可拓理论在矿区土地破坏程度评价中的应用

将矿区破坏土地、评价指标、指标现状结合为一体,利用可拓集理论,通过关联函数,给出了各评价指标影响矿区土地破坏程度的量化描述,进而确定了所选矿区土地的破坏程度,并结合Arcmap软件精确确定了不同破坏程度土地的面积;采用了集值统计的方法确定了物元特征权重,从而提高了评价的精确性;科学地确定了评价单元划分要求,使得评价结果更能指导实际工作,评价结果能够为矿区破坏土地的合理利用提供有利的依据,同时也证明了可拓理论在矿区土地破坏程度评价中的应用是可行的。     

Mesozoic–Tertiary structural evolution of an extensional gneiss dome—the Kesebir–Kardamos dome, eastern Rhodope (Bulgaria–Greece)

The tectonic evolution of the Rhodope massif involves Mid-Cretaceous contractional deformation and protracted Oligocene and Miocene extension. We present structural, kinematic and strain data on the Kesebir–Kardamos dome in eastern Rhodope, which document early Tertiary extension. The dome consists of three superposed crustal units bounded by a low-angle NNE-dipping detachment on its northern flank in Bulgaria. The detachment separates footwall gneiss and migmatite in a lower unit from intermediate metamorphic and overlying upper sedimentary units in the hanging wall. The high-grade metamorphic rocks of the footwall have recorded isothermal decompression. Direct juxtaposition of the sedimentary unit onto footwall rocks is due to local extensional omission of the intermediate unit. Structural analysis and deformational/metamorphic relationships give evidence for several events. The earliest event corresponds to top-to-the SSE ductile shearing within the intermediate unit, interpreted as reflecting Mid-Late Cretaceous crustal thickening and nappe stacking. Late Cretaceous–Palaeocene/Eocene late-tectonic to post-tectonic granitoids that intruded into the intermediate unit between 70 and 53 Ma constrain at least pre-latest Late Cretaceous age for the crustal-stacking event. Subsequent extension-related deformation caused pervasive mylonitisation of the footwall, with top-to-the NNE ductile, then brittle shear. Ductile flow was dominated by non-coaxial deformation, indicated by quartz c-axis fabrics, but was nearly coaxial in the dome core. Latest events relate to brittle faulting that accommodated extension at shallow crustal levels on high-angle normal faults and additional movement along strike-slip faults. Radiometric and stratigraphic constraints bracket the ductile, then brittle, extensional events at the Kesebir–Kardamos dome between 55 and 35 Ma. Extension began in Paleocene–early Eocene time and displacement on the detachment led to unroofing of the intermediate unit, which supplied material for the syn-detachment deposits in supra-detachment basin. Subsequent cooling and exhumation of the footwall unit from beneath the detachment occurred between 42 and 37 Ma as indicated by mica cooling ages in footwall rocks, and extension proceeded at brittle levels with high-angle faulting constrained at 35 Ma by the age of hydrothermal adularia crystallized in open spaces created along the faults. This was followed by Late Eocene–Oligocene post-detachment overlap successions and volcanic activity. Crustal extension described herein is contemporaneous with the closure of the Vardar Ocean to the southwest. It has accommodated an earlier hinterland-directed unroofing of the Rhodope nappe complex, and may be pre-cursor of, and/or make a transition to the Aegean back-arc extension that further contributed to its exhumation during the Late Miocene. This study underlines the importance of crustal extension at the scale of the Rhodope massif, in particular, in the eastern Rhodope region, as it recognizes an early Tertiary extension that should be considered in future tectonic models of the Rhodope and north Aegean regions.     

琼中麻粒岩的成因及地质意义

对琼中前寒武纪高级变质杂岩中的麻粒岩进行了较系统的岩石学和矿物学研究,并利用不同的矿物温压计估算了麻粒岩形成的温压条件。结果表明,本区麻粒岩形成于高温低压(低p/T)环境,属于典型的低压麻粒岩,其峰期变质温度为824±15℃,压力小于0.5GPa,晚期岩石发生了退变冷却,终止温度为705℃左右,压力与峰期时的压力相近;麻粒岩相变质作用具有顺时针的p-T轨迹,早期可能经历了一个缓慢降压升温的过程,峰期之后的退变则表现出近等压冷却(IBC)的特点。结合岩石变形作用较弱的特点及区域大地构造背景,认为琼中低压麻粒岩形成于陆缘拉张环境,其可能的机制是,由于地壳拉伸减薄,导致软流圈减压上隆产生岩浆,上覆地壳岩石(包括已经结晶的岩浆)受到下部岩浆热源的影响而发生进变质,随后受拉伸扰动的地热梯度向正常地热梯度恢复,从而形成具有降压升温过程和IBC过程的顺时针p-T轨迹。     

基于最优组合赋权理论的可拓学评价模型的应用

地质灾害易发区的划分对科学防治地质灾害具有重要的指导意义。根据易发区划分原理,提出已有灾害点数量、地形地貌、地质构造、岩土体类型、多年平均降雨量、植被覆盖率以及人类工程活动影响7个参评指标。将偏好比率法和熵值函数进行最优组合,确定权系数,并应用于可拓学评价中,提出了地质灾害易发区划分的一种新模型——基于最优组合赋权理论的可拓学评价模型。吉林省地质灾害易发区划分与野外调查情况相吻合。     

