Thermal and exhumation history of the Songnan Low Uplift,Qiongdongnan Basin:constraints from the apatite fission-track and zircon(U-Th)/He thermochronology

Significant advancements have been made in the study of Mesozoic granite buried hills in the Songnan Low Uplift(SNLU)of the Qiongdongnan Basin.These findings indicate that the bedrock buried hills in this basin hold great potential for exploration.Borehole samples taken from the granite buried hills in the SNLU were analyzed using apatite fission track(AFT)and zircon(U-Th)/He data to unravel the thermal history of the basement rock.This information is crucial for understanding the processes of exhumation and alteration that occurred after its formation.Thermal modeling of a sample from the western bulge of the SNLU revealed a prolonged cooling event from the late Mesozoic to the Oligocene period(~80-23.8 Ma),followed by a heating stage from the Miocene epoch until the present(~23.8 Ma to present).In contrast,the sample from the eastern bulge experienced a more complex thermal history.It underwent two cooling stages during the late Mesozoic to late Eocene period(~80-36.4 Ma)and the late Oligocene period(~30-23.8 Ma),interspersed with two heating phases during the late Eocene to early Oligocene period(~36.4-30 Ma)and the Miocene epoch to recent times(~23.8-0 Ma),respectively.The differences in exhumation histories between the western and eastern bulges during the late Eocene to Oligocene period in the SNLU can likely be attributed to differences in fault activity.Unlike typical passive continental margin basins,the SNLU has experienced accelerated subsidence after the rifting phase,which began around 5.2 Ma ago.The possible mechanism for this abnormal post-rifting subsidence may be the decay or movement of the deep thermal source and the rapid cooling of the asthenosphere.Long-term and multi-episodic cooling and exhumation processes play a key role in the alteration of bedrock and contribute to the formation of reservoirs.On the other hand,rapid post-rifting subsidence(sedimentation)promotes the formation of cap rocks.

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.

(U-Th)/He热年代学方法研究进展及其应用

(U-Th)/He热年代学方法基于矿物中U、Th、Sm发生衰变产生和累积的4He进行定年。由于低的封闭温度和对近地表地质过程的敏感性,因此在定量揭示地壳浅部所经历冷却及剥露事件的时间-空间-温度特征方面具有不可替代的优势。本文简要回顾了(U-Th)/He定年原理并对不同测试方法的优缺点进行评述,在此基础上总结探讨了(U-Th)/He热年代学在辐射损伤影响机制、退火动力学以及4He扩散模型方面取得的进展以及存在的不足,并对如何完善这些不足进行未来展望。此外本文还综述了(U-Th)/He热年代学方法在约束成矿时代、造山带剥露历史研究、矿床保存性评价方面的应用实例以及部分局限性。

Thermal History of the Naruo Porphyry Deposit in the Duolong Ore District,Western Tibet:Evidence from U-Pb,^(40)Ar/^(39)Ar and(U-Th)/He Thermochronology

The Naruo porphyry copper deposit containing more than 2 Mt of copper is located in the Duolong ore district in the west of the Bangongco–Nujiang belt in central Tibet.New zircon U-Pb,biotite^(40)Ar/^(39)Ar,zircon(U-Th)/He ages,published age data together with thermal modeling were presented in this paper to investigate the thermal history of Naruo deposit.Thermal modeling reveals a prolonged magmatic-hydrothermal evolution firstly cooling from~700℃to~350℃at 120 Ma,then cooling to 230℃at 106 Ma and maintaining at 200℃from 106 to 90 Ma which is attributed to multiple magmatic events and thermal effect of strike-slip fault.Affected by thrust nappe structure,the sample was consistent with 120℃from 70 to 63 Ma.The Naruo deposit started to experience exhumation at a rate of~0.07 km/Myr since 60 Ma which is related to India-Asia collision.The prolonged magmatic-hydrothermal evolution process might have important influence on the Naruo deposit.The ore-related intrusions preserved in the foot walls of strike-slip fault and thrust nappe structure are the objects of future exploration in the Duolong ore district.

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.

Fish Canyon Tuff榍石He扩散及(U-Th)/He年代学研究

榍石富含U和Th,是(U-Th)/He定年的理想矿物之一。本文以Fish Canyon Tuff榍石为例,开展了榍石He扩散行为和榍石(U-Th)/He定年实验方法研究。榍石分步加热扩散实验结果表明He扩散系数ln(D/a2)与温度倒数呈负相关,与期望的热活化扩散过程一致。测试Fish Canyon Tuff榍石(U-Th)/He年龄分布在28.3~24.6 Ma之间,平均值为26.7±1.2 Ma(1σ),Th/U分布在4.6~5.5之间,平均值为5.2±0.2,在误差范围内与国际上已出版数据一致,表明建立的榍石(U-Th)/He定年实验方法可靠。本次测试15粒榍石碎片外表层(~20μm)存在不同程度的磨蚀(即不完整晶体),且榍石表层磨蚀厚度随着等效半径的增加而增大。榍石碎片(U-Th)/He年龄介于完整晶体(U-Th)/He年龄和真实(U-Th)/He年龄之间,且随着榍石等效半径及表层磨蚀厚度(<20μm)的增大,(U-Th)/He年龄更接近真实年龄,这表明榍石(U-Th)/He年龄不确定度与等效半径大小和表层磨蚀厚度有关。

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.

