特朗普政府以来的美国中东欧政策：调整、目标与展望

自“17+1合作”机制创设以来,中东欧在中欧合作中扮演的角色越来越重要。中国作为一个中东欧地区的“晚到者”,不得不面临长期以来“美、欧、俄”三方地缘博弈的影响。尤其是特朗普上任以来,一方面继承了奥巴马政府末期的中东欧政策,另一方面在能源、地缘和军事方面强化了美国的政策部署。在能源方面,美国进一步强化了将能源外交作为权力资源,平衡美欧俄关系的外交杠杆的作用。在地缘方面,波兰作为该地区的政策支轴国更加受到美国倚重。在军事方面,特朗普政府增强了在中东欧地区的军事存在和军费开支,推进驻欧美军基地的战略东移。通过对美国官方文本的文献考察发现,特朗普政府加强以上三个方面的政策部署,旨在实现以下三个政策目标：制衡俄罗斯、对欧盟分而治之和排挤中国。展望拜登政府,安全与能源仍是美国中东欧政策的首要关切。     

新疆东天山土墩铜镍硫化物矿床中铂的赋存形式及其地质意义

土墩铜镍矿床位于东天山黄山—镜儿泉铜镍成矿带的西端,具有较好的铜、镍资源前景。铜镍矿石中主要金属矿物为黄铜矿、磁黄铁矿、镍黄铁矿、磁铁矿以及黄铁矿等。在详细研究土墩铜镍矿床成矿地质背景的基础上,通过对土墩铜镍矿床中浸染状矿石和块状矿石中主要金属矿物进行电子探针原位测试发现,金属矿物中Pt含量较高,范围在490~2 450 g/t之间,平均为1 713 g/t,而Pd含量则较低。进一步研究Pt的赋存形式及矿石中伴生元素Co、Se、Ag、Sb等的元素地球化学特征,结果表明,晚期成矿热液对早期镍黄铁矿和磁黄铁矿的交代使Pt常发生扩散交代作用,这种热液改造作用对贵金属元素的活化和再富集具有重要意义。此外,土墩铜镍矿床中具有高Se含量、较低S/Se比值以及高R因子值的矿段是极有可能形成铂族元素(PGE)的矿化富集带。     

Stratigraphy and sedimentology of phosphate-rich sediments in Malta and south-eastern Sicily (latest Oligocene to early Late Miocene)

The Maltese archipelago and south‐eastern Sicily include an Uppermost Oligocene to Upper Miocene hemipelagic sedimentary succession representing the Malta‐Hyblean plateau, which limits the eastern Mediterranean to the west. This succession hosts a unique and well‐exposed series of condensed and allochthonous phosphate‐rich beds, which were formed in a sedimentary regime of erosion, sediment reworking and frequent gravity‐flow deposition. The combination of nannofossil biostratigraphy and ⁸⁷Sr/⁸⁶Sr isotope stratigraphy allows for the precise attribution of ages to the phosphate deposits and for the distinction of three periods of major phosphogenesis. The first phase occurred between 24·5 and 21 Ma and 25 and 18·9 Ma (clustering of ages between 25 and 22·5 Ma) on Malta and Sicily, respectively. The second and third phases of phosphogenesis are documented from the Maltese Islands and are dated as 17·2 to 13·1 Ma and 10·9 to 9·8 Ma, respectively. The phosphate‐rich beds are associated with hiatuses and phases of important condensation which, for the oldest phosphogenic period, envelop the time period of 23·2 to 22 Ma for the Fomm Ir Rhi Bay section (Malta) and from 19·1 to 16·3 Ma for the sections of Sampieri and Modica (Sicily). For the second phase of phosphogenesis on the Maltese Islands, a consistent hiatus was found which embraces the time period of approximately 17 to 15 Ma. Also the third phase of phosphogenesis appears to be associated with a major hiatus, which probably envelops the time period between 12·5 and 10·9 Ma, but a better age control is needed here. The correspondence in timing of the Maltese‐Sicilian phases of phosphogenesis with major phases of phosphogenesis outside the Mediterranean realm, to maxima in oceanic phosphorus‐burial rates and maxima in the δ¹³C benthic foraminiferal record suggests that the palaeoceanographic evolution of the eastern Mediterranean was well in phase with that of other ocean basins until at least the early Late Miocene, despite its increasing isolation due to the gradual closure of the Eurasian‐Arabian Strait and progressive sea‐level fall.     

