Combining Thermochronology and Geochronology to Constrains Orogenic Processes in the Alps and Tibet

Deciphering the kinematics of deformation is key to understand the crustal evolution.In the last decades several techniques have been developed to help constraining the timing of deformation.On one side geochronology techniques allow the dating of a wider range of minerals with higher spatial resolution.On the other side thermochronology,with the help of numerical simulations(PeCube,QTQt…),help to constrain the rock exhumation history that is often linked to the vertical component of deformation.In both cases the deformation timing can accurately be discussed only together with a serious structural analysis.

Reconstruction of the thermal evolution since the late paleozoic in the Ounan Sag, Eastern Qaidam Basin, NW China: New constraints from vitrinite reflectance data and(U-Th)/He thermochronology

Reconstructing the thermal evolution of the eastern Qaidam Basin is important for gaining a deeper understanding of its lithospheric geodynamics and for more accurate hydrocarbon evaluation and prediction. This article presents a set of new apatite and zircon(U-Th)/He thermochronological ages.Combined with 336 vitrinite reflectance(R_(o)) data, the thermal history of the Ouanan Sag in the eastern Qaidam Basin has been reconstructed using inversion models. Three detrital samples from the Ounan Sag shows that the apatite(U-Th)/He ages are primarily concentrated in the range of 17.0 Ma to 76.5 Ma and that the zircon(U-Th)/He ages range from 200 Ma to 289.3 Ma. The time-temperature models demonstrate that the Ounan Sag experienced rapid subsidence and heating from the Carboniferous to late Permian, and exhumation/cooling events from the end of Permian to the Triassic. This thermal evolution was influenced by the widespread intrusion of plutons, and the collision and orogenesis caused by asthenosphere upwelling below the Qaidam arc, and slab rollback of the Southern Kunlun oceanic lithosphere, respectively. Additionally, our models depict the main exhumation/cooling stages since the Paleogene and a reheating event in the Miocene as a result of the intensifying growth of the Qinghai-Tibet Plateau and local sedimentary loading, followed by the initial India-Eurasia collision. Furthermore, the eastern Qaidam Basin experienced consistent heating during the late Paleozoic, reaching the maximum paleotemperature and geothermal gradient in the late Permian, with values of ~230℃ and~43-44℃/km, respectively. This study suggests that the source rocks in the most upper member of upper Carboniferous Keluke(C_(2)k) Formations in the Ounan Sag reached the gas generation stage in the late Permian.

从中亚岩石冷却的时空差异性浅析天山中新生代隆升剥露的动力来源

本文基于系统收集的天山及北部中亚区域磷灰石裂变径迹年龄、U-Th/He年龄和裂变径迹长度数据,通过频度分析和年龄分阶段插值分析,综合刻画了天山和中亚地区中新生代的岩石快速冷却事件的时空差异。结合不同阶段不同区域构造变形的表现,探讨了天山地区不同阶段不同区段岩石快速冷却事件与不同板块边界动力之间的联系。结果显示,天山地区主要经历了晚三叠世、晚侏罗世—早白垩世、晚白垩世—古新世、新生代中晚期4次快速冷却事件。晚三叠世的快速冷却主要分布于天山西段,反映逆冲断层活动引起的岩石抬升剥露,受控于西部图兰(Turan)地体与古亚洲大陆的碰撞。晚侏罗世—早白垩世的快速冷却主要分布于西部的吉尔吉斯天山和东部的东天山地区,均表现为逆冲断层活动引起的岩石抬升剥露。其中西部吉尔吉斯天山的逆冲抬升主要受控于南部的拉萨地体与古亚洲大陆碰撞的远程效应,而东天山主要受控于北部蒙古—鄂霍茨克洋主体闭合的远程效应。晚白垩世—古新世的快速冷却主要为沿大型断裂分布的热冷却事件。其中,西部吉尔吉斯天山、中国西天山和东部东天山南部的觉罗塔格地区,断裂活动引发的快速冷却事件主要发生在晚白垩世晚期—古新世,受控于Kohistan-Dras等岛弧的增生拼贴和最后的印度与欧亚大陆的碰撞,而东天山北部哈尔里克山,右旋转换伸展断裂导致的快速热冷却事件主要发生在相对较早的晚白垩世中期,与北部蒙古—鄂霍茨克造山带后碰撞伸展塌陷事件同步。新生代中晚期的快速冷却主要表现在帕米尔及其以北的天山西段,反映为印度与欧亚板块碰撞后高原崛起向北扩展导致的陆内强烈挤压的远程效应。总之,天山造山带不同区段中新生代不同阶段的岩石快速冷却事件是南部特提斯构造域多块体碰撞和北部蒙古—鄂霍茨克构造域洋盆闭合以及其后的后碰撞伸展塌陷等板块边界动力远程效应综合影响的结果。

