The age of continental roots   总被引：39，自引：0，他引：39  

D. G. Pearson 《Lithos》1999,48(1-4):171-194

Determination of the age of the mantle part of continental roots is essential to our understanding of the evolution and stability of continents. Dating the rocks that comprise the mantle root beneath the continents has proven difficult because of their high equilibration temperatures and open-system geochemical behaviour. Much progress has been made in the last 20 years that allows us to see how continental roots have evolved in different areas. The first indication of the antiquity of continental roots beneath cratons came from the enriched Nd and Sr isotopic signatures shown by both peridotite xenoliths and inclusions in diamonds, requiring isolation of cratonic roots from the convecting mantle for billions of years. The enriched Nd and Sr isotopic signatures result from mantle metasomatic events post-dating the depletion events that led to the formation and isolation of the peridotite from convecting mantle. These signatures document a history of melt– and fluid–rock interaction within the lithospheric mantle. In some suites of cratonic rocks, such as eclogites, Nd and Pb isotopes have been able to trace probable formation ages. The Re–Os isotope system is well suited to dating lithospheric peridotites because of the compatible nature of Os and its relative immunity to post-crystallisation disturbance compared with highly incompatible element isotope systems. Os isotopic compositions of lithospheric peridotites are overwhelmingly unradiogenic and indicate long-term evolution in low Re/Os environments, probably as melt residues. Peridotite xenoliths from kimberlites can show some disturbed Re/Os systematics but analyses of representative suites show that beneath cratons the oldest Re depletion model ages are Archean and broadly similar to major crust-forming events. Some locations, such as Premier in southern Africa, and Lashaine in Tanzania, indicate more recent addition of lithospheric material to the craton, in the Proterozoic, or later. Of the cratons studies so far (Kaapvaal, Siberia, Wyoming and Tanzania), all indicate Archean formation of their lithospheric mantle roots. Few localities studied show any clear variation of age with depth of derivation, indicating that >150 km of lithosphere may have formed relatively rapidly. In circum-cratonic areas where the crustal basement is Proterozoic in age kimberlite-derived xenoliths give Proterozoic model ages, matching the age of the overlying crust. This behaviour shows how the crust and mantle parts of continental lithospheric roots have remained coupled since formation in these areas, for billions of years, despite continental drift. Orogenic massifs show more systematic behaviour of Re–Os isotopes, where correlations between Os isotopic composition and S or Re content yield initial Os isotopic ratios that define Re depletion model ages for the massifs. Ongoing Sr–Nd–Pb–Hf–Os isotopic studies of massif peridotites and new kimberlite- and basalt-borne xenolith suites from new areas, will soon enable a global understanding of the age of continental roots and their subsequent evolution.  相似文献   

中国中部高铝质超高压变质岩   总被引：6，自引：3，他引：3  

..  硬水铝石 《岩石学报》1999,15(4):548-556

我国中部在超高压条件下形成的高铝质变质岩石, 以蓝晶黄玉石英岩为特征, 具有以蓝晶石、富水黄玉、富镁硬绿泥石、柯石英、硬水铝石等为代表的高压－超高压变质矿物, 矿物组合主要为蓝晶石＋ 黄玉＋ 石英 （柯石英）、蓝晶石＋ 蓝刚玉±富镁硬绿泥石等。化学成分富铝而贫镁, 其原岩为陆缘高铝质泥质沉积岩。实验岩石学的研究表明, 蓝晶石＋ 黄玉在１０００℃～１２００℃,３．１～３．７７ＧＰａ 条件下仍可稳定存在,而石英已部分转变为柯石英。蓝晶石＋ 黄玉与柯石英一起稳定于超高压条件下。这表明以高铝质岩石为代表的地壳物质已进入到地幔深度, 达到这样的深度只能由会聚板块的俯冲作用而引起。因此,高铝质岩石的存在可以作为Ａ型俯冲作用的指示剂。超高压变质的高铝质岩石将成为陆－陆碰撞事件的重要研究内容。  相似文献   

Towards an operational use of space imagery for oil pollution monitoring in the Mediterranean basin: a demonstration in the Adriatic Sea     

