苏北盆地高邮凹陷侵入岩形成时期及成因机制探讨

通过对苏北盆地高邮凹陷的上、下两套侵入岩与断层的错断及其与构造运动强弱的关系、与油气成藏期的关系以及侵入岩的平面分布研究,提出了侵入岩的侵入时期为三垛期,而非盐城期。通过对晚白垩世以来苏北盆地各期构造运动及其伴生火山活动的分析,认为高邮凹陷侵入岩的成因主要由于晚始新世至渐新世末,该区发生了三垛运动,并发育一系列北东及北西向的断裂构造,导致了岩浆活动,并以侵入特征为主。     

准噶尔盆地南缘新生代地层时代研究

对准噶尔盆地南缘金沟河剖面进行了磁性地层学研究,建立了该剖面精细的磁极性年代框架,并探讨了准噶尔盆地南缘新生代地层的年代。金沟河剖面出露的新生代地层厚约4160m,由老到新依次为安集海河组、沙湾组、塔西河组、独山子组和西域组。通过系统热退磁和剩磁测量,1285块样品获得特征剩磁,并由此建立该剖面自出露的安集海河组底部至西域组中部厚约3250m地层的磁极性柱。根据该剖面极性柱的变化特征和剖面中发现的两处脊椎动物化石,与2004年标准磁极性柱进行了对比。结果表明,金沟河剖面研究段地层的年代约为28.0—4.0Ma,其中安集海河组、沙湾组、塔西河组和独山子组的年代分别约为28.0—23.3Ma、23.3—17.5Ma、17.5—13.2Ma和13.2—6.0Ma,根据沉积速率外推得到的西域组的年代约为6.0—1.1Ma。与前人划分的准噶尔盆地南缘新生代地层的年代相比较,金沟河剖面磁性地层学确定的安集海河组、沙湾组和塔西河组的年代与前人的划分基本相符,而独山子组和西域组的年代则明显偏老。     

Abrasion-derived sediments under intensified winds at the latest Pleistocene leading edge of the advancing Sinai-Negev erg

Quaternary desert loess and sandstone-loessite relationships in the geological record raise questions regarding causes and mechanisms of silt formation and accretion. In the northern Sinai-Negev desert carbonate terrain, only sand abrasion in active erg could have produced the large quantities of quartzo-feldspathic silts constituting the late Quaternary northwestern Negev loess. In the continuum of source (medium to fine sand of dunes) to sink (silts in loess) the very fine sand is unaccounted for in the record. This weakens the sand abrasion model of silt formation as a global process. Here, we demonstrate that, as predicted by experiments, abrasion by advancing dunes generated large quantities of very fine sand (60-110 μm) deposited within the dune field and in close proximity downwind. This very fine sand was generated 13-11 ka, possibly synchronous with the Younger Dryas under gusty sand/dust storms in the southeastern Mediterranean and specifically in the northern Sinai-Negev erg. These very fine sands were washed down slope and filled small basins blocked by the advancing dunes; outside these sampling basins it is difficult to identify these sands as a distinct product. We conclude that ergs are mega-grinders of sand into very fine sand and silt under windy Quaternary and ancient aeolian desert environments.     

Late glacial vegetation and climate oscillations on the southeastern Tibetan Plateau inferred from the Lake Naleng pollen profile

We present a late glacial pollen record (17,700 to 8500 cal yr BP) from a Lake Naleng sediment core. Lake Naleng is located on the southeastern Tibetan Plateau (31.10°N 99.75°E, 4200 m) along the upper tree-line. Variations in the summer monsoon are evident from shifts in vegetation that correspond to late glacial climate trends from other monsoon-sensitive regions. Alpine steppe was recorded between 17,700 and 14,800 cal yr BP, indicating low effective moisture at the study site. Expansion of alpine meadows followed by advances in the position of tree-line around Lake Naleng suggest that climate became warmer and wetter between ∼ 14,800 and 12,500 cal yr BP, probably representing an enhancement of the Asian monsoon. Climatic cooling and reduced effective moisture are inferred from multivariate analysis and the upward retreat of tree-line between ∼ 12,500 and 11,700 cal yr BP. The timing and nature of these shifts to warm, wet and then cold, dry climatic conditions suggest that they correspond to the Bølling/Allerød and Younger Dryas intervals. Abies-Betula forests, representing warm and moist conditions, spread during the early Holocene.     

