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1.
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.  相似文献   

2.
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.  相似文献   

3.
New apatite and zircon (U–Th)/He and apatite fission‐track (FT) data allow constraining the timing of Miocene–Pliocene extensional exhumation that affected the central part of the Dinarides‐Albanides‐Hellenides orogen. Apatite (U–Th)/He ages in the northern and western Internal Albanides range from 57 to 17 Ma, contrasting to younger ages of 5.2–9.3 Ma in the eastern Internal Albanides. Eastward younging is also reflected in zircon (U–Th)/He ages varying from 101 Ma in the north‐western Internal Albanides to 19–50 Ma in the east, as well as in recently published apatite FT ages. Thermal history predictions with the new data point to a phase of rapid exhumation of the eastern Internal Albanides around 6–4 Ma, while the western Internal Albanides record slower continuous exhumation since the Eocene. This asymmetric exhumation pattern is most likely linked to extensional reactivation of NE–SW‐trending thrusts east of the Mirdita zone and within the Korabi zone of the eastern Internal Albanides.  相似文献   

4.
Gangdese batholith in the southern Lhasa block is a key location for exploring the Tibetan Plateau uplift and exhumation history. We present the new low-temperature thermochronological data from two north–south traverses in the central Gangdese batholith to reveal their cooling histories and corresponding controls. Zircon fission track ages show prominent clusters ranging from 23.7 to 51.6 Ma, apatite fission track ages from 9.4 to 36.9 Ma, apatite (U–Th)/He ages between 9.5 and 12.3 Ma, and one zircon (U–Th)/He age around 77.8 Ma. These new data and thermal modeling, in combination with the regional geological data, suggest that the distinct parts of Gangdese batholith underwent different cooling histories resulted from various dynamic mechanisms. The Late Eocene–Early Oligocene exhumation of northern Gangdese batholith, coeval with the magmatic gap, might be triggered by crust thickening followed by the breakoff of Neotethyan slab, while this stage of exhumation in southern Gangdese batholith cannot be clearly elucidated probably because the most of plutonic rocks with the information of this cooling event were eroded away. Since then, the northern Gangdese batholith experienced a slow and stable exhumation, while the southern Gangdese batholith underwent two more stages of exhumation. The Late Oligocene–Early Miocene rapid cooling might be a response to denudation caused by the Gangdese Thrust or related to the regional uplift and exhumation in extensional background. By the early Miocene, the rapid exhumation was associated with localized river incision or intensification of Asian monsoon, or north–south normal fault.  相似文献   

5.
A combination of four thermochronometers [zircon fission track (ZFT), zircon (U–Th)/He (ZHe), apatite fission track (AFT) and apatite (U–Th–[Sm])/He (AHe) dating methods] applied to a valley to ridge transect is used to resolve the issues of metamorphic, exhumation and topographic evolution of the Nízke Tatry Mts. in the Western Carpathians. The ZFT ages of 132.1 ± 8.3, 155.1 ± 12.9, 146.8 ± 8.6 and 144.9 ± 11.0 Ma show that Variscan crystalline basement of the Nízke Tatry Mts. was heated to temperatures >210°C during the Mesozoic and experienced a low-grade Alpine metamorphic overprint. ZHe and AFT ages, clustering at ~55–40 and ~45–40 Ma, respectively, revealed a rapid Eocene cooling event, documenting erosional and/or tectonic exhumation related to the collapse of the Carpathian orogenic wedge. This is the first evidence that exhumation of crystalline cores in the Western Carpathians took place in the Eocene and not in the Cretaceous as traditionally believed. Bimodal AFT length distributions, Early Miocene AHe ages and thermal modelling results suggest that the samples were heated to temperatures of ~55–90°C during Oligocene–Miocene times. This thermal event may be related either to the Oligocene/Miocene sedimentary burial, or Miocene magmatic activity and increased heat flow. This finding supports the concept of thermal instability of the Carpathian crystalline bodies during the post-Eocene period.  相似文献   

