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1.
A thermal event reduces the number of previously registered fission tracks in a mineral dependent upon the track retention properties of the individual mineral. Apatite, sphene and zircon have retention properties over a wide range of temperatures (from 100° to 550°C); apatite data reveal information at lowest temperatures while sphene and zircon data are useful for higher temperatures.Thermal events within this temperature range of 100°C to about 550°C are suitable for study with this technique. The age of the event is determined from samples in which the fission tracks are completely erased, while minerals containing partially removed (erased) tracks provide information on the temperatures occurring during the thermal event.As a test case, the analysis of the temperatures developed by the meteorite impact which produced the Ries crater at 14.7 m.y. ago is presented. 相似文献
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Absolute uplift rates, regional uplift patterns, and time limits for uplift and fault movements can be studied with fission tracks in apatite. This is demonstrated for about 50 apatites from the Swiss and Italian Alps. Due to the relatively low thermal stability of tracks in apatite, the fission track ages of apatites from this area define the time when these rocks cooled down to temperatures to 125 ± 20°C. 相似文献
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Fission track analysis of apatites from basement rocks of the Wright Valley in southern Victoria Land provides information about the timing, the amount and hence the rate of uplift of the Transantarctic Mountains in this area. Apatite ages increase systematically with elevation, and a pronounced break in the age versus elevation profile has been recognised at about 800 m on Mt. Doorly near the mouth of Wright Valley. The apatite age of about 50 Ma at this point approximates the time at which uplift of the mountain range began. Samples lying above the break in slope lay within the apatite fission track annealing zone prior to uplift, during a Cretaceous to Early Cenozoic period of relative thermal and tectonic stability. At the lower elevations samples had a zero apatite fission track age before the onset of rapid uplift and have track length distributions indicating rapid cooling. Some 4.8–5.3 km of uplift are estimated to have occurred at an average rate of about 100 ± 5m/Ma since uplift began. From the total stratigraphic thickness known above the uplifted apatite annealing zone it can be estimated that the Late Cretaceous/Early Cenozoic thermal gradient in the area was about 25–30°C/km.The occurrence and pattern of differential uplift across the Transantarctic Mountains can be estimated from the vertical offsets of different apatite fission track age profiles sampled across the range. These show the structure of the mountain range to be that of a large tilt block, dipping gently to the west under the polar ice-cap and bounded by a major fault zone on its eastern side. Offset dolerite sills at Mt. Doorly show the mountain front to be step-faulted by 1000 m or more down to the McMurdo Sound coast from an axis of maximum uplift just inland from Mt. Doorly. 相似文献
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Forty fission-track ages of apatite, zircon and sphene, and nine horizontal “confined” track-length distribution patterns in apatite have been used to establish the cooling history of nine Silurian to Late Cretaceous alkaline ring complexes which intrude Precambrian basement in the southern Eastern Desert of Egypt. Zircon or sphene fission-track ages were determined from three complexes for whichK/Ar andRb/Sr ages on the same samples were also available, these ages are concordant and are interpreted as emplacement ages resulting from rapid cooling following high level crustal intrusion into relatively thick volcanic piles.Average apatite ages for each of the eight ring complexes range from 33 to 167 m.y. Track-length distribution patterns for apatites taken together with their ages invite subdivision into two groupings. Those complexes yielding Early Oligocene apparent apatite ages suggest cooling from the total track annealing zone followed by a relatively lengthy residence near the base of the partial annealing zone whereas those with Late Cretaceous ages indicate cooling from a shallower level in the partial annealing zone. Variations in cooling history resulted from differential uplift between fault-bound blocks. One block, that containing the Late Cretaceous Abu Khruq complex, was relatively stable and the different degrees of partial resetting recorded in apatites of this complex are attributed to the thermal effect of localised Tertiary dyke intrusion.Fission-track analysis in combination with geologic data indicates that in the south Eastern Desert of Egypt a phase of uplift commenced in Late Oligocene time and was accompanied by paleogeothermal gradients of ca. 40–50°C/km. Uplift was more pronounced (at least 2–2.5 km) in areas within about 100 km from the present Red Sea coast. This uplift, which is viewed as part of a broader regional tectonism related to the opening of the Red Sea, occurred along a northwest fracture pattern and was controlled by pre-existing lines of weakness in the basement complex. 相似文献
