利用中国地震科学台阵研究青藏高原东南缘地壳各向异性:第一期观测资料的剪切波分裂特征

中国地震科学台阵第一期(2011—2013年)布设在南北地震带南段,本研究利用中国地震科学台阵布设在云南及相邻地区的部分流动台站记录到的2011年6月至2013年3月的数字地震波形资料,开展地壳各向异性分析.本文使用剪切波分裂系统分析方法(SAM方法),获得了研究区内67个台站的剪切波分裂参数.研究结果表明,受到云南及周边地区复杂的构造、应力环境和纵横交错的断裂分布的影响,该地区快剪切波偏振方向(PAZ)整体上显示出NNE向和NE向的优势取向,但在空间分布上比较复杂,虽然大部分台站的PAZ与构造应力场方向一致,但部分断裂附近台站的PAZ受到断裂的影响.结果显示,本研究区内不同区域的PAZ有一定差异性.本研究划分了5个子区,西部3个不同区域的PAZ从北到南分别为NNW向、近N-S向和NE向,有顺时针旋转的趋势,而东部的2个区域PAZ分别为NEE向和NNW向.研究证实,青藏东南缘地区的地壳各向异性空间分布虽然非常复杂,但大体上与区域内的主压应力的方向和断裂分布相关.     

n-alkane distribution coupled with organic carbon isotope composition in the shell bar section, Qarhan paleolake, Qaidam basin, NE Tibetan Plateau

Lipids extracted from lacustrine deposits in the paleolake Qarhan of the Qaidam basin in the northeastern Tibetan Plateau were determined by conventional gas chromatography-mass spectrometry. Several series of biomarkers were identified, mainly including n-alkanes, n-alkan-2-ones, n-alkanoic acids, branched alkanes, triterpenoids and steroids, indicative of various biogenic contributions. On the basis of cluster analysis, the n-C₁₅, n-C₁₇, n-C₁₉ alkanes were proposed to be derived from algae and/or photosynthetic bacteria, the n-C₂₁, n-C₂₃, n-C₂₅ homologues from aquatic plants, and the n-C₂₉, n-C₃₁ homologues from vascular plants. In contrast, the n-C₂₇ alkane is not categorized in the n-C₂₉ and n-C₃₁ group of alkanes, probably due to more complex origins including both aquatic and vascular plants, and/or differential biodegradation. Stratigraphically, layers-2, 4 and 5 were found to show a close relationship in n-alkane distribution, associated with a positive shift in carbon isotope composition of bulk organic matter (δ¹³C_org), inferring a cold/dry period. Layers-1 and 6 were clustered together in association with a negative δ¹³C_org, excursion, probably indicating a relatively warm/humid climate. The potential coupling between the n-alkane distributions and δ¹³C_org, suggests a consequence of vegetation change in response to climate change, with the late MIS3 being shown to be unstable, thought to be the climatic optimum in the Tibetan Plateau. Our results suggest that the cluster analysis used in this study probably provides an effective and authentic method to investigate the n-alkane distribution in paleolake sediments.     

Formation of Fe-oxyhydroxides from the East Pacific Rise near latitude 13°N: Evidence from mineralogical and geochemical data

