伊犁盆地南缘隆升剥蚀及其盆地南部的沉积——利用磷灰石裂变径迹分析

分析了伊犁盆地南缘蚀源区14件磷灰石样品,其中南缘中西部10件,东部4件。磷灰石裂变径迹表观年龄及其与高程的关系、单颗粒年龄、封闭径迹分布特征表明,伊犁盆地南缘样品均遭受了不同程度的退火,但没有发生明显的区域性热事件。通过封闭径迹正演热史模拟得出,伊犁盆地南缘中新生代构造演化经历了三叠纪—侏罗纪晚期快速隆升,白垩纪—古近纪相对稳定和新构造快速隆升三个阶段。东西两段略有不同,西段隆升时间较早,样品所在地在早三叠世就开始强烈隆升,说明当时该处离原型盆地边界较近,而东段此时样品所在位置还可能接受沉积,直至中侏罗世末期才开始隆升剥蚀。侏罗纪原型盆地南部边界至少跨过大板煤矿,因为在该处出露中侏罗世西山窑组残留地层。相应的稳定阶段东段要滞后一些,稳定时间相对较短,西段该时段长达100Ma,而东段多在50～60Ma。新构造运动强烈活动的时间东段相对较早,局部地段在38Ma就开始隆升。盆地南缘沉积相带的发育特征和新近纪(或第四纪)内给出的电子自旋共振年龄(ESR)均说明,沉积对构造具明显的响应,盆缘快速隆升阶段其盆地内相应的沉积物较粗,相对稳定阶段对应的沉积较细或缺失。     

伊犁盆地南缘构造活动及对砂岩型铀矿的制约:来自磷灰石裂变径与U-Pb定年的证据

为了探讨伊犁盆地南缘构造活动与铀成矿关系,通过采取砂岩型铀矿含矿层砂岩样品,利用磷灰石裂变径迹热年代学与U-Pb等时线定年的方法,对伊犁盆地南缘构造活动与砂岩型铀矿成矿年龄进行了研究。研究结果表明：①伊犁盆地南缘自中生代以来经历了三期强烈的隆升—剥蚀事件,三叠纪末—中侏罗世、晚侏罗世—早白垩世、中新世—现今,对应印支末期、燕山期与喜马拉雅期三期构造活动;②盆地南缘中—西段砂岩型铀矿成矿年龄可分为158~153 Ma、108~60.5 Ma、55~15 Ma,12~0.3 Ma四期,盆地东段铀成矿年龄比较新,为7.8~5.5 Ma之间;③盆地南缘构造活动时间与铀成矿年龄具有非常好的对应性,将伊犁盆地南缘铀成矿作用过程划分为三个阶段,物源区快速抬升—含矿建造形成期及铀的预富集阶段、主成矿阶段、后生叠加改造阶段。     

羌塘盆地中央隆起带的抬升演化:构造-热年代学约束

本文综合磷灰石裂变径迹年龄(113~43 Ma)、锆石裂变径迹年龄(169~103 Ma)、锆石U-Pb年龄(215~206 Ma)、黑云母K-Ar年龄(186~178 Ma),通过磷灰石热史模拟,TASC图谱分析和矿物封闭温度年龄等手段,获得了中央隆起晚三叠世至今较为完整的冷却抬升历史。中央隆起主要经历了早侏罗世、晚侏罗世-早白垩世、晚白垩世-中新世早期和中新世晚期至今四期冷却事件,与南北羌塘板块后碰撞伸展、拉萨羌塘板块碰撞、新特提斯洋板片俯冲、印度欧亚板块碰撞以及中新世南北向走滑伸展存在动力学联系,造成11.4 km、2.85 km、4.3~5 km和0.85 km的抬升量。中央隆起在侏罗纪相对两侧盆地抬升,随着两侧盆地经历了侏罗纪的沉积增厚,与两侧盆地高差减小,在早白垩世早期可能位于海平面附近,随后快速抬升至2~2.5 km,统一接受晚白垩世红层沉积,并经历长期持续的逆冲推覆构造活动,进一步抬升至5 km,随后受到中新世古大湖夷平和南北向伸展作用影响,中央隆起相对盆地发生差异抬升。     