Exhuming the Meso-Cenozoic Kyrgyz Tianshan and Siberian Altai-Sayan:A review based on low-temperature thermochronology

Thermochronological datasets for the Kyrgyz Tianshan and Siberian Altai-Sayan within Central Asia reveal a punctuated exhumation history during the Meso-Cenozoic. In this paper, the datasets for both regions are collectively reviewed in order to speculate on the links between the Meso-Cenozoic exhumation of the continental Eurasian interior and the prevailing tectonic processes at the plate margins. Whereas most of the thermochronological data across both regions document late Jurassic -Cretaceous regional basement cooling, older landscape relics and dissecting fault zones throughout both regions preserve Triassic and Cenozoic events of rapid cooling, respectively. Triassic cooling is thought to reflect the Qiangtang-Eurasia collision and/or rifting/subsidence in the West Siberian basin. Alternatively, this cooling signal could be related with the terminal terrane-amalgamation of the Central Asian Orogenic Belt. For the Kygyz Tianshan, late Jurassic-Cretaceous regional exhumation and Cenozoic fault reactivations can be linked with specific tectonic events during the closure of the Palaeo-Tethys and Neo-Tethys Oceans, respectively. The effect of the progressive consumption of these oceans and the associated collisions of Cimmeria and India with Eurasia probably only had a minor effect on the exhumation of the Siberian Altai-Sayan. More likely, tectonic forces from the east （present-day co- ordinates） as a result of the building and collapse of the Mongol-Okhotsk orogen and rifting in the Baikal region shaped the current Siberian Altai-Sayan topography. Although many of these hypothesised links need to be tested further, they allow a first-order insight into the dynamic response and the stress propagation pathways from the Eurasian margin into the continental interior.

Latest Triassic to Early Jurassic Thrusting and Exhumation in the Southern Ordos Basin, North China: Evidence from LA-ICP-MS-based Apatite Fission Track Thermochronology

The contractional structures in the southern Ordos Basin recorded critical evidence for the interaction between Ordos Basin and Qinling Orogenic Collage. In this study, we performed apatite fission track （AFT） thermochronology to unravel the timing of thrusting and exhumation for the Laolongshan-Shengrenqiao Fault （LSF） in the southern Ordos Basin. The AFT ages from opposite sides of the LSF reveal a significant latest Triassic to Early Jurassic time-temperature discontinuity across this structure. Thermal modeling reveals at the latest Triassic to Early Jurassic, a ~50~C difference in temperature between opposite sides of the LSF currently exposed at the surface. This discontinuity is best interpreted by an episode of thrusting and exhumation of the LSF with -1.7 km of net vertical displacement during the latest Triassic to Early Jurassic. These results, when combined with earlier thermochronological studies, stratigraphic contact relationship and tectono-sedimentary evolution, suggest that the southern Ordos Basin experienced coeval intense tectonic contraction and developed a north-vergent fold-and-thrust belt. Moreover, the southern Ordos Basin experienced a multi-stage differential exhumation during Mesozoic, including the latest Triassic to Early Jurassic and Late Jurassic to earliest Cretaceous thrust-driven exhumation as well as the Late Cretaceous overall exhumation. Specifically, the two thrust-driven exhumation events were related to tectonic stress propagation derived from the latest Triassic to Early Jurassic continued compression from Qinling Orogenic Collage and the Late Jurassic to earliest Cretaceous intracontinental orogeny of QinUng Orogenic Collage, respectively. By contrast, the Late Cretaceous overall exhumation event was related to the collision of an exotic terrain with the eastern margin of continental China at -100 Ma.

