从"障塞"一词看海上丝路的起始年代

针对 2 0 0 1年“海上丝绸之路与南方大港学术研讨会”上 ,许多学者认为《汉书·地理志》中“日南障塞”的“障塞”是军事要塞、军事屏障 ,并据此推导出海上丝绸之路徐闻开港时间是汉武帝元鼎六年 (公元前 1 1 1年 )的观点 ,认为 :“障塞”只是一个普通的动词 ,是阻塞不通的意思 ;徐闻的开港时间也不是元鼎六年 ,而是元鼎六年之后、汉元帝之前 ,即大约公元前 1 1 0年—公元前 1年之间     

塔里木地块新元古代冰期事件研究进展

新元古代冰碛岩地层记录了“雪球地球”极端气候事件重要的地质信息。塔里木地块东北缘库鲁克塔格地区、西北缘阿克苏地区和西南缘叶城地区新元古代冰碛岩地层露头发育,是研究新元古代冰期事件的理想基地。文章基于塔里木地块周缘新元古界详实的野外地质调查工作,综合了地层学、同位素年代学、岩石地球化学等研究,聚焦冰碛岩地层沉积时代这一核心问题,建立新元古代冰期格架。冰期事件对比显示,贝义西冰期(库鲁克塔格地区)相当于Kaigas冰期(国际),阿勒通沟冰期(库鲁克塔格地区)、巧恩布拉克冰期(阿克苏地区)、波龙冰期(叶城地区)相当于Sturtian冰期(国际),特瑞爱肯冰期(库鲁克塔格地区)、尤尔美那克冰期(阿克苏地区)、雨塘冰期(叶城地区)相当于Marinoan冰期(国际),汉格尔乔克冰期(库鲁克塔格地区)相当于Gaskiers冰期(国际)。同时基于冰期事件对比关系,建议根据国际地层委员会的最新划分方案将塔里木地块南华系底界调整为与全球性Sturtian冰期沉积底界相当的层位。通过探讨新元古代冰期事件与古老烃源岩发育的耦合关系,分析了新元古界优质烃源岩的发育潜力,指出塔里木地块新元古界具备良好的油气成藏地...     

扬子地块西缘中元古界登相营群年代学及地质意义

扬子板块西缘中元古界登相营群为一套与裂谷相关的沉积- 火山岩序列,其年代学和构造背景对理解扬子板块前寒武纪构造演化具有重要意义。本文获得登相营群松林坪组、则姑组和朝王坪组火山岩LA- ICP- MS锆石U- Pb年龄分别为1166±6 Ma、1040±4 Ma和1020±4 Ma,精确限制了登相营群时代为1166~1020 Ma。松林坪组砂岩碎屑锆石年龄具有多峰值特征,地球化学特征表明砂岩物源主要来自酸性火山岩以及花岗岩。则姑组英安岩具有较高的Ga/Al比值和Zr、Hf、Ga和HREE含量以及高的锆石饱和温度,属于A型花岗岩系列,锆石εHf(t)值为~15. 1~9. 1,说明来自花岗质地壳物质的部分熔融。构造背景判别图解显示登相营群砂岩和英安岩形成于大陆裂谷盆地。结合前人的研究成果,笔者认为扬子地块西缘中元古代晚期构造属性为被动大陆边缘裂谷,新元古代早期构造动力学背景转为活动大陆边缘洋- 陆俯冲,扬子板块应位于超大陆的边缘位置。     

Dynamic responses of two blocks under dynamic loading using experimental and numerical studies

Block type quay walls are one of the most generally used type of gravity quay walls however seismic risks of this kind of structures have not already received the proper amount of attention. In this study, stability of block type quay wall which consists of two concrete blocks is investigated experimentally and numerically. 1 g shaking table tests are used for experimental study. Model scale is 1/10 and model is placed on rigid bed to ignore damage due to foundation deformation. Two different granular materials (Soil 1 and Soil 2) which have different nominal diameters are used as backfill materials to understand the effect of nominal diameters on structure's stability. During the experiments accelerations, pore pressures, soil pressures and displacements are measured for two blocks under different cycling loadings. Soil pressure test results are presented in non-fluctuating and fluctuating components to determine the distribution and application point of the fluctuating component on two blocks. By using experiment results, the friction coefficients between the rubble-block and block-block are determined and compared with recommended friction coefficients in standards. PLAXIS V8.2 software program is used for numerical study to determine the material properties.     