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Fission track ages have been determined on sphene, apatite, and zircon separated from fresh and highly weathered rock samples. Sphene and zircon ages are unaffected by even extreme weathering. Apatite from partially weathered granite gives a similarly unaffected age. Badly corroded apatites from a residual clay, however, do show a 17% reduction in apparent age, involving loss of both spontaneous fission tracks and uranium from the crystals. 相似文献
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Abstract Apatite and zircon fission track ages from Ryoke Belt basement in northeast Kyushu show late Cretaceous, middle to late Eocene, middle Miocene and Quaternary groupings. The basement cooled through 240 ± 25°C, the closure temperature for fission tracks in zircon, mainly during the interval 74-90 Ma as a result of uplift and denudation, the pattern being uniform across northeast Kyushu. In combination with published K-Ar ages and the Turonian-Santonian age of sedimentation in the Onogawa Basin, active suturing along the Median Tectonic Line from 100-80 Ma, at least, is inferred. Ryoke Belt rocks along the northern margin of Hohi volcanic zone (HVZ) cooled rapidly through ∼100°C to less than 50°C during the middle Eocene to Oligocene, associated with 2.5-3.5 km of denudation. The timing of this cooling follows peak heating in the Eocene-Oligocene part (Murotohanto subbelt) of the Shimanto Belt in Muroto Peninsula (Shikoku) inferred previously, and coincides with the 43 Ma change in convergence direction of the Pacific-Eurasian plate and the demise of the Kula-Pacific spreading centre. Ryoke Belt rocks along the southern margin of HVZ have weighted mean apatite fission track ages of 15.3 ± 3.1 Ma. These reset ages are attributed to an increase in geothermal gradient in the middle Miocene combined with rapid denudation and uplift of at least 1.4 km. These ages indicate that heating of the overriding plate associated with the middle Miocene start of subduction of hot Shikoku Basin lithosphere extended into the Ryoke Belt in northeast Kyushu. Pleistocene apatite fission track ages from Ryoke Belt granites at depth in the centre of HVZ are due to modern annealing in a geothermal environment. 相似文献
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An attempt was made to determine the absolute age of faulting by measuring fission track ages of epidotes from mineralization veins along fault and joint planes. The method was applied to epidotes from along faults and fissures in the Sinai Peninsula, which cut Precambrian rocks. Most samples yield Tertiary ages (32-11 m.y.) An Early Cretaceous event is also recorded (120-103 m.y.). Samples from country rocks (igneous and metamorphic) give ages older than 325 m.y. The results are compatible with previous geological information, and suggest that the method can be potentially useful for dating faults. 相似文献
10.
The mineralization ages reported in the past in the Tuwu-Yandong copper district not only are different,but also fall into the Hercynian epoch.This study has achieved 9 zircon and 7 apatite fission track analysis results.The zircon fission track ages range from 158 Ma to 289 Ma and the apatite ages are between 64 Ma and 140 Ma.The mineralization accords with the regional tectonics in the copper district.We consider that the zircon fission track age could reveal the mineralization age based on annealing zone temperature of 140―300℃ and retention temperature of ～250℃ for zircon fission track,and metallogenetic temperature of 120―350℃ in this ore district.Total three mineralization epochs have been identified,i.e.,289―276 Ma,232―200 Ma and 165―158 Ma,and indicate occurrence of the min-eralization in the Indosinian and Yanshan epochs.Corresponding to apatite fission track ages,the three tectonic-mineralizing epochs are 140―132 Ma,109―97 Ma and 64 Ma,which means age at about 100℃ after the mineralization.The three epochs lasted 146 Ma,108 Ma and about 100 Ma from ～250℃ to ～100℃ and trend decrease from early to late.It is shown by the fission track modeling that this district underwent three stages of geological thermal histories,stable in Cretaceous and cooling both before Cretaceous and after 20 Ma. 相似文献
11.
