Hf–Nd isotopic decoupling in continental mantle lithosphere beneath Northeast China: Effects of pervasive mantle metasomatism

Nd–Hf isotopic decoupling has frequently been observed in the continental and oceanic mantle, but its origin remains controversial. Here we present combined elemental and Sr–Nd–Hf isotopic study on peridotite xenoliths entrained in Cenozoic basalts from Shuangliao and Jiaohe in Northeast China, which provides insight into this issue. The data reveal a heterogeneous lithospheric mantle beneath Northeastern China, consisting of fertile (type I) to strongly refractory (type II) peridotites. Type I peridotites are largely shielded from late metasomatism, thus preserving information of depletion events. Nd model age suggests a Proterozoic lithospheric mantle beneath NE China. Type II peridotites are mostly refractory harzburgites and show ubiquitous enrichment of incompatible elements. They are further divided into two sub-groups. Clinopyroxenes from type IIa samples have high and wide Lu/Hf (0.34–1.3) and very radiogenic Hf isotopic ratios (ε_Hf = 44.4–63.8). Hf concentration is generally low (0.12–0.43 ppm) and plots along or slightly above the modeled partial melting depletion trend. In contrast, Nd content in type IIa clinopyroxenes is significantly higher than the modeled concentrations in residues at a given degree of melt depletion. The difference in enrichment of Hf and Nd translates to decoupling of Lu/Hf–Sm/Nd ratios and of Nd–Hf isotopes (ε_Nd = −1.3 to 8.4). Clinopyroxenes from most of type IIb peridotites have relatively low Lu/Hf ratios (0.04–0.24) and coupled Nd–Hf isotopes. Both Hf and Nd plot significantly above the depletion trend; their concentrations are governed by the equilibrium partitioning between percolating melt and peridotites. The distinct geochemical characteristics of type IIa and type IIb clinopyroxenes may have resulted from chromatographic percolation of small volumes of silicate melts, in which percolation fronts of incompatible elements are dependent on their relative incompatibilities.     

Geochronology and geochemistry of Cenozoic basalts from eastern Guangdong, SE China: constraints on the lithosphere evolution beneath the northern margin of the South China Sea

The ⁴⁰Ar–³⁹Ar dating reveals three episodes of basaltic volcanism in eastern Guangdong of SE China since the late Eocene (i.e., 35.5, ~20 and 6.6 Ma). The Miocene alkali olivine basalts (~20 and 6.6 Ma) have OIB-like trace element characteristics, which is coupled with low (⁸⁷Sr/⁸⁶Sr)_i, high ε_Nd(t), and high ε_Hf(t). In contrast, the late Eocene basalts (35.5 Ma) have overall characteristics of “Island Arc” basalts with strong negative Ta–Nb–Ti anomalies in the primitive mantle-normalized multi-element diagram with high (⁸⁷Sr/⁸⁶Sr)_i, negative ε_Nd(t), and relatively low ε_Hf(t). All basalts have unexpectedly high ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb, delineating a DUPAL signature in the sources. The late Eocene Arc-like basalts may reflect contributions of relict ancient metasomatized mantle lithosphere that melted as the result of extension-induced asthenospheric upwelling and heating, whereas the Miocene OIB-like basalts may represent partial melting of the asthenospheric mantle beneath the thickened lithosphere. We propose that the Cenozoic basaltic volcanism in eastern Guangdong records an overall lithospheric thickening process beneath SE China, that is, a continental rift system from its maximum extension in the late Eocene to its waning in the Miocene. This interpretation is consistent with the evolution of the South China Sea, whose origin is most consistent with the development of a passive continental margin. The seafloor spreading of the South China Sea during ~ 32–16 Ma may not result from the effect of the “Hainan” mantle plume, but rather played a positive role in allowing the mantle plume to express on the surface.     