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.

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.

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.

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.

Meso-Cenozoic tectonic evolution of the Talas-Fergana region of the Kyrgyz Tien Shan revealed by low-temperature basement and detrital thermochronology

This study provides new low-temperature thermochronometric data, mainly apatite fission track data on the basement rocks in and adjacent to the Talas-Fergana Fault, in the Kyrgyz Tien Shan in the first place.In the second place, we also present new detrital apatite fission track data on the Meso-Cenozoic sediments from fault related basins and surrounding intramontane basins. Our results confirm multistaged Meso-Cenozoic tectonic activity, possibly induced by the accretion of the so-called Cimmerian blocks to the Eurasian margin. New evidence for this multi-staged thermo-tectonic activity is found in the data of both basement and Meso-Cenozoic sediment samples in or close to the Talas-Fergana Fault.Zircon(U-Th)/He and apatite fission track data constrain rapid Late TriassiceE arly Jurassic and Late JurassiceE arly Cretaceous basement cooling in the Kyrgyz Tien Shan around 200 Ma and 130 -100 Ma respectively. Detrital apatite fission track results indicate a different burial history on both sides of the Talas-Fergana Fault. The apatite fission track system of the Jurassic sediments in the Middle Tien Shan unit east of the Talas-Fergana Fault is not reset, while the Jurassic sediments in the Fergana Basin and Yarkand-Fergana Basin, west of the fault zone, are partially and in some cases even totally reset. The totally reset samples exhibit Oligocene and Miocene ages and evidence the Cenozoic reactivation of the western Kyrgyz Tien Shan as a consequence of the India-Eurasia convergence.

帕米尔东缘晚中新世以来多阶段隆升-剥露过程:来自裂变径迹和(U-Th)/He低温热年代学的制约

帕米尔东缘发育帕米尔造山带内最大的东西向伸展系统,对理解区域构造演化具有重要意义。然而,该地区的隆升时限和动力学机制等仍缺乏有效的限制。本文选取帕米尔东缘塔什库尔干地区的新生代侵入岩开展磷灰石裂变径迹和锆石、磷灰石(U-Th)/He定年研究,并结合前人的热年代学成果,探讨帕米尔东缘晚新生代以来的构造热演化和动力学机制。低温热年代学数据显示,磷灰石裂变径迹中心年龄为2.5~2.7Ma和8.7~11.5Ma,磷灰石(U-Th)/He年龄为2.3~4.5Ma,锆石(U-Th)/He年龄为3.2±0.3Ma。通过上述样品的剥露速率计算,我们认为帕米尔东缘发生了两期快速冷却期:晚中新世(12~8Ma)和上新世-第四纪(5~1Ma),其对应的剥露速率分别为0.19~0.48mm/yr和0.58~4.00mm/yr。晚中新世期间,帕米尔东缘构造变形、岩浆作用、变质作用几乎同时发生。这些事件可能和帕米尔与南天山造山带在晚中新世初次碰撞有关,该碰撞是由印度板块向北俯冲到帕米尔地体下方引起的。这次碰撞进一步促使地壳增厚,导致帕米尔岩石圈重力分布不均,从而引发重力坍塌。上新世至第四纪的冷却可能受到重力坍塌后持续伸展变形的影响,同时冰川、河流和气候变化引起的侵蚀进一步加剧了剥露作用,导致剥露速率比晚中新世时期显著增加。

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

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.

New insights from low-temperature thermochronology into the tectonic and geomorphologic evolution of the south-eastern Brazilian highlands and passive margin

The South Atlantic passive margin along the south-eastern Brazilian highlands exhibits a complex landscape,including a northern inselberg area and a southern elevated plateau,separated by the Doce River valley.This landscape is set on the Proterozoic to early Paleozoic rocks of the region that once was the hot core of the Aracuai orogen,in Ediacaran to Ordovician times.Due to the break-up of Gondwana and consequently the opening of the South Atlantic during the Early Cretaceous,those rocks of the Araquai orogen became the basement of a portion of the South Atlantic passive margin and related southeastern Brazilian highlands.Our goal is to provide a new set of constraints on the thermo-tectonic history of this portion of the south-eastern Brazilian margin and related surface processes,and to provide a hypothesis on the geodynamic context since break-up.To this end,we combine the apatite fission track(AFT)and apatite(U-Th)/He(AHe)methods as input for inverse thermal history modelling.All our AFT and AHe central ages are Late Cretaceous to early Paleogene.The AFT ages vary between 62 Ma and90 Ma,with mean track lengths between 12.2μm and 13.6μm.AHe ages are found to be equivalent to AFT ages within uncertainty,albeit with the former exhibiting a lesser degree of confidence.We relate this Late Cretaceous-Paleocene basement cooling to uplift with accelerated denudation at this time.Spatial variation of the denudation time can be linked to differential reactivation of the Precambrian structural network and differential erosion due to a complex interplay with the drainage system.We argue that posterior large-scale sedimentation in the offshore basins may be a result of flexural isostasy combined with an expansion of the drainage network.We put forward the combined compression of the Mid-Atlantic ridge and the Peruvian phase of the Andean orogeny,potentially augmented through the thermal weakening of the lower crust by the Trindade thermal anomaly,as a probable cause for the uplift.

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。

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。