Tectonic-thermal history and hydrocarbon potential of the Pearl River Mouth Basin,northern South China Sea:Insights from borehole apatite fission-track thermochronology

The Pearl River Mouth Basin(PRMB)is one of the most petroliferous basins on the northern margin of the South China Sea.Knowledge of the thermal history of the PRMB is significant for understanding its tectonic evolution and for unraveling its poorly studied source-rock maturation history.Our investigations in this study are based on apatite fission-track(AFT)thermochronology analysis of 12 cutting samples from 4 boreholes.Both AFT ages and length data suggested that the PRMB has experienced quite complicated thermal evolution.Thermal history modeling results unraveled four successive events of heating separated by three stages of cooling since the early Middle Eocene.The cooling events occurred approximately in the Late Eocene,early Oligocene,and the Late Miocene,possibly attributed to the Zhuqiong II Event,Nanhai Event,and Dongsha Event,respectively.The erosion amount during the first cooling stage is roughly estimated to be about 455-712 m,with an erosion rate of 0.08-0.12 mm/a.The second erosion-driven cooling is stronger than the first one,with an erosion amount of about 747-814 m and an erosion rate between about 0.13-0.21 mm/a.The erosion amount calculated related to the third cooling event varies from 800 m to 3419 m,which is speculative due to the possible influence of the magmatic activity.

Cenozoic Exhumation and Thrusting in the Northern Qilian Shan,Northeastern Margin of the Tibetan Plateau:Constraints from Sedimentological and Apatite Fission-Track Data

The Qilian Shan lies along the northeastern edge of the Tibetan Plateau. To constrain its deformation history, we conducted integrated research on Mesozoic-Cenozoic stratigraphic sections in the Jiuxi Basin immediately north of the mountain range. Paleocurrent measurements, sandstone compositional data, and facies analysis of Cenozoic stratigraphic sections suggest that the Jiuxi Basin received sediments from the Altyn Tagh Range in the northwest, initially in the Oligocene （-33 Ma）, depositing the Huoshaogou Formation in the northern part of the basin. Later, the source area of the Jiuxi Basin changed to the Qilian Shan in the south during Late Oligocene （-27 Ma）, which led to the deposition of the Baiyanghe Formation. We suggest that uplift of the northern Qilian Shan induced by thrusting began no later than the Late Oligocene. Fission-track analysis of apatite from the Qilian Shan yields further information about the deformation history of the northern Qilain Shan and the Jiuxi Basin. It shows that a period of rapid cooling, interpreted as exhumation, initiated in the Oligocene. We suggest that this exhumation marked the initial uplift of the Qilian Shan resulting from the India-Asia collision.

Late Cretaceous-Cenozoic Exhumation History of the L(u|¨)liang Mountains,North China Craton:Constraint from Fission-track Thermochronology

The Lüliang Mountains, located in the North China Craton, is a relatively stable block, but it has experienced uplift and denudation since the late Mesozoic. We hence aim to explore its time and rate of the exhumation by the fission-track method. The results show that, no matter what type rocks are, the pooled ages of zircon and apatite fission-track range from 60.0 to 93.7 Ma and 28.6 to 43.3 Ma, respectively; all of the apatite fission-track length distributions are unimodal and yield a mean length of -13 μm; and the thermal history modeling results based on apatite fission-track data indicate that the time-temperature paths exhibit similar patterns and the cooling has been accelerated for each sample since the Pliocene （c.5 Ma）. Therefore, we can conclude that a successive cooling, probably involving two slow （during c.75-35Ma and 35-5Ma） and one rapid （during c.5 Ma-0 Ma） cooling, has occurred through the exhumation of the Liiliang Mountains since the late Cretaceous. The maximum exhumation is more than 5 km under a steady-state geothermal gradient of 35℃/km. Combined with the tectonic setting, this exhumation may be the resultant effect from the surrounding plate interactions, and it has been accelerated since c.5 Ma predominantly due to the India-Eurasia collision.