The mineralogical and geochemical characteristics of Fe-oxyhydroxide samples from one dredge station (long. 103°54.48′W, lat. 12°42.30′N, water depth 2655 m) on the East Pacific Rise near lat 13°N were analyzed by XRD, ICP-AES, and ICP-MS. Most Fe-oxyhydroxides are amorphous, with a few sphalerite microlites. In comparison with Fe-oxyhydroxides from other fields, the variable ranges in the chemical composition of Fe-oxyhydroxide samples are very narrow; their Fe, Si, and Mn contents were 39.90%, 8.92%, and 1.59%, respectively; they have high Cu (0.88%–1.85%) and Co (65×10⁻⁶−704×10⁻⁶) contents, and contain Co+Cu+Zn+Ni> 1.01%. The trace-element (As, Co, Ni, Cu, Zn, Ba, Sr) and major-element (Fe, Ca, Al, Mg) contents of these samples are in the range of hydrothermal sulfide from the East Pacific Rise near 13°N, reflecting that this type of Fe-oxyhydroxide constitutes a secondary oxidation product of hydrothermal sulfide. The Fe-oxyhydroxide samples from one dredge station on the East Pacific Rise near 13°N are lower in ΣREE (5.44×10⁻⁶–17.01×10⁻⁶), with a distinct negative Ce anomaly (0.12–0.28). The Fe-oxyhydroxide samples have similar chondrite-normalized rare-earth-element (REE) patterns to that of seawater, and they are very different from the REE composition characteristics of hydrothermal plume particles and hydrothermal fluids, showing that the REEs of Fe-oxyhydroxide are a major constituent of seawater and that the Fe-oxyhydroxides can become a sink of REE from seawater. The quick settling of hydrothermal plume particles resulted in the lower REE content and higher Mn content of these Fe-oxyhydroxides, which are captured in part of the V and P from seawater by adsorption. The Fe-oxyhydroxides from one dredge station on the East Pacific Rise near 13°N were formed by secondary oxidation in a low temperature, oxygenated environment. In comparison with the elemental (Zn, Cd, Pb, Fe, Co, Cu) average content of hydrothermal sulfide samples from the East Pacific Rise near 13°N, the Zn, Cd, and Pb contents of the Fe-oxyhydroxides are lower, and their Fe, Co, and Cu contents are higher. Supported in part by the Pilot Project of Knowledge Innovation Project, Chinese Academy of Sciences (Grant No. KZCX3-SW-223), and the Special Foundation for the Tenth Five Plan of COMRA (Grant No. DY105-01-03-1)     

Alkaline rocks of Samchampi-Samteran, District Karbi-Anglong, Assam, India

The Samchampi-Samteran alkaline igneous complex (SAC) is a near circular, plug-like body approximately 12 km² area and is emplaced into the Precambrian gneissic terrain of the Karbi Anglong district of Assam. The host rocks, which are exposed in immediate vicinity of the intrusion, comprise granite gneiss, migmatite, granodiorite, amphibolite, pegmatite and quartz veins. The SAC is composed of a wide variety of lithologies identified as syenitic fenite, magnetite ± perovskite ± apatite rock, alkali pyroxenite, ijolite-melteigite, carbonatite, nepheline syenite with leucocratic and mesocratic variants, phonolite, volcanic tuff, phosphatic rock and chert breccia. The magnetite ± perovskite ± apatite rock was generated as a cumulus phase owing to the partitioning of Ti, Fe at a shallow level magma chamber (not evolved DI = O1). The highly alkaline hydrous fluid activity indicated by the presence of strongly alkalic minerals in carbonatites and associated alkaline rocks suggests that the composition of original melt was more alkalic than those now found and represent a silica undersaturated ultramafic rock of carbonated olivine-poor nephelinite which splits with falling temperature into two immiscible fractions—one ultimately crystallises as alkali pyroxenite/ijolite and the other as carbonatite. The spatial distribution of varied lithotypes of SAC and their genetic relationships suggests that the silicate and carbonate melts, produced through liquid immiscibility, during ascent generated into an array of lithotypes and also reaction with the country rocks by alkali emanations produced fenitic aureoles (nephelinisation process). Isotopic studies (δ¹⁸O and δ¹³C) on carbonatites of Samchampi have indicated that the δ¹³C of the source magma is related to contamination from recycled carbon.     

13kaBP以来滇池地区古环境演化

根据DC93一1孔孢粉组合、总有机碳（TOC）、总氮（TN）、碳氮比（C／N）、有机碳同位素δ13Corg、磁化率（χ）、频率磁化率（χfd）等资料,结合14C、210Pb和137Cs测年,滇池地区13ka以来的古环境演化历史经历了以下几个阶段：13—10．2kaBP．气候偏凉湿,湖水深度不大;10．2－7．5kaBP,气候向暖湿过渡．湖水渐深;7．5－4．0kaBP,气候暖湿,出热条件达到最佳配制,湖水也最深．6．5kaBP前后,气温最高,这一时段古气候状况存在次级波动;4．0－2．7kaBP,气候突转干旱．湖水最浅;2．7－1．7kaBP,气候温湿,湖面扩大,湖水变深;1．7kaBP,人类活动影响的加剧,使湖泊环境的变化更为复杂．     

Predation by jellyfish on large and emergent zooplankton: Implications for benthic–pelagic coupling

