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1.
《Geodinamica Acta》2013,26(1):49-50
New structural data and P–T estimates of syn-deformational assemblages within the Beni Bousera peridotites and their crustal envelope are used to explain their Alpine exhumation. The Beni Bousera peridotites occur as thin sheets within high grade crustal units of the lower Sebtides (inner Rif, Morocco) and are composed of weakly deformed spinel lherzolite in the core of the massif and garnet-spinel mylonite at the rim. The main foliation trajectories in both the peridotites and overlying crustal units show systematic rotation towards their mutual contact, indicating a kilometer-scale top to the NW shearing with a dextral component along this crust/mantle contact. Widespread top to the NW shear criteria within the crustal units overlying the peridotite support this feature. Available ages constrain the development of the main foliation in both the peridotites and crustal rocks between 25 and 20 Ma. New P–T data from the peridotites show that deformation occurs during decompression from ≈ 22 kbar, 1050°C to ≈ 9-15 kbar, 800°C. As a consequence, exhumation of the Beni Bousera peridotites takes place during the Oligo-Miocene lithosphere thinning in the footwall of a lithospheric extensional shear zone. The exceptional preservation of garnet within the mylonitic peridotites results from rapid cooling of the border of the massif due to the juxtaposition with colder crustal rocks along this shear zone. Uplifting of the hot mantle rocks simultaneously induces high temperature metamorphism in the overlying crustal units. These new findings allow us to reconstruct the deformation history of the Beni Bousera region and the Alboran domain in the framework of the western Mediterranean geodynamics during the last 40 Myrs.  相似文献   

2.
《Geodinamica Acta》2013,26(6):455-473
Apatite/zircon fission track (FT) records of the Argentera external crystalline massif (Western Alps) show three tectonic pulses, respectively at 22 Ma (zircons), 6 and 3.5 Ma (apatites). The first pulse is consistent with the basement exhumation and initiation of the major deformation recorded in the foreland of the belt from Middle to early Upper Miocene. The two others might be respectively local expressions of the syncollisional extension mainly controlled by a westward sedimentary cover detachment and a Plio-Quaternary uplift acceleration. Zircon ages of 50-80 Ma in a limited NW area and evidence of an uplift elsewhere show that in a large fraction of the massif, temperatures in post-Variscan times never reached 320°C. Finally, FT data show that the Argentera massif did not behave as a single block during its denudation. First, in the NW of the massif, a small fault-limited block was already separated since the Cretaceous and later on recorded the 6 Ma denudation event, the 22 Ma pulse being recorded only in the remaining part of the massif. Second, less than 3.5 Ma ago, the northeastern part of the massif overthrust the southwestern block along the Bersézio-Veillos fault zone.  相似文献   

3.
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.  相似文献   

4.
The metamorphic core of the Betic-Rif orogenic chain (Alboran Domain) is made up of lower crustal rocks forming the envelope of the Ronda (Spain) and Beni Bousera (Morocco) peridotites. The deepest sections of the crustal envelopes are made of migmatitic granulites associated with diffuse acidic magmatic products, making these exposure and ideal site to investigate the textural and petrological connection between crustal anatexis and granite magmatism in the contintental crust. However, still debated is the timing of intracrustal emplacement of the peridotite bodies, with models proposing either Alpine (early Miocene) or Hercynian ages, and still uncertain is the linkage between peridotite emplacement and crustal anatexis. In this study, by combining rock textures with whole-rock geochemistry, metamorphic thermobarometry, the U-Pb zircon geochronology and the analysis of the garnet and zircon REE chemistry, we document the P-T-t evolution of the granulite facies migmatites that form the immediate envelope of the Beni Bousera peridotites of the Rif belt. A main episode of Permo-Carboniferous (ca. 300–290 Ma) deep crustal anatexis, melt extraction and migration is documented that we link to the crustal emplacement of the Beni Bousera peridotites during collapse of the Hercynian orogen. Correlation at a regional scale suggests that the Beni-Bousera section can be tentatively correlated with the pre-Alpine (Permo-Carboniferous) basement units tectonically interleaved within the orogenic structure of the Alpine chain. The results of this study provide ultimate constraints to reconstruct the tectono-metamorphic evolution of the Alboran Domain in the Western Mediterranean and impose re-assessment of the modes and rates through which Alpine orogenic construction and collapse occurred and operated in the region.  相似文献   

