地表基质分类及调查初步研究

地表基质分类研究是开展地表基质调查的基础,而厘清地表基质的科学内涵、时空展布特征、支撑服务目标及调查精度等是开展调查的前提条件。文章充分借鉴区域地质、水文地质、工程地质、第四纪地质、环境地质等学科分类和图件表达方式,综合岩石、砾石、沙、土壤等的物质组成、成因类型、地貌形态和粒度质地等,初步将地表基质的类型划分为四个层级,并提出了地表基质层的物质组成、成因属性和研究深度范围,指出了未来开展地表基质调查和编图的主要方向,结果为地表基质统一分类体系构建和全国范围开展的地表基质调查提供了参考依据。     

3.2 ka BP以来念青唐古拉山东部则普冰川波动与环境变化

基于野外考察和 14C 年代测定, 确定了3.2 ka BP以来念青唐古拉山东部则普冰川的冰进序列.新冰期冰进可明显分为3次: 即大拿[ 14C ( 3 242 ±101)a BP]、大拿顶[ 14C ( 1 920 ±110)～ (1 540 ±85)a BP]和白同[ 14C ( 1 056 ±115)a BP]冰进.新冰期盛时, 则普冰川比现代长6.9 km, 面积大17.10 km2, 雪线降低约157 m, 温度降低1.0～1.9 ℃. 小冰期可分出2次: 即15世纪或16世纪[ 14C (580±130)a BP]和19世纪[ 14C (197±80)a BP, (190±80)a BP]冰进. 小冰期盛时, 则普冰川比现代长2.0 km, 面积大11.16 km2, 雪线降低约100 m, 温度降低0.65～1.23 ℃. 现代则普冰川, 冰面表碛特别发育, 其厚度亦很大, 冰舌末端退缩难以辨认. 但冰川减薄很强烈, 边缘两侧形成2～3道现代侧碛, 并高出现代冰面20～30 m. 对埋藏腐殖质土壤层和木炭碎屑经 14C 年代测定, 结果表明在(720±210)～( 2 010 ±120)a BP间, 波堆藏布流域存在砍伐森林、开垦田地和放牧的人类活动.     

Role of tonalite-trodhjemite-granite (TTG) crust subduction on the mechanism of supercontinent breakup

The tonalite-trondhjemite-granite (TTG) crust has been considered to be buoyant and hence impossible to be subducted into the deep mantle. However, recent studies on the juvenile arc in the western Pacific region indicate that immature island arcs subduct into the deep mantle in most cases, except in the case of parallel arc collision. Moreover, sediment trapped subduction and tectonic erosion are also common. This has important implications in evaluating the role of TTG crust in the deep mantle and probably on the bottom of the mantle. Because the TTG crust is enriched in K, U and Th, ca. 20 times more than that of CI chondrite, the accumulated TTG on the Core Mantle Boundary (CMB) would have played a critical role to initiate plumes or superplumes radiating from the thermal boundary layer, particularly after 2.0 Ga, related to the origin of superplume-supercontinent cycle. This is because selective subduction of oceanic lithosphere including sediment-trapped subduction, tectonic erosion and arc- and microcontinent-subduction proceeded under the supercontinent before the final amalgamation ca. 200-300 million years after the formation of the nuclei. We speculate the mechanism of superplume evolution through the subduction of TTG-crust and propose that this process might have played a dominant role in supercontinent breakup.     

Granite subduction: Arc subduction, tectonic erosion and sediment subduction

Continental growth has been episodic, reflecting the episodic nature of mantle dynamics as well as surface dynamics of the Earth, the net result of which is exhibited by the present mantle with two huge reservoirs of TTG rocks, one on the surface continents and the other on the D″ layer on the Core-Mantle Boundary (CMB). During the early half of the Earth history, the felsic continental crust on the surface which formed in an intra-oceanic environment has mostly been subducted into the deep mantle, except in the rare case of parallel arc collision. The growth history of continental crust shows that with its simultaneous formation, a considerable amount must have also been subducted. Such ongoing subduction processes can be seen in the western Pacific region, through tectonic erosion, arc subduction, and sediment-trapped subduction.     

天山南北麓新生代地理环境演变

本文阐明了晚第三纪以来天山的大幅度隆起及南北麓沉积过程,着重从古植被变化论述了区内新生代的环境演变,并对天山南北麓的沉积环境异同作了对比。文章中首次提出天山地区第三纪以来可分为两个湿润期(古新世-始新世,渐新世晚期-中新世)和三个干旱期(渐新世早中期、上新世、第四纪)。     

Semi-empirical estimation of ground motion using observed records at a site in Shikoku, Japan

A semi-empirical approach using fore- or after-shockrecords as Green's functions is applicable to thesimulation of strong ground motion, however suchrecords are obviously not available for predictionpurposes. Thus we have predicted ground motion fora hypothetical large earthquake from other minorevents by adopting a distance correction based ongeometrical spreading. Another difficulty inprediction is fault modeling. Surface traces weresimplified as fault models 27, 46, 55, and 77 km inlength. Further, the actual fault rupture may beinhomogeneous, so an asperity distribution isassumed. This asperity model assumes thatdislocation and stress drop are double than theaverage values. Although, the near field term isneglected in our simulation, no significantdifference was seen in the motions estimated byindividual models for periods up to 2.0 seconds. This indicates that the dependence of source size issmall for strong motion, perhaps as a result of therandom summation of high-frequency phases.     

Growth of Emerald Crystals by Evaporation of Na2O—MoO3 Flux

Well-formed crystals of emerald, Be3AI2Si6O18:Cr, were easily grown from an Na2O-MoO3 flux by an isothermal technique. The crystal growth was conducted by heating a mixture of solute and flux at 1 100 ℃ for 24 h. The evaporation loss of flux depended on the amount of Na2O added to MoO3. Emerald crystals of lengths up to 2.1 mm and widths of 1. 4 mm were grown. The crystal sizes were dependent on the evaporation loss of the flux. The obtained crystals were transparent and exhibited the typical emerald-green color. The form of the emerald crystals was a twelve-sided prism bounded by well-developed faces. The aspect ratios were in the region of 1. 4 to 2. 3. The density was (2. 64±0.02) g/cm3. The IR absorption bands were in good agreement with the literature data.