar window further to the north are consistent with AHe data from the Sub‐Himalayan structures. The pattern of cooling ages and rates indicates that exhumation occurs in association with changes in the Himalayan basal décollement ramp geometry. Hinterland zircon (U‐Th)/He (ZHe) data show a pronounced abundance and probability spike in cooling ages between 14 and 21 Ma, a period when Main Central thrust motion is well documented throughout the Himalaya. ZHe single‐grain ages from Sub‐Himalayan samples contain a nearly identical cluster from 16 to 23 Ma. Cooling patterns across the Kashmir Himalayas do not correlate spatially with modern monsoon precipitation, suggesting that climate‐related precipitation and exhumation are decoupled. Coeval translation over the basal décollement and distributed imbricate thrust deformation of the foreland in the upper plate characterizes fault‐related exhumation of the Sub‐Himalayan orogenic belt after 4 Ma.

Precambrian-Cambrian provenance of Matinde Formation, Karoo Supergroup, northwestern Mozambique, constrained from detrital zircon U-Pb age and Lu-Hf isotope data

The Permian-Triassic time interval was a period of high sedimentation rates in the intracontinental Karoo rift basin of northwestern Mozambique, reflecting high exhumation rates in the surrounding high ground Precambrian-Cambrian basement and juxtaposed nappes. U-Pb LA-MC-ICPMS dating and Lu-Hf isotopic analysis of detrital zircons from the Late Permian-Early Triassic Matinde Formation of the Karoo Supergroup is used as a reliable proxy to map denudation patterns of source regions. Data allow discrimination of U-Pb age populations of ca. 1250-900 Ma, a secondary population between ca. 900-700 and a major contribution of ages around ca. 700-490 Ma. Zircon grains of the Mesoproterozoic age population present Mesoproterozoic (1000–1500 Ma) to Paleoproterozoic (1800–2300 Ma) Hf TDM ages, with positive (0 to +11) and negative εHf values (−3 to −15), respectively. The younger U-Pb age population also presents two different groups of zircon grains according to Lu-Hf isotopes. The first group comprise Paleoproterozoic (1800–2300 Ma) ages, with highly negative εHf values, between −10 and −22, and the second group exhibits Mesoproterozoic ages (1200–1500 Ma), with increased juvenile εHf values (ca. 0 to −5). These Hf isotopes reinforce the presence of unexposed ancient crust in this region. The oldest U-Pb age population resembles the late stages of Grenville Orogeny and the Rodinia Supercontinent geotectonic activity mostly represented by magmatic rocks, which are widely present in the basement of northern Mozambique. The juvenile Hf-isotope signature with an older age component is associated to rocks generated from subduction processes with crust assimilation by continental arcs, which we correlate to rocks of the Nampula Complex, south and east of the Moatize-Minjova Basin. The U-Pb ages between 900 and 700 Ma were correlated to the calc-alkaline magmatism registered in the Guro Suite, related to the breakup phase of Rodinia, and mark the western limit of the Moatize-Minjova rift basin together with the Mungari Nappe and Chacocoma Granite, also probable sources. The εHf-isotopic signature (ca. −23 to 0) with Meso- and Paleoproterozoic Hf model ages of these zircons suggest assimilation of older crust by the Guro Suite continental arc. The Late Neoproterozoic - Cambrian U-Pb ages (ca. 700-490 Ma) comprise the wide interval of high-grade metamorphism, klippen and plutonism related to the Pan-African Orogeny. Hf-isotope pattern indicate high remelting of the older Mesoproterozoic and Paleoproterozoic crust. These ages correspond to magmatic and granulite metamorphic ages of the Monapo and Mugeba klippen, Nampula Complex and Guro Suite/Mungari Nappe/Chacocoma Granite rocks. The data suggests that these units were main source areas for the sediments of the Matinde Formation. The main Cambrian ages are related to the late stages of Pan-African Orogeny, marked by crustal delamination in NE Mozambique that was responsible for an extensive crustal partial melting associated to high-grade granulitic metamorphism and generation of large granitic plutons. The Nampula Complex was probably a large geotectonic entity in the Late Mesoproterozoic and reworked during the Pan-African Orogeny. This evidence, added to the N-NW paleoflow of the Proto-Zambezi river and provenance data, suggests that the Nampula Complex, Guro Suite and its juxtaposed nappes formed a high ground source area for fluvial sediments that fills the Moatize-Minjova Basin. Permian-Triassic rifting in northern Mozambique was induced by far-field stresses transferred from Gondwana margins. This stress disrupted the Nampula Complex reactivating Precambrian structures and fabrics, while the Jurassic-Cretaceous breakup of Gondwana and latter landscape evolution led to its actual morphology and configuration.