5.
The Beni Bousera massif forms part of the Sebtide units in the internal Rif Mountain (Morocco). It is mainly composed of mantle peridotites surrounded by crustal metamorphic rocks (kinzigites, micaschists, and schists). The serpentinization affects all of peridotite massif to various degrees. Serpentinization is concentrated at the top of the peridotites, along the mylonitized zone, and in the NE part of the massif. It is manifested by the formation of mesh and hourglass textures along the tectonic foliation in the highly serpentinized peridotites; and brecciated texture in the least serpentinized peridotites. Pyroxene minerals are still intact hosting few serpentine veins. These petrographic features are consistent with the geochemical data, marked by the increasing of LOI and decreasing of MgO and FeO toward the top of the massif and Aaraben fault. The Raman characterization of serpentine with the brecciated mesh and hourglass textures correspond to lizardite type whereas the serpentine with the vein texture is formed by lizardite + chrysotile.  相似文献   

6.
In the Rif (northern Morocco) and the Western Betics (southern Spain), the Alboran Domain forms a complex stack of metamorphic nappes including mantle peridotites (Beni Bousera and Ronda). We present in this paper new temperature data obtained in the Alboran Domain based on Raman spectroscopy of carbonaceous material (RSCM thermometry). In the lower metamorphic nappes of the Alboran Domain (lower Sebtides–Alpujárrides) temperature ranges from > 640 °C at the base of the metapelitic sequence to 500 °C at the top. The relationships between field isotherms and nappe structure show that peak temperatures were reached during strong ductile thinning of these nappes whereas they partly postdate this main episode in the Rif. In the upper nappes of the Alboran Domain (Ghomarides–Maláguides), generally supposed to be only weakly metamorphosed, temperatures range from ～500 °C at their base down to < 330 °C at the top. This temperature gradient is consistent with progressive Cenozoic resetting of K–Ar and 40Ar–39Ar ages. These nappes were thus affected by a significant thermal metamorphism, and the available age data in the underlying Sebtides–Alpujárrides show that this metamorphism is related to the metamorphic evolution of the whole Alboran Domain during the Late Oligocene–Early Miocene. Such thermal structure and metamorphic evolution can be explained by generalized extension in the whole Alboran Domain crustal sequence. At a larger scale, the present thermal structure of the Alboran Domain is roughly spatially consistent around the Beni Bousera peridotites in the Rif, but much more affected by late brittle tectonics around the Ronda peridotites in the Western Betics. Therefore, on the basis of the observed thermal structure, the metamorphic evolution of the Alboran Domain can be interpreted as the result of the ascent of hot mantle units contemporaneous with thinning of the whole lithosphere during an Oligo‐Miocene extensional event. The resulting structure has however been dismembered by late brittle tectonics in the Western Betics.  相似文献   

7.
A suite of pyroxenites from the Beni Bousera peridotite massif,northern Morocco, have been analysed for Re–Os and Lu–Hfisotopic compositions. Measured sections of the massif indicatethat pyroxenite layers make up between 1 and 9% by volume ofthe total outcrop. Clinopyroxenes from two Cr-diopside pyroxeniteshave unradiogenic Hf isotope compositions (  相似文献   