6.
Thermal history modelling based on zircon‐ and apatite fission track and apatite (U–Th)/He data constrain and refine the near‐surface exhumation of the south‐eastern Tauern Window (Penninic units) and neighbouring Austroalpine basement units in the Eastern Alps. Fast exhumation on both sides of the Penninic/Austroalpine boundary coincides with a period of lateral extrusion and tectonic denudation of the Penninic units in Miocene time (22–12 Ma). The jump to older ages occurs within the Austroalpine unit along the Polinik fault, which therefore defines the boundary between the tectonically denuded units and the hangingwall at that time. According to the different (U–Th)/He ages between the Penninic Hochalm‐ and Sonnblick Domes we demonstrate a differential cooling history of these two domes in the latest Miocene and early Pliocene.  相似文献   

7.
札达盆地是中新世9.5 Ma以来发育的新生代沉积盆地.沉积厚度、砾石成分和古流向分析显示札达盆地新生代沉积的物源主要来自盆地北部的阿伊拉日居山系.札达盆地系列样品碎屑锆石裂变径迹年龄结构显示存在两个明显的峰值年龄区间, 分别为12.6~15.3 Ma(P1峰值年龄)与19.8~22.2 Ma(P2峰值年龄).锆石裂变径迹年龄的滞后时间(lag time)与沉积时代对比分析显示, P1和P2峰值年龄为快速冷却事件的静态峰, 与北部阿伊拉日居地区基岩U-Pb年代研究揭示的热事件时间具有良好的可对比性.因此, 札达盆地碎屑裂变径迹年龄两个峰值年龄区间记录了源区阿伊拉日居的两次构造事件, 可能对应于喀喇昆仑断裂在中新世的两次强烈的构造活动.综合碎屑锆石、磷灰石裂变径迹年龄信息, 估算源区在32.6~9.5 Ma之间的平均冷却速率是15.4 ℃/Ma, 上新世末期—第四纪(3.6~1.4 Ma)之间再次发生了一次快速的隆升剥露事件.札达盆地中新生代沉积地层碎屑裂变径迹热年代学结构与喀喇昆仑断裂东南段阿伊拉日居的热事件年龄格局吻合, 从碎屑裂变径迹年代学角度揭示了造山带地区的盆山耦合过程.   相似文献   

8.
Zircon and apatite fission track ages were determined on granulites dredged along the Bay of Biscay margins. A sample from Ortegal Spur (Iberia margin) yielded 725 ± 67 Ma (zircon). A sample from Le Danois Bank (Iberia margin) yielded 284 ± 58 Ma (zircon), indicating post‐Variscan cooling. Apatite from this sample gave 52 ± 2 Ma, interpreted as final cooling after ‘Pyrenean’ thrust imbrication. Two other samples from Le Danois Bank have Early Cretaceous apatite ages (138 ± 7 and 120 ± 8 Ma), interpreted to result from exhumation during rifting. Finally, a granulite from Goban Spur (Armorican margin) gave 212 ± 10 Ma (apatite), coinciding with a precursory rifting phase. Together with published radiometric results, these data indicate a Precambrian high‐grade terrane at the site of the current margins. The distribution of the granulites on the seafloor reflects tectonic and erosional processes related to (a) Mesozoic rifting and (b) Early Tertiary incipient subduction of the Bay of Biscay beneath Iberia.  相似文献   

9.
The Zedong ophiolite is the largest ophiolite massif east of Dazhuqu in the Yarlung Zangbo Suture Zone in the southern Tibetan Plateau. However, its age, geodynamic setting and relationship to the Xigaze ophiolite remain controversial. New zircon U–Pb ages, whole-rock geochemical and Nd–Pb isotopic data from ophiolitic units provide constraints on the geodynamic and tectonic evolution of the Zedong ophiolite. U–Pb zircon geochronology of dolerite lavas and late gabbro–diabase dikes yield weighted mean ages of 153.9 ± 2.5 Ma and 149.2 ± 5.1 Ma, respectively. Strong positive εNd(t) and positive Δ7/4Pb and Δ8/4Pb values indicate derivation from a highly depleted mantle source with an isotopic composition similar to that of the Indian MORB-type mantle. The geochemistry of ophiolitic lavas and early dikes are analogous to typical island arc tholeiites whereas late dikes are similar to boninites. The geochemistry of these rock types suggests multi-stage partial melting of the mantle and gradually enhanced subduction influences to the mantle source through time. Combined with the MORB-like 162.9 ± 2.8 Ma Luobusha ophiolitic lavas, we suggest that the Luobusha lavas, Zedong lavas and early dikes originated in an infant proto-arc setting whereas late dikes in the Zedong ophiolite originated in a forearc setting. Together, they represent a Neo-Tethyan subduction initiation sequence. The Late Jurassic intra-oceanic proto-arc to forearc setting of the Zedong ophiolite contrasts with the continental margin forearc setting for the Xigaze ophiolite, which suggests a laterally complex geodynamic setting for ophiolites along the Yarlung Zangbo Suture Zone.  相似文献   

