米仓山-汉南隆起白垩纪以来的剥露作用：磷灰石(U-Th)/He年龄记录

对米仓山南江-南郑剖面上的13个花岗岩类样品进行了磷灰石(U-Th)/He测年和剥露速率计算,分析过程综合考虑了样品冷却速率、晶体大小等因素对磷灰石(U-Th)/He封闭温度的影响和地形起伏、岩体热传导、热对流及放射性元素生热等因素对地温场的影响.研究表明,米仓山南部沉积变形区自~50 Ma以来发生快速剥露 (剥露速率为~70 m/Ma),新生代以来的剥蚀量超过了3 km;中部光雾山杂岩体记录了~90 Ma时一次快速剥露事件(剥露速率>75 m/Ma);北部汉南隆起区~100 Ma以前以快速剥露为特点,平均剥露速率>40 m/Ma,此后转为缓慢剥露.整个米仓山-汉南隆起区在90~50 Ma基本处于缓慢剥露状态,平均剥露速率仅有10~25 m/Ma.     

河砂岩屑磷灰石裂变径迹模拟流域热史——以藏东南察隅河为例

河砂岩屑热年代学被广泛应用于揭示造山带和流域范围内热演化历史.由于受到地貌特征、剥蚀速率的空间分布、年龄与高程关系等多种因素的影响,河砂岩屑热年代学年龄所代表的意义存在多解性.本文提出了一种利用地貌形态特征和实测河砂热年代学数据模拟流域热史的计算模型.该模型首先利用DEM数据计算流域高程分布特征,通过数据中各象元对应的坡度角大小定量计算剥蚀速率的空间分布,以确定不同高程区域对河砂岩屑样品组分的贡献量.然后根据区域地质特征建立多种可能的热史年龄-高程关系,并模拟计算出与设定的年龄-高程关系相对应的河砂年龄概率分布曲线.最后,通过对模拟河砂年龄概率分布曲线与实测分布曲线的匹配度进行卡方检验,选取最可能形成实测河砂年龄分布的年龄-高程关系,即代表了流域真实的热史演化.通过河砂岩屑磷灰石裂变径迹方法将该模型应用于藏东南地区察隅河两条支流桑曲和贡日嘎布曲流域,模拟计算结果表明两个地区的热史演化均具有多阶段的特征,桑曲流域在38~7Ma之间均匀冷却,对应的剥露速率约为0.14km/Ma,7 Ma以来剥露速率加快,达到1.62km/Ma;贡日嘎布曲的热史年龄记录比桑曲新,18~14 Ma的隆升速率为0.32km/Ma,14~8 Ma比较稳定;8 Ma以来隆升速率逐渐加快,8~5 Ma对应的隆升速率为0.21km/Ma,5~3 Ma为0.43km/Ma,3~1.1 Ma为0.83km/Ma.桑曲的模拟计算结果与前人利用该区域基岩年龄数据所揭示的热史演化特征及剥露速率基本吻合,表明该方法可以准确模拟河砂岩屑年龄所代表的流域热史特征.因此,在地形险峻或者冰川覆盖而无法获取基岩样品的野外地区,可以通过采集河砂样品替代基岩剖面模拟地质体热史特征.     

大别山区域低温剥露作用: 基于(U-Th)/He和裂变径迹年代学数据的模拟

大别山高温剥露作用研究已相当成熟, 而白垩纪特别是晚白垩世以来的区域低温剥露研究还比较薄弱, 低温年代学即是解决这一问题的重要途径之一. 本文依据大别山现有岩浆岩与变质岩的磷灰石、锆石裂变径迹和(U-Th)/He数据, 综合考虑热传导、热对流、地形及放射性热产生等因素对地温场造成的影响, 应用Mancktelow法和Braun法, 系统地对整个区域的低温年代学测年结果进行剥露速率计算, 获得了大别山白垩纪以来尤其是晚白垩世以来的剥露速率等值线图以及区域差异剥露趋势. 大别山白垩纪以来天堂寨地区及郯庐断裂带南部剥露速率(0.08~ 0.10 km/Ma)大于大别山其他地区(0.04~0.07 km/Ma). 这种区域差异剥露可能与NNE向断裂系区域差异走滑引发的构造推隆作用有关.     