8.
《International Geology Review》2012,54(15):1873-1883
Mt Sanqingshan, a global Geopark and world natural heritage site located in Jiangxi Province, China, is famous for its eroded granite peaks. The uplift and denudation history of the area has been reconstructed using fission track methods for the first time. Apatite fission track ages (AFTAs) cluster into three groups at ca. 25 Ma, 45–55 Ma, and 70 Ma. These ages can be related to ancient multilevel denudation planes at about 900, 1200, and 1500 m above sea level, respectively. The apatite data also reveal four cooling stages for the Mt Sanqingshan region, from ca. 90 to 65–60 Ma, 65–60 to 45 Ma, 45 to 20–15 Ma, and 20–15 Ma to the present, with cooling rates of 1.96°C, 1.18°C, 0.37°C, and 3.78°C per million years, respectively, and an average cooling rate of 1.80°C per million years. Calculated uplift rates are 0.055, 0.034, 0.011, and 0.11 mm year?1 in the four stages, yielding uplifts of 4140, 570, 290, and 1940 m, respectively. The uplift rate of the last stage was significantly faster than that of the other three preceding stages, reflecting rejuvenation of Mt Sanqingshan, as a result of new tectonism. The average uplift rate at Mt Sanqingshan is 0.053 mm year?1, and the average denudation rate is 0.048 mm year?1, resulting in 3550 m of uplift and 2540 m of denudation relative to eustatic sea level. The 1010 m difference is very close to the average elevation of about 1000 m at present. A comparison of uplift–denudation histories for Mt Sanqingshan and Mt Huangshan shows that fission track results can be useful for defining geomorphological development stages.  相似文献   

9.
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   

10.
Four samples from the metamorphic aureole around the Beni Bousera ultramafic massif were studied in detail for U–Th–Pb electron microprobe dating on monazite. The samples include three meta-sedimentary granulites (kinzigites), collected at variable distance from the peridotites, and one kyanite-bearing leucosome in the kinzigite. Two types of monazite were identified in thin section, using SEM. The main population consists of interstitial grains, 20–70  μ m in size, while the second population consists of small grains (<20  μ m), included in garnet. A total of 64 U–Th–Pb electron microprobe measurements on 53 monazite crystals were undertaken. Most crystals have a Pb content lower than the Pb detection limit, indicating that they crystallized, or were reset, during a young event, probably Cainozoic in age. Few crystals, all entirely included in garnet, have Hercynian age, the best estimate of which is 284±27 Ma. This is a direct demonstration of the shielding effect of garnet for the U–Th–Pb system in monazite. The grains in inclusion in garnet are not reset by the post-Hercynian events, despite the high temperature reached at this time (>850 °C). Thus, the monazite closure temperature depends on its textural position in the host rock. The data also show that a Hercynian event occurred in the Beni Bousera granulitic metapelites, which equates with a high- P , high- T  event. The emplacement of the peridotite in the Cainozoic may be linked a low- P , high- T  event, followed by a low- P , low- T  retrogression. These two events reset the U–Th–Pb system in almost all monazite grains, except for the few crystals shielded by garnet.  相似文献   

11.
Petrological and geochronological investigations were carried out on metamorphic rocks of the Veporic unit (Inner Western Carpathians) in northern Hungary. K/Ar and Ar/Ar data on micas and amphibole show only Alpine ages (mostly in the range of 87-95 Ma) in this basement unit. Thermobarometric calculations yield lower amphibolite facies peak conditions (ca. 550냴 °C and 9ǃ kbar) for the Eoalpine metamorphic event. Complex evolution of gneissic rocks is reflected by the presence of discontinuously zoned garnets, the cores of which may represent relics of a pre-Alpine (presumably Variscan) thermal event. Zircon fission track (FT) data in the narrow range of 75-77.5 Ma indicate that this portion of the Veporic unit was emplaced to shallow crustal levels already during the Senonian time. The relative minor difference between zircon FT and K/Ar or Ar/Ar ages suggests very rapid cooling during the Late Cretaceous, most probably related to the extensional unroofing of the Veporic core complex. The obtained cooling ages do not support previous models of Tertiary uplift and exhumation of the Veporic unit along the Hurbanovo-Diósjeni Line.  相似文献   

