Fission track thermochronology of the Beni Bousera peridotite massif (Internal Rif,Morocco) and the exhumation of ultramafic rocks in the Gibraltar Arc

The Beni Bousera peridotite massif and its metamorphic surrounding rocks have been analyzed by the fission track (FT) method. The aim was to determine the cooling and uplift history of these mantle and associated crustal rocks after the last major metamorphic event that dates back to the Lower Miocene–Upper Oligocene time (～22–24 Ma). The zircon FT analyses give an average cooling—i.e., below 320 °C—age of ～19.5 Ma. In addition, the apatite FT data give an average cooling—i.e., below 110 °C—age of ～15.5 Ma. Taking into account the thermal properties of the different thermochronological systems used in this work, we have estimated a rate of cooling close to 50 °C/Ma. This cooling rate constrains a denudation rate of about ～2 mm year^?1 from 20 to 15 Ma. These results are similar to those determined in the Ronda peridotite massif of the Betic Cordilleras documenting that some ultrabasic massifs of the internal zones of the two segments of the Gibraltar Arc have a similar evolution. However, Burdigalian sediments occur along the Betic segment (Alozaina area, western Betic segment) unconformably overlying peridotite. At this site, ultramafic rock was exposed to weathering at ages ranging from 20.43 to 15.97 Ma. Since the Beni Bousera peridotite was still at depth until 15.5 Ma, we infer that no simple age projection from massif to massif is possible along the Gibraltar Arc. Moreover, the confined fission track lengths data reveal that a light warming (～100 °C) has reheated the massif during the Late Miocene before the Pliocene–Quaternary tectonic uplift.     

Low Temperature History of the Tiegelongnan Porphyry–Epithermal Cu (Au) Deposit in the Duolong Ore District of Northwest Tibet,China

The Tiegelongnan is the first discovered porphyry–epithermal Cu (Au) deposit of the Duolong ore district in Tibet, China. In order to constrain the thermal history of this economically valuable deposit and the rocks that host it, eight samples were collected to perform a low‐temperature thermochronology analysis including apatite fission track, apatite, and zircon (U‐Th)/He. Apatite fission track ages of all samples are between 34 ± 3 and 67 ± 5 Ma. Mean apatite (U‐Th)/He ages show wide distribution, ranging from 29.3 ± 2.5 to 56.4 ± 9.1 Ma. Mean zircon (U‐Th)/He ages range from 79.5 ± 12.0 to 97.9 ± 4.4 Ma. The exhumation rate of the Tiegelongnan deposit was 0.086 km m.y.^?1 between 98 and 47 Ma and decreased to 0.039 km m.y.^?1 since 47 Ma. The mineralized intrusion was emplaced at a depth of about 1400 m in the Tiegelongnan deposit. Six cooling stages were determined through HeFTy software according to low‐temperature thermochronology and geochronology data: (i) fast cooling stage between 120 and 117 Ma, (ii) fast cooling stage between 117 and 100 Ma, (iii) slow cooling stage between100 and 80 Ma, (iv) fast cooling stage between 80 and 45 Ma, (v) slow cooling stage between 45 and 30 Ma, and (vi) slow cooling stage (<30 Ma). Cooling stages between 120 and 100 Ma are mainly caused by magmatic–hydrothermal evolution, whereas cooling stages after 100 Ma are mainly caused by low‐temperature thermal–tectonic evolution. The Bangong–Nujiang Ocean subduction led to the formation of the Tiegelongnan ore deposit, which was buried by the Meiriqiecuo Formation andesite lava and thrust nappe structure; then, the Tiegelongnan deposit experienced uplift and exhumation caused by the India–Asia collision.     

Meso‐Cenozoic Tectonothermal History of Permian Strata,Southwestern Weibei Uplift: Insights from Thermochronology and Geothermometry