Accelerated Exhumation During the Cenozoic in the Dabie Mountains: Evidence from Fission-Track Ages

Abstract: Zircon and apatite fission-track dating indicates that the exhumation of the Dabie Mountains tended to be accelerated in the Cenozoic and that the exhumation of the eastern Dabie Mountains was more and more intense from south to north, which is in accordance with the more and more intense dissection from south to north, as is reflected by the modern geomorphologic features of the Dabie Mountains. The accelerated exhumation during the Cenozoic was related to the high elevation of the Dabie Mountains resulting from Late Cretaceous-Palaeogene detachment faulting and subsequent fault-block uplift and subsidence. The average elevation at that time was at least about 660 m higher than that at the present. The intense exhumation lagged behind intense uplift.

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.

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

INVESTIGATION OF THE PALEOGEOTHERMAL TECTONIC HISTORY ON DONGPU DEPRESSION AND OIL/GAS FORMATION BY FISSION-TRACK METHOD

Dongpu depression is a fault basin at residual-mobility period of Diwa stage, it developed on the strata of the Mesozoie and Pre-Mesozoie. It is one of the important oil/gas- bearing basin during Cenozoie era along the East China. The strueture in Dongpu geodepression is very complex. There exists a strueture pattern with east- and west-depression belts and one central swell belt, it is divided into the southern- and northern-division by Gaopingji (orMeng Ju ) -Xieheng fault.

New Apatite Fission-Track Ages of the Western Kuqa Depression:Implications for the Mesozoic–Cenozoic Tectonic Evolution of South Tianshan,Xinjiang

The Mesozoic–Cenozoic uplift history of South Tianshan has been reconstructed in many ways using thermochronological analyses for the rocks from the eastern Kuqa Depression. The main difference in the reconstructions concerns the existence and importance of Early Cretaceous and Paleogene tectonic activities, but the existence of a Cenozoic differential uplift in the Kuqa Depression remains enigmatic. Here, we present new apatite fission-track ages obtained for 12 sandstone samples from the well-exposed Early Triassic to Quaternary sequence of the Kapushaliang section in the western Kuqa Depression. The results reveal that there were four pulses of tectonic exhumation, which occurred during the Early Cretaceous（peak ages of 112 and 105 Ma）, Late Cretaceous（peak age of 67 Ma）, Paleocene–Eocene（peak ages at 60, 53, and 36 Ma）, and early Oligocene to late Miocene（central ages spanning 30–11 Ma and peak ages of 23 and 14 Ma）, respectively. A review of geochronological and geological evidence from both the western and eastern Kuqa Depression is shown as follows.（1） The major exhumation of South Tians Shan during the Early Cretaceous was possibly associated with docking of the Lhasa block with the southern margin of the Eurasian plate.（2） The Late Cretaceous uplift of the range occurred diachronically due to the far-field effects of the Kohistan-Dras Arc and Lhasa block accretion.（3） The Paleogene uplift in South Tianshan initially corresponded to the far-field effects of the India–Eurasia collision.（4） The rapid exhumation in late Cenozoic was driven by the continuous far-field effects of the collision between India and Eurasia plates. The apatite fission-track ages of 14–11 Ma suggest that late Cenozoic exhumation in the western Kuqa Depression prevailed during the middle to late Miocene, markedly later than the late Oligocene to early Miocene activity in the eastern segment. It can be hypothesized that a possible differential uplift in time occurred in the Kuqa Depression during the late Cenozoic.

Evolution of Tectonic Uplift, Hydrocarbon Migration, and Uranium Mineralization in the NW Junggar Basin： An Apatite Fission-Track Thermochronology Study

