Thermal history of the Rio Muni (West Africa)–NE Brazil margins during continental breakup     

Jonathan P. Turner  Paul F. Green  Simon P. Holford  Stephen R. Lawrence 《Earth and Planetary Science Letters》2008,270(3-4):354-367

We document the thermal record of breakup of the conjugate Rio Muni (West Africa) and NE Brazil margins using apatite fission track analysis, vitrinite reflectance data and stratigraphic observations from both margins. These results permit determination of the timing of four cooling episodes, and the temperature of samples at the onset of each episode. All samples are interpreted to have experienced higher temperatures in the geological past due to i) elevated basal heatflow (palaeogeothermal gradient in Rio Muni-1 well decaying from 58 °C/km during the Mid Cretaceous to 21.5 °C/km in the Late Cenozoic) and ii) progressive exhumation from formerly greater burial depth. A well constrained history of changing palaeogeothermal gradient allows for much more precise quantification of the thickness of eroded section (exhumation) than if a constant heatflow is assumed. Cooling episodes identified from the palaeotemperature data at 110–95 Ma (both margins) and 85–70 Ma (Rio Muni only) coincide with major unconformities signifying, respectively, the cessation of rifting (breakup) and compressional shortening that affected the African continent following the establishment of post-rift sedimentation (drift). The interval between these separate unconformities is occupied by allochthonous rafts of shallow-water carbonates recording gravitational collapse of a marginal platform. The rift shoulder uplift that triggered this collapse was enhanced by local transpression associated with the obliquely divergent Ascension Fracture Zone, and thermal doming due to the coeval St Helena and Ascension Plumes. The data also reveal a c.45–35 Ma cooling episode, attributed to deep sea erosion at the onset of Eo-Oligocene ice growth, and a c.15–10 Ma episode interpreted as the record of Miocene exhumation of the West African continental margin related to continent-wide plume development. Integration of thermal history methods with traditional seismic- and stratigraphy-based observations yields a dynamic picture of kilometre-scale fluctuations in base level through the breakup and early drift phases of development of these margins. Major unconformities at ocean margins are likely to represent composite surfaces recording not only eustasy, but also regional plate margin-generated deformation, local ‘intra-basinal’ reorganization, and the amplifying effect of negative feedbacks between these processes.  相似文献   

裂变径迹法对兰坪盆地构造热演化与成矿作用的初步研究   总被引：7，自引：0，他引：7  

李小明  谭凯旋  龚革联  龚文君 《矿物岩石》2000,20(2):40-42

兰坪盆地位于澜沧江断裂带与衰牢册推覆体之间内有丰富的钨矿床与盐类矿床,大部分是新生代形成的,且大多为低温热液矿床。裂变径迹法对兰坪盆地构造热演化与成矿作用的研究结果表明：盆地自中生代以来,至少经历了三次构造热事件,出现了三次成矿作用过程,成矿作用是由盆地西缘向中央地带逐渐发展的。  相似文献   

滇西姚安金矿床磷灰石化学特征及指示意义     

郑瑜林  张长青  刘欢  孙嘉  张盼盼 《矿床地质》2021,40(1):156-168

姚安金矿床位于金沙江-哀牢山富碱斑岩带中段,大地构造位置处于扬子板块西缘与三江特提斯造山带结合部位,其成矿与新生代富碱岩浆-岩浆热液密切相关.野外调查发现矿化仅存在于黑云母正长斑岩体内,而与黑云母正长斑岩空间关系密切的石英正长斑岩却未发现矿化.为探讨黑云母正长斑岩与石英正长斑岩岩体含矿性差异,运用电子探针、LA-ICP...  相似文献   