秭归盆地中新生代构造-热演化的裂变径迹约束

通过磷灰石裂变径迹年龄的测定以及时间-温度热历史的反演,揭示了秭归盆地中新生代构造-热演化过程。结果表明:秭归盆地自120 Ma左右开始缓慢隆升,主要经历了3个强烈的隆升阶段:(1)晚白垩世100~80 Ma开始强烈隆升,是燕山期造山运动在该地区作用的结果,也可能是黄陵背斜晚白垩世强烈抬升向西延伸的响应;(2)晚始新世40 Ma的强烈隆升,可能是印度板块和亚欧板块碰撞初期作用的远程响应;(3)中新世中期到末期10~5 Ma的强烈隆升,是青藏高原东部边界向东扩展及亚洲季风气候变化的响应。秭归盆地内部自白垩纪以来一直隆升剥蚀,展现出与盆地边缘构造-热演化的差异。通过与黄陵背斜东部的当阳盆地构造-热事件的对比,暗示了黄陵背斜在晚白垩世已隆升剥露至地表,分割了两个盆地。晚侏罗世—早白垩世,秦岭大规模挤压变形逆冲推覆构造作用使得米仓山—汉南隆起和黄陵背斜地区成为中上扬子地区磷灰石裂变径迹年龄相对最大的区域,江南—雪峰陆内造山作用向西北方向的扩展使得湘鄂西地区向川东地区磷灰石裂变径迹年龄具有整体变年轻的趋势。晚白垩世以来太平洋板块俯冲挤压效应使得川东褶皱带周缘及川东北磷灰石裂变径迹年龄自南东向北西方向减小,江汉盆地、当阳盆地及龙泉山以西记录的年轻的磷灰石裂变径迹年龄则与青藏高原隆升及其向南东方向构造逃逸的挤压作用和亚洲季风等气候变化的影响有关。     

宁武盆地中-新生代构造演化的裂变径迹证据

为深入研究宁武盆地中-新生代的构造演化及煤层气资源的赋存条件,采集样品进行裂变径迹测试。锆石裂变径迹年龄为156～139 Ma,磷灰石裂变径迹年龄为97～47 Ma。宁武盆地中-新生代的构造演化历史可分为3个阶段。晚侏罗世(156 Ma),盆地两翼的岩体开始缓慢隆升,核部坳陷沉积,到早白垩世晚期(100 Ma),宁武盆地古地温达到最高,烃源岩达到了生气高峰期。白垩世晚期-古新世(79～59 Ma),快速抬升剥蚀。之后,虽有短暂埋藏,但总体处于隆升状态。渐新世晚期(40～30 Ma)以来快速抬升到现今位置。宁武盆地抬升剥蚀具有空间上的不均衡性。北东部抬升剥蚀早于南部,周缘岩体隆升剥蚀速率大于核部。宁武盆地是在中生代山西地块上形成一系列雁行状排列的复背斜和复向斜的构造背景下,新生代受印度洋板块挤压欧亚大陆,两翼山体强烈抬升推挤作用形成,属于华北克拉通区域构造事件的响应。     

黄陵隆起中-新生代隆升作用的裂变径迹证据

通过对8个样品磷灰石裂变径迹年龄和3个样品锆石裂变径迹年龄的测定以及时间-温度热演化历史的反演,研究黄陵隆起中新生代的隆升作用过程,结果表明：黄陵隆起自晚三叠世200Ma开始隆升,表现为持续的隆升过程,经历了4个阶段：200Ma～160Ma±的缓慢隆升冷却作用阶段;160Ma～98．4Ma的快速隆升冷却阶段,岩体进入磷灰石部分退火带中;之后进入了一个构造相对稳定的阶段,样品滞留在部分退火带中;随后36．7Ma～28．4Ma以来,再次快速隆升剥蚀冷却。两次快速的隆升作用指示了中扬子地区两次强烈的构造活动和构造变革。作为印支期以来持续的古隆起,黄陵隆起周缘地区是中扬子地区海相油气运聚有利的指向区。     