华北板块东南缘五河杂岩的麻粒岩相变质、部分熔融与交代作用

华北板块东南缘五河杂岩属于前寒武纪变质基底,出露于蚌埠及相邻地区,主要由变质的镁铁质和长英质火成岩以及表壳岩系组成,并伴生有古元古代片麻状花岗岩和中生代花岗岩类,构成了"蚌埠隆起"。五河杂岩中主要有石榴斜长角闪岩/榴闪岩、石榴麻粒岩、异剥钙榴岩、石榴斜长角闪片麻岩、花岗片麻岩、云母片岩、大理岩和变质砂岩等岩石类型。这些不同类型的变质岩具有类似的峰期变质矿物,如石榴子石、单斜辉石、斜长石、金红石和石英等;结合其锆石U-Pb年龄,表明它们共同经历了古元古代高压麻粒岩相变质作用。石榴斜长角闪岩的石榴子石包体中存在钾长石+斜长石+石英+黑云母等矿物交生体,指示早期花岗质熔体的存在,证明五河杂岩在古元代变质过程中发生了部分熔融作用。此外,部分变基性岩中存在方解石、绿帘石和绿泥石等蚀变矿物,沿石榴子石的裂隙中分布有钾长石+斜长石+石英+黑云母+角闪石等矿物,表明它们经历了含碳酸盐的熔/流体交代作用以及绿帘石化和绿泥石化作用等。遭受过古元古代含碳酸盐的熔/流体交代作用的变基性岩表现为高放射成因Pb同位素组成,而未遭受含碳酸盐的熔/流体交代作用的变基性岩则表现为典型华北板块前寒武纪麻粒岩地体和下地壳包体岩石的低放射成因Pb同位素组成。     

SHRIMP U–Pb zircon dating of Grenville-age events in the western part of the Musgrave Block, central Australia

Shrimp U–Pb zircon dating of structurally constrained felsic orthogneiss samples in the western Musgrave Block has been used to delineate discrete magmatic and metamorphic events at c . 1300 and c . 1200  Ma. The dating of pre-D₁ and post-D₁ felsic orthogneiss constrains D₁ to have occurred at 1312±16 to 1324±4  Ma. This is the first geochronological study to identify such a metamorphic and deformation event in the Musgrave Block. D₁ was accompanied by a major magmatic event involving the emplacement of voluminous felsic orthogneiss between 1296 and 1324  Ma. Zircon overgrowths on numerous igneous zircon cores give a consistent age of c . 1200  Ma, reflecting zircon growth during a second high-grade metamorphic event (D₂). This c . 1200  Ma metamorphic event was followed by the intrusion of a c . 1190  Ma megacrystic granite. The c . 1300 and c . 1200  Ma events in the Musgrave Block can be tentatively correlated with metamorphic events in the Albany-Fraser Orogen, and the Windmill Islands and Bunger Hills in east Antarctica. A major continuous Grenville-age orogenic belt joining these areas may have represented a plate boundary between the pre-Rodinian proto-Australian continent and proto-Antarctica during the formation of Rodinia in the Mesoproterozoic.     