10.
LOW TEMPERATURE DATING OF HIGH MOUNTAIN ROCKS:(U-Th)/He AGES FROM HIGHER HIMALAYAN SAMPLES, EASTERN NEPAL1　HouseMA ,WernickeBP ,FarleyKA .DatingtopographyoftheSierraNevada ,California ,usingapatite (U Th) /Heages[J].Nature,1998,396 (5 ) :6 6～ 6 9. 2　HubbardMS ,Harrison .4 0 Ar/ 3 9ArageconstraintsondeformationandmetamorphismintheMainCentralThrustzoneandTibetanSlab ,EasternNepalHimalaya[J].Tectonics,1989,8(4) :86 5～ 880 . 3　HubbardMS …  相似文献   

11.
The ability to deduce exhumation mechanisms from thermochronological data is hampered by the fact that assumptions on the thermal state of the lithosphere have to be made. Additional argumentation is generally required to discriminate between erosion-controlled and tectonically induced exhumation. This problem can be overcome by studying the spatial distribution of zircon and apatite (U-Th)/He and fission track data. In this work the variation of four different low temperature isotopic systems generating age trends along a sampling line is used to infer mechanisms of Quaternary exhumation in the Central High Himalayan Metamorphic Belt. Observed zircon age trends with southwards increasing cooling ages (from 0.5 to 1.7 Ma) are attributed to tectonically induced exhumation. The uniform apatite cooling ages clustered c. 0.5 Ma are attributed to erosion.  相似文献   

12.
The Dexing porphyry copper and Yinshan polymetallic deposits in Dexing City, southeastern China are both giant porphyry ore systems. Located 15 km apart, they formed synchronously and share a similar magma source and metallogenic evolution, but their metal endowment, dominant rock types, and alteration assemblages differ significantly. In this contribution, we investigate the cause of these distinctions through new molybdenite Re–Os ages and zircon and apatite (U–Th)/He thermochronology data. Dexing has a molybdenite Re–Os age of ~170.3 Ma, zircon (U–Th)/He (ZHe) ages of 110 to 120 Ma and apatite (U–Th)/He (AHe) ages of 7 to 9 Ma. In contrast, Yinshan has older ZHe ages of 128 to 140 Ma and an AHe age of ~30 Ma. Viewed in combination with previously published data, we conclude that the apparently slow cooling experienced by these bodies is primarily a reflection of their experiencing multiple episodes of thermal disturbance. We tentatively infer that both deposits were exposed in the Late Miocene or more recent time, with the Dexing deposit more deeply exhumed than Yinshan. Our study has exploration implications for deeper porphyry-style ores at Yinshan and for porphyry deposits in non-arc (intraplate) settings in general.  相似文献   

13.
Independent geochronological and thermal modelling approaches are applied to a biostratigraphically exceptionally well‐controlled borehole, Alcsútdoboz‐3 (Ad‐3), in order to constrain the age of Cenozoic geodynamic events in the western Pannonian Basin and to test the efficacy of the methods for dating volcanic rocks. Apatite fission track and zircon U–Pb data show two volcanic phases of Middle Eocene (43.4–39.0 Ma) and Early Oligocene (32.72 ± 0.15 Ma) age respectively. Apatite (U–Th)/He ages (23.8–14.8 Ma) and independent thermal and subsidence history models reveal a brief period of heating to 55–70 °C at ~17 Ma caused by an increased heat‐flow related to crustal thinning and mantle upwelling. Our results demonstrate that, contrary to common perception, the apatite (U–Th)/He method is likely to record ‘apparent’ or ‘mixed’ ages resulting from subsequent thermal events rather than ‘cooling’ or ‘eruption’ ages directly related to distinct geological events. It follows that a direct conversion of ‘apparent’ or ‘mixed’ (U‐Th)/He ages into cooling, exhumation or erosion rates is incorrect.  相似文献   