天山中新世早期快速剥露：磷灰石裂变径迹与（U-Th）／He低温热年代学证据

天山造山带新生代剥露过程与构造演化历史一直是国内外地学界关注的热点．本文联合运用磷灰石裂变径迹（AFT）和（u—Th）／He（AHe）低温热年代学技术,重建了新疆天山巴仑台剖面基岩山体的热演化历史,分析了剥露速率的变化特征,结合前人研究成果进一步探讨了新生代天山地区剥露作用过程的基本特点．结果表明,巴仑台剖面磷灰石样品的裂变径迹年龄集中在40～60Ma,（U—Th）／He年龄为10～40Ma;裂变径迹时间一温度史模拟结果表明巴仑台地区中新世早期以来剥露作用明显增速,剥露速率由之前的〈30mMa-1增大为〉1001TIMa-1;基于AFT与AHe年龄,利用年龄～封闭温度法以及矿物对法计算得到的剥露速率也表明该地区新生代剥露作用自中新世早期开始加速,并且在晚中新世剥露作用进一步增强．本文所揭示的快速剥露过程也存在于天山造山带其他地区．从整个天山造山带来看,开始于中新世早期的快速剥露是新生代天山地区一次重要的剥露作用过程．     

一种基于温度历史和瞬态地温场模拟的剥露历史反演方法

根据低温热年代学数据,提取岩石从深部剥露到地表的信息,对理解诸多地质问题(如造山带演化、地表过程及其相互作用等)具有重要意义.本文提出一种基于岩石温度历史(可利用古温标、热年代计等方法制约),并考虑剥露过程对地温场扰动的剥露历史反演计算方法.基于假定的与真实数据的正反演模拟和参数敏感性分析表明:热扩散率的变化对剥蚀量计算影响不大,在常规岩石热扩散率变化范围内(20～35km2/Ma),总剥蚀量变化小于10%;传统计算方法低估了剥蚀总量,对于现今地温梯度小于20℃/km、冷却速率大于2～3℃/Ma,或现今地温梯度大于30℃/km、冷却速率大于5～10℃/Ma的地区,需要考虑热平流对剥蚀量计算的影响;匀速冷却的热历史指示剥蚀速率持续减小,而非匀速剥蚀.本文将该方法应用到龙门山南段和四川盆地,反演计算显示龙门山南段15Ma以来的剥蚀总量为8km,四川盆地中部80Ma以来剥蚀总量约为3km、东部约5km.     

青藏高原东南缘大凉山新生代隆升建造过程——多封闭系统低温热年代学与热模型限制

长波长、低起伏度大凉山构造带新生代隆升剥露与建造过程是解译青藏高原东向扩展过程的关键核心地区之一.本文基于大凉山构造带喜德剖面和沐川剖面9件样品的多封闭系统低温热年代学年龄(即磷灰石(U-Th)/He(AHe)、磷灰石裂变径迹(AFT)和锆石(U-Th)/He(ZHe))定年,揭示出多封闭系统热年代学年龄与古岩性柱深度具有明显的正相关性,即伴随古岩性柱深度增大,多封闭系统热年代学年龄明显减小.喜徳剖面多封闭系统低温热年代学AHe、AFT和ZHe年龄值分别为7—9Ma、14—22Ma和25—38Ma;沐川剖面多封闭系统低温热年代学AHe和AFT年龄值分别为10—26Ma、23—85Ma,ZHe年龄值为未完全退火年龄.多封闭系统热年代学和QTQt热史模拟揭示,大凉山构造带喜徳和沐川剖面岩性柱所有样品都经历大致相似的三阶段热演化过程,尤其是晚新生代快速隆升剥露阶段(30—20 Ma以来),其平均剥露速率分别为~0.15mm·a-1和~0.20mm·a-1,抬升剥露量分别为~3.0km和~1.5km.结合区域低温热年代学特征的大凉山构造带地表隆升动力学模型,揭示出重力均衡作用下地壳缩短与剥露作用(即构造隆升剥露机制)控制形成了现今大凉山造山带长波长、低起伏和高海拔地貌建造过程.     