Ferraro G  Bernardini A  David M  Meyer-Roux S  Muellenhoff O  Perkovic M  Tarchi D  Topouzelis K 《Marine pollution bulletin》2007,54(4):403-422

Studies of operational pollution carried out by European commission - Joint Research Centre in the Mediterranean Sea for the years 1999-2004 are briefly introduced. The specific analysis of the Adriatic Sea for the same period demonstrates that this area has been characterized by a relevant number of illegal discharges from ships. After setting the historical background of the project AESOP (aerial and satellite surveillance of operational pollution in the Adriatic Sea), the content, partners and aim of the project are presented. Finally, the results of the first phase of the AESOP project are presented. The results seem very encouraging. For the first time in the Adriatic, real time detection of oil spills in satellite images and an immediate verification by the Coast Guard has been undertaken. An exploratory activity has also been carried out in collaboration with the University of Ljubljana to use automatic information system (AIS) to identify the ships detected in the satellite images.  相似文献   

海洋教育：教育思想与实践的嬗变          下载免费PDF全文

肖圆  郭新丽  宁波 《海洋开发与管理》2022,39(3):101-105

当今世界,国与国之间海洋实力的竞争,已经从最初对海洋资源的竞争变成海洋人才竞争,而海洋教育则是海洋人才的摇篮,逐渐成为教育体系中不容忽视的重要实践。从少数人海洋教育意识的觉醒,再到如今面向普罗大众的社会海洋教育,由海洋教育衍生的知行、创新、问题思维教育模式,成为推动教育思想与教育实践嬗变的活力因素。文章梳理海洋教育思想及教育实践发展的特点,围绕发展过程中存在的优势与不足,提出海洋教育发展的新路径,使海洋教育更好地服务建设“海洋强国”等国家战略。  相似文献   

湄洲湾海雾的初步分析   总被引：1，自引：0，他引：1  

陈玉珍  黄玉藻 《台湾海峡》1999,18(1):49-54

分析福建湄洲湾1985－1992年海雾的气候特点,发现79％的海雾发生在2－5月。应用中国气象局北京气象中心出版的历史天气图,对本区海雾进行天气学分型,结果表明,有89％的海雾出现在锋面偏北,南高北低,东脊型中,利用850hPa天气型的消空条件,结合气象因子和单站资料,得出了湄洲湾海雾的短期预报指标,并建立了预报方程。  相似文献   

Multilateralism in the Straits of Malacca and Singapore     

《Marine Policy》2014

This paper analyzes International Maritime Organization (IMO) involvement in maritime cooperation regime in the Straits of Malacca and Singapore through multilateralism. It begins by introducing the maritime cooperation regime prior to 2001, which was mainly trilateral in nature through Tripartite Technical Expert Group on the Safety of Navigation (TTEG). Although TTEG managed to increase the level of safety of navigation in the Straits of Malacca and Singapore through the implementation of the Traffic Separation Scheme (TSS) in 1981 and Mandatory Ship Reporting System (STRAITREP) in 1998, such cooperation was beset by financial strain and conflict of interests. Subsequently, there was a change in the cooperation regime after 9/11 incident. This paper identifies that the change was contributed by the IMO through a methodology called multilateralism. Three important principles were adopted by IMO in implementing multilateralism in the Straits of Malacca and Singapore, namely generalized principles of conduct (respect for sovereignty and compliance with burden sharing principle under Article 43 of UNCLOS 1982), diffuse reciprocity, and indivisibility. This paper concludes that multilateralism by IMO has transformed trilateral cooperation into multilateral cooperation in the Straits of Malacca, combining state actors (littoral states and user states) and non-state actors (non-governmental organizations and international shipping industries).  相似文献   