14.
Suture zones often archive complex geologic histories underscored by episodes of varying style of deformation associated with intercontinental collision. In the Lopukangri area of south-central Tibet (29°54′N, 84°24′E) field relationships between tectonic units juxtaposed by the India–Asia suture are well exposed, including Indian passive margin rocks (Tethyan Sedimentary Sequence), forearc deposits (Xigaze Group), magmatic arc rocks (Gangdese batholith and Linzizong Formation) and syncollision deposits (Eocene–Miocene conglomerates). To better understand the structural history of this area, we integrated geologic mapping with biotite 40Ar/39Ar thermochronology and zircon U–Pb geochronology. The first-order structure is a system of north-directed thrusts which are part of the Great Counter thrust (GCT) that places Indian passive margin rocks and forearc deposits on top of magmatic arc rocks and syn-tectonic conglomerates. We infer the south-directed Late Oligocene Gangdese Thrust (GT) exists at unexposed structural levels based on field mapping, cross sections, and regional correlations as it has been documented immediately to the east. A granite in the footwall has a U–Pb zircon age of 38.4 ± 0.4 Ma, interpreted to be the age of emplacement of the granite, and a younger 40Ar/39Ar biotite age of 19.7 ± 0.1 Ma. As the granite sample is situated immediately below a nonconformity with low grade greenschist facies rocks, we interpret the younger age to reflect Miocene resetting of the biotite Ar system. Syn-tectonic deposits in the Lopukangri area consist of three conglomerate units with a total thickness of ∼1.5 km. The lower two units consist of cobble gravel pebble conglomerates rich in volcanic and plutonic clasts, transitioning to conglomerates with only sedimentary clasts in the upper unit. We correlate the syncollision deposits to the Eocene–Oligocene Qiuwu Formation based on field relationships, stratigraphy and petrology. Petrology and clast composition suggest the lower two units of the Qiuwu Formation had a northern provenance (Lhasa block and magmatic arc) and the upper unit had a southern provenance (Tethyan Sedimentary Sequence). Our observations are consistent with paleocurrent data from other studies which suggest a predominant south-directed paleoflow for this formation. We propose a model in which: (1) granites intrude at 38.4 ± 0.4 Ma; (2) are exhumed by erosion; (3) and buried due to regional subsidence and initial deposition of a conglomerate unit; (4) exposed by the GT at ∼27–24 Ma to provide detritus; (5) buried a second time by hanging wall-derived sedimentary deposits and the GCT, then (6) exposed from a depth of ∼12–10 km by a blind thrust at ∼19 Ma. An alternate model describes: (1) intrusion of the granites at 38.4 ± 0.4 Ma, followed by (2) exhumation of the granites via normal faulting to provide detritus; (3) then burial by the GCT at ∼24 Ma, followed by (4) exhumation via regional erosional denudation at ∼19 Ma. Exposure of the GT west of Xigaze has not been confirmed. We suggest that shallower structural levels of the India-Asia suture zone are exposed to the west of the study area, compared to the east, where the GT has been previously documented. The GCT in the area is short-lived, as it is cut and offset by a Middle Miocene ∼N-striking W-dipping oblique normal fault system.  相似文献   

15.
On the eastern extremity of the Jiaodong peninsula, China, shoshonitic magmas have been injected into the supracrustal rocks of the Sulu ultra-high pressure (UHP) terrane during the crustal exhumation phase. These granitoids (collectively termed the Shidao igneous complex or Jiazishan alkaline complex) show geochemical and isotopic signatures of an enriched subcontinental lithospheric mantle and intruded soon after the subducted Yangtze crust had reached peak metamorphic pressure conditions (240–220 Ma). We have applied various geochronometers to an alkali-gabbro sample from the Jiazishan pluton and the results allow reconstruction of the Triassic-to-present thermal history. Initial rapid cooling of the gabbro at crustal depths is indicated by the close agreement between the Sm-Nd mineral isochron age (228?±?36 Ma) and the Rb-Sr biotite age (207?±?1) Ma. This interpretation is confirmed by previously published U-Pb zircon ages (225–209 Ma), and 40Ar/39Ar amphibole and K-feldspar ages (～214 Ma) from the Jiazishan syenites. A titanite fission-track age of 166?±?8 Ma (closure temperature range 285–240°C) records widespread Jurassic magmatism in the Jiaodong peninsula, indicating that the gabbro reached upper crustal levels before it was reheated by nearby Jurassic plutons. A subsequent cooling and reheating event is indicated by an apatite fission-track age of 106?±?6 Ma which coincides with the emplacement of the adjacent Weideshan pluton (108?±?2 Ma) and postdates a period of regional lithospheric thinning beneath eastern China. A period of slow cooling (or thermal stability) from late Cretaceous to early Tertiary, documented by an apatite (U-Th)/He age of 39?±?5 Ma, was followed by a final stage of more enhanced cooling since the late Eocene. Results of this work imply that the eastern Sulu terrane has experienced a complex cooling and reheating history. Our data are consistent with a model of initial rapid cooling (sudden exhumation) of the UHP terrane, driven by the release of buoyancy forces, followed by two progressively slower cooling intervals (both after renewed crustal reheating) during the Jurassic and Cretaceous.  相似文献   