四川盆地南部地区新生代隆升剥露研究——低温热年代学证据

本文通过背斜褶皱变形与低温热年代学年龄(磷灰石和锆石(U-Th)/He、磷灰石裂变径迹)端元模型研究,约束低起伏度、低斜率地貌特征的四川盆地南部地区新生代隆升剥露过程.四川盆地南部沐川和桑木场背斜地区新生代渐新世-中新世发生了相似的快速隆升剥露过程(速率为~0.1 mm/a、现今地表剥蚀厚度1.0~2.0 km),反映出盆地克拉通基底对区域均一性快速抬升冷却过程的控制作用.川南沐川地区磷灰石(U-Th)/He年龄值为~10-28.6 Ma, 样品年龄与古深度具有明显的线性关系,揭示新生代~10-30 Ma以速率为0.12±0.02 mm/a的稳态隆升剥露过程.桑木场背斜地区磷灰石裂变径迹年龄为~36-52 Ma,古深度空间上样品AFT年龄变化不明显(~50 Ma)、且具有相似的径迹长度(~12.0 μm).磷灰石裂变径迹热演化史模拟表明桑木场地区经历三个阶段热演化过程:埋深增温阶段(~80 Ma以前)、缓慢抬升冷却阶段(80-20 Ma)和快速隆升剥露阶段(~20 Ma-现今),新生代隆升剥露速率大致分别为~0.025 mm/a和~0.1 mm/a.新生代青藏高原大规模地壳物质东向运动与四川盆地克拉通基底挤压,受板缘边界主断裂带差异性构造特征控制造就了青藏高原东缘不同的边界地貌特征.     

(U-Th)/He年龄约束下的塔里木盆地早古生代构造-热演化

塔里木盆地早古生代碳酸盐岩沉积时期的热历史由于缺乏有效的古温标进行热史恢复,一直是困扰该区下古生界烃源岩演化研究的难题.磷灰石和锆石的(U-Th)/He热定年技术是近年来用于沉积盆地热史研究的新技术,可以用来揭示地层的构造抬升和热历史.本文利用塔里木盆地典型井中古生界层系的古温标来恢复古生代的热史.这些井在海西期长期隆升、遭受强烈的剥蚀、后期埋藏深度较小,因而古生界层系中的古温标可以保留原始热信息,从而反映古生代的温度状况.本文通过对这些钻井样品进行磷灰石和锆石(U-Th)/He年龄测试,并结合磷灰石裂变径迹和等效镜质体反射率等古温标,综合模拟计算了塔里木盆地不同构造单元的KQ1和T1井早古生代的构造-热演化历史.模拟结果表明,塔里木盆地塔东北和巴楚隆起区古生代热演化存在差异.巴楚隆起区T1井在寒武纪末期的古地温梯度仅为28～30℃/km,奥陶纪的地温梯度增高至30～33℃/km之间,志留-泥盆纪地温梯度为31～34℃/km;塔东北的KQ1井区奥陶纪的地温梯度可达35℃/km,志留-泥盆纪地温梯度为32～35℃/km.因此,(U-Th)/He年龄结合其他古温标综合模拟的方法可以很好地揭示沉积盆地的热历史,特别是该方法为塔里木盆地早古生代的热史恢复提供了新的途径.     