Paleostress evolution during the exhumation of high-P marbles, Samaná Complex, northern Hispaniola

The marble of the Samaná complex presents a widespread foliation formed during its exhumation following a general decompressive strain path from high pressure (2.0&gt;P&gt;0.7 GPa) and low temperature (&lt;500 ºC) conditions. The foliation is plano-linear and blastomylonitic. Deformation distribution is highly heterogeneous. Calcite preferred orientation is poor, even though the marble has a well-defined tectonic fabric. The blastomylonitic fabric is masking an earlier tectonic fabric. Cathodoluminescence images reveal that intense fracturing formed prior to foliation development in the marbles. The thermodynamic modelling of mineral phase transformations during prograde metamorphism indicate an increase in water content (1.2%&lt;w.t.H2O&lt;1.8%) that may have involved an increase in fluid pressure and triggered rock embrittlement and subsequent exhumation. Stress drops after a cataclastic event, as well as grain-size reduction by abrasion, may have activated dissolution-precipitation processes along cataclastic bands. Differential stress |σ1-σ3| increased as exhumation progressed after the cataclastic event. Estimates of paleostress based on calcite mechanical twinning indicate values of |σ1-σ3| &gt;350 MPa during deformation. In contrast, mean flow stress during grain-boundary migration is estimated in |σ1-σ3| &lt;150 MPa. The high paleostress record and microstructures of the marble are consistent with the high exhumation rate calculated (&gt;110 MPa Ma-1). All of these data suggest that exhumation always occurred near the brittle-ductile regime of deformation.

Thermochronological evidence of a low‐angle, mid‐crustal detachment plane beneath the central South Island, New Zealand

AbstractOblique continental convergence and uplift in the Southern Alps, New Zealand is largely accommodated by dextral transpression on the Alpine Fault. However, toward the south of the orogen the Alpine Fault becomes increasingly strike‐slip, despite evidence for high exhumation rates in the Pacific plate. Here we present 41 new apatite and zircon fission‐track ages to investigate the role of the southern Alpine Fault in Pacific plate exhumation since the Miocene. Through development of a new, maximum likelihood fission‐track age calculation method (to overcome extremely low (&lt;0.1 ppm) 238U concentrations in apatites) we estimate the width of the fully reset apatite zone (ages &lt;5 Ma) southeast of the southern Alpine Fault, which has been previously overestimated. Instead, this zone is ∼30 km wide, rather than 60 km. We combine our exhumation profile with thermo‐kinematic modeling to impose constraints on fault kinematics and deformation history. The surface cooling age pattern can be well reproduced by exhumation along a listric reverse fault, which shallows to a low‐angle (6–10°) mid‐crustal detachment beneath the Southern Lakes. This structure is comparable to the listric central Alpine Fault geometry previously constrained by thermo‐kinematics models to the north of our study region. We propose this detachment plane is continuous beneath a large region of central South Island and may be acting to accommodate underthrusting of Australian crust beneath the Pacific plate.

Graphical methods of river profile analysis to unravel drainage area change, uplift and erodibility contrasts in the Central Range of Taiwan

AbstractTo reveal river channel steepness patterns and variance in settings with significant variation in rock uplift rate, rock erodibility and moving water divides, we present a series of graphical methods to interpret channel profiles. To complement Cartesian χ plots, longitudinal profiles and mapping methods, we introduce a new method based on a radial coordinate system. We map each basin onto polar coordinates in which the radial dimension is χ and the azimuthal coordinate, ϕ, is calculated with an increment (Δϕ) scaled to the distance to neighboring channel heads. The elevation is contoured on this mapping. Average channel steepness is estimated by fitting a conical surface to the elevation. The graph simplifies the comparison of χ and elevation between channels that share a divide, and helps identify spatial changes in drainage area and patterns of erodibility.We apply this approach to derive the uplift pattern in the eastern and southern Central Range of Taiwan, where the high tectonic convergence and uplift rates combined with sub‐tropical climate and frequent typhoons results in high exhumation rate, and well‐developed, detachment‐limited river networks. Additionally, the tectonic activity leads to drainage basin reorganization. We identify examples of divide migration, discrete river capture as well as anomalous steepness that we attribute to local variability in rock erodibility.Estimated basin‐average steepness values show the highest and a near constant value from Hsinwulu basin to Liwu basin in the center of the Island. To the north and south of this region, the values gradually decrease. These estimates show good correlation with the topography of the Central Range and erosion rates derived from in situ 10Be concentrations in river‐borne quartz. We conclude that the basin steepness reflects systematic differences in rock uplift rate and erosion rate. Copyright © 2016 John Wiley &amp; Sons, Ltd.

The Exhumation history of the European Alps inferred from linear inversion of thermochronometric data

Thermochronometric data collected across the Alps over the last three decades allows for investigation of the evolution of this orogen, which is subject to changes in climate and geodynamics. Exhumation rates are inferred from the thermochronometric ages using a statistical inversion method based on the fact that the distance a sample traveled since closure is equal to the integral of the exhumation rate from the present day to the age of the sample. Exhumation rates are assumed to be spatially correlated but are free to vary through time. This results in the quantification of exhumation rates across the Alps, since 32 Ma, along with assessments of the quality of these inferences. We find that exhumation rates are initially fast in the internal arc of the Western Alps at rates up to 0.8 km/Myr at 30 Ma, decreasing at 20 Ma to 0.3 km/Myr to remain slow to the present. At the same time, around 20 Ma, rates across the External Crystalline Massifs of Western Alps increase to 0.6 km/Myr. We also find that the onset of high exhumation rates in the Tauern Window and the Lepontine Dome occurs at around 20 Ma, a time characterized by major reorganizations in the Alpine chain. A general increase in exhumation rates at around 5 Ma over the entire Alps is not confirmed. Instead we find that the Western Alps exhibit a 2 to 3 fold increase in exhumation rate over the last 2 Ma, during a recent event not seen further east, in spite of very similar topographic characteristics. We attribute this strong signal to detachment of the European slab in the Western Alps, combined with efficient glacial erosion.