16.
We present a database of geochronological data documenting the post-collisional cooling history of the Eastern Alps. This data is presented as (a) georeferenced isochrone maps based on Rb/Sr, K/Ar (biotite) and fission track (apatite, zircon) dating portraying cooling from upper greenschist/amphibolite facies metamorphism (500–600 °C) to 110 °C, and (b) as temperature maps documenting key times (25, 20, 15, 10 Ma) in the cooling history of the Eastern Alps. These cooling maps facilitate detecting of cooling patterns and cooling rates which give insight into the underlying processes governing rock exhumation and cooling on a regional scale.The compilation of available cooling-age data shows that the bulk of the Austroalpine units already cooled below 230 °C before the Paleocene. The onset of cooling of the Tauern Window (TW) was in the Oligocene-Early Miocene and was confined to the Penninic units, while in the Middle- to Late Miocene the surrounding Austroalpine units cooled together with the TW towards near surface conditions.High cooling rates (50 °C/Ma) within the TW are recorded for the temperature interval of 375–230 °C and occurred from Early Miocene in the east to Middle Miocene in the west. Fast cooling post-dates rapid, isothermal exhumation of the TW but was coeval with the climax of lateral extrusion tectonics. The cooling maps also portray the diachronous character of cooling within the TW (earlier in the east by ca. 5 Ma), which is recognized within all isotope systems considered in this study.Cooling in the western TW was controlled by activity along the Brenner normal fault as shown by gradually decreasing ages towards the Brenner Line. Cooling ages also decrease towards the E–W striking structural axis of the TW, indicating a thermal dome geometry. Both cooling trends and the timing of the highest cooling rates reveal a strong interplay between E–W extension and N–S orientated shortening during exhumation of the TW.  相似文献   

17.
The Cretaceous to Palaeogene Alpine exhumation of previously buried Variscan basements is recorded in the southern portion of the Western Carpathians in the Gemeric and Veporic units. The Meso-Cenozoic collisional processes resulted in basement exhumation of the Tatric Unit from Palaeogene to Neogene times. According to zircon and apatite fission track data, the Gemeric Unit, an uppermost thick-skinned thrust sheet, cooled from depth levels of ∼10 up to 2.5 km (temperature interval of ∼250–60 °C) about 88–64 Ma ago, after the collapse of overlying Meliata-Turňa-Silica Mesozoic accretionary prism. The middle and lower thick-skinned thrust sheets, Veporic and Tatric units, cooled from the depths of ∼10 up to 2.5 km ∼110–40 Ma ago. The process was controlled by unroofing of footwall from beneath the Gemeric Unit. About 50–20 Ma ago, the internal zone of Tatric Unit gradually exhumed to depth of <2 km and some parts of the unit appeared at the surface level. However, the external zone of Tatric Unit was buried beneath the Eocene to Lower Miocene sedimentary successions and exhumed to the subsurface level at ∼21–8 Ma ago, as a result of oblique collision of the Western Carpathians with the European Platform.  相似文献   