Rhenium–osmium systematics of the Mount Isa copper orebody and the Eastern Creek Volcanics,Queensland, Australia: implications for ore genesis

The syn-tectonic breccia-hosted Mount Isa Cu deposit in northwest Queensland is the largest sediment-hosted Cu deposit in Australia. Whole-rock samples of chalcopyrite-rich Cu ore form an isochron with a Re–Os age of 1,372 ± 41 Ma. This age is more than 100 Ma younger than the previously accepted age of Cu ore formation, an Ar–Ar mineral age for biotite separated from the host rocks within the alteration envelope to the Cu orebody. This discrepancy cannot be unequivocally resolved due to a lack of other absolute geochronological constraints for Cu mineralisation or the deformation event associated with Cu emplacement. The 1,372 ± 41 Ma date may reflect (a) the time of Cu deposition, (b) the time of a hydrothermal event that reset the Re–Os signature of the Cu ore or (c) mixing of the Re–Os isotope systematics between the host rocks and Cu-bearing fluids. However, a range of published Ar–Ar and Rb–Sr dates for potassic alteration associated with Cu mineralisation also records an event between 1,350 and 1,400 Ma and these are consistent with the 1,372 Ma Re–Os age. The 1.8 Ga Eastern Creek Volcanics are a series of tholeiitic basalts with a primary magmatic Cu enrichment which occur adjacent to the Mount Isa Cu deposit. The whole-rock Os isotopic signature of the Eastern Creek Volcanics ranges from mantle-like values for the upper Pickwick Member, to more radiogenic/crustal values for the lower Cromwell Member. The Re–Os isotope signature of the Cu ores overlaps with those calculated for the two volcanic members at 1,372 Ma; hence, the Os isotope data are supportive of the concept that the Os in the Cu ores was sourced from the Eastern Creek Volcanics. By inference, it is therefore postulated that the Eastern Creek Volcanics are the source of Cu in the Mount Isa deposit, as both Os and Cu are readily transported by oxidised hydrothermal fluids, such as those that are thought to have formed the Cu orebody. The Pickwick Member yields a Re–Os isochron age of 1,833 ± 51 Ma, which is within error of previously reported age constraints. The initial ¹⁸⁷Os/¹⁸⁸Os isotopic ratio of 0.114 ± 0.067 (γOs = −0.7) is slightly subchondritic, and together with other trace element geochemical constraints, is consistent with a subcontinental lithospheric mantle source. The Pickwick Member records a minimum age of ca. 1.95 Ga for melt depletion in the subcontinental lithospheric mantle beneath the Mount Isa Inlier prior to the extraction of the magmas which formed the Eastern Creek Volcanics. This corresponds with the end of subduction-related magmatism along the eastern margin of the Northern Australian Craton, which included the Mount Isa Inlier.     