鄂尔多斯地块北部中、新生代玄武岩地球化学特征及其地质意义

通过对分布于鄂尔多斯地块北部杭锦旗与和林格尔玄武岩地球化学特征的研究,探讨了该区中、新生代岩浆源区的组成、变化及其所反映的地质意义。杭锦旗与和林格尔分别有早白垩世(Ar-Ar年龄为126.2Ma)和晚中新世(Ar-Ar年龄为6.4Ma)玄武岩分布。杭锦旗早白垩世玄武岩的SiO2(46.93%～47.93%)较低而碱含量较高(K2O+Na2O为5.75%～6.21%),组合指数σ为6.7～8.0,K2O(Na2O-2),属于碱性系列的钾质粗面玄武岩;其Mg#值为32.4～32.8,Ni、Cr含量低于20μg/g,反映玄武岩浆形成后经历过橄榄石和单斜辉石分离结晶等后期演化作用;其Nb、Ta相对于La亏损,初始87Sr/86Sr为0.7062,εNd(t)为-12.25,反映岩浆源区主要为富集EMI型地幔。和林格尔晚中新世玄武岩为橄榄拉斑玄武岩,其组合指数σ为2.1～2.8,Mg#值变化于46.7～52.4,Ni含量变化于111.1～125.8μg/g,Cr为123～178μg/g,Mg#值和Ni、Cr含量的变化反映岩浆原生程度随时间变新有所增大;其Nb、Ta相对富集,具有相似于OIB的微量元素特征,但仍表现相对富集的Sr-Nd同位素性质,初始87Sr/86Sr比值变化于0.7051～0.7053,εNd(t)为-1.91～-0.74,推测为软流圈与EMI型岩石圈地幔相互作用的产物。杭锦旗与和林格尔玄武岩的207Pb/204Pb比值都较低,△207/204为3.6～6.5,△208/20460,均具EMI型Dupal异常。玄武岩地球化学特征进一步表明,华北克拉通西部的鄂尔多斯地块所处的岩石圈自早白垩世以来发生过较小规模的伸展减薄作用,但其伸展减薄和被改造的程度远弱于华北东部。     

西藏西北部旋风沟地区古近纪潜花岗斑岩的发现及意义

潜花岗班岩为火山颈相,其锆石U-Pb同位素年龄为32±0.2Ma。岩石具有富Al、Th和LREE特征,Eu负异常不明显,表明不是由基性浆演化而成,而是由加厚陆壳底部熔融形成的。结合区域构造、沉积记录和火山岩组合特征,潜花岗斑岩形成于大陆拉张环境。潜花岗斑岩年龄的确定制约了新生代沉积地层的年代,同时也为藏北地区陆内拉张时代的确定提供了依据。     

云南大坪金矿床矿化剂来源及其对金成矿的制约

本文基于对大坪金矿成矿流体中矿化剂来源、成矿时代和成矿流体形成演化过程中水－硫化剂－－金耦合作用关系的研究,探讨了大坪金矿床形成的可能机制。研究结果表明,大坪金矿的成矿时代约为５０Ｍａ,金成矿所需的矿化为自深部。大坪金矿床之所以形成在喜山早期,主要是通过喜山早期富矿化剂的深源流体上升,加入原在闪长岩体内循环的贫矿化剂本,从而使这种贫矿化剂的流体转化成富矿化剂进而能够浸取金的成矿流体来实现的。     

Interaction between Downslope and Alongslope Processes on the Margins of Daihai Lake,North China: Implication for Deltaic Sedimentation Models of Lacustrine Rift Basin

Daihai Lake, a modern lacustrine rift basin, located in Inner Mongolia, North China, serves as an important modern analog for understanding deltaic depositional processes in an active rift setting. Two of the deltas (Yuanzigou delta and Bulianghe delta) on the margins of Daihai Lake were surveyed to compare and contrast stacking patterns using aerial photographs, field trenching and sediment sampling. Shallow cores and trench data collected from the margins of Daihai Lake indicate that a variety of depositional processes have been active since Daihai Lake formed. Two 3-D sedimentation models which employ chronostratigraphic correlation technique were generated. The chronostratigraphic sedimentation models predict and represent the architectures and sand-body continuity of sediments. Stratigraphical coincidence of the broad sheeted drifts and channel erosion suggests a coupling between downslope and alongslope processes. Distributary mouth bars are prevalent in the front of deltas on steeper slopes due to the dominance of down-slope flows. On the contrary, the along-slope currents favor the development of distal bar deposits with sheeted sandbodies on gentle depositional slopes. This study provides an insight into the architecture of complex sedimentary facies associated with highlighting key differences between downslope flows and alongslope currents. The distribution of sand within these deltas is of particular interests, with applications in understanding the architecture of hydrocarbon reservoirs formed in lacustrine rift basin.     

黄骅坳陷孔南地区新生代断裂特征及其与油气关系

黄骅坳陷孔南地区新生代盆地演化经历了断陷期、断坳期及坳陷期。盆地内部发育复杂断裂系统,根据断层活动特征可以分为沧东伸展断裂系统与徐西右旋走滑断裂系统。沧东断层剖面上具有铲式正断层特征,向深部滑脱,控制了孔南地区的构造变形;徐西断层可以看作是其上盘上的次级断层。在孔店组沉积期,沧东断层与徐西断层均表现出伸展正断层的特征,控制了其上盘孔店组沉积。在沙河街组三段沉积期,受基底断层右旋走滑影响,徐西断层及其上盘分支断层表现出右旋走滑特征。在伸展与走滑的共同作用下,在孔南地区中北部聚集了丰富的油气。     

广西钦州地区那丽花岗岩LA-ICP-MS锆石U-Pb定年及其地质意义

位于广西南部钦州地区的那丽岩体是华南地区(除海南岛外)报道的、具精确同位素年龄的海西期花岗岩岩体,LA-ICP-MS锆石U-Pb定年结果显示其形成时代为262Ma。二叠纪时期,羌塘-中缅Sibumasu地块与印支地块碰撞拼合,导致华南陆块俯冲于印支陆块之下,那丽花岗岩可能形成于这种俯冲作用的较晚阶段——弧后伸展环境。