Meso-Cenozoic Tectonothermal History of Permian Strata, Southwestern Weibei Uplift: Insights from Thermochronology and Geothermometry

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℃,~196℃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℃to^53℃and a cooling rate of^3℃/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℃to^47℃and a cooling rate less than^0.1℃/Ma,an erosion thickness of^300 m and an uplift rate of^3 m/Ma;(3)(~52 Ma to^8 Ma)with^47℃to^43℃and^0.1℃/Ma,an erosion thickness of^500 m and an uplift rate of^11 m/Ma;(3)(~8 Ma to present)with^43℃to^20℃and^3℃/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.

A Compilation of New and Existing Thermochronology Data Concerning the Lhasa Terrane Combined with a Geological Synthesis of the Area

The history and geodynamic mechanisms of Cenozoic exhumation and denudation of the Lhasa terrane(LT),southern Tibetan Plateau, remain poorly constrained. Most previous studies investigating the exhumation of the LT have relied on extrapolating interpretations based on a few well-studied but small areas, which inevitably introduce bias. Here,our compilation of new and published thermochronologic ages are plotted against latitude, longitude, and elevation, to illustrate the distribution of cooling ages across broad regions of the LT. Primary results reveal that(1) the north LT experienced significant exhumation during 80–40 Ma;(2) compared with north LT, exhumation and erosion in the south LT continued after ~40 Ma;and(3) N–S striking rifting, E–W striking river incision, and thrusts led to continued local denudation of the south LT between 20–5 Ma.

Thermo-tectonic history of the Junggar Alatau within the Central Asian Orogenic Belt(SE Kazakhstan,NW China):Insights from integrated apatite U/Pb,fission track and(U-Th)/He thermochronology

The Junggar Alatau forms the northern extent of the Tian Shan within the Central Asian Orogenic Belt(CAOB)at the border of SE Kazakhstan and NW China.This study presents the Palaeozoic-Mesozoic post-collisional thermo-tectonic history of this frontier locality using an integrated approach based on three apatite geo-/thermochronometers:apatite U-Pb,fission track and(U-Th)/He.The apatite U-Pb dates record Carboniferous-Permian post-magmatic cooling ages for the sampled granitoids,reflecting the progressive closure of the Palaeo-Asian Ocean.The apatite fission track(AFT)data record(partial)preservation of the late Palaeozoic cooling ages,supplemented by limited evidence for Late Triassic(~230-210 Ma)cooling and a more prominent record of(late)Early Cretaceous(~150-110 Ma)cooling.The apatite(U-Th)/He age results are consistent with the(late)Early Cretaceous AFT data,revealing a period of fast cooling at that time in resulting thermal history models.This Cretaceous rapid cooling signal is only observed for samples taken along the major NW-SE orientated shear zone that dissects the study area(the Central Kazakhstan Fault Zone),while Permian and Triassic cooling signals are preserved in low-relief areas,distal to this structure.This distinct geographical trend with respect to the shear zone,suggests that fault reactivation triggered the Cretaceous rapid cooling,which can be linked to a phase of slab-rollback and associated extension in the distant Tethys Ocean.Similar conclusions were drawn for thermochronology studies along other major NW-SE orientated shear zones in the Central Asian Orogenic Belt,suggesting a regional phase of Cretaceous exhumation in response to fault reactivation at that time.

Post-Triassic thermal history of the Tazhong Uplift Zone in the Tarim Basin, Northwest China: Evidence from apatite fssion-track thermochronology