藏北羌塘中央隆起带果干加年山晚三叠世珊瑚化石发现及其地质意义

藏北羌塘盆地中央隆起带果干加年山北坡首次发现了较丰富的珊瑚化石。珊瑚主要属种有8属10种及未定种:Distichophyllia norica(Frech),Gablonzeria irregularis DengZhang,Margarophyllia stylophylloides(Vinassa deRegny),M.zogangensisDengZhang,Margarophyllia? sp.,Montlivaltia tenuise DengZhang,Pamiroserisrectilamellosa(Winkler),Paradistichophyllum verticalis DengZhang,Paradistichophyllum?sp.,StylophyllopsismosjvariFrech等。产出这些珊瑚化石的灰岩地层原来被认为是混杂在晚三叠世望湖岭组碎屑岩中的古生代灰岩断块,而新发现的珊瑚指示地层时代并非是古生代,而是晚三叠世。这说明果干加年山地区不存在上三叠统碎屑岩和古生界灰岩混杂的现象。果干加年山地区的晚三叠世沉积不仅包含有望湖岭组的碎屑岩,还包含有夹在碎屑岩之间的浅海相灰岩。本次研究和前人的资料表明羌塘中央隆起带在晚三叠世并非是隆起剥蚀区,而是海洋沉积区。因而,以往建立在中央隆起带为隆起剥蚀区认识基础上的羌塘盆地晚三叠世沉积古地理环境和"一隆两坳"的大地构造格局认识需要重新考虑。     

The role of glacio-isostasy in the formation of post-glacial river terraces in relation to the MIS 2 ice limit: evidence from northern England

In recent years it has been demonstrated that the formation of long-timescale river terrace sequences, which are generally found in areas beyond the extent of most if not all of the Middle and Late Pleistocene ice sheets, has invariably been a response to uplift during the Late Cenozoic and especially the Quaternary. Climatic fluctuation at a Milankovitch timescale has driven the alternations of aggradation and incision recorded in such terraces. It has been widely observed, however, that fluvial terraces also occur in areas glaciated during the Last Glacial Maximum (LGM), which coincides with marine oxygen isotope stage (MIS) 2. This paper, in seeking to compare records from inside and outside of the LGM ice limit, concentrates on a single English river system, that of the Humber. The Humber estuary is shared by the largely Pennine-derived drainage of the Yorkshire Ouse, to the north and entirely within the MIS 2 glacial limit, and, to the south, the Trent, which is almost wholly outside the LGM limit. Thus the Trent has a terrace sequence extending back to the Middle Pleistocene, whereas in the component rivers of the Ouse system, records begin with the melting of the last glacial ice. Importantly, there is considerable difference in the disposition of the post-LGM fluvial deposits in these two subsystems. In the Ouse system there are modest terrace staircases, commencing with full glacial deposits that stand up to 30 m above the modern floodplain. In the Trent, in contrast, last glacial gravels form the foundation of the modern floodplain, with Holocene sediments emplaced directly above them. Thus there is little or no post-LGM incision in the Trent, whereas in the Ouse several incision events are recorded, continuing into the later stages of the Holocene. Wider comparison reveals that the Ouse system is an exemplar for other sequences within the MIS 2 limit, whereas systems beyond this glaciation typically have last glacial sediments beneath their modern floodplains and show little evidence of Holocene incision. The various possible explanations of these differences are discussed, with emphasis placed on glacio-isostatic uplift of areas glaciated during MIS 2 as the main reason for the significant post-glacial incision that typifies valleys in such regions. A new approach to modelling glacio-isostatic adjustment is outlined, from which it is concluded that lower-crustal flow plays a significant role in this process in regions of relatively hot and dynamic crust, like northern England, in addition to the mantle flow that is considered in conventional analyses of glacio-isostasy. Lower-crustal flow has a significant effect due to the combination of the small spatial scale of the glaciated region of northern England and the high mobility of the lower-crustal layer beneath it, due to the heating effect of the widespread Palaeozoic granite in the area.     