The Mesozoic–Cenozoic tectonic movement largely controls the northwest region of the Junggar Basin（NWJB）, which is a significant area for the exploration of petroleum and sandstone-type uranium deposits in China. This work collected six samples from this sedimentary basin and surrounding mountains to conduct apatite fission track（AFT） dating, and utilized the dating results for thermochronological modeling to reconstruct the uplift history of the NWJB and its response to hydrocarbon migration and uranium mineralization. The results indicate that a single continuous uplift event has occurred since the Early Cretaceous, showing spatiotemporal variation in the uplift and exhumation patterns throughout the NWJB. Uplift and exhumation initiated in the northwest and then proceeded to the southeast, suggesting that the fault system induced a post spread-thrust nappe into the basin during the Late Yanshanian. Modeling results indicate that the NWJB mountains have undergone three distinct stages of rapid cooling： Early Cretaceous（ca. 140–115 Ma）, Late Cretaceous（ca. 80–60 Ma）, and Miocene–present（since ca. 20 Ma）. These three stages regionally correspond to the LhasaEurasian collision during the Late Jurassic–Early Cretaceous（ca. 140–125 Ma）, the Lhasa-Gandise collision during the Late Cretaceous（ca. 80–70 Ma）, and a remote response to the India-Asian collision since ca. 55 Ma, respectively. These tectonic events also resulted in several regional unconformities between the J3/K1, K2/E, and E/N, and three large-scale hydrocarbon injection events in the Piedmont Thrust Belt（PTB）. Particularly, the hydrocarbon charge event during the Early Cretaceous resulted in the initial inundation and protection of paleo-uranium ore bodies that were formed during the Middle–Late Jurassic. The uplift and denudation of the PTB was extremely slow from 40 Ma onward due to a slight influence from the Himalayan orogeny. However, the uplift of the PTB was faster after the Miocene, which led to re-uplift and exposure at the surface during the Quaternary, resulting in its oxidation and the formation of small uranium ore bodies.

Apatite Fission-Track Datings on Hercynian Granites from Rehamna and Jebilet Massifs(Western Meseta,Morocco):Paleogeographic Implications and Interpretation of AFT Age Discrepancies

This work is based on apatite fission-track analysis of samples(mostly granites)from the basement of the Cretaceous-Tertiary Phosphate and Ganntour Plateaus, exposed in the Jebilet and Rehamna massifs (Western Meseta,Morocco).This basement

Apatite fission-track study on the thermo-tectonic history of the Huainan Coalfield in Anhui Province, China: Tectonic implications for the potential coalbed methane resource

Coalbed methane (CBM) is a kind of burgeoning and enormously potential clean energy resource, and the temperature of the thermogenic CBM generation is close to that of the partial annealing zone (PAZ) of apatite fission tracks (AFT). In this study the thermo-tectonic history of the Huainan Coalfield and the potential CBM resource were studied and discussed by using the AFT method. The AFT data indicate that the apparent ages of AFT vary from 45.5 to 199.1 Ma. They are younger than the ages of their host strata (255–1800 Ma) except one sample, and the single-grain ages of AFT can be classified as a single age group for each sample. In combination with the geological setting, modeling results of the AFT ages, average lengths, and the thermal history based on the AFT single-grain ages and length distributions, some preliminary conclusions can be drawn as follows: (1) at least three thermo-tectonic events (in the periods of ～240, 140 and 80 Ma, respectively) have occurred in the study area since the Late Paleozoic. The occurrence of both the first (during 240–220 Ma) and second (during 160–120 Ma) thermo-tectonic events is possibly responsible for the establishment of the patterns of gas generation and reservoir formation. The second thermo-tectonic event also led to slight accumulation of hydrocarbons and generation of thermogenic gas; (2) the AFT ages of most coal-bearing strata lie between 50 and 70 Ma. They should represent the cooling ages and the ages of inferred uplift and denudation, as well as the possible CBM release history. Therefore, the maximum burial depth of coal-bearing strata and the denudation thickness of the overlying strata are over 3000 and 2000 m in the Upper Cretaceous and Paleogene series, respectively; and (3) subsequently, a spot of secondary biogenic and scarcely thermogenic gas generation occurred due to negligible sedimentation during the Neogene and Quaternary periods. Thus, it can be presumed that subsequent tectonism would destroy the CBM reservoir after its formation in the Huainan Coalfield, especially in its structural development region. These AFT data may be helpful for a better understanding of the thermo-tectonic history of the Huainan Coalfield, as well as of CBM generation, storage and release in the Huainan Coalfield.