欧亚大陆春季融雪与长江流域夏季降水的可能联系   总被引：1，自引：1，他引：0       下载免费PDF全文

韩冬  陈海山  许蓓  齐铎  吴波 《气象科学》2014,34(3):237-242

利用1979—2007年全球月平均的积雪水当量资料,定义了春季积雪水当量增量指数,该指数可以较为直观地反映春季融雪的情况。通过这一纽带,分析了欧亚大陆春季融雪与长江流域夏季降水之间的联系。研究表明:欧亚大陆春季融雪与中国长江流域夏季降水是负相关关系,这与高原积雪的影响是不一致的。春季融雪量的减少,使得欧亚大陆北部夏季剩余积雪偏多,夏季融雪增多。融雪的局地效应使得土壤湿度增加,加大了欧亚大陆南北热力差异。从而,夏季中纬度的纬向风切变增大,对流层上层的副热带西风急流增强,副热带高压增强西伸,但是北抬受到抑制。长江流域位于异常西南暖湿气流与冷空气的辐合带上,上升运动活跃,有利于降水偏多。  相似文献   

The Portuguese maritime spatial plan     

《Marine Policy》2013

Numerous national governments and supranational organizations such as the OSPAR Commission, the European Union and the United Nations Educational, Scientific and Cultural Organization (UNESCO) have underlined the importance of maritime spatial planning (MSP) for balancing and solving conflicts between the needs of different sectors and conservation in the marine space. In the last decade, many maritime spatial plans have been developed around the world. The drivers to develop these plans and the approaches to find solutions for the particular problems differ significantly. The Portuguese national marine jurisdiction is one of the largest in Europe. For the continental part, a maritime spatial plan was initiated in 2009, and entered in 2010 in the final stage of approval. One of the driving forces for this MSP initiative was the claim to extend its continental shelf. The development process was led by a multidisciplinary team. Despite the challenges, the existing as well as potential future marine resources and activities were characterized, mapped and categorized. To overcome conflicts resulting from the many overlapping uses and to assure sustainable development of all sectors, a conflict analysis and evaluation of potential future uses were necessary. The applied zoning scheme represented an exercise of conflict solving and proved to be a powerful tool to promote discussion and participation among stakeholders. The successful implementation of Portuguese MSP will rely largely on its ability to provide efficient management, financial and legal mechanisms to achieve the integration of all strategies and spaces under the Portuguese maritime jurisdiction.  相似文献   

海洋强国战略下涉海大学生海洋领域就业研究          下载免费PDF全文

车淼洁  王睿 《海洋开发与管理》2020,37(11):40-44

当代涉海专业大学生是建设海洋强国、实现国家发展战略的关键接班人和后备军。文章围绕某高校涉海大学生展开调查发现，海洋领域就业意向与专业满意度、家人的态度、实习经历等显著相关；影响择业的主要因素是收入和地域。文章提出，传播海洋强国战略、加强理想信念教育，弘扬海洋精神、培育敬业奉献素质，深化校企合作、拓宽海洋领域实习实践，细化职业规划、精准开展就业指导等途径，有助于培养和输送涉海大学生服务海洋战略、投身海洋重点领域就业。  相似文献   

海上丝路背景下南亚地缘格局的解构与再建构     

马亚华  周亚兰  黄丹华 《世界地理研究》2020,29(3):439-450

印巴战略平衡是南亚地区格局形成的基础，是影响中国海上丝路地缘安全最重要的变量之一。进入21世纪以来，由于印度和巴基斯坦在经济和军事尤其是核力量方面持续不平衡增长以及美国南亚战略发生转向，持续多年的南亚地区均势走向瓦解，以中美印大三角为核心的弹性均势体系正逐步取代过去中印巴和美印巴并行的双三角体系。一个缺少制衡且向西方倾斜的印度，可能会给中国印度洋海上油路安全以及西南边疆稳定带来更多不确定性；巴基斯坦的战略处境更加困难，其作为中国与穆斯林世界桥梁、屏蔽极端势力向新疆渗透的能力会有所削弱。未来中国应积极参与南亚地区再平衡建设，在利用经济合作增进地区互信的同时，还应强化对巴基斯坦的经济和军事支持，并在南亚次大陆周边寻找更多战略立足点，谨防在西太平洋和北印度洋两个方向被美日印联合压制，力求把海上丝路沿线地缘安全风险降到最小。  相似文献