Stable carbon isotopes were used to determine the contribution of emergent demersal zooplankton to the diet of the scyphozoan jellyfish Catostylus mosaicus at Smiths Lake, New South Wales, Australia. A preliminary study in 2004 indicated that there was no difference in the δ¹³C of ectodermal tissue and mesoglea of the medusae. In 2005, medusae and zooplankton present during the day and night were sampled and isotopic signatures were modelled using IsoSource. Modelling indicated that: (1) mollusc veligers and copepods sampled during the day contributed <13% of the carbon to the jellyfish; (2) copepods sampled at night contributed up to 25%; and (3) the large, emergent decapod Lucifer sp. contributed 88–94%. We hypothesised, therefore, that medusae derive most of their carbon from emergent species of zooplankton. In 2006, sampling done in 2005 was repeated three times over a period of 4 weeks to measure short-term temporal variation in isotopic signatures of medusae and zooplankton, and emergent demersal zooplankton was specifically sampled using emergence traps. Short-term temporal variation in isotopic signatures was observed for some taxa, however, actual variations were small (<1.5‰) and the values of medusae and zooplankton remained consistent relative to each other. IsoSource modelling revealed that mysid shrimp and emergent copepods together contributed 79–100% of the carbon to the jellyfish, and that the maximum possible contribution of daytime copepods and molluscs was only 22%. Jellyfish apparently derive most of their carbon from emergent zooplankton and by capturing small numbers of relatively large taxa, such as Lucifer sp. or mysid shrimp. Small but abundantly captured zooplankton (such as mollusc veligers) contribute only minor amounts of carbon. Jellyfish have a major role in the transfer of carbon between benthic and pelagic food webs in coastal systems.     

泥炭记录的帕米尔高原晚全新世温度变化研究

近年来,“全新世温度谜题”已经受到全球古气候学者的广泛关注,为了解决这一谜题,需要在全球不同区域进行更多的全新世温度重建。帕米尔高原位于亚洲内陆核心区域,目前有关帕米尔高原全新世气候变化的研究相对较少,且已有的研究主要集中于相对湿度(或降水)变化的研究,而涉及温度变化的成果则相对较少。论文首先研究了表土碳同位素与气候因子之间的相关关系,结果显示帕米尔高原的δ¹³C_org与温度正相关;进一步在 7 个AMS¹⁴C 测年数据的支持之下,基于 175 个泥炭δ¹³C_α-cellulose分析,重建了帕米尔高原过去约5000 a的温度变化历史。结果发现：帕米尔高原晚全新世以来整体呈现波动升温趋势,约5000～3600 cal a BP阶段处于缓慢降温期;约3600～200 cal a BP 处于波动升温期;驱动机制分析显示,约 3600 cal a BP 之前温度下降主要是夏季太阳辐射下降导致的,约3600 cal a BP之后温度上升是由温室气体辐射强迫增强导致的。     

夏季洪水对长江口及邻近海域颗粒有机碳分布与来源的影响

基于2020年7月洪水期间采集的长江口及邻近海域的温度、盐度、总悬浮物(Total Suspen-ded Matter,TSM)质量浓度、颗粒有机碳(Particulate Organic Carbon,POC)质量浓度和颗粒有机碳稳定同位素(δ13 CPOC)等数据,分析了洪水事件对该区域POC分布与来源的影响.结果...     

天目山树轮碳同位素与周边地区旱涝变化关系的研究

根据帕尔默干旱模式的基本思路,建立动态的能反应旱涝持续特征的适合于天目山地区的旱涝指数。对采自天目山的柳杉树轮进行交叉定年后,测得树轮的δ^13C年序列,将δ^13C去除大气CO2趋势影响后的高频变化与不同时段的旱涝指数进行相关分析,结果显示：春夏季的旱涝指数与当年和滞后一年的δ^13C序列有着比较显著的相关性,表明树轮δ^13C对春夏季旱涝的发生有着比较好的响应。根据此显著相关性,利用多元回归方程重建了历史时期的春夏季旱涝指数,分析表明天目山地区春夏季旱涝的发生具有比较明显的年代际变化特征,为研究该地区气候变化特征提供了较可靠的参考依据。     

四川宁南银厂沟震旦-寒武纪交变期碳、氧同位素地球化学特征

扬子地台西缘攀西地区,晚震旦世-早寒武世为一套连续沉积碳酸盐岩,众多科研文献中时代地层、岩性地层和生物地层的划分各异。在此交变期及其近前后,随之发生诸多地质事件,成为地学研究的热点之一。于宁南等四幅1：5万区调工作中,实测灯影组麦地坪段地层剖面,采集新鲜岩样,测试碳、氧同位素,试从稳定同位素地球化学角度阐述其指示意义,提供研究震旦一寒武纪交变期的地球化学资料。