Apatite Fission-Track Thermochronology in the Tamusu Area,Bayingobi Basin,NW China,and its Geological Significance

The Bayingobi basin is located in the middle of Central Asia Orogenic Belt,at the intersection of Paleo-Asian Ocean and Tethys Ocean,as well as the junction of multiple tectonic plates.This unique tectonic setting underpins the basin's intricate history of tectonic activity.To unravel the multifaceted tectono-thermal evolution within the southwestern region of the basin and to elucidate the implications of sandstone-hosted uranium mineralization,granitic and clastic rock samples were collected from the Zongnai Mts.uplift and Yingejing depression,and apatite fission track(AFT)dating and thermal history simulation analysis were performed.AFT dating findings reveal that the apparent ages of all samples fall within the range of 244 Ma to 112 Ma.In particular,the bedrock of the Zongnai Mts.and Jurassic detrital apatite fission tracks have undergone complete annealing,capturing the uplift-cooling age.Meanwhile,the AFT ages of Cretaceous detrital rocks are either equivalent to or notably exceed the age of sedimentary strata,signifying the cooling age of the provenance.A comprehensive examination of AFT ages and palaeocurrent direction analyses suggests that the Cretaceous source in the Tamusu area predominantly originated from the central and southern sectors of the Zongnai Mts.uplift.However,at a certain juncture during the Late Early Cretaceous,the Cretaceous provenance expanded to include the northern part of the Zongnai Mts.uplift.Based on the results of thermal history simulations and previous studies,it is considered that the Tamusu area has undergone four distinct tectonic uplift events since the Late Paleozoic.The first is the Late Permian to Early Triassic(260-240 Ma),which is associated with the closure of the Paleo-Asian Ocean and the accretionary orogeny within the Alxa region.The second uplift event took place in the Early Jurassic(190-175 Ma)and corresponded to intraplate orogeny following the closure of the Paleo-Asian Ocean.The third uplift event is the Late Jurassic to Early Cretaceous(160-120 Ma),which is linked to the East Asia's position as the convergence center of multiple tectonic plates during this period.The fourth uplift event is linked to the Late Early Cretaceous(112-100 Ma),driven either by the westward subduction of the eastern Pacific plate or the mantle upwelling resulting from the Bangong-Nujiang oceanic lithosphere subduction and slab break-off.The primary stress orientation for the first three tectonic uplift phases approximated a nearly SN direction,while the fourth stage featured a principal stress direction of NW.The fourth tectonic uplift event of the Late Early Cretaceous and basaltic eruption thermal event during this period likely exerted a significant influence on the formation of the Tamusu sandstone-hosted uranium deposit.

Mesozoic Tectonothermal Evolution of the Southern Central Asian Orogenic Belt: Evidence from Apatite Fission-Track Thermochronology in Shalazha Mountain, Inner Mongolia

Mesozoic intracontinental orogeny and deformation were widespread within the southern Central Asian Orogenic Belt(CAOB). Chronological constraints remain unclear when assessing the Mesozoic evolution of the central segment of this region. The tectonic belt of Shalazha Mountain located in the center of this region is an ideal place to decode the deformation process. Apatite fission-track(AFT) thermochronology in Shalazha Mountain is applied to constrain the Mesozoic tectonothermal evolution of the central segment of southern CAOB. The bedrock AFT ages range from 161.8 ± 6.9 to 137.0 ± 7.3 Ma, and the first reported detrital AFT obtained from Lower Cretaceous strata shows three age peaks: P1(ca. 178 Ma), P2(ca. 149 Ma) and P3(ca. 105.6 Ma). Bedrock thermal history modeling indicates that Shalazha Mountain have experienced three stages of differential cooling: Late Triassic–Early Jurassic(~230–174 Ma), Late Jurassic–Earliest Cretaceous(~174–135 Ma) and later(~135 Ma). The first two cooling stages are well preserved by the detrital AFT thermochronological result(P1, P2) from the adjacent Lower Cretaceous strata, while P3(ca. 105.6 Ma) records coeval volcanic activity. Furthermore, our data uncover that hanging wall samples cooled faster between the Late Triassic and the Early Cretaceous than those from the footwall of Shalazha thrust fault, which synchronizes with the cooling of the Shalazha Mountain and implies significant two-stage thrust fault activation between ca. 230 and 135 Ma. These new low-temperature thermochronological results from the Shalazha Mountain region and nearby reveal three main phases of differential tectonothermal events representing the Mesozoic reactivation of the central segment of the southern CAOB. In our interpretations, the initial rapid uplift in the Late Triassic was possibly associated with intracontinental orogenesis of the CAOB. Subsequent Middle Jurassic–Earliest Cretaceous cooling is highly consistent with the Mesozoic intense intraplate compression that occurred in the southern CAOB, and is interpreted as a record of closure of the Mongol-Okhotsk Ocean. Then widespread Cretaceous denudation and burial in the adjacent fault basin could be linked with the oblique subduction of the Izanagi Plate along the eastern Eurasian Plate, creating a northeast-trending normal fault and synchronous extension. However, our AFT thermochronometry detects no intense Cenozoic reactivation information of Shalazha Mountain region.