The Tarim Basin is a representative example of the basins developed in the northwest China that are characterized by multiple stages of heating and cooling.In order to better understand its complex thermal history,apatite fission track （AFT） thermochronology was applied to borehole samples from the Tazhong Uplift Zone （TUZ）.Twelve sedimentary samples of Silurian to Triassic depositional ages were analyzed from depths coinciding with the apatite partial annealing zone （～60-120 ℃）.The AFT ages,ranging from 132 ± 7 Ma （from a Triassic sample） to 25 ± 2 Ma （from a Carboniferous sample）,are clearly younger than their depositional ages and demonstrate a total resetting of the AFT thermometer after deposition.The AFT ages vary among different tectonic belts and decrease from the No.Ten Faulted Zone （133-105 Ma） in the northwest,the Central Horst Zone in the middle （108-37 Ma）,to the East Buried Hill Zone in the south （51 25 Ma）.Given the low magnitude of post-Triassic burial heating evidenced by low vitrinite reflectance values （Ro ＜ 0.7％）,the total resetting of the AFT system is speculated to result from the hot fluid flow along the faults.Thermal effects along the faults are well documented by younger AFT ages and unimodal single grain age distributions in the vicinity of the faults.Permian-early Triassic basaltic volcanism may be responsible for the early Triassic total annealing of those samples lacking connectivity with the fault.The above arguments are supported by thermal modeling results.

Cenozoic Exhumation of Larsemann Hills,East Antarctica:Evidence from Apatite Fission-track Thermochronology

Does Cenozoic exhumation occur in the Larsemann Hills, East Antarctica？ In the present paper, we conducted an apatite fission-track thermochronologic study across the Larsemann Hills of East Antarctica. Our work reveals a Cenozoic exhumation event at 49.8 ± 12 Ma, which we interpret to be a result of exhumation caused by crustal extension. Within the uncertainty of our age determination, the timing of extension in East Antarctica determined by our study is coeval with the onset time of rifting in West Antarctica at c.55 Ma. The apatite fission-track cooling ages vary systematically in space, indicating a coherent block rotation of the Larsemann Hills region from c.50 Ma to c.10 Ma. This pattern of block tilting was locally disrupted by normal faulting along the Larsemann Hills detachment fault at c.5.4 Ma. The regional extension in the Larsemann Hills, East Antarctica was the result of tectonic evolution in this area, and may be related to the global extension. Through the discussion of Pan-Gondwanaland movement, and Mesozoic and Cenozoic extensions in West and East Antarctica and adjacent areas, we suggest that the protracted Cenozoic cooling over the Larsemann Hills area was caused by extensional tectonics related to separation and formation of the India Ocean at the time of Gondwanaland breakup.

Study on Late Cretaceous-Cenozoic exhumation of the Yanji area,NE China: insights from low-temperature thermochronology

The Yanji area,northeastern China,a part of the orogenic collage between the North China Block in the south and the Jiamusi-Khanka Massifs in the northeast,is the most likely location where the Pacific Plate subduction・related magmatic activities and subsequent exhumation processes occurred.Here,we report new low-temperature thermochronology of apatite and zircon data from the granitoid samples in the Yanji area.The exhumation rates of Tianfozhishan,Yanji area,were〜0.049 and〜0.073 mm/year,interpreted from the elevations and apatite and zircon fission track ages,respectively.The exhumation,integrated with the geological setting,suggested that the paleogeothermal gradient of the Tianfozhishan,even extending to the Yanji area,was possibly to be greater than 35℃/km in the Late Cretaceous.The thermal history modeling of the data indicates a basically similar pattern,but the various timing for different samples between the Oligocene-Early Miocene and the Middle Miocene in the Yanji area.We hence conclude that a fourstages of cooling,from〜6.7℃/Ma(during the Late Cretaceous),to〜0.8℃/Ma(during the Late Cretaceous to the Oligocene-Early Miocene),then to〜2-3℃/Ma with varied styles(between the Oligocene-Early Miocene and the Middle Miocene),and finally to<0.2℃/Ma(since the Middle Miocene),has taken place through the exhumation of the Yanji area.The maximum exhumation is>3 km under a reasonable paleogeothermal gradient(>35℃/km),speculated from the possible exhumation rate of Tianfozhishan.Combined with the tectonic setting,this exhumation,including two stages of pronounced tectonic uplift and denudation and two stages of weak exhumation driven by the low regional erosion rate,is possibly related to the subduction of the Pacific Plate beneath the Eurasian Plate since the Late Cretaceous.This study used more robust evidence to propose higher paleogeothermal gradient(>35℃/km),reflecting exhumation of>3 km in the Yanji area since the Late Cretaceous.