This study provides an integrated interpretation for the Mesozoic-Cenozoic tectonothermal evolutionary history of the Permian strata in the Qishan area of the southwestern Weibei Uplift, Ordos Basin. Apatite fission-track and apatite/zircon(U-Th)/He thermochronometry, bitumen reflectance, thermal conductivity of rocks, paleotemperature recovery, and basin modeling were used to restore the Meso-Cenozoic tectonothermal history of the Permian Strata. The Triassic AFT data have a pooled age of ～180±7 Ma with one age peak and P(χ2)=86%. The average value of corrected apatite(U-Th)/He age of two Permian sandstones is ～168±4 Ma and a zircon(U-Th)/He age from the Cambrian strata is ～231±14 Ma. Bitumen reflectance and maximum paleotemperature of two Ordovician mudstones are 1.81%, 1.57% and ～210°C, ～196°C respectively. After undergoing a rapid subsidence and increasing temperature in Triassic influenced by intrusive rocks in some areas, the Permian strata experienced four cooling-uplift stages after the time when the maximum paleotemperature reached in late Jurassic:(1) A cooling stage(～163 Ma to ～140 Ma) with temperatures ranging from ～132°C to ～53°C and a cooling rate of ～3°C/Ma, an erosion thickness of ～1900 m and an uplift rate of ～82 m/Ma;(2) A cooling stage(～140 Ma to ～52 Ma) with temperatures ranging from ～53°C to ～47°C and a cooling rate less than ～0.1°C/Ma, an erosion thickness of ～300 m and an uplift rate of ～3 m/Ma;(3)(～52 Ma to ～8 Ma) with ～47°C to ～43°C and ～0.1°C/Ma, an erosion thickness of ～500 m and an uplift rate of ～11 m/Ma;(3)(～8 Ma to present) with ～43°C to ～20°C and ～3°C/Ma, an erosion thickness of ～650 m and an uplift rate of ～81 m/Ma. The tectonothermal evolutionary history of the Qishan area in Triassic was influenced by the interaction of the Qinling Orogeny and the Weibei Uplift, and the south Qishan area had the earliest uplift-cooling time compared to other parts within the Weibei Uplift. The early Eocene at ～52 Ma and the late Miocene at ～8 Ma, as two significant turning points after which both the rate of uplift and the rate of temperature changed rapidly, were two key time for the uplift-cooling history of the Permian strata in the Qishan area of the southwestern Weibei Uplift, Ordos Basin.     

Fission track data from the Bathurst Batholith: Evidence for rapid mid‐Cretaceous uplift and erosion within the eastern highlands of Australia

Apatite fission track thermochronology reveals that uplift and erosion occurred during the mid‐Cretaceous within the Bathurst Batholith region of the eastern highlands, New South Wales. Apatite fission track ages from samples from the eastern flank of the highlands range between ca 73 and 139 Ma. The mean lengths of confined fission tracks for these samples are > 13 μm with standard deviations of the track length distributions between 1 and 2 μm. These data suggest that rocks exposed along the eastern flank of the highlands were nearly reset as the result of being subjected to palaeotemperatures in the range of approximately 100–110°C, prior to being cooled relatively quickly through to temperatures < 50°C in the mid‐Cretaceous at ca 90 Ma. In contrast, samples from the western flank of the highlands yield apparent apatite ages as old as 235 Ma and mean track lengths < 12.5 μm, with standard deviations between 1.8 and 3 μm. These old apatite ages and relatively short track lengths suggest that the rocks were exposed to maximum palaeotemperatures between approximately 80° and 100°C prior to the regional cooling episode. This cooling is interpreted to be the result of kilometre‐scale uplift and erosion of the eastern highlands in the mid‐Cretaceous, and the similarity in timing of uplift and erosion within the highlands and initial extension along the eastern Australian passive margin prior to breakup (ca 95 Ma) strongly suggests these two occurrences are related.     

Late Cretaceous-Cenozoic Exhumation History of the Lüliang Mountains, North China Craton: Constraint from Fission-track Thermochronology

The Lüliang Mountains, located in the North China Craton, is a relatively stable block, but it has experienced uplift and denudation since the late Mesozoic. We hence aim to explore its time and rate of the exhumation by the fission-track method. The results show that, no matter what type rocks are, the pooled ages of zircon and apatite fission-track range from 60.0 to 93.7 Ma and 28.6 to 43.3 Ma, respectively; all of the apatite fission-track length distributions are unimodal and yield a mean length of ~13?μm; and the thermal history modeling results based on apatite fission-track data indicate that the time-temperature paths exhibit similar patterns and the cooling has been accelerated for each sample since the Pliocene (c.5 Ma). Therefore, we can conclude that a successive cooling, probably involving two slow (during c.75-35 Ma and 35-5 Ma) and one rapid (during c.5 Ma-0 Ma) cooling, has occurred through the exhumation of the Lüliang Mountains since the late Cretaceous. The maximum exhumation is more than 5 km under a steady-state geothermal gradient of 35°C/km. Combined with the tectonic setting, this exhumation may be the resultant effect from the surrounding plate interactions, and it has been accelerated since c.5 Ma predominantly due to the India-Eurasia collision.     