Exhumation and Deformation of the Daba Shan Orocline as Determined from Modern River Sands Apatite Fission-Track

The Daba Shan orocline is located at the northeastern margin of the Sichuan Basin and has been inferred as a foreland thrust-fold belt of the Qinling Orogen since the Late Triassic.A complete understanding of rock exhumation history is critical to elucidate how and when this typical orocline structure is developed.Detrital apatite fission-track dating of modern river sands is employed to reveal the regional exhumation history of the Daba Shan orocline.Four age peaks are identified and interpreted as the results of tectonic exhumation.Two older age peaks at ~150–140 and ~116–86 Ma are agreement with two main shortening deformation episodes of the Yanshanian Movement in the eastern China.The other two younger age peaks at ~69 and ~37 Ma support that the Daba Shan was reactivated by the Late Cretaceous to Cenozoic deformation which were likely related to the subduction of the Pacific Ocean and eastward growth of the Tibetan Plateau,respectively.It is worth noting that in contrast to the ~150–140 Ma rapid rock uplift and exhumation,the Middle Cretaceous exhumation(~116–86 Ma) shifted southward and continued to spread to southern tips of the Daba Shan.These exhumation variations in temporal and spatial allow a southward thrust deformation with piggyback style during the Yanshanian.

中非乍得Bongor盆地北部斜坡下白垩统油气成藏期次

基于流体包裹体均一温度测试和磷灰石裂变径迹分析,对乍得Bongor盆地北部斜坡下白垩统油气成藏时间和期次开展研究。研究表明,下白垩统Kubla组和Prosopis组储集层样品中与油气共生的盐水流体包裹体均一温度总体上表现为高、低温两组峰值区间,低温峰值区间和高温峰值区间分别为75~105℃和115~135℃;Kubla组和Prosopis组样品均经历了5个构造演化阶段,即早白垩世发生快速沉降,晚白垩世晚期发生构造反转,古近纪发生小幅沉降,古近纪与新近纪之交抬升,中新世以来则处于沉降阶段;其中晚白垩世剥蚀厚度约1.8km,古近纪与新近纪之交剥蚀厚度约0.5 km,两期剥蚀叠加厚度约2.3 km。与油气包裹体共生的盐水包裹体的均一温度用以作为油气捕获温度,结合磷灰石裂变径迹热演化史模拟研究,结果表明Bongor盆地北部斜坡下白垩统Kubla组和Prosopis组具有一致的油气成藏时间和期次,均在距今80~95 Ma和65~80 Ma分别经历了两期油气充注。第1期充注对应于油气初始运移,为早白垩世快速沉积末期,第2期充注处于晚白垩世构造强烈反转阶段。