日喀则弧前盆地的埋藏和剥蚀历史——来自低温热年代学的约束

日喀则弧前盆地紧邻印度板块与欧亚大陆碰撞带,研究其剥蚀历史对理解印度板块与欧亚大陆碰撞对造山带剥蚀的影响具有重要意义。文中利用磷灰石裂变径迹(AFT)及锆石和磷灰石的(U-Th)/He(ZHe和AHe)年龄数据,结合已发表的低温热年代数据探讨日喀则弧前盆地的热演化和剥露历史。日喀则弧前盆地磷灰石裂变径迹年龄存在明显的南北差异,南部磷灰石裂变径迹年龄为74～44Ma,对应的剥蚀速率为0. 03～0. 1km/Ma,剥蚀量≤2km;北部磷灰石裂变径迹年龄为27～15Ma,剥蚀速率为0. 09～0. 29km/Ma,但缺失早新生代的热演化历史。而磷灰石的(U-Th)/He年龄表明15Ma BP之后日喀则弧前盆地整体呈现一致的剥露历史。低温热年代数据表明日喀则弧前盆地南部自新生代以来尽管受到印度板块与欧亚大陆碰撞及后期断层活动的影响,海拔由海平面抬升至4. 2km,但一直保持缓慢的剥蚀,表明高原隆升并未直接促使该地区的岩石剥蚀速率加快,这与快速剥蚀即代表造山带开始隆升的假设不相符。此外,日喀则弧前盆地北部的低温热年代学研究表明晚渐新世—早中新世Kailas盆地仅发育于日喀则弧前盆地与冈底斯造山带之间的狭长地带,并在短期内经历了快速的埋藏和剥露。     

(U-Th)/He年龄在沉积盆地构造—热演化研究中的应用——以塔里木盆地KQ1井为例

(U-Th)/He热定年技术是近年来用于沉积盆地热史研究的新技术,目前主要是利用磷灰石和锆石的He年龄来揭示地层的构造抬升和热历史.本文依据塔里木盆地钻井样品的实测磷灰石和锆石(U-Th)/He年龄数据,初步得出了该地区磷灰石(U-Th)/He年龄的封闭温度为85℃,并建立了深度/温度－年龄演化模式;锆石则未达到其较高的封闭温度.综合利用本次实测的He年龄数据结合磷灰石裂变径迹和等效镜质组反射率等古温标,模拟计算了塔里木盆地孔雀1井（KQ1）自奥陶纪末期以来的热历史.模拟结果表明,孔雀1井区奥陶纪末期的地温梯度可达35.5℃/km,志留纪—泥盆纪时期的地温梯度为33.3～34.5℃/km,白垩纪末期地温梯度27.6℃/km左右.因此,(U-Th)/He年龄结合其他古温标综合模拟的方法可以很好地揭示沉积盆地的热历史.特别是该技术为缺乏常规古温标的塔里木盆地下古生界碳酸盐岩层系所经受热史的恢复提供了新的方法.     

Late Cretaceous-Cenozoic exhumation of the Yanji area, northeast China: Constraints from fission-track thermochronology

The Yanji area, located at the border of China, Russia, and Korea, where the Phanerozoic granitoids have been widely exposed, was considered part of the orogenic collage between the North China Block in the south and the Jiamusi–Khanka Massifs in the northeast. In this study, the cooling and inferred uplift and denudation history since the late Mesozoic are intensively studied by carrying out apatite and zircon fission-track analyses, together with electron microprobe analyses (EMPA) of chemical compositions of apatite from the granitoid samples in the Yanji area. The results show that: (i) zircon and apatite fission-track ages range 91.7–99.6 Ma and 76.5–85.4 Ma, respectively; (ii) all apatite fission-track length distributions are unimodal and yield mean lengths of 12–13.2 µm, and the apatites are attributed to chlorine-bearing fluorapatite as revealed by EMPA results; and (iii) the thermal history modeling results based on apatite fission-track grain ages and length distributions indicate that the time–temperature paths display similar patterns and the cooling has been accelerated for each sample since ca 15 Ma. Thus, we conclude that sequential cooling, involving two rapid (95–80 Ma and ca 15–0 Ma) and one slow (80–15 Ma) cooling, has taken place through the exhumation of the Yanji area since the late Cretaceous. The maximum exhumation is more than 5 km under a steady-state geothermal gradient of 35°C/km. Combined with the tectonic setting, this exhumation is possibly related to the subduction of the Pacific Plate beneath the Eurasian Plate since the late Cretaceous.     