Thermal history of the Hodgkinson Province and Laura Basin,Queensland: Multiple cooling episodes identified from apatite fission track analysis and vitrinite reflectance data

Apatite fission track analysis and vitrinite reflectance data from outcrop and well samples in the Hodgkinson Province and Laura Basin reveal regional Cretaceous cooling. Apatite fission track analysis appears to define two discrete cooling episodes, in the mid‐Cretaceous (110–100 Ma) and Late Cretaceous (80–70 Ma), although in most samples data allow only definition of a single episode. Rocks now at outcrop cooled from Cretaceous palaeotemperatures generally between 50 and 130°C in the south of the region, and from >100°C in the north. Some samples from the Hodgkinson Province also show evidence for an Early Jurassic cooling episode, characterised by maximum palaeotemperatures varying from at least 95°C (from apatite fission track analysis) to ～200–220°C (from vitrinite reflectance), with cooling beginning at around 200 Ma. Apatite fission track analysis data do not reveal the earlier event in the Laura Basin, but on the basis of vitrinite reflectance data from Permian? units this event is also inferred to have affected the pre‐Jurassic basin units in this region. The regional extent of the Cretaceous cooling episode in the Hodgkinson Province suggests that the elevated palaeotemperatures in this region were most likely due to greater depth of burial, with subsequent cooling due to kilometre‐scale denudation. For a palaeogeothermal gradient of 30°C/km and a palaeosurface temperature of 25°C the total degree of Cretaceous cooling experienced by the samples corresponds to removal of between ～0.8 and >3.0 km of Triassic and younger section removed by denudation, beginning some time between ca 110 and 80 Ma. Higher palaeogradients would require correspondingly lower amounts of removed section. The geology of the Laura Basin suggests that an explanation of the observed Cretaceous palaeotemperatures in this region in terms of deeper burial may be untenable. Heating due to hot fluid flow may be a more realistic mechanism for producing the observed Cretaceous palaeothermal effects in the Laura Basin.     

Exhumation rates and age of metamorphism in the Sanbagawa belt: new constraints from zircon fission track analysis

Zircon fission track dating and track length analysis in the high‐grade part of the Asemigawa region of the Sanbagawa belt demonstrates a simple cooling history passing through the partial annealing zone at 63.2 ± 5.8 (2 σ) Ma. Combining this age with previous results of phengite and amphibole K–Ar and ⁴⁰Ar/³⁹Ar dating gives a cooling rate of between 6 and 13 °C Myr^?1, which can be converted to a maximum exhumation rate of 0.7 mm year^?1 using the known shape of the P–T path. This is an order of magnitude lower than the early part of the exhumation history. In contrast, zircon fission track analyses in the low‐grade Oboke region show that this area has undergone a complex thermal history probably related to post‐orogenic secondary reheating younger than c. 30 Ma. This event may correlate with the widespread igneous activity in south‐west Japan around 15 Ma. The age of subduction‐related metamorphism in the Oboke area is probably considerably older than the generally accepted range of 77–70 Ma.     

Thermal History since the Paleozoic in the Eastern Qaidam Basin,Northwest China

The Qaidam Basin is the one of the three major petroliferous basins in northeastern Tibetan Plateau, which has experienced multiphase superimposition and transformation. The study of thermal history not only plays an important role on revealing the tectonic origin of the Qaidam Basin and the forming mechanism and uplift history of the Tibetan Plateau,but also can provide scientific evidence for the assessment of oil and gas resources. This work used balanced cross-section technique and apatite fission track ages with modeling of fission track length distribution to infer that the eastern Qaidam Basin has experienced significant tectonic movement in the Early Jurassic movement(～200 Ma), which caused the carboniferous uplift and denudation, the geological movement in the Late Cretaceous, characterized by early stretching and late northeast-southwest extrusion; the Himalayan movement in multi-stage development in eastern Qaidam Basin, which can be divided into the early Himalayan movement(41.1–33.6 Ma) and the late Himalayan movement(9.6–7.1 Ma, 2.9–1.8 Ma), and large-scale orogeny caused pre-existing faults reactivated in late Himalayan movement. On the basis of burial history reconstruction, the thermal history of eastern Qaidam Basin was restored. The result shows that the thermal history in eastern Qaidam Basin shows slow cooling characteristics; the paleo-geothermal gradient of eastern Qaidam Basin was 38–41.5℃/km, with an average value of 39.0℃/km in the Late Paleozoic, 29–35.2℃/km, with an average value of 33.0℃/km in the Early Paleogene; the geothermal gradient of the Qaidam Basin increased in the Late Paleogene, which was similar to the present geothermal gradient in the Late Neogene. The characteristics of the tectono-thermal evolution since Paleozoic in the eastern Qaidam Basin are mainly controlled by magmatic thermal events in the study area.     