Apatite fission track and (U-Th)/He thermochronology from the Archean Tanzania Craton: Contributions to cooling histories of Tanzanian basement rocks

Borehole and surface samples from the Archean Tanzania Craton were analysed for apatite fission track(AFT) and(U-Th)/He data with the aim of deciphering cooling histories of the basement rocks. Fission track dates from borehole and outcrop samples are Carboniferous-Permian(345± 33.3 Ma to271±31.7 Ma) whereas(U-Th)/He dates are Carboniferous-Triassic(336±45.8 Ma to 213±29 Ma) for outcrop grains and are consistently younger than corresponding AFT dates. Single grain(U-Th)/He dates from the borehole are likely to be flawed by excessive helium implantation due to their very low effective uranium contents, radiation damage and grain sizes. All AFT and(U-Th)/He dates are significantly younger than the stratigraphic ages of their host rocks, implying that the samples have experienced Phanerozoic elevated paleo-temperatures. Considerations of the data indicate removal of up to 9 km overburden since the Palaeozoic.Thermal modelling reveals a protracted rapid cooling event commencing during the early Carboniferous(ca. 350 Ma) at rates of 46 m/Ma ending in the Triassic(ca. 220 Ma). The model also suggests minor cooling during the Cretaceous of the samples to surface temperatures. The suggested later cooling event remains to be tested. The major cooling phase during the Carboniferous is interpreted to be associated with compressional tectonics during the Variscan Orogeny sensu far field induced stresses. Coeval sedimentation in the Karoo basins in the region suggests that most of the cooling of cratonic rocks during the Carboniferous was associated with denudation.

Application of low-temperature thermochronology on ore deposits preservation framework in South China:a review

South China can be divided into four metallogenic belts:The Middle-Lower Yangtze Metallogenic Belt(MLYB),Qinzhou-Hangzhou Metallogenic Belt(QHMB),Nanling Metallogenic Belt(NLMB),and Wuyi Metallogenic Belt(WYMB).The major mineralization in the four metallogenic belts is granite-related Cu–Au–Mo and porphyrite Fe-apatite,porphyry Cu(Au),and epithermal Pb–Zn–Ag,hydrothermal Cu–Au–Pb–Zn–Ag,and granite-related skarn-type and quartz-veins W–Sn,respectively.Low-temperature thermochronology,including fissiontrack and U-Th/He dating,has been widely used to constrain tectonic thermal evolution and ore deposits preservation.Understanding fission-track annealing and He diffusion kinetics in accessory minerals,such as zircon and apatite,is essential for dating and applications.In this study,previous zircon fission-track(ZFT)and apatite fission-track(AFT)ages in South China were collected.The result shows that the ZFT ages are mainly concentrated at140–90 Ma,and the AFT ages are mainly distributed at70–40 Ma.The age distribution and inversion temperature–time paths reveal heterogeneous exhumation histories in South China.The MLYB experienced Late CretaceousCenozoic extremely slow exhumation after rapid cooling in the Early Cretaceous.The northern QHMB(i.e.from southern Anhui province to the Hangzhou Bay)had a relatively faster rate of uplifting and denudation than the southern QHMB in the Cretaceous.Subsequently,the northern QHMB rapidly exhumed,while the continuously slow exhumation operated the southern QHMB in the Cenozoic.The southern NLMB had a more rapid cooling rate than the northern NLMB during the Cretaceous time,and the whole NLMB experienced rapid cooling in the Cenozoic,except that the southern Hunan province had the most rapid cooling rate.The WYMB possibly had experienced slow exhumation since the Late Cretaceous.The exhumation thickness of the four metallogenic belts since90 Ma is approximately calculated as follows:the MLYB≤3.5 km,the northern QHMB concentrated at3.5–5.5 km,and the southern QHMB usually less than3.5 km,the NLMB 4.5–6.5 km and the WYMB<3.5 km.The exhumation thickness of the NLMB is corresponding to the occurrence of the world-class W deposits,which were emplaced into a deeper depth of 1.5–8 km.As such,we infer that the uplifting and denudation processes of the four metallogenic belts have also played an important role in dominated ore deposits.