鄂尔多斯盆地东南缘金锁关地区延长组构造-热演化特征

采用野外剖面勘测与磷灰石裂变径迹(AFT)分析相结合的研究方法,综合分析了鄂尔多斯盆地东南缘金锁关地区上三叠统延长组的中-新生代构造-热演化特征。金锁关-淌泥河剖面延长组总体呈现为褶皱-冲断构造变形样式,剖面北段的淌泥河处发育较为强烈的斜歪褶皱-冲断构造;该冲断构造属于瑶曲-云梦山冲断构造带的重要组成部分,且中侏罗统卷入了与延长组协同的褶皱变形,并与其上覆的下白垩统呈角度不整合接触关系,表明其构造变形时间主要发生在燕山中期的晚侏罗世。剖面上强、弱变形区段2件延长组砂岩样品的磷灰石裂变径迹(AFT)中值年龄和池年龄非常接近地分布在(105±7)Ma和(93±6)~(94±6)Ma,表明金锁关地区延长组抬升冷却至AFT封闭温度以浅的峰值年龄主要集中在100 Ma左右;砂岩样品AFT热史模拟结果进一步揭示,延长组最晚在早白垩世中期的120 Ma左右已达到最大埋深增温,之后经历了早白垩世晚期120~115 Ma的快速抬升、115~40 Ma的缓慢抬升和40~17 Ma以来的快速隆升剥露过程。     

西天山山脉多期次隆升-剥露的裂变径迹证据

磷灰石的裂变径迹法已经广泛地应用于限定山脉的隆升剥露历史研究。天山山脉的隆升历史一直存在争议,西天山山脉的构造隆升研究则相对更为缺乏。野外系统采集三个横穿西天山察汗乌苏山剖面的花岗岩、火山岩等样品,挑选磷灰石开展了裂变径迹测试分析工作。测试结果表明,西天山可能存在多期次的构造隆升事件;进一步利用实测的磷灰石裂变径迹年龄数据和径迹长度,开展了磷灰石的温度时间反演模拟研究。模拟结果结合区域性的地质资料分析推断,西天山山脉自中生代以来存在4个阶段构造隆升剥露事件,分别为:三叠纪末—早侏罗纪(220～180Ma)、侏罗纪中期(170～140Ma)、白垩纪中期(110～80Ma)和晚新生代(24Ma以来)。     

西天山隆升-剥露过程初步研究

天山造山带是在古生代造山基础上,在新生代由于印亚碰撞的远程效应而陆内再造成山。本文主要用磷灰石裂变径迹测年分析来限定西天山的隆升-剥露过程。野外系统采集西天山山脉及其伊犁盆地钻孔中的样品,挑选磷灰石进行了裂变径迹测试分析工作,着重开展了磷灰石的温度-时间反演模拟研究。根据温度-时间模拟结果推断,西天山在中新生代期间共发生了3期次的快速冷却作用,分别为早侏罗纪(200～180Ma)、白垩纪中期(115～95Ma)和新生代期间(24Ma以来);根据样品位置分析表明,西天山的隆升-剥露作用并不均一,开始于侏罗纪早期的山脉抬升范围有限,仅局限于中天山;白垩纪中期(115～95Ma),整个西天山山脉和伊犁盆地一起发生整体的抬升和剥露;新生代24Ma以来,西天山的山体块体抬升与山间盆地的断陷同时发育。     

札达盆地碎屑裂变径迹揭示的盆山耦合过程

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.      

裂变径迹定年方法的进展及应用

裂变径迹分析方法利用裂变径迹年龄及裂变径迹长度分布形态来反映随时间产生的裂变径迹积累及由温度控制的退火(裂变径迹缩短或消失)两种因素综合作用的结果。近几年来，有关磷灰石的退火特征进行了大量实验和野外研究，取得了较大进展。本文通过对80年代以来国内外裂变径迹研究状况的追踪调研结果，简要介绍裂变径迹定年方法的主要进展及应用情况。     

怒江河砂岩屑磷灰石裂变径迹结果与流域地貌演化

河流搬运沉积的河砂作为流域内地质体的平均产物,可以有效地揭示整个流域内区域性的地质体热史演化。对同一河流进行分段采样能够揭示更为详实的热史演化差异。本文对滇西境内怒江上游至下游采集了7个河砂样品进行磷灰石裂变径迹定年,主要年龄峰值依次为: 12.2 Ma和12.8 Ma, 7.7 Ma, 5.3 Ma、4.4 Ma和4.9 Ma, 7.3 Ma,总体上呈现出上游老、中游年轻、下游老的年龄格局。怒江中游河段相对年轻的流域热史经历说明中游河段较其他区域经受了构造地貌的快速演化。由于这一位置对应三江并流,而且气候作用与现代西南季风的水汽通道吻合,降雨量与上、下游流域截然不同。可以推断,气候因素导致了其快而新的构造地貌演化,促成代表年轻冷却历史信息的地质体被迅速剥露造就了怒江河道不同位置流域热史演化的差异。测得的7个样品所有年龄峰值可分为5个区段: 5.3～4.4 Ma、7.7～7.3 Ma、12.8～10.7 Ma、26.8～22.2.3 Ma、48.7～30.1 Ma,基本反映了流域范围新生代以来主要的热史演化阶段。此外,怒江不同河段河砂样品的分段性特征,证实河砂岩屑磷灰石裂变径迹分析方法在解释流域区域热史演化方面具有独特的优点。     