CCSD主孔榴辉岩中磷灰石的矿物化学特征及对榴辉岩中F、Cl、Sr等元素地球化学行为的影响   总被引：10，自引：1，他引：9  

陈振宇  曾令森  梁凤华  张泽明 《地质学报》2006,80(12):1842-1850

为探讨榴辉岩中磷灰石的矿物化学特征及榴辉岩中某些相关元素的地球化学行为,对中国大陆科学钻探(CCSD)主孔500~540m深度的榴辉岩样品进行了岩石化学及磷灰石的矿物化学分析。这些榴辉岩具有不同的矿物组成和化学成分,并可据此分为上下两段,上段500~530m为正常榴辉岩,下段530~540m为高Ti榴辉岩和高Ti-Fe榴辉岩,其原岩可能为类似于辉长质和苦橄质的基性—超基性岩石。其中的磷灰石成分没有明显差别,均为氟—磷灰石,其富F贫Cl的特征可能是造成榴辉岩中高盐度流体包裹体和全岩高F低Cl的主要原因。磷灰石普遍含有一定的Sr、S、Fe元素,多数还含有Cu、Pb、Zn等元素。榴辉岩中P2O5含量与其F、Cl、Sr、S元素的相关程度表明,磷灰石是榴辉岩中F元素的最主要储存库,也是Sr元素的重要储存库之一,而对于Cl元素则只是部分控制,与S元素则没有相关性。榴辉岩中F、Sr及Cl元素的地球化学行为主要受控于磷灰石,因此,在榴辉岩从进变质—退变质过程中,这些元素的活动性直接受控于磷灰石的稳定性。  相似文献   

花海拗陷的热演化和生烃期的磷灰石裂变径迹证据   总被引：5，自引：1，他引：5  

王世成  袁万明  王兰芬  任战利 《地球学报》1999,20(4):428-432

利用裂变径迹分析方法测量了取自花海拗陷的钻井磷灰石样品的裂变径迹年龄和长度。结果表明,随井深增加年龄减小,平均径迹长度亦变短。取自白垩纪地层的磷灰石样品的裂变径迹年龄都比地层年龄年轻得多,表明沉积后曾长时间处于磷灰石裂变径迹退火带中,沉积前的径迹记录已部分消失,古地温高于今地温。利用蒙特卡罗随机取样的热史模拟方法对裂变径迹数据进行了分析,结果表明白垩纪地层沉积后曾经历过超过110 ℃的加热,达到最高古地温的地质时代是早白垩世晚期—晚白垩世末,为主要生烃期。新生代以来盆地变冷,生油岩的成熟度主要受古地温控制  相似文献   

东昆仑山小南川岩体裂变径迹年代与中新世晚期以来的构造地貌演化   总被引：2，自引：0，他引：2  

王岸  王国灿  谢德凡  刘德民 《地球科学》2007,32(1):51-58

对昆仑垭口地区小南川岩体7件样品进行磷灰石裂变径迹年代学测试, 分析了岩体的冷却过程及岩体的剥露与构造地貌演化的关系.结果表明东昆仑山区中新世晚期视剥蚀速率极为缓慢, 为0.020~0.035mm/a, 反映的是构造隆升作用微弱、地貌缓和的地质环境, 因而构造隆升速率与低的视剥蚀速率相当.上新世以来小南川岩体突发性快速隆升冷却, 造成超过3km的物质揭顶, 这不是由单纯的剥蚀过程导致, 而是反映了昆仑山上新世以来的强烈构造隆升驱动下的成山作用过程.岩体上新世的裂变径迹年龄与近东西向的昆仑河-野牛沟谷地断裂断陷、昆仑垭口盆地断陷以及后期西大滩谷地断陷的综合构造地貌演化有密切的成因联系.此外裂变径迹年龄的空间分布格局反映了区域性的差异隆升作用, 由南向北、由西向东, 隆升和剥蚀作用逐渐衰减, 这与东昆仑山南北向以及东、西昆仑山之间地貌发育的差异性以及新生代火山作用分布是吻合的.   相似文献   

南方志留系碎屑矿物热年代学分析及其地质意义   总被引：7，自引：1，他引：6  

李双建  汪新伟  张荣强  沃玉进  周雁  蔡立国 《地质学报》2008,82(8):1068-1076

碎屑矿物热年代学是恢复多旋回沉积盆地构造演化的有利手段。本文通过对南方5个地区志留系的碎屑锆石和磷灰石的裂变径迹年龄和热历史模拟研究认识到,印支期以来研究区志留系至少经历了3次区域性的岩石抬升、冷却事件,即早中三叠世（235～250 Ma）、晚侏罗世—早白垩世（110～140 Ma）和始新世—渐新世（45～25 Ma）。其中晚侏罗世—早白垩世和始新世—渐新世是志留系后期改造的两个关键时期,前者是志留系烃源岩生烃基本停止的时期,后者是志留系抬升到地表,油气盖层受到广泛破坏的时期。  相似文献   