12.
The Songshugou ultramafic massif is located to the north of the Shang‐Dan fault, the Palaeozoic suture between the North and South China blocks. It is the largest Apline‐type ultramafic body in the Qinling orogenic belt of central China, consisting mainly of dunite with a small amount of harzburgite and minor pyroxenite. We present new LA‐ICP‐MS U?Pb dating and trace element results for zircon from two garnet amphibolite samples in the contact metamorphic zone surrounding the massif. One was sampled ～1 m from the massif, the other ～5 m away. The studied zircon grains are small, anhedral, and display typical metamorphic characteristics of low Th/U values (<0.1). The U and Th concentrations of zircon range from several hundred ppm to less than 10 ppm. Cathodoluminescence images show two apparent generations of zircon, with lighter cores and darker rims. Core and rim ages however, are identical within error. These two samples yield identical concordant ages of 506±7 and 510±7 Ma, suggesting that the Songshugou ultramafic massif was emplaced at ～510 Ma. Low HREE concentrations and the absence of Eu anomalies in most analysed zircons suggest that the studied grains most likely formed during garnet amphibolite metamorphism induced by emplacement of the ultramafic massif.

To better understand the cooling history of the massif, 40Ar/39Ar ages of amphibole from three garnet amphibolite specimens in the contact metamorphic zone and one amphobolite sample about 20 m away from the massif were determined. The 40Ar/39Ar ages increase from 372±15 Ma (JSM‐01) near the massif to disturbed, unreliable ‘plateau’ ages of 474±8 Ma (JSM‐03) and 781±146 Ma (JSM‐04) with increasing distance from the ultramafic massif, showing limited heating during exhumation of the massif, followed by slow cooling. Therefore, the Songshugou ultramafic massif does not reflect the Jining orogeny at ～1 Ga. Instead, it was emplaced into the Proterozoic, Qinling Group during the Palaeozoic, probably due to the subduction along the Shang‐Dan fault.  相似文献   

13.
Thermotectonic history of the Trans-Himalayan Ladakh Batholith in the Kargil area, N. W. India, is inferred from new age data obtained here in conjunction with previously published ages. Fission-track (FT) ages on apatite fall around 20±2 Ma recording cooling through temperatures of ∼100°C and indicating an unroofing of 4 km of the Ladakh Range since the Early Miocene. Coexisting apatite and zircon FT ages from two samples in Kargil show the rocks to have cooled at an average rate of 5–6°C/Ma in the past 40 Ma. Zircon FT ages together with mica K−Ar cooling ages from the Ladakh Batholith cluster around 40–50 Ma, probably indicating an Eocene phase of uplift and erosion that affected the bulk of the batholith after the continental collision of India with the Ladakh arc at 55 Ma. Components of the granitoids in Upper Eocene-Lower Oligocene sediments of the Indus Molasse in Ladakh supports this idea. Three hornblende K−Ar ages of 90 Ma, 55 Ma, and 35 Ma are also reported; these distinctly different ages probably reflect cooling through 500–550°C of three phases of I-type plutonism in Ladakh also evidenced by other available radiometric data: 102 Ma (mid-Cretaceous), 60 Ma (Palaeocene), and 40 Ma (Late Eocene); the last phase being localised sheet injections. The geodynamic implications of the age data for the India-Asia collision are discussed.  相似文献   

14.
Large variations in clinopyroxene-garnet (cpx-grt) temperatures are recorded in thin peraluminous eclogite layers from Beni Bousera ultramafic massif (Morocco): cpx-grt temperatures in the core of layers < 20 cm thick are higher by up to 300°C than in the margins. The cpx-grt temperatures are correlated to both Al-concentration in cpx and Ca-concentration in grt, the two latter parameters being themselves closely intercorrelated. It is demonstrated that the regular interaction parameter ΔwgrtCa calculated from the Beni Bousera natural data is very close to ΔwgrtCa calculated from experimental data analysis for Ca-rich garnet. It is concluded that: (i) Al-concentration in cpx has no significant effect on the distribution of Fe and Mg between cpx and grt; and (ii) cpx-grt temperature variations observed across Beni Bousera peraluminous eclogite layers do not correspond to real thermal gradients, but merely result from the inadequacy of the thermometric equations in Ca-rich systems (XgrtCa > 0.15).  相似文献   