青藏高原西北缘祁漫塔格山中新世快速抬升的磷灰石裂变径迹证据

对祁漫塔格山体不同海拔高度所取的9个磷灰石样品的裂变径迹分析结果表明,东昆仑西段中新世早中期为主要的隆升期且隆升速率较高,早期隆升速率为111m／Ma,晚期隆升速率为98m／Ma,总体隆升速率为100m／Ma。样品显示出磷灰石裂变径迹长度大致分2类,一类磷灰石裂变径迹长度为（12．21±10．20）-（13．75±0．30）μm,径迹长度分布图基本上为窄而对称的正态分布,反映具有快的剥露冷却速率,未受到后期热事件的干扰。另一类磷灰石裂变径迹长度为（11．88±0．33）～（13．32±0．27）μm,较前一类具有稍慢的剥露冷却速率,并且受到了后期热事件的干扰。     

川东南地区燕山期以来的隆升剥蚀历史研究

川东南地区侏罗系砂岩的磷灰石裂变径迹T—t热史模拟表明,燕山期以来研究区经历了两个阶段的隆升剥蚀。127～105Ma为初始缓慢隆升阶段,隆升剥蚀速率约为5m／Ma,使106m厚的早白垩世地层被剥蚀;105～75Ma间转入快速沉降,75～0Ma由快速沉降转入全面不等速隆升。其中,75—65Ma为快速隆升．隆升剥蚀速率为28m／Ma;65～20Ma为缓慢隆升,隆升剥蚀速率为14m／Ma;20～10Ma期间,研究区由缓慢隆升转为急剧隆升,隆井剥蚀速率为147m／Ma;10Ma到现今,该地区再次由快速隆升转为缓慢隆升。隆升剥蚀速率为10m／Ma。燕山期以来的隆升使大约2580m厚的地层被剥蚀掉。     

Mesozoic exhumation history and palaeolandscape of the Iberian Massif in eastern Galicia from apatite fission-track and (U+Th)/He data

Apatite fission-track (AFT) and (U+Th)/He (AHe) data, combined with time–temperature inverse modelling, reveal the cooling and exhumation history of the Iberian Massif in eastern Galicia since the Mesozoic. The continuous cooling at various rates correlates with variation of tectonic boundary conditions in the adjacent continental margins. The data provide constraints on the 10⁷ timescale longevity of a relict paleolandscape. AFT ages range from 68 to 174 Ma with mean track lengths of 10.7 ± 2.6 to 12.6 ± 1.8 μm, and AHe ages range from 73 to 147 Ma. Fastest exhumation (≈0.25 km/Ma) occurred during the Late Jurassic to Early Cretaceous main episode of rifting in the adjacent western and northern margins. Exhumation rates have decreased since then and have been approximately one order of magnitude lower. Across inland Galicia, the AFT data are consistent with Early Cretaceous movement on post-Variscan NE trending faults. This is coeval with an extensional episode offshore. The AHe data in this region indicate less than 1.7 km of denudation in the last 100 Ma. This low exhumation suggests the attainment of a mature landscape during Late Cretaceous post-rift tectonic stability, whose remains are still preserved. The low and steady rate of denudation prevailed across inland Galicia despite minor N–S shortening in the northern margin since ≈45 Ma ago. In north Galicia, rock uplift in response to NW strike-slip faulting since Early Oligocene to Early Miocene has caused insufficient exhumation (<3 km) to remove the Mesozoic cooling signal recorded by the AFT data.     