东秦岭南洛河中游地区发现的旧石器和黄土堆积

对2006～2007年在东秦岭南洛河中游地区河南省卢氏和洛宁两县发现的8处旷野类型旧石器地点的160余件石制品进行了初步研究,并对产出石制品的黄土堆积剖面进行了地层学分析和光释光测年。初步结果表明,南洛河中游地区的旧石器工业很丰富,石制品的加工技术与上游洛南盆地一致,同样采取硬锤直接打击法;加工石制品的原料来自于河流堆积物中的石英岩和石英砾石等;石制品中有相当数量的小型石片和由小型石片二次加工修理而成的工具,还有直接由砾石加工而成的重型工具,如手镐等;除此之外,大型石片以及以大型石片加工而成的重型工具,如重型刮削器也多有所见。由于工作范围和力度的局限,南洛河中游地区目前尚未发现上游洛南盆地旧石器遗址中广泛存在的手斧、三棱手镐、薄刃斧和大型石刀等Acheulian类型两面加工技术生产的工具。新发现的南洛河中游旧石器地点分布在不同时期形成的河流阶地和黄土地层中。地层分析和光释光年代测试表明,南洛河中游地区的黄土堆积至少从中更新世便已经开始,并一直持续到全新世,至少在黄土剖面中S₁,S₃和S₄的3个层位有石器分布;其黄土-古土壤旋回不仅可以用于石制品产出层位的准确定年,还指示了早期人类石器工业演化和人类生存环境变化的过程。     

Structural and geochronological constraints on the tectono-thermal evolution of the Danba domal terrane, eastern margin of the Tibetan plateau

The Songpan-Ganze terrane of the Tibetan plateau is underlain by Neoproterozoic crystalline basement rocks of the Yangtze block. These basement rocks are exposed as a series of extensional tectonic domes that form a nearly north–south trending extensional belt more than 1000 km long in the eastern margin of the Tibetan plateau. In the Danba area, detachment faults separate the basement core complexes (e.g., the Gezong and Gongcai complexes) from the Paleozoic strata which have been thinned or removed completely. The cover sequences have undergone upper greenschist to lower amphibolite facies metamorphism to form the Danba schist and are overlain by the Triassic Xikang Group, a thick flysch sequence. Both the basement rocks and the Paleozoic rocks have undergone multiple stages of deformation and thus provide an excellent opportunity to study the tectono-thermal evolution of the eastern margin of the Tibetan plateau. Two stages of deformation, corresponding to three generations of foliation (S₁, , and ), have been recognized on the basis of structural and microscopic observations. We selected amphibole and biotite separates associated with distinct generations of foliation for ⁴⁰Ar/³⁹Ar dating using laser microprobe incremental heating technique to place numerical constraints on the major tectono-thermal events within the Danba area. The geochronogical results reveal an earliest metamorphic event at 258.6 ± 0.5 Ma (S₁ biotite) and 263.6 ± 0.8 Ma (S₁ amphibole), coinciding temporally with the mantle plume that produced the voluminous Emeishan flood basalts. The second event was a progressive extensional deformation first occurred at 159–166 Ma ( amphibole) responsible for the earlier tectonic doming of the crystalline basement, and then the final tectono-thermal overprint recorded by foliation and metamorphism locally in the core complexes at 47–58 Ma for the Gezong complex and 64–81 Ma for the Gongcai complex. This major post-orogenic extensional event is believed to be a consequence of collision between the North China and South China blocks. The apparent discrepancy of the ⁴⁰Ar/³⁹Ar ages observed between localities suggests a slow cooling process associated with progressive uplift.     

浙东沉积岩顺层滑坡预应力锚索加固治理设计与施工

在浙江中东部地区,沉积岩分布较广泛,由于层面发育及存在软弱夹层,顺层滑坡时有发生。结合工程实例,对采用预应力锚索加固治理顺层滑坡的设计过程及施工方法进行了分析。监测结果表明治理措施安全有效。     