利用磷灰石裂变径迹对断层摩擦生热探测或测量的初步探讨

以青藏高原东北缘断裂带为研究对像,对利用磷灰石裂变径迹热年代学对地震断层滑动摩擦生热的探测或测量进行了初步探讨。其基本思路是利用磷灰石裂变径迹热年代计的热敏感,通过对横跨断层垂直方向断层岩和围岩的磷灰石裂变径迹年龄及围限径迹长度分布的对比分析,对断层滑动摩擦生热进行探测。本次研究对来自3个断层剖面的13个样品进行了磷灰石裂变径迹分析,样品包括断层主滑动面上的断层泥、碎裂岩和断层围岩,分析结果并没有获得断层摩擦生热的证据,表明这些断层在地震滑动过程中的摩擦增温非常有限,没有达到磷灰石裂变径迹热年代计体系可加载热信息的温度－时间要求。结合前人已有的相关研究,对利用磷灰石裂变径迹热年代学对地震断层滑动摩擦生热进行探测或测量存在的主要问题及可行性进行了初步总结和探讨,认为只适应于对震级大、断层滑动距离和速率大,摩擦强度强,位于一定深度有大量摩擦热生成,并使断层附近增温达到或超过磷灰石裂变径迹部分或完全退火温度的断层进行滑动摩擦生热的探测或测量,将是一种潜在的能对地震断层滑动摩擦生热或增温进行测量的“热量计或温度计”。     

Interpreting data dispersion and “inverted” dates in apatite (U-Th)/He and fission-track datasets: An example from the US midcontinent

New apatite (U-Th)/He (AHe) and apatite fission-track (AFT) data were acquired for cratonic basement samples from an 80 m span of drillcore in northeastern Kansas. The short depth interval over which the samples were collected indicates that they should have undergone thermal histories that would be indistinguishable using low temperature thermochronometry techniques. Individual AHe dates from four samples range from 99 to 464 Ma. Three samples yield dates <300 Ma that display a correlation with apatite eU (9-34 ppm) and a weaker correlation with grain size. eU concentration maps of apatites from these samples reveal low to moderate zonation in eU. Results for a fourth sample are characterized by dates >300 Ma, higher eU (39-113 ppm), and substantial data dispersion uncorrelated with eU and grain size. These apatites have strong and variable eU zonation. AFT dates for five samples range from 242 to 291 Ma. The sample with the highest eU apatites and oldest AHe dates yields the youngest AFT results. These results are “inverted”, with AHe dates distinctly older than the corresponding AFT date.We explore both the causes of data dispersion and the overall compatibility of this cratonic dataset. We find that geologically reasonable thermal histories can (1) explain the distribution of the moderate eU AHe data when accounting for the influence of radiation damage, grain size, and eU zonation on apatite He diffusivity, (2) reproduce the observed dispersion in the high eU AHe data when using a viable range of eU zonation and grain size, and (3) explain the AFT data for the same samples. The AHe and AFT data are mutually consistent, and viable thermal histories successfully predict the observed pattern of older AHe than AFT dates for the high eU apatites. Together these results suggest that appropriately accounting for the known controls on apatite He diffusivity can explain the observed dispersion and “inverted” AHe and AFT results in some thermochronometry datasets. A range of AHe dates should be especially common in cratonic data, because small differences in apatite He diffusivity are amplified by the thermal histories that typify cratonic settings. We use these results to develop some guidelines for interpreting dispersed AHe datasets. First, date-eU and date-grain size correlations should be evaluated, and if these patterns occur they can be used to better resolve the thermal history. Second, for samples that yield inexplicably large dispersion of AHe dates uncorrelated with eU and crystal size, the appropriate strategy is either to reject these samples from the suite used for thermal history interpretation or to acquire additional data to help decipher the significance of the age distribution.     

Age and Thermal History of the East Ore Section,Bayan,Obo Deposit—A Fission Track Study

Considerable attention has been paid in recent years to the study of geothermal history by using spontaneous fission tracks of 238U recorded in minerals.Apatite and zircon were used for fission track study in this paper because apatitie has been widely used as a natural geothermometer(Wang Shicheng et al., 1994) to reveal the thermal evolution of sedimentary rocks based on its low annealing temperature of fission tracks and zircon is characterized by a closing temperature above 700℃,The samples were collected from ferruginous,siliceous slate wall rock at the upper levels of the orebody and Nb-REE-Fe ores from deep tunnels.The age and thermal evolution of the orebody were discussed in terms of fission track characters and their length variations observed in the coexisting apatite and zircon in the same specimen.     