喜马拉雅造山带晚新生代构造隆升的裂变径迹证据

喜马拉雅造山带的隆升,在地质学研究中是一个非常让人感兴趣的问题,为了对其进行定量研究,揭示隆升历史及幅度等相关问题,运用磷灰石、锆石裂变径迹法对研究区淡色花岗岩进行了分析,所取样品的裂变径迹年龄位于17.0~5.7 Ma之间,小于其地层时代或侵入年龄(40~17 Ma),表明研究区喜马拉雅造山带的强烈隆升开始于晚新生代.用磷灰石裂变径迹年龄来计算可知,研究区内花岗岩5.7 Ma以来的冷却速率和剥蚀速率分别为18.421 ℃/Ma和0.526 mm/a.5.7~9.2 Ma间的相对抬升与剥蚀速率为0.229 mm/a,9.2~17.0 Ma间的相对抬升与剥蚀速率为0.032 mm/a.用锆石裂变径迹年龄来计算知,研究区内花岗岩16.2 Ma以来的冷却速率和剥蚀速率分别为12.963 ℃/Ma和0.370 mm/a,冷却速率和剥蚀速率均小于用磷灰石计算的结果.因此说喜马拉雅造山带从9.2 Ma到现在隆升和剥蚀的速率是处于加快的状态.      

Neotectonics and recent uplift at Kamchatka and Aleutian arc junction, Kamchatka Cape area, NE Russia

The tectonic position of the Kamchatka Cape Peninsula at the junction of the active Kuril–Kamchatka and Aleutian arcs exposes the coastline of the peninsula to strong neotectonic activities. Fracture zones have variable influence on uplift of the Kamchatka Cape Peninsula. Relevant morphologic indicators of neotectonic activity are multilevel, highly uplifted marine terraces and terraces displaced along active faults. Recent uplift rates of coastal sediments are determined by remote sensing via ASTER and SRTM DEM combined with optically stimulated luminescence dating (OSL). On the Kamchatka Cape Peninsula, terraces from the same generation are mapped at different elevations by remote sensing methods. After defining different areas of uplifted terraces, four neotectonic blocks are identified. According to apatite fission track data, the mean differential exhumation rates range from 0.2 to 1.2 mm year^?1 across the blocks since Late Miocene. The OSL data presented point to significant higher uplift rates of up to 3 ± 0.5 and 4.3 ± 1 mm year^?1, which indicates an acceleration of the vertical movement along the coast of Kamchatka Cape Peninsula in Upper Pleistocene and Holocene times.     

Denudation history and landscape evolution of the northern East-Brazilian continental margin from apatite fission-track thermochronology

We reconstruct the history of denudation and landscape evolution of the northern East- Brazilian continental margin using apatite fission-track thermochronology and thermal history modeling. This part of the Brazilian Atlantic margin is morphologically characterized by inland and coastal plateaus surrounding a wide low-lying inland region, the Sertaneja Depression. The apatite fission track ages and mean track lengths vary from 39 ± 4 to 350 ± 57 Ma and from 10.0 ± 0.3 to 14.2 ± 0.2 μm, respectively, implying a protracted history of spatially variable denudation since the Permian at relatively low rates (<50 m My⁻¹). The Sertaneja Depression and inland plateaus record Permian-Early Jurassic (300–180 Ma) denudation that precedes rifting of the margin by > 60 Myrs. In contrast, the coastal regions record up to 2.5 km of Late Jurassic-Early Cretaceous (150–120 Ma) denudation, coeval with rifting of the margin. The samples from elevated coastal regions, the Borborema Plateau and the Mantiqueira Range, record cooling from temperatures above 120 °C since the Late Cretaceous extending to the Cenozoic. We interpret this denudation as related to post-rift uplift of these parts of the margin, possibly resulting from compressional stresses transmitted from the Andes and/or magmatism at that time. Several samples from these areas also record accelerated Neogene (<30 Ma) cooling, which may record landscape response to a change from a tropical to a more erosive semi-arid climate during this time. The inferred denudation history is consistent with the offshore sedimentary record, but not with evolutionary scenarios inferred from the recognition of “planation surfaces” on the margin. The denudation history of the northeastern Brazilian margin implies a control of pre-, syn- and post-rift tectonic and climatic events on landscape evolution.     