东天山石炭纪雅满苏组火山岩特征及地质意义

雅满苏组火山岩是东天山石炭纪火山岩的重要组成部分,也是东天山地区海相火山岩型铁多金属矿床的赋矿地层。其年代学及地球化学研究对探讨该区古生代构造演化和火山岩型铁多金属矿床成因具有重要意义。本文对东天山地区雅满苏组火山岩的岩石学、地球化学和同位素年代学进行了系统研究。结果显示:雅满苏组是一套海相火山岩夹碳酸盐岩建造,其上亚组英安岩的LA-ICP-MS锆石U-Pb年龄为334.4±1.7 Ma(MSWD=0.67),代表了雅满苏上亚组火山岩形成时代,切穿雅满苏铁矿区矽卡岩及矿体的正长岩的LA-ICP-MS锆石U-Pb年龄为325.5±1.7 Ma(MSWD=0.34),表明雅满苏铁矿床形成不晚于325 Ma。雅满苏上亚组英安岩和玄武岩显示了富集LREE、U、Sr,相对亏损Nb、Ta等元素的特征,且英安岩锆石的(176Hf/177Hf)i比值介于0.282 644~0.282 802之间,εHf(334 Ma)为3.0~8.0,表明它们是活动大陆边缘弧环境的产物,英安岩是新生地壳物质部分熔融的结果,玄武岩是软流圈地幔与受俯冲板片流体交代地幔的混合熔体演化的产物。结合前人研究成果,认为雅满苏组火山岩是早石炭世中期古亚洲洋俯冲作用的产物,石炭纪时期古亚洲洋尚未闭合,雅满苏铁矿床形成介于334~325 Ma之间,是与石炭纪火山岩有成因联系的铁矿床。     

Metamorphism of high‐P metagreywacke from the Eastern Himalayan syntaxis: phase equilibria and P–T path

High‐pressure (HP) metagreywacke from the Namche Barwa Complex, Eastern Himalayan Syntaxis (EHS), consists of garnet, biotite, plagioclase, quartz, rutile and ilmenite with or without K‐feldspar, sillimanite, cordierite, spinel and orthopyroxene. Two types of metagreywacke are recognized: medium‐temperature (MT) and high‐temperature (HT) types. Garnet in the MT metagreywacke shows significant growth zoning and contains lower MgO than the weakly zoned garnet in the HT metagreywacke. Petrographic observations and phase equilibria modelling for four representative samples indicate that both types of metagreywacke experienced clockwise P–T paths subdivided into three stages: stage I is the pre‐peak prograde to pressure peak (P_max) stage characterized by progressive increase in P–T conditions. The P_max conditions are estimated using the garnet composition with maximum CaO, being 12.5–13.5 kbar and 685–725 °C for the MT metagreywacke, and 15–16 kbar and 825–835 °C for the HT one. Stage II is the post‐P_max decompression with heating or near‐isothermal to T_max stage and the T_max conditions, constrained using the garnet compositions with maximum MgO, are 11 kbar and 760 °C for the MT metagreywacke, and ~12 kbar and 830–845 °C for the HT one. The modelled mineral assemblages at T_max are garnet + biotite + K‐feldspar + rutile + plagioclase ± ilmenite in the presence of melt for both types of metagreywacke, consistent with the petrographic observations. Stage III is the post‐T_max retrograde metamorphism, characterized by decompression and cooling. The modelling suggests that the melts with high Na/K ratios (1.7–5.2) have been produced during stages I and II, which could be responsible for the formation of sodium‐rich leucogranites. This study and previous results indicate that the Higher Himalayan Crystallines in the EHS consist of MT–HP and HT–HP metamorphic units separated by a speculated tectonic contact. Petrological and structural discontinuities within the EHS cannot be easily interpreted with ‘tectonic aneurysm’ model.     

深海柱样粒度分维特征及其古海洋学意义

对南海69柱样粒度数据分析表明,晚更新世以来,粒度在0,2～11um的标度范围内具有分形特征,粒度分维值为1．72～2．02,平均1．84。与同期亚北极B2-9柱地层对比,69柱粒度分维值明显比B2—9柱的高,B2—9柱的粒度在0,2～16um标度范围内具有分形特征,粒度分维值为1.74～1．79,平均1．77。同一柱样不同时期粒度分维值明显不同,南海69柱氧同位素1期(冰后期)为1．88,氧同位素2期(冰期)为1．81,温暖的冰后期粒度分维值高且变化幅度大,寒冷的冰期粒度分维值低且变化幅度小,表明粒度分维值对沉积物的形成环境演化具有良好的指示意义。