内蒙古牙克石地区晚古生代弧岩浆岩:年代学及地球化学证据

在内蒙古牙克石地区晚古生代岩浆岩中发现了岛弧火山岩和埃达克质花岗闪长岩。火山岩由玄武岩、安山岩、英安岩及凝灰岩组成,属于钙碱性系列,它们富集大离子亲石元素(LILE)、轻稀土元素(LREE),亏损高场强元素(HFSE)。玄武岩的SHPIMP锆石U-Pb年龄表明其形成于373.2±5.3Ma。锆石εHf(t)值为+14.67～+18.67,类似大洋中脊玄武岩(MORB)和现代俯冲带玄武岩的Hf同位素特征。上述特征说明,玄武岩很可能起源于受俯冲板片流体改造的亏损地幔楔,形成于活动大陆边缘。花岗闪长岩的结晶年龄为331.2±3.7Ma。岩石高SiO2、Sr,高Sr/Y比值,富集轻稀土元素,亏损重稀土元素和Y及高场强元素,铕异常基本不明显,具备埃达克岩的地球化学特征。锆石εHf(t)值较高(+12.78～+14.54),说明源区可能为亏损地幔或新生的玄武质下地壳。根据微量元素组成认为花岗闪长岩主要起源于晚古生代底侵的岛弧玄武-安山质下地壳。弧火山岩和埃达克质花岗闪长岩的发现表明,区内晚泥盆世-早石炭世发生过大洋板片的俯冲作用,可能与额尔古纳-兴安地块与松嫩地块的碰撞拼合密切相关。     

浙闽晚中生代辉绿岩脉的岩石成因:年代学与地球化学制约

来自浙江文成和福建永泰两地的侵位于晚中生代中酸性火山岩地层中辉绿岩脉的形成于90～94Ma,为晚白垩世岩石圈伸展作用产物。两地辉绿岩的SiO2=48.61%～55.54%,Na2O=1.98%～3.89%,K2O=0.28%～2.26%,为钙碱性系列;岩浆在演化过程中经历了一定程度的镁铁质矿物、斜长石和副矿物的分离结晶作用。在微量元素特征上LILE(如Ba、Th)和LREE富集、HFSE亏损;具高放射成因Sr和低放射成因Nd同位素组成(文成辉绿岩:87Sr/86Sr(i)=0.7080～0.7097,εNd(t)=-7.7～-3.4;永泰辉绿岩:87Sr/86Sr(i)=0.7061～0.7062,εNd(t)=-1.2～+0.5),明显不同于亏损软流圈来源岩浆。地壳混染/AFC、岩浆混合等过程不足以解释这些辉绿岩的元素-同位素变化特征。结合主、微量元素和Sr-Nd同位素组成,我们认为区域晚中生代辉绿岩为伸展拉张背景下,软流圈上涌与富集岩石圈地幔相互作用,两种源区共同发生部分熔融的结果,其中文成辉绿岩有更大比例的富集岩石圈组分参与,而永泰辉绿岩的熔融源区中软流圈组分则更高。     

新疆阿克苏地区新元古代晚期地层沉积相及层序地层研究

通过阿克苏地区尤尔美那克村、尤尔美那克村西、阿克苏水泥厂实测剖面研究,将该地区南华系晚期和震旦系地层由下向上划分为：冰成相、浅海陆棚相、潮坪相、滨岸相、浅海相以及碳酸盐台地相。这些地层可分为两个层序（Sq1和Sq2）,Sq1层序由尤尔美那克组地层和苏盖特布拉克组下亚组组成,包括冰成相、浅海陆棚相、潮坪相和滨岸相,属典型的冰期地层层序。Sq2层序由苏盖特布拉克组上亚组和奇格布拉克组组成,包括滨岸相,浅海相和碳酸盐台地相,属于潮汐作用为主的滨浅海碎屑岩-碳酸盐岩层序。根据年龄、碳同位素和冰期沉积特征综合对比,阿克苏地区晚元古代Sq1和Sq2层序应分别对比于鲁克塔格地区的第4和第5层序,说明尤尔美那克冰期相当于特瑞艾肯冰期,并揭示阿克苏地区在晚元古代早期应有较长阶段的缺失或剥蚀。     

西秦岭天水地区新生代酸性火山岩地球化学特征及其构造意义

西秦岭天水地区分布有新生代陆相酸性火山岩，主要由流纹岩、流纹质角砾凝灰熔岩、流纹质熔结(角砾)凝灰岩及少量角砾凝灰岩、火山角砾岩等组成，具有富硅、富碱、低铝、低钙特征，属于非造山偏碱性岩石，类似于大陆裂谷碱性流纹岩。研究表明，新生代陆相酸性火山岩为地壳岩石部分熔融作用的产物，形成于陆内拉张构造环境，与新生代早期渭河断裂带的左行走滑剪切构造作用有关。