新疆阿尔泰造山带构造活动的磷灰石裂变径迹证据

从对新疆阿尔泰造山带西部构造活动的研究中获得一批较为系统的磷灰石裂变径迹分析结果。 32个磷灰石裂变径迹年龄为 (16 3.0± 6 .4 )～ (4 6 .9± 7.2 )Ma ,平均径迹长度为 (14 .5± 0 .1)～(11.3± 0 .4 ) μm ,长度标准差为 1.4～ 2 .7μm。区内具有 3阶段热历史 :约 110Ma之前处于约 10 0～12 0℃较高温稳定阶段 ,然后在约 110～ 4 0Ma期间发生快速冷却与隆升事件 ,从约 4 0Ma开始发生另一较为缓慢的冷却事件。总体上自北而南 ,剥蚀速率和冷却速率均逐渐变小。文中裂变径迹资料表明 ,阿尔泰山西段主要断裂带现在向南倾斜 ,区内构造演化亦主要受Tesbahan、Kulti和Basei三条断裂带逆冲热事件的控制。     

Denudation history of the Southeastern Highlands of Australia

The low-relief summit plateaus (high plains) of the Southeastern Highlands are remnants of a widespread peneplain that was initially uplifted in the mid-Cretaceous and reached its current elevation in the Miocene–Pliocene. There are two mutually exclusive scenarios for the origin of the high plains: an uplifted peneplain originally formed by long-term denudation through the Mesozoic and late Paleozoic, contrasting with creation by ～1.5 km of erosion following the mid-Cretaceous uplift (based on fission track data). The hypothesis of a Mesozoic peneplain is consistent with the low relief of the high plains, the ca 200 Ma available to form the peneplain, and the pre-late Mesozoic oxygen-isotope composition of secondary kaolinites in weathering profiles on the high plains. If the ca 30 Ma cooling event recorded by the fission track data is due to ～1.5 km of denudation, then the high plains peneplain formed in the Late Cretaceous–early Paleogene, close to sea-level, and was uplifted in the early Paleogene, because evidence from basalts and fossil floras shows that the high plains surface was moderately elevated in the Eocene. This scenario is difficult to reconcile with the long-term erosion necessary to form such an extensive peneplain, the lack of sedimentary evidence for early Paleogene uplift, and the relatively small reduction in elevation (～250 m) that would have resulted from ～1.5 km of erosion (because the crust in this area is in isostatic equilibrium). Furthermore, extensive Cretaceous–early Paleogene denudation should have removed the pre-late Mesozoic secondary kaolinites present in weathering profiles in the highlands. There is no evidence that the Mesozoic peneplain was buried by kilometres of sediment and then exhumed in the Cretaceous–early Paleogene. I therefore conclude that the high plains of the Southeastern Highlands are the remnants of a Mesozoic peneplain uplifted in the mid-Cretaceous and again in the Miocene–Pliocene.     

Late Mesozoic‐Cenozoic exhumation history of the Lesser Hinggan Mountains,NE China,revealed by fission track thermochronology

This study uses zircon and apatite fission‐track (FT) analyses to reveal the exhumation history of the granitoid samples collected from the Lesser Hinggan Mountains, northeast China. A southeast to northwest transect across the Lesser Hinggan Mountains yielded zircon FT ages between 89.8 ± 5.7 and 100.4 ± 8.6 Ma, and apatite FT ages between 50.6 ± 13.8 and 74.3 ± 4.5 Ma with mean track lengths between 11.7 ± 2.0 and 12.8 ± 1.7 µm. FT results and modelling identify three stages in sample cooling history spanning the late Mesozoic and Cenozoic eras. Stage one records rapid cooling from the closure temperature of zircon FT to the high temperature part of the apatite FT partial annealing zone (∼210–110 °C) during ca. 95 to 65 Ma. Stage two records a period of relative slow cooling (∼110–60 °C) taking place between ca. 65 and 20 Ma, suggesting that the granitoids had been exhumed to the depth of ∼1−2 km. Final stage cooling (60–20 °C) occurred since the Miocene at an accelerated rate bringing the sampled rocks to the Earth's surface. The maximum exhumation is more than 5 km under a steady‐state geothermal gradient of 35 °C/km. Integrated with the tectonic setting, this exhumation is possibly led by the Pacific Plate subduction combined with intracontinental orogeny associated with asthenospheric upwelling. Copyright © 2010 John Wiley & Sons, Ltd.     