15.
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   

16.
Following Appalachian orogenesis, metamorphic rocks in central Newfoundland were exhumed and reburied under Tournaisian strata. New zircon fission‐track (ZFT) ages of metamorphic rocks below the Tournaisian unconformity yield post‐depositionally reset ages of 212–235 Ma indicating regional fluid‐absent reheating to at least ≥220°C. Post‐Tournaisian sedimentary thicknesses in surrounding basins show that burial alone cannot explain such temperatures, thus requiring that palaeo‐geothermal gradients increased to ≥30–40°C/km before final late Triassic accelerated cooling. We attribute these elevated palaeo‐geothermal gradients to localized thermal blanketing by insulating sediments overlying radiogenic high‐heat‐producing granitoids. Late Triassic rifting and magmatism before break up of Pangaea likely also contributed to elevated heat flow, as well as uplift, triggering late Triassic accelerated cooling and exhumation. Thermochronological ages of 240–200 Ma are seen throughout Atlantic Canada, and record rifting and basaltic magmatism on the conjugate margins of the Central Atlantic Ocean preceding the onset of oceanic spreading at ~190 Ma.  相似文献   

17.
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.  相似文献   

18.
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   

19.
Apatite fission-track analysis has been applied to the Raniganj and Panchet formations of Raniganj basin of Gondwana Supergroup to unravel its thermal and provenance history. Apatite fission track age population from both Raniganj and Panchet formations indicate partial annealing and point to a maximum temperature of around ～100-110°C during their post depositional evolution. The sandstone of Raniganj Formation has five peak ages at 26.3, 59.3, 109.7, 173.7 and 299.9 Ma, while Panchet Formation has three peak ages at 25.4, 143.5 and 281.3 Ma. This implies that the provenance of the Raniganj Formation of late Permian and Panchet Formation of early Triassic changed obviously. According to thermotectonic evolution of the Gondwana basin, these apatites with different FT ages possibly represent different source components, although partial annealing had occurred to these apatites. Possibly all the apatites had transported from the Precambrian basement which was undergoing deformation due to Gondwana rifting initiated during Carboniferous period. Due to this, the basement was undergoing inhomogeneous thermal history which became source of sediments for Raniganj basin. Apatite FT ages of both Raniganj and Panchet formations have peak ages between 25 and 60 Ma, which perhaps recorded the cooling/uplift history during Cenozoic Alpine-Himalayan orogeny. Given a palaeo-thermal gradient of 40° C/km, it can be deduced that the Raniganj basin has uplifted about 3km at an average rate of about 0.09mm/a since 25–60 Ma.  相似文献   

20.
96 new fission track (FT) apatite and zircon, K/Ar and Rb/Sr biotite and muscovite ages are presented for 19 samples (mainly acid gneisses) from a 40 km traverse through the Lepontine Alps in the Maggia Valley, South Central Switzerland. Plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample. The entire profile shows a fairly uniform Late Neogene-Recent mean uplift rate of 0.5 mm/a, confirmed by a gradient of FT apatite age with elevation. Cooling from higher temperatures occurred earlier in the south, where uplift rates of 2.2 mm/a in the Steep Belt (root zone) indicate >9 km Early Miocene uplift of the northern Pennine block. This uplift started before 23 Ma and is interpreted as resulting from a major phase of backthrusting along the Insubric Line, and as dating the formation of the mylonite belt. Estimated cooling rates constrain the timing of Lepontine Mid-Tertiary metamorphism: 3 schematic models are proposed which also consider published Rb/Sr, K/Ar mica and hornblende and U/Pb monazite ages. Slow cooling, differential initial heating and subsequent cooling of different parts of the Central Alps and post-38 Ma cooling with syntectonic metamorphism at 27 Ma are postulated as alternative interpretations of isotopic data and geologic evidence. From extrapolation between K/Ar and Rb/Sr mica ages and apatite FT ages, 240±50° C is proposed as the closure temperature for the retention of fission tracks in zircon.  相似文献   

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