Rapid cooling and geospeedometry of granitic rocks exhumation within a volcanic arc: A case study from the Central Slovakian Neovolcanic Field (Western Carpathians)

U–Pb Sensitive High‐Resolution Ion MicroProbe (SHRIMP) dating of zircon in combination with (U–Th)/He dating of zircon and apatite is applied to constrain the emplacement and exhumation history of the youngest granitic rocks in the Western Carpathians collected in the Central Slovakian Neovolcanic Field. Two samples of diorite from the locality Banky, and granodiorite from Banská Hodru?a yield the U–Pb zircon concordia ages of 15.21 ±0.19 Ma and 12.92 ±0.27 Ma, respectively, recording the time of zircon crystallization and the intrusions’ emplacement. Zircon (U–Th)/He ages of 14.70 ±0.94 (Banky) and 12.65 ±0.61 Ma (Banská Hodru?a), and apatite (U–Th)/He ages of 14.45 ±0.70 Ma (diorite) and 12.26 ±0.77 Ma (granodiorite) are less than 1 Myr younger than the corresponding zircon U–Pb ages. For both diorite and granodiorite rocks their chronological data thus document a simple cooling process from magmatic crystallization/solidification temperatures to near‐surface temperatures in the Middle Miocene, without subsequent reheating. Geospeedometry data suggest for rapid cooling at an average rate of 678 ±158 °C/Myr, and the exhumation rate of 5 mm/year corresponding to active tectonic‐forced exhumation. The quick cooling is interpreted to record the exhumation of the studied granitic rocks complex that closely followed its emplacement, and was likely accompanied by a drop in the paleo‐geothermal gradient due to cessation of volcanic activity in the area.     

Quantifying the effect of recent relief changes on age–elevation relationships

The effect that recent relief changes may have on the distribution of rock ages with elevation is investigated for a range of thermochronometers. From the solution of the heat transport equation in a crustal block undergoing uplift and surface erosion, the temperature history of rock particles that are exhumed at the Earth’s surface today is computed. These T-t paths are then used to calculate apparent isotopic ages for the (U–Th)/He system in apatite, characterized by a low (≈70°C) closure temperature. The results show that recent relief changes strongly affect the distribution of ages with elevation (notably the slope of the age–elevation relationship). The calculations presented here predict that, in most situations, regions that have undergone a steady decrease in surface relief in the recent past should be characterized by an inverted age–elevation relationship, that is older ages should be found near valley bottoms and younger ages near summit tops. It is also shown how the wavelength of the topography, the geothermal gradient, the exhumation rate and the duration of the relief reduction event affect this result.     

Uplift history and structure of the Transantarctic Mountains: new evidence from fission track dating of basement apatites in the Dry Valleys area, southern Victoria Land

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.     

Exhumation history of the Jiaodong and its adjacent areas since the Late Cretaceous:Constraints from low temperature thermochronology

The thermal history of the Jiaodong region and adjacent provinces(Shandong and northern Jiangsu) have been extensively studied,particularly by apatite fission track(AFT) dating.However,the AFT ages from surface outcrops range broadly and do not show an apparent relationship between age and elevation.This work provides a multiple low temperature thermochronological dataset including zircon and apatite(U-Th)/He ages(ZHe and AHe),and AFT ages from a 1000-m-deep borehole at the Jiaojia goldneld in the northwest of Jiaodong Peninsula.ZHe,AFT and AHe ages range from-100-70,-85-50and-65-50 Ma,respectively.These data conform to the principles of age vs.closure temperature and age vs.elevation and thus can be employed to estimate the exhumation history.Based on the density histogram of fission track length calculation,thermal history modeling,and previously published AFT ages from the Chinese Continental Science Drill program,this work concludes that compared to the AFT ages from surface outcrops,the low temperature thermochronological ages from the boreholes show a better relationship between age,elevation and closure temperature,and the age becomes younger with increasing depth.In addition,the exhumation history in the Jiaodong and adjacent areas can be divided into two distinct stages:a short,rapid tectonic exhumation(~100-95 Ma) and a long,slow exhumation since 95 Ma.The rate and amount of tectonic exhumation since 95 Ma are inferred as ~30 m Ma~(-1) and ~3 km,respectively.     