Cenozoic Magmatism and Tectonic Framework of Western Yunnan, China: Constrained from Geochemistry, Sr–Nd–Pb Isotopes and Fission Track Dating

Western Yunnan is composed of several extruded continental microblocks that were generated by the oblique collision between the Indian and Asian continents during the Cenozoic. In this study, the magmatic and tectonic frameworks of western Yunnan in the Cenozoic were analyzed based on geochemistry, Sr–Nd–Pb isotopes, and apatite/zircon fission track dating. Magmatism during the Cenozoic in western Yunnan was then divided into three distinctive episodes: alkali granite rocks produced from 55 to 46 Ma were derived from the anatexis of crustal materials; bimodal igneous rocks formed between 37 and 24 Ma were possibly derived from an EMII mantle with a contribution from continental materials; and intermediate–basic volcanic rocks produced in the Tengchong microblocks since ~16 Ma are considered to be generated by the partial melting of the upper mantle that was induced by the pulling apart of the dextral Gaoligong strike–slip fault system. Moreover, fission track analysis of apatite and zircon indicates that the regional crustal uplift in western Yunnan possibly began at ~34 Ma, with accelerated annealing occurring at ~24 Ma, ~13 Ma, and ~4 Ma. During the past 24 Ma, the average denudation rate was ~0.32 mm/yr for the faulted block controlled by the Chongshan–Lancang River fault. However, crustal uplift has been relatively gentle in places lacking influence from strike–slip shear zones, with an average denudation rate of ~0.2 mm/yr. Combined with strike–slip shear and block rotation in the Cenozoic, the tectonic evolution of western Yunnan since ~45 Ma can thus be divided into four stages occurring at 45–37 Ma, 37–24 Ma, 24–13 Ma, and 13–0 Ma.     

Cretaceous and Cenozoic cooling history of the eastern Qilian Shan,north‐eastern margin of the Tibetan Plateau: evidence from apatite fission‐track analysis

The exhumation history and tectonic evolution of the Qilian Shan at the north‐eastern margin of the Tibetan Plateau has been widely debated. Here, we present apatite fission‐track (AFT) data for 12 Ordovician granodiorite samples along a vertical transect in the eastern Qilian Shan. These thermochronometry data indicate that the eastern Qilian Shan experienced a three‐stage cooling history, including: (i) rapid initial cooling in the late Cretaceous; (ii) a stage of quasi isothermal quiescence from ~ 80 to 24 Ma; and (iii) rapid subsequent cooling beginning in the early Miocene. The inferred cooling rates for the three stages are 6.8 ± 4.9 °C Ma^?1, 0.6 ± 0.2 °C Ma^?1 and 2.7 ± 0.9 °C Ma^?1 respectively (±1 σ). Assuming a geothermal gradient of 25 °C km^?1, the exhumation rates for the three stages are 0.27 ± 0.20 mm a^?1, 0.017 ± 0.007 mm a^?1 and 0.11 ± 0.04 mm a^?1 respectively (±1 σ). We suggest that the late Cretaceous cooling records collision of the Lhasa block with the Eurasian continent and that the Miocene cooling represents uplift/exhumation of the Qilian Shan.     

Low‐temperature thermochronology of the Mt Painter Province,South Australia

Apatite fission track results are reported for 26 outcrop samples from the Mt Painter Inlier, Mt Babbage Inlier and adjacent Neoproterozoic rocks of the northwestern Curnamona Craton of South Australia. Forward modelling of the data indicates that the province experienced variable regional cooling from temperatures >110°C during the Late Palaeozoic (Late Carboniferous to Early Permian). The timing of this cooling is similar to that previously reported from elsewhere in the Adelaide Fold Belt and the Curnamona Craton, suggesting that the entire region underwent extensive Late Palaeozoic cooling most likely related to the waning stages of the Alice Springs or Kanimblan Orogenies. Results from the Paralana Fault Zone indicate that the eastern margin of the Mt Painter Inlier experienced a second episode of cooling (～40–60°C) during the Paleocene to Eocene. The entire region also experienced significant cooling (less than ～40°C) during the Late Cretaceous to Palaeogene in response to unroofing and/or a decrease in geothermal gradient. Regional cooling/erosion during this time is supported by: geomorphological and geophysical evidence indicating Tertiary exhumation of at least 1 km; Eocene sedimentation initiated in basins adjacent to the Flinders and Mt Lofty Ranges sections of the Adelaide Fold Belt; and Late Cretaceous ‐ Early Tertiary cooling previously reported from apatite fission track studies in the Willyama Inliers and the southern Adelaide Fold Belt. Late Cretaceous to Palaeogene cooling is probably related to a change in stress field propagated throughout the Australian Plate, and driven by the initiation of sea‐floor spreading in the Tasman Sea in the Late Cretaceous and the Eocene global plate reorganisation.