在利用磷灰石裂变径迹热年代学方法来约束岩体冷却史的应用中,由于地质条件和磷灰石退火性质的限制,表观年龄往往不能直接代表特定地质事件的时间.利用封闭径迹的长度直方图模式和高程-年龄模式可定性地反映出岩体冷却史是否遭受过干扰.平均径迹长度-年龄(或香蕉图)模式、径迹年龄谱模式以及反演模拟在某种程度上可用来限定地质过程中冷却启动的时间.然而,对于多阶段的冷却史,模式和模拟分析的不确定性仍较显著,对早期时限的定量揭示仍是研究和应用中的一个难点.只有结合多种方法、模式和模拟的运用并考虑地质背景才能较清晰地约束岩体的冷却历史. 相似文献
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Peter K. Zeitler Rashid A.K. Tahirkheli Charles W. Naeser Noye M. Johnson 《Earth and Planetary Science Letters》1982,57(1):227-240
The uplift history of the Swat Valley and Hazara region of northwestern Pakistan has been established using 22 fission-track dates on apatite, zircon and sphene. A major fault, the Main Mantle Thrust (MMT) strikes east-west across the Swat Valley, separates regions of markedly differing fission-track age regimesm, and may be a suture zone separating an extinct island arc terrane on the north from the Indian plate to the south. Fission-track ages ranging from about 55 to 58 m.y. for sphene, 18 to 53 m.y. for zircon, and 9 to 17 m.y. for apatite were obtained from the region north of the MMT. To the south the fission-track age ranges are 20 to 25 m.y. for sphene, 17 to 26 m.y. for zircon, and 16 to 23 m.y. for apatite. Disparate zircon and sphene ages on each side of the MMT imply different cooling histories for each side of the fault prior to 15 m.y. Similar apatite ages on both sides of the fault imply similar cooling histories during the past 15 m.y. This may indicate that faulting ceased by 15 m.y. Mean uplift rates have been derived from the fission-track data using mainly the mineral-pair method. Uplift rates in the region north of the MMT increased from 0.07 to 0.20 mm/yr during the period 55 to 15 m.y. South of the fault, uplift rates averaged in excess of 0.70 mm/yr for the period 25 to 15 m.y. During the past 15 m.y. uplift across the MMT in the Swat Valley showsno discontinuities, ranging from 0.16 mm/yr in the south to 0.39 mm/yr in the north. A plausible interpretation for the fission-track uplift data has the MMT verging to the south with overthrusting taking place at a depth between 3.5 and 6.0 km, juxtaposing two terranes that were originally separated by a substantial, but unknown distance. In this model, regional uplift followed cessation of faulting just prior to 15 m.y. 相似文献
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运用裂变径迹分析方法,探讨分析了合肥盆地中新生代的构造热演化特征. 上白垩统和古近系下段样品的磷灰石裂变径迹（AFT）数据主体表现为靠近部分退火带顶部温度(±65℃)有轻度退火,由此估算晚白垩世至古近纪早期合肥盆地断陷阶段的古地温梯度接近38℃/km,高于盆地现今地温梯度(275℃/km).下白垩统、侏罗系及二叠系样品的AFT年龄(975～25Ma)和锆石裂变径迹(ZFT)年龄(118～104Ma)均明显小于其相应的地层年龄,AFT年龄－深度分布呈现冷却型曲线形态,且由古部分退火带、冷却带或前完全退火带及其深部的今部分退火带组成,指示早白垩世的一次构造热事件和其随后的抬升冷却过程. 基于AFT曲线的温度分带模式和流体包裹体测温数据的综合约束,推算合肥盆地早白垩世走滑压陷阶段的古地温梯度接近67℃/km. 径迹年龄分布、AFT曲线拐点年龄和区域抬升剥蚀时间的对比分析结果表明,合肥盆地在早白垩世构造热事件之后的104Ma以来总体处于抬升冷却过程,后期快速抬升冷却事件主要发生在±55Ma. 相似文献
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O. M. Rosen A. V. Soloviev D. Z. Zhuravlev 《Izvestiya Physics of the Solid Earth》2009,45(10):914-931
Thermal evolution of the continental crust beneath the northeastern Siberian craton was studied based on the interpretation
of apatite fission-track ages. The samples selected for AFT dating were collected from depths between 2 and 3 km along a 1000-km-long
profile, from the crystalline basement of the Siberian platform. The AFT ages range from 185 to 222 Ma, indicating that in
the late Triassic-early Cretaceous, the top of the crystalline basement was cooled below ∼100°C. Once the apatite cooled below
this temperature, it began to accumulate and preserve tracks produced by spontaneous fissioning of 238U, and the number of tracks preserved is effective in determining the ages of events using the apatite fission-track method
(AFT).