Late Miocene to present-day exhumation and uplift of the Internal Zone of the Rif chain: Insights from low temperature thermochronometry and basin analysis

Located on the margin of the west Alboran basin, the Gibraltar Arc (Betic-Rif mountain belt) displays post-Pliocene vertical movements evidenced by uplifted marine sedimentary basins and marine terraces. Quantification of vertical movements is an important clue to understand the origin of present-day relief generation in the Betic-Rif mountain chain together with the causes of the Messinian Salinity Crisis. In this paper, we present the results of a pluridisciplinary study combining an analysis of low temperature thermochronology and Pliocene basins evolution to constrain the exhumation history and surface uplift of internals units of the Rif belt (Northern Morocco). The mean (U-Th)/He apatite ages obtained from 11 samples are comprised between 14.1 and 17.8 Ma and display a wide dispersion, which could be explained by a great variability of apatite chemistries in the analyzed samples. No correlations between altitude and age have been found along altitudinal profile suggesting a rapid exhumation during this period. Thermal modeling using our (U-Th)/He apatite ages and geochronological data previously obtained in the same area (⁴⁰Ar/³⁹Ar and K/Ar data on biotite, zircon and apatite fission track) allow us to propose a cooling history. The rocks suffered a rapid cooling at 60–100 °C/Ma between 22.5 and 19 Ma, then cooled to temperatures around 40 °C between 19 and 18 Ma. They were re-heated at around 110 °C between 18 and 15 Ma then rapidly cooled and exhumed to reach the surface temperature at around 13 Ma. The re-heating could be related to a renewal in thrusting and burying of the inner zones. Between 15 and 13 Ma the cooling resumed at a rate of 50 °C/Ma indicating an exhumation rate of 0.8 mm/y considering an average 40 °C/km geothermal gradient. This exhumation may be linked to the extension in the Alboran Sea. Otherwise biostratigraphic and sedimentological analysis of Pliocene basins of the internal Rif provided informations on the more recent events and vertical movements. Pliocene deposits of the Rifian coast represent the passive infilling of palaeo-rias between 5.33 and 3.8 Ma. The whole coastal area was uplifted at slow average rates (0.01–0.03 mm/y) in relation with a northeastward tilting of 0.2–0.3° since the Lower-Pliocene. A late Pliocene to present extensional tectonics associated to uplift has been identified all along the coastal ranges of the Internal Zone of the Rif chain. This extension was coeval with the major late Pliocene to Pleistocene extensional episode of the Alboran Sea and appears to be still active nowadays. No significant late Messinian uplift was evidenced, thus calling into question the geodynamic models relating the closure of the marine gateways and the MSC to slab roll back.     