Cenozoic Exhumation History of the East Kunlun Orogenic Belt Constrained by Apatite Fission-Track Thermochronology

Objective The East Kunlun Orogenic belt constitutes the first marked change in the topographic reliefs north of the Qinghai-Tibet Plateau.The Cenozoic tectonic evolution of this orogenic belt is crucial for understanding the remote deformational effects of the Eurasian plate collision and the migration track at the northern margin of the plateau.However,when and how the uplift occurred remains

粤北长江铀矿田隆升剥露历史和矿床保存——来自磷灰石裂变径迹热年代学的启示

粤北长江铀矿田是中国南方最重要和最具代表性的花岗岩型铀矿田之一。前人关于长江铀矿田的研究工作主要涉及铀矿成因、成岩成矿时代和铀矿化机制等方面,关于控矿构造研究也集中在矿床形成过程方面(如导矿、运矿和储矿构造),对成矿后矿床的剥露历史和保存研究甚少。本文通过磷灰石裂变径迹测试,恢复了长江铀矿田热演化历史,结果显示晚白垩世末以来表现为单向隆升剥露降温过程,在约63~55 Ma和44~34 Ma存在两次快速隆升过程,约34~5 Ma冷却速率较慢,为构造平静期,5 Ma以来又发生了快速隆升。自75 Ma至今长江铀矿田的隆升剥蚀量为3 km左右。矿田内被NEE向棉花坑断裂和NWW向油洞断裂分割的书楼丘、棉花坑和长排三个矿区隆升剥蚀量差异非常微小,说明棉花坑断裂两侧和油洞断裂两侧在新生代时期没有明显的差异升降,也进一步佐证了棉花坑断裂和油洞断裂的活动性不大。结合控矿构造的发育特点、3.2~5.6 km的成矿深度以及相关的成矿温压条件,表明长江铀矿田深部资源保存良好,深部具有很大的找矿潜力。

方解石热释光定年技术的发展历史与展望

矿物晶体中累积的释光信号与其暴露在辐射环境中的时间相关,可用于测定沉积物年代。近年来,依托石英和长石2种矿物释光信号的测年方法日臻成熟,但这2种矿物的释光信号过早饱和,限制了其测年上限(通常<300ka)。前人研究表明,方解石亦有可能成为热释光测年材料,因为其热释光信号对剂量响应的灵敏度高,且特征饱和剂量约可达3000~5000Gy,有望将释光测年范围扩展至第四纪尺度。特别地,这一技术的发展也将拓展目前仅限于剥露速率极高地区的释光低温热年代学的应用范围,使其更好地贡献于地貌演化和构造活动的研究。文中对方解石热释光的基本原理和测年流程进行了简要概括,总结了方解石热释光测年应用及动力学参数的研究成果。此外,利用方解石热释光技术对虎跳峡段的基岩样品进行了测试,结果表明,ITL-235℃释光信号可用于该地区剥露历史的恢复工作。同时,文中基于上述内容讨论了方解石热释光技术的应用潜力和待解决问题,以期为该技术在构造地貌领域的应用提供帮助。

低温热年代学和构造模拟约束下逆冲推覆带的构造-热演化及剥露历史恢复

利用古温标进行热史模拟时,需要设置时间域和温度域的地质约束,其中时间域约束条件的设置限制了热史结果的准确性。逆冲推覆带发生逆冲推覆时,地层抬升和冷却的同时也发生差异水平滑移,使得同一逆冲席的构造抬升过程存在差异,但古温标模拟热史仅揭示样品的冷却过程,无法获得水平位移的信息,因此如何设置合适的时间域约束模拟热史并准确揭示逆冲推覆带的构造-热演化过程是低温热年代学领域探索研究的科学难题。本文以华南地区川东逆冲推覆带为示例,介绍了一种联合构造模拟、平衡剖面解析和低温热年代学、镜质组反射率等多种古温标的热运动学方法,实现“点-面”结合和整体-局部定量耦合,精细剖析逆冲推覆过程抬升剥露的起始时间、方式、速率、期次和幅度,为逆冲推覆带构造-热演化研究提供思路参考。