18.
The Shi-Hang Belt is a Mesozoic tectonic zone and has always been regarded as the boundary between the Yangtze and Cathaysia blocks. It occupies a key tectonic location and attracts considerable attention due to its dynamic formation mechanism. However, its Cenozoic dynamic process is poorly constrained. The Cenozoic activation of the Shi-Hang Belt, as well as its cooling and exhumation, aids in dating the onset time of the formation of the mountain ranges and reveals the deformation process of the South China Block. To uncover the history of its Cenozoic cooling and denudation, apatite fission-track (AFT) thermochronology was applied to batholiths and strata spread across the Shi-Hang Belt in the Hunan Province. Twenty-three samples are dated with ages ranging from 23.6 ± 1.5 to 45.8 ± 3.0 Ma. Except for two older ages (42.1 ± 2.6 and 45.8 ± 3.0 Ma), the other ages range from 23 to 36 Ma with less variation on both sides of the Chenzhou–Linwu fault. The thermochronological modelling of 15 measured samples demonstrates that rocks rapidly passed through the AFT partial annealing zone to the near surface at different onset times from 36 to 23 Ma. The regional AFT cooling pattern is unrelated to the internal structures of the Shi-Hang Belt characterized by a Mesozoic fold-thrust feature. We attribute the Cenozoic exhumation of the Shi-Hang Belt to the dynamic topography of the South China Block, which is related to mantle downwellings and upwellings due to several episodes of quick subduction of the Pacific Plate underneath Eurasia during the Late Cretaceous–early Cenozoic and the Oligocene–early Miocene. The far-field effect of the India–Tibet collision may have contributed to the exhumation of the Shi-Hang Belt.  相似文献   

19.
The accuracy and validation of geo- and thermochronological dating hinges on the availability of well-characterised age reference materials. The Mesoproterozoic gabbroic anorthosite FC1 from the Duluth Complex, Minnesota is a reference material for zircon U-Pb and a suggested reference material for apatite fission-track dating. We evaluate FC1 as (U-Th)/He reference material, and determine its apatite U-Pb, and zircon and apatite (U-Th)/He age. Our dating results constrain the thermal history of FC1, showing that fast cooling occurred between ~ 1099 and 1040 Ma from ≥ 600 °C to ~ 200 °C. The zircon (U-Th)/He data from air-abraded grains give a robust isochron age of 1037 ± 25 Ma (2s) without overdispersion. The within-grain homogeneity of U and Th, the availability of FC1 zircon, and the absence of radiation-damage effects on the (U-Th)/He age support its use as reference material. Unabraded zircon grains give lower and more dispersed ages, highlighting the usefulness of air abrasion to control for α-ejection in (U-Th)/He dating. Our apatite (U-Th-Sm)/He single-grain ages vary between 180 and 300 Ma. Their wide dispersion argues against the use of FC1 apatite as (U-Th-Sm)/He reference material and makes the interpretation of their low-temperature thermal history complicated.  相似文献   

20.
The extent to which ore bodies are preserved in orogenic belts remains a poorly understood area of ore deposit research. Using zircon and apatite fission track analysis together with apatite (U-Th)/He dating we constrained the erosion history of the ore bodies in the Harizha–Halongxiuma mining area of the East Kunlun Range, Northern Tibetan Plateau, China. Apatite fission-track ages range from 114 ± 8 to 87 ± 6 Ma, with mean track lengths varying from 11.4 ± 1.9 to 12.9 ± 2.0 μm. Zircon fission-track ages vary from 205 ± 14 to 142 ± 7 Ma. In addition, apatite (U–Th)/He dating yielded ages of 60–56 Ma. The thermal history of Jiapigou was modelled based on the apatite fission-track data, including ages and track lengths, with constraints of zircon fission-track ages and (U-Th)/He ages. The exhumation history of the Harizha–Halongxiuma mining area was reconstructed with these age data, revealing that since the early Mesozoic the area has undergone three cooling stages: (1) rapid cooling from 175 ± 30 Ma to 100 ± 10 Ma with a cooling rate and inferred exhumation of 2.0 ± 0.8 °C/Myr and 4.3 ± 1.7 km, respectively; (2) a relatively stable stage from 100 ± 10 Ma to 40 ± 10 Ma with a cooling rate and inferred exhumation of 0.3 ± 0.1 °C/Myr and 0.5 ± 0.2 km, respectively; and (3) rapid cooling since 40 ± 10 Ma with a cooling rate and inferred exhumation of 1.2 ± 0.6 °C/Myr and 1.4 ± 0.4 km, respectively. This exhumation history is consistent with the subduction process of Pacific plate and the strike slip movements of Dunmi fault. The total exhumation after main mineralization is calculated to be 7.6 ± 3.2 km, suggesting that ore bodies in the Harizha–Halongxiuma mining area remain partially preserved.  相似文献   

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