BURIAL AND EXHUMATION OF THE XIGAZE FORE-ARC BASIN FROM LOW TEMPERATURE THERMOCHRONOLOGICAL EVIDENCE

The Xigaze fore-arc basin is adjacent to the Indian plate and Eurasia collision zone. Understanding the erosion history of the Xigaze fore-arc basin is significant for realizing the impact of the orogenic belt due to the collision between the Indian plate and the Eurasian plate. The different uplift patterns of the plateau will form different denudation characteristics. If all part of Tibet Plateau uplifted at the same time, the erosion rate of exterior Tibet Plateau will be much larger than the interior plateau due to the active tectonic action, relief, and outflow system at the edge. If the plateau grows from the inside to the outside or from the north to south sides, the strong erosion zone will gradually change along the tectonic active zone that expands to the outward, north, or south sides. Therefore, the different uplift patterns are likely to retain corresponding evidence on the erosion information. The Xigaze fore-arc basin is adjacent to the Yarlung Zangbo suture zone. Its burial, deformation and erosion history during or after the collision between the Indian plate and Eurasia are very important to understand the influence of plateau uplift on erosion. In this study, we use the apatite fission track(AFT)ages and zircon and apatite(U-Th)/He(ZHe and AHe)ages, combined with the published low-temperature thermochronological age to explore the thermal evolution process of the Xigaze fore-arc basin. The samples' elevation is in the range of 3 860~4 070m. All zircon and apatite samples were dated by the external detector method, using low~U mica sheets as external detectors for fission track ages. A Zeiss Axioskop microscope(1 250×, dry)and FT Stage 4.04 system at the Fission Track Laboratory of the University of Waikato in New Zealand were used to carry out fission track counting. We crushed our samples finely, and then used standard heavy liquid and magnetic separation with additional handpicking methods to select zircon and apatite grains. The new results show that the ZHe age of the sample M7-01 is(27.06±2.55)Ma(Table 2), and the corresponding AHe age is(9.25±0.76)Ma. The ZHe and AHe ages are significantly smaller than the stratigraphic age, indicating suffering from annealing reset(Table 3). The fission apatite fission track ages are between(74.1±7.8)Ma and(18.7±2.9)Ma, which are less than the corresponding stratigraphic age. The maximum AFT age is(74.1±7.8)Ma, and the minimum AFT age is(18.7±2.9)Ma. There is a significant north~south difference in the apatite fission track ages of the Xigaze fore-arc basin. The apatite fission track ages of the south part are 74~44Ma, the corresponding exhumation rate is 0.03~0.1km/Ma, and the denudation is less than 2km; the apatite fission track ages of the north part range from 27 to 15Ma and the ablation rate is 0.09~0.29km/Ma, but it lacks the exhumation information of the early Cenozoic. The apatite(U-Th)/He age indicates that the north~south Xigaze fore-arc basin has a consistent exhumation history after 15Ma. The results of low temperature thermochronology show that exhumation histories are different between the northern and southern Xigaze fore-arc basin. From 70 to 60Ma, the southern Xigaze fore-arc basin has been maintained in the depth of 0~6km in the near surface, and has not been eroded or buried beyond this depth. The denudation is less than the north. The low-temperature thermochronological data of the northern part only record the exhumation history after 30Ma because of the young low-temperature thermochronological data. During early Early Miocene, the rapid erosion in the northern part of Xigaze fore-arc basin may be related to the river incision of the paleo-Yarlungzangbo River. The impact of Great Count Thrust on regional erosion is limited. The AHe data shows that the exhumation history of the north-south Xigaze fore-arc basin are consistent after 15Ma. In addition, the low-temperature thermochronological data of the northern Xigaze fore-arc basin constrains geographic range of the Kailas conglomerate during the late Oligocene~Miocene along the Yarlung Zangbo suture zone. The Kailas Basin only develops in the narrow, elongated zone between the fore-arc basin and the Gangdese orogenic belt. The southern part of the Xigaze fore-arc basin has been uplifted from the sea level to the plateau at an altitude of 4.2km, despite the collision of the Indian plate with the Eurasian continent and the late fault activity, but the plateau has been slowly denuded since the early Cenozoic. The rise did not directly contribute to the accelerated erosion in the area, which is inconsistent with the assumption that rapid erosion means that the orogenic belt begins to rise.     

球面圆弧数字地形剖面提取方法研究

带状地形剖面是以高程为纵向参考,以距剖面起始端点的距离为横向参考进行制图表达。由于其可真实地反映地表形态,是新构造和活动构造地貌研究中的基本参考和研究对象。随着数字化基础地理信息成果的普及,很多GIS软件可实现地形剖面的自动化提取。但以往方法的位置信息均是建立在剖面投影平面的基础上,当研究区域范围过大,会引入非构造变形,为消除该影响,提出基于球面坐标系统的带状地形剖面图制作方法。该方法不仅适用于小型地质构造,也适用于喜马拉雅弧形造山带等大型地质构造,可提取出更接近真实地形的地形剖面。