济阳坳陷新生代热演化特征研究   总被引：1，自引：0，他引：1  

柳忠泉  韩立国  徐佑德  许世红  任凤楼  周丽 《地质学报》2008,82(5):663-668

本文综合应用镜质组反射率法和磷灰石裂变径迹法恢复了济阳坳陷新生代地温演化历史,结果表明济阳坳陷古地温梯度在新生代是逐渐降低的,其中古近纪比新近纪下降的幅度大;同时济阳坳陷内各凹陷的古地温梯度演化也存在差异,特别是古近纪末期的东营构造运动后,各凹陷的地温梯度演化差异更加明显;根据各凹陷的古热场恢复,新近纪以来东营凹陷的古地温最高,其次是沾化凹陷,惠民凹陷和车镇凹陷的古地温较低;烃源岩的生烃演化历史与其经历的古热场密切相关,古地温梯度越高的地区,烃源岩进入生烃门限的深度就越浅、时间越早。  相似文献   

柴达木盆地北缘中新生代热演化及其对铀成矿的意义     

邵雨萌  颜丹平  赵兴齐  刘武生  史清平  刘林  孙琦 《铀矿地质》2016,(5):287-293

文章在阐述柴达木盆地北缘砂岩型铀矿成矿地质特征的基础上,以磷灰石裂变径迹特征分析为依据,系统研究了该地区中新生代热演化及其与砂岩型铀矿成矿作用的关系。资料显示,区内中侏罗统具备较好的铀成矿条件,成矿类型以层间氧化带型和潜水氧化带型为主。磷灰石裂变径迹分析结果表明,样品的平均径迹长度为(11.71±0.17)μm±1σ~(12.58±0.18)μm±1σ,说明均经历过退火作用;样品的表观年龄为64.4~85Ma,说明区内构造活动具有多期、多阶段特点;基于裂变径迹的t-T曲线模拟结果表明,自120Ma以来,该地区的构造演化可以分为挤压隆升、断陷沉降、快速抬升3个阶段。因此,认为区内砂岩型铀矿主体应是早白垩世早期-古新世早期挤压隆升阶段形成的古矿体。现今的找矿方向,应是在活动强度相对较弱的构造活化区中寻找残留铀矿体,同时注重深部找矿。  相似文献   

Shaping the Australian crust over the last 300 million years: Insights from fission track thermotectonic imaging and denudation studies of key terranes     

B. P. Kohn  A. J. W. Gleadow  R. W. Brown  K. Gallagher  P. B. O'Sullivan  D. A. Foster 《Australian Journal of Earth Sciences》2013,60(4):697-717

Apatite fission track thermochronology is a well‐established tool for reconstructing the low‐temperature thermal and tectonic evolution of continental crust. The variation of fission track ages and distribution of fission track lengths are primarily controlled by cooling, which may be initiated by earth movements and consequent denudation at the Earth's surface and/or by changes in the thermal regime. Using numerical forward‐modelling procedures these parameters can be matched with time‐temperature paths that enable thermal and tectonic processes to be mapped out in considerable detail. This study describes extensive Australian regional fission track datasets that have been modelled sequentially and inverted into time‐temperature solutions for visualisation as a series of time‐slice images depicting the cooling history of present‐day surface rocks during their passage through the upper crust. The data have also been combined with other datasets, including digital elevation and heat flow, to image the denudation history and the evolution of palaeotopography. These images provide an important new perspective on crustal processes and landscape evolution and show how important tectonic and denudation events over the last 300 million years can be visualised in time and space. The application of spatially integrated denudation‐rate chronology is also demonstrated for some key Australian terranes including the Lachlan and southern New England Orogens of southeastern Australia, Tasmania, the Gawler Craton, the Mt Isa Inlier, southwestern Australian crystalline terranes (including the Yilgarn Craton) and the Kimberley Block. This approach provides a readily accessible framework for quantifying the otherwise undetectable, timing and magnitude of long‐term crustal denudation in these terranes, for a part of the geological record previously largely unconstrained. Discrete episodes of enhanced denudation occurred principally in response to changes in drainage, base‐level changes and/or uplift/denudation related to far‐field effects resulting from intraplate stress or tectonism at plate margins. The tectonism was mainly associated with the history of continental breakup of the Gondwana Supercontinent from Late Palaeozoic time, although effects related to compression are also recorded in eastern Australia. The results also suggest that the magnitude of denudation of cratonic blocks has been significantly underestimated in previous studies, and that burial and exhumation are significant factors in the preservation of apparent ‘ancient’ features in the Australian landscape.  相似文献