裂变径迹法在研究造山带隆升过程中的应用介绍

介绍了４种类型的造山带隆升－冷却模式,不同模式对应不同的磷灰石裂变径年龄－－高程图特征;了不同构造造背景下的热历史特征一裂变径迹年龄序列。裂变径变宅遮挡同统计分布型式对应于不同的热历史,具有不同的年代学意义。     

Zircon and apatite fission-track thermochronology of Late Carboniferous volcanic rocks of the NE German Basin

Zircon and apatite fission-track analyses from Late Carboniferous felsic volcanic rocks of the NE German Basin (Halle area and Friedland drilling) reveal at least two major post-emplacement thermal events. After initial cooling at ca. 300 Ma, the volcanic pile underwent a major thermal event at ca. 200 Ma that reached in most places ca. 250-280 °C and led to the new growth of clay minerals. This event is recorded in the zircon fission-track data and can be related to Jurassic-Triassic rifting in Europe. Another thermal event is recorded in the apatite samples at ca. 100 Ma. A close correlation is observed between apatite fission-track age, texture, and sample alteration. Coarse-grained samples are stronger altered and have younger fission-track ages. Hydrothermal alteration coupled with advective heating probably caused these Upper Cretaceous fission-track ages. The latter event can be related to block faulting and inversion of the European plate during the early stages of the Alpine orogeny.     

中－新生代龙门山的差异隆升

通过对采自龙门山南段、中段和北段花岗岩与砂岩样品中的磷灰石、锆石的裂变径迹年龄的分析,发现中生代以来龙门山的隆升在走向上存在分段性,在近东西方向上存在分带性。从松潘－甘孜褶皱带→龙门山冲断带→川西前陆盆地：松潘－甘孜褶皱带整体发生区域隆升,裂变径迹年龄与高程呈正相关关系;在龙门山冲断带,裂变径迹年龄与高程呈负相关关系或无关,说明冲断层在隆升过程中起主导作用;在川西前陆盆地,样品随埋深发生部分或全部退火。茂县－汶川断裂两侧锆石裂变径迹年龄差异明显而磷灰石裂变径迹年龄无明显差异,显示茂县－汶川断裂以西地区在38～10 Ma发生过更为快速的隆升;北川断裂两侧磷灰石裂变径迹年龄差异明显,表明北川断裂以西地区在10～0 Ma发生过快速隆升。从走向上看,从龙门山北段向南段,锆石裂变径迹年龄呈逐渐增大的趋势,这可能意味着印支末期或燕山早期,龙门山北段发生了更快的隆升;而磷灰石裂变径迹年龄总体上从龙门山北段向中段和南段呈递减趋势,反映新生代期间龙门山中、南段隆升更快。     

Evaluating thermal history models for the Otway Basin, southeastern Australia, using (U-Th)/He and fission-track data from borehole apatites

New apatite helium and fission-track data from the Otway Basin are consistent with previously published borehole ages, confirming earlier suggestions that existing thermal models for basin evolution should be reevaluated. Analysis of the relationship between helium ages and grain size in newly analyzed samples, as well as in samples previously reported, reveals that grain size variations may contribute to the previously reported scatter in helium ages among aliquots of the same sample. In addition, systematic variations in apatite grain size with borehole depth or temperature may also have a significant effect on the interpretation of borehole helium age data. Incorporation of the observed grain size variations in Otway borehole apatites into forward models based on published thermal histories, principally based on vitrinite reflectance and fission-track data, suggests that existing models for the eastern Otway Basin are broadly consistent with the helium data. In contrast, thermal histories for western basin boreholes, now thought to be at maximum temperatures, predict helium ages that are generally older than the observed ages, implying that basin temperatures were hotter than indicated by the models. This discrepancy is consistent with a Cenozoic heating event in parts of the western Otway Basin similar to that documented for the eastern basin. The relatively wide spread of apparent apatite fission-track (AFT) ages and compositions compared to the restricted age range of helium measurements on coexisting grains, although not conclusive, supports previous suggestions that composition does not appear to affect the sensitivity of the He closure temperature in apatite.