The study showed that the apatite from Archean rocks was largely formed at 1.8–1.9 Ga as a result of a Paleoproterozoic metamorphic
overprinting during the terrane collision and the subsequent accretion of the Siberian craton. The last thermal event, the
self-heating of the collision prism, was terminated by cooling at ∼1.3 Ga. At that time, the Rb-Sr isotopic system became
closed and the upper crust passed the ~300°C isograd. The calculation results showed that on further cooling, the ∼100°C isograd
was passed at 1143 Ma. This age estimate could be obtained using AFT dating if the above event had been the last one in the
thermal history of the Siberian craton. The obtained track ages indicate the existence of a repeated, significantly younger,
heating of the crystalline crust due to some local reason. 相似文献
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Early Cretaceous uplift and erosion of the northern Appalachian Basin, New York, based on apatite fission track analysis 总被引：1，自引：0，他引：1
The thermal history of outcropping Devonian sediments of the northern Appalachian Basin, New York, has been investigated using fission track analysis of detrital apatites from 57 sandstone samples. Based on lengths and apparent age measurements using fission tracks in apatite it is concluded that Lower Devonian sediments presently at the surface in the Catskill region were cooled rapidly from temperatures higher than about 110°C during Early Cretaceous times (120–140 Ma ago). In the western part of New York (Wellsville-Buffalo) data from late Devonian sediments are consistent with cooling at the same time as that identified for the Catskill region but from lower temperatures, in the range of approximately 80–110°C, the maximum temperature these sediments experienced since deposition. For a pre-uplift paleogeothermal gradient of 25–35°C/km, the confined track length data indicates uplift and erosion of 2–3 km for western New York and greater than 3–4 km for the Catskill region, a differential uplift pattern which is consistent with the historical stratigraphic data from the region. This conclusion is at variance with earlier interpretations put forth by others.Rapid broad scale uplift and erosion of the scale identified imply that large volumes of sediment could have been supplied from the northern Appalachian Basin during the Early Cretaceous. This timing for the dominant post-Devonian cooling phase in the basin is not accounted for by recent models of the tectonic evolution of the Appalachian Orogen but is compatible with the change from carbonate to siliciclastic deposition in the Atlantic coastal plain. It is suggested that this style of broad regional uplift without significant deformation is characteristic of a tectonic regime associated with, and subsequent to, continental rifting.Apatite fission track analysis is shown to be a basic tool in providing fundamental limits for thermal history assessment in regional tectonic problems. 相似文献
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鄂尔多斯盆地东南缘处于渭北隆起、晋西挠褶带和东秦岭造山带的转折地带,构造位置独特,演化历史复杂.本文选取东缘韩城地区和南缘东秦岭洛南地区上三叠统延长组为研究对象,采集6件砂岩样品进行锆石、磷灰石裂变径迹分析,对关键构造-热事件提供热年代学约束,恢复盆地东南缘不同构造带的热演化史,深化对盆地东南部油气资源赋存条件的认识,以期实现油气勘探的新突破.研究表明韩城和洛南地区的抬升冷却史存在明显差异.磷灰石裂变径迹年龄表现为从南到北减小的趋势.东缘韩城剖面磷灰石裂变径迹记录51.6~66.3 Ma、33 Ma两次抬升冷却的峰值年龄.南缘洛南剖面锆石裂变径迹年龄和磷灰石裂变径迹年龄分别记录89~106 Ma和59~66 Ma的冷却抬升年龄.洛南地区抬升冷却时间较早,剥蚀速率(106m/Ma)大于韩城地区(68m/Ma),且持续时间长.磷灰石裂变径迹(Apatite Fission Track,AFT)热史模拟显示,晚中生代,受燕山运动的影响,东秦岭地区发生强烈的构造岩浆事件,洛南地区热演化程度明显高于韩城地区.洛南剖面的热演化主要受岩浆活动的控制,韩城剖面为埋藏增温型.鄂尔多斯盆地东南缘的裂变径迹年龄格局基本受控于白垩纪以来的抬升冷却事件. 相似文献
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U-Pb and Rb-Sr dating of a polymetamorphic nappe terrain: The Caledonian Jotun nappe,southern Norway
Urs Schärer 《Earth and Planetary Science Letters》1980,49(2):205-218