Geological and palaeomagnetic significance of the Kulgera Dyke Swarm, Musgrave Block, NT, Australia

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The Kulgera Dyke Swarm consists of olivine tholeiites which have intruded late Proterozoic transitional-granulite gneisses and granites of the eastern Musgrave Block, in central Australia. Preliminary Rb/Sr results suggest that the dolerites were emplaced at 1054 ± 14 Ma. In addition, a Rb/Sr age of 1060 ± 10 Ma on a biotite from a pegmatite indicates thermal resetting of the country rock minerals during dyke emplacement. Palaeomagnetic investigations of the dykes yield a primary thermoremanent magnetization direction corresponding to a palaeomagnetic pole at 17S, 266E ( A ₉₅= 12). In addition to this primary magnetization, an overprint component was present in many of the samples, providing a palaeomagnetic pole at 30S, 138E ( A ₉₅= 24), which is similar to previous results from other central Australian rocks affected by the Alice Springs Orogeny. The results extend the area of influence of the Carboniferous Alice Springs Orogeny southward into the Musgrave Block. Further, the results provide no evidence for an earlier, Late Proterozoic, Petermann Orogeny affecting the Musgrave Block in the Kulgera region. However, the possibility that a Petermann Orogeny thermal overprint has been erased by the Alice Springs Orogeny cannot be dismissed.     

Indosinian Orogenesis in the Lhasa Terrane,Tibet: New Muscovite 40Ar‐39Ar Geochronology and Evolutionary Process

Muscovite 40Ar-39Ar dating of muscovite-quartz schist, eclogite and retrograde eclogite indicates an Indosinian orogenesis occurred at 220–240 Ma in the Lhasa terrane, which is caused by the closure of Paleo-Tethyan ocean basin and the following collision of the northern Lhasa terrane and southern Gondwana land. This Indosinian orogenesis is further confirmed by the regional sedimentary characteristics, magmatic activity and ophiolite mélange. This evidence suggests that the Indosinian orogenic belt in the Lhasa terrane is widely distributed from the Coqen county in the west, and then extends eastward through the Ningzhong and Sumdo area, finally turning around the eastern Himalayan syntaxis into the Bomi county. Based on the evolutionary process, the geological development of Lhasa terrane from early Paleozoic to early Mesozoic can be divided into seven stages. All of the seven stages make up a whole Wilson circle and reveal a perfect evolutionary process of the Paleo-Tethys ocean between the northern Lhasa terrane and southern Gondwana land. The Indosinian orogenisis is a significant event for the evolution of the Lhasa terrane as well as the Tibetan Plateau.     

藏东同卡石榴辉石岩和拉萨地体松多蓝片岩

元古宇卡穷岩群位于班公湖-怒江缝合带内,岩性为黑云斜长片麻岩、黑云斜长变粒岩,花岗片麻岩、大理岩及斜长角闪岩.黑云斜长片麻岩中具铁铝榴石、矽线石、蓝晶石组合.锆石U-Pb同位素年龄为1334 Ma,花岗片麻岩锆石U-Pb年龄(507±10)Ma(SHRIMP),后者可能属稍晚期变形变质的花岗岩侵入体.卡穷岩群属冈瓦纳大陆北缘裂离出来的微陆块.黑云斜长片麻岩中首次发现石榴辉石岩、榴闪岩包体.较新鲜的石榴辉石岩由角闪石、透辉石、石榴石及少量石英、金红石组成,无长石.包体岩石化学成分中SiO_248.65%～51.18%,K_2O＜1%,稀土配分形式为平坦型,无明显的Eu异常.微量元素Rb、Ba、Th富集,低Sr,具洋脊玄武岩特征.石榴石端元组分中铁铝榴石51.44%、镁铝榴石26.73%、钙铝榴石17.29%.透辉石端元组分中,硬玉分子平均为6.40%.镜下常见石榴石、辉石退变为角闪石和斜长石,包体岩石应为榴辉岩退变的产物.     

兰坪铅锌矿跑马坪矿段EH-4法探测矿化异常

兰坪超大型铅锌矿部分矿体埋深达几百米,为寻找矿区及外围深部隐伏铅锌矿,在跑马坪矿段开展EH-4探测,取得较好效果。