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。

北山东南部早白垩世伸展构造变形:二维反射地震剖面解释与磷灰石裂变径迹测年的制约

为深入认识中亚造山带南缘晚中生代陆内变形过程及其动力学机制,通过野外地质观察、二维反射地震剖面解释及磷灰石裂变径迹测年,对北山东南部早白垩世伸展构造及早期挤压构造进行了详细解析。结果表明,一系列逆冲断层与褶皱构造造成下—中侏罗统发生强烈的挤压变形。地震剖面揭示出2条早白垩世伸展正断层,其中梭梭井断层为南东倾向的低角度铲式正断层,五道明断层为北西倾向的高角度正断层,二者共同切割了早期形成的褶皱-冲断系统,指示挤压-伸展构造的转换;梭梭井断层与五道明断层分别限定了早白垩世总口子盆地的北西和南东边界,使得其具有“地堑”样式,盆地内沉积的下白垩统生长地层发育,表明伸展正断层的活动时间为早白垩世晚期。磷灰石裂变径迹热史模拟结果显示,梭梭井断层下盘于132~110 Ma经历了快速冷却和剥露事件,该事件与其持续的正断层活动密切相关,进一步证实北山东南部晚中生代挤压-伸展构造的转换很可能发生在早白垩世晚期(133~129 Ma)。增厚地壳的重力垮塌与局部地幔上涌共同导致了中亚造山带南缘早白垩世的区域伸展作用。

南海北部扩张的地表过程响应:来自海南岛五指山的磷灰石裂变径迹年龄证据

海南岛是南海地块的重要组成部分,其构造演化很大程度上能够反映整个南海的构造活动特征。新生代,海南岛在新构造运动作用下,断块差异升降比较明显,形成了大致以王五-文教断裂为界,北为沉降区,南为断隆区的构造格局。对断隆区隆升过程的研究能够帮助揭示海南岛新构造活动历史,但至今为止,琼中南山地隆升的原因和时限仍存在争议。为了厘清海南岛中部的剥露隆升事件,本文选择琼中南地区海拔最高、高差最大的五指山为研究区,采集8组高程岩石样品,高程范围为203.55~1153.52 m。对采集的样品进行了磷灰石裂变径迹测试和热历史模拟分析,结果表明海南岛五指山地区新生代主要经历了两期快速隆升剥露。第一期为渐新世—中新世(32~17 Ma):隆升速率较快,此时期太平洋板块向欧亚板块俯冲后撤,南海正经历第二次扩张,使得海南岛拉张,活动强烈,造成琼中山地区快速隆升,直到中中新世转为缓慢隆升。第二期为中新世末期(5 Ma)的快速剥蚀隆升阶段:南海扩张已经结束,随着菲律宾板块俯冲亚洲板块,南海北部陆缘整体处于加速热沉降阶段,且全球气候变化加快,造成了海南岛广泛的隆起和加速剥蚀。

太岳山脉中段中生代—新生代隆升演化裂变径迹约束

应用磷灰石裂变径迹年代学方法研究太岳山脉中段构造隆升与剥露过程,这对于进一步认识华北地块构造演化过程具有重要的意义。结果表明:太岳山脉中段自中侏罗世末期以来经历了持续隆升剥露过程,并受到了热事件的影响。模拟结果显示,太岳山脉中段中生代—新生代共经历了4期快速隆升剥露:165~112Ma、103~85Ma、80~50Ma及28Ma以来。样品裂变径迹年龄与海拔高程呈正相关关系,隆升速率为8.4 m/Ma。剥蚀速率从早白垩世晚期以来的14.9~18.1m/Ma逐渐增加到始新世以来的50.5~64.7m/Ma,太岳山脉中段早白垩世晚期以来的隆升过程具有多期性,总体上呈加速隆升的特点。太岳山脉中段中生代—新生代的隆升史与太行山、吕梁山等山西地块的同期演化史具有一定的一致性,与汾渭裂谷系的快速沉降相耦合。

川北米仓山隆起构造-热演化特征

本文基于实测锆石(U-Th)/He和磷灰石裂变径迹年龄的联合热史模拟明确了米仓山隆起自新元古代以来的构造-热演化史。米仓山隆起前寒武系样品锆石(U-Th)/He年龄和磷灰石裂变径迹年龄分别为190~138 Ma和106.1~120.6 Ma,均小于地层年龄或成岩结晶年龄,有效地记录了早期热信息。热史模拟结果表明米仓山隆起自新元古代以来主要经历了早侏罗世—早白垩世和晚中新世至今两期快速冷却事件,分别与扬子-华北板块碰撞和印度-欧亚板块碰撞的东扩作用有关,而白垩纪—早中新世的缓慢冷却过程则与当时的古夷平面发育有关。本文不仅丰富完善了川北地区构造-热演化成果,而且对于该地区下一步油气勘探具有重要的指导意义。