The Caledonian Jotun nappe in the Tyin area of southern Norway has been investigated using U-Pb analysis of zircon and sphene and Rb-Sr measurements of minerals and whole rocks, with special reference to the reaction of the isotope systems to various kinds of metamorphic event. The nappe consists of Precambrian basement rocks and their cover, inversely thrust over the Baltic shield and its parautochthonous, presumably lower Paleozoic sediments during the Caledonian orogeny. While the nappe basement retained its pre-Caledonian structures, the nappe cover was penetratively deformed and metamorphosed to lower greenschist facies conditions.U-Pb analyses of zircon and sphene ofnappe basement rocks point to the crystallization of a syenitic to monzonitic magma at 1694± 20m.y., the intrusion of gabbros into the syenites and monzonites at 1252?25+28 m.y., and the metamorphism (upper greenschist-lower amphibolite facies) and deformation (gneissification and mylonitization) of the whole complex at 909± 16m.y. Although this latest event caused strong lead loss in all zircon populations, it had no influence on the Rb-Sr system on a whole rock scale. The Caledonian movements did not disturb the U-Pb system of zircon and sphene but strongly influenced the Rb-Sr system in certain minerals and zircon and/or its inclusions (K-feldspar and brown biotite partially, green biotite completely reset).In contrast to the nappe basement, zircons from thecover rocks show pronounced lead loss during the Caledonian metamorphism/deformation — U-Pb analysis give discordia lower intercept ages of 415± 21 m.y. and 395± 6m.y. Again, however, the Rb-Sr whole-rock system has not been reset in Caledonian time. Minerals from the same rocks which provided the zircons give Rb-Sr isochron ages of 390± 11m.y. and 386 ± 20 m.y.Comparison of U-Pb and Rb-Sr results from the nappe basement demonstrates that only the analysis of U-Pb systematics in zircon and especially sphene resolved the 900-m.y. event. Rb-Sr mineral data alone yield ambiguous results.The results from the nappe cover confirm that U-Pb analyses from penetratively deformed sediments are very useful in dating a metamorphic/tectonic event in lower greenschist facies conditions.From the measured cell dimensions of the zircon populations it is concluded that lead can be completely retained in zircon during recrystallization. 相似文献
19.
温度是控制烃源岩有机质生烃的主要因素,构造-热事件下的高温作用对烃源岩的增熟和生烃历程具有显著影响.通过地质分析和磷灰石、锆石裂变径迹、磷灰石U-Th/He低温热年代学数据、火山岩年龄数据分析认为,下扬子中生代存在印支期(T_3-J_2),燕山期(J_3-K_1)构造-热事件,沉积盆地达到最高古热流的时间大约为130~110Ma.古温标镜质体反射率热史反演结果揭示句容地区最高地表古热流达到~94mW·m~(-2),泰兴地区为~78mW·m~(-2),热事件的强度由西至东减弱.基于EASY%Ro模型的生烃史正演结果揭示:寒武系烃源岩在常州地区主生气期为早二叠世晚期至晚三叠世末,在句容、泰兴地区主生气期为晚三叠世-早白垩世.由于T_3-J_(1-2)前陆盆地沉积和早白垩世岩浆活动热事件的双重作用,海相烃源岩有机质在早白垩世末达到最高古地温.虽然K_2-E期间在句容、泰兴和常州部分地区具有一定的沉降幅度,甚至使得部分地区海相烃源岩的埋深超过早期的埋深,但由于K_2以来大地热流降低,海相烃源层地层温度却低于早期的地温,有机质未能普遍进一步增熟生烃,即这些地区不存在大面积的二次生烃. 相似文献
20.
Summary The ages of forty six muscovite samples obtained from mines in the three main mica belts of India, viz. Bihar, Rajasthan and Andhra Pradesh, and areas around Delhi have been measured using improved fission track dating technique. The effect of geological annealing in the samples has been assessed and suitable correction applied to the ages, wherever required; also, uranium concentration has been measured in tight cleavages so as to avoid errors due to epigenetically introduced uranium.The ages agree with the main orogenic-metamorphic cycles in the respective regions and also the ages of pegmatites measured by other radiometric methods. The ages of the three belts have been measured as follows: Bihar mica belt, 700–1100 m.y.; Rajasthan mica belt and Delhi samples 700–1050 m.y.; Andhra Pradesh (Nellore) mica belt, 470–650 m.y. Occurrence of metamorphic event 600 m.y. in Rajasthan is supported by the age of one of the samples. 相似文献