显微激光拉曼光谱锆石定年方法及其应用

锆石是岩浆岩、沉积岩和变质岩中的常见副矿物,由于其具有高Th、U含量的特点,已成为地质年代学研究的理想矿物之一。显微激光拉曼光谱锆石定年方法的原理是锆石中U、Th原子自发的α衰变而引起其自身晶格的辐射损伤,锆石晶格破坏的积累和时间呈正相关关系,并且与锆石拉曼光谱半高宽Γ具有相关性。利用锆石显微激光拉曼光谱仪测量锆石特征峰的半高宽可以计算出锆石的辐射损伤累积,进而计算得到锆石发生辐射损伤所累计的时间。锆石辐射损伤定年方法具有空间分辨率高、样品制备和测试方法简单等优势。但是此方法也受控于诸多影响因素,例如锆石自身结构的不均一性、锆石发生热退火作用的速率、锆石重结晶作用及辐射损伤饱和度等对定年结果均具有影响。显微激光拉曼光谱锆石定年方法的建立将有助于判定碎屑锆石物源区、揭示岩体热演化史以及识别继承锆石经历的后期构造热事件等研究。本文从显微激光拉曼光谱锆石定年方法的基本原理、计算过程及年龄影响因素等方面对该方法进行了介绍,并通过对松多高压变质带中变泥质岩中锆石的年代学研究,结合前人的应用实例,对该方法的应用前景进行了展望,为锆石年代学研究提供新的技术手段。

青藏高原南羌塘坳陷白垩纪以来的隆升剥蚀历史——来自低温热年代学的约束

为了重建青藏高原的形成过程和评价羌塘盆地油气的保存条件,对南羌塘坳陷隆升剥蚀历史进行了研究。利用锆石和磷灰石(U-Th)/He和磷灰石裂变径迹技术,对南羌塘坳陷中部嘎尔敖包地区的侏罗系砂岩样品进行了分析,数据显示大部分颗粒经历完全退火阶段;基于实验数据对盆地热史进行反演,并结合区域低温热年代学研究,认为南羌塘坳陷共经历了3期隆升剥蚀历史,即早白垩世、古新世—始新世和中新世以来,分别造成了南羌塘坳陷中部地区1.7~2.6 km、1.89 km和1.13 km的剥蚀量。热历史结果显示,早白垩世南羌塘坳陷中部地区首先遭受剥蚀,随后剥蚀逐渐向南、北两侧传递。南羌塘坳陷第一期冷却历史可能受到羌塘地体和拉萨地体碰撞的影响;第二期冷却历史可能受到印度—亚洲大陆碰撞的影响;第三期冷却历史可能与印度—亚洲大陆持续会聚下羌塘盆地发育大量近南北向断层有关。南羌塘坳陷中部地区位于不同构造位置的样品的热历史显示,其经历了不同的剥蚀过程,这可能受到印度—亚洲大陆的碰撞和随后持续会聚造成的区域性近南北向断裂差异性活动的影响。基于不同构造位置样品热历史的差异性,认为区域性南北向断裂开始活动时间为65~45 Ma。

六盘山地区新生代构造演化:来自锆石和磷灰石裂变径迹的证据

青藏高原的隆升与扩展不仅导致欧亚大陆内部发生强烈的构造变形,亦对高原周缘的地貌格局及气候变化产生了重大影响.青藏高原东北缘新生代以来的隆升时代与响应过程一直备受争议,而界定青藏高原东北缘构造带隆升时序是解决争议的关键之一.本研究围绕青藏高原东北缘,在陇中盆地、六盘山褶皱逆冲带和鄂尔多斯地块西南缘地区进行了磷灰石和锆石裂变径迹测试分析和热史模拟.测试分析结果表明研究区样品的磷灰石裂变径迹年龄范围分布于136~16 Ma,裂变径迹的长度范围介于11.9~13.3μm;锆石裂变径迹年龄结果为258~79 Ma,但多数样品的年龄介于160~99 Ma;热史模拟结果揭示了研究区新生代以来至少经历了两期隆升和冷却降温事件,即始新世期间(55~30 Ma)和中中新世(17~12 Ma)以来.始新世期间(55~30 Ma)发生的隆升事件可能是印度大陆与欧亚大陆陆陆碰撞远程效应的直接响应,表明印度与欧亚大陆碰撞之初或不久,其应力即已传导至东北缘边界;中中新世(17~12 Ma)以来的隆升剥露冷却事件奠定了青藏高原东北缘现今构造格局.