旅游目的地区域(TDD)及其空间结构研究——以西安为例

在对国内外相关研究进行综述的基础上,以西安为例,对旅游目的地区域(TDD)进行了界定。以"一日游"旅游行为基准给出了西安旅游目的地区域范围,即以250 km为半径,相当于单程旅行2.5小时的通达范围。并发现西安TDD对周边地区旅游客源产生了明显的截流效应。分析了主要旅游景点(3A以上)的空间分布特征,认为呈现集聚分布,有利于旅游资源组团式开发。运用洛仑兹曲线,发现西安市出行的5条主要旅游路径利用强度存在严重不均衡。文章结论主要包括:TDD的核心表现为旅游区、旅游节(景)点和旅游路径三种空间要素,其中对旅游目的地区域发展影响较大的两个要素是高级别景区与旅游路径,二者决定了区域旅游产业的规模、空间分布和旅游流向。随着区域旅游一体化的推进,客观上要求以西安为中心的关中旅游热点地区要逐步打破地区壁垒,共同开拓市场,优化旅游景点组合,打造旅游精品群,以促进旅游业的持续发展。     

云南个旧卡房蚀变玄武岩金云母40Ar-39Ar同位素年龄研究及意义

云南个旧锡铜多金属矿床是世界级超大型矿床,个旧矿集区内与蚀变玄武岩有关的(似)层状铜矿床是其重要的矿床类型。该类型矿床的围岩玄武岩均发生蚀变,且蚀变强度与矿化关系密切。本文对个旧卡房矿化玄武岩中的金云母进行40Ar-39Ar同位素定年分析,得到其坪年龄为(85.49±0.63)Ma,等时线年龄为(85.62±0.42)Ma,反等时线年龄为(85.59±0.81)Ma,三者基本一致,代表了变玄武岩的蚀变年龄及同期矿化年龄,属于晚白垩世,可与个旧锡铜多金属矿床的成矿时代进行对比。     

起伏地表叠前逆时偏移理论及GPU加速技术

从起伏地表直接进行叠前逆时偏移是解决地表起伏大并且地下构造复杂这种双复杂结构地区成像问题的有力工具.本文给出了起伏地表直接进行叠前逆时偏移的实现过程,针对有限差分方法处理起伏地表自由边界条件的复杂性,采用了一种简化的自由边界条件,避免了大量的逻辑判断,在此基础上,采用图形处理器(Graphic Processing U...     

城市-区域竞争力建设的实践评析——以江苏省沿江开发为例

经济全球化时代下,地方政府热衷于通过实施空间规划来提升城市-区域的竞争力。在区域规划与区域竞争力建设的理论框架下,对江苏省沿江开发区域政策进行了评估和分析。研究发现,江苏省沿江开发战略是一个区域竞争力建设的规划,配套支撑政策对区域规划的实施至关重要。经过6 a的开发建设,沿江地区经济社会发展、基础设施和宜居环境建设等取得了明显成效,同时,沿江开发在空间开发秩序、联动机制、发展方式等方面出现了一些问题,需要通过完善发展规划、加强规划实施、加快体制机制创新等途径完善区域竞争力体系。     

泥蚶(Tegillarca granosa)基因组SSR和EST-SSR的开发及比较研究

采用SSPHunter软件在泥蚶(Tegillarca granosa)磁珠富集文库和454转录组文库中搜索核心序列长度12bp以上的2—6核苷酸重复序列,根据富集文库所得基因组SSR侧翼序列设计47对引物,可成功扩增17对且均为多态性引物,多态率100%,平均等位基因数(Na)、观测杂合度(Ho)、期望杂合度(He)、多态性信息含量(PIC)分别为6.8、0.468、0.785、0.733。11344条EST序列中得到1683个SSR位点,检出率14.83%,平均每3.85kb出现1个位点。根据部分EST序列设计120对引物,62对可扩增出目的片段,其中29个位点具有多态性,多态率为46.77%,平均Na、Ho、He、PIC分别为4.2、0.372、0.554、0.500,均低于基因组SSR。双变量相关性分析的结果表明,46个多态性SSR位点的核心序列长度与其Na、Ho、He、PIC极显著正相关,Spearman相关系数分别为0.632、0.387、0.657、0.6640     

单环刺螠转录因子基因Sp8的克隆、原核表达和重组蛋白纯化

转录因子Sp是一类广泛存在的锌指蛋白超家族成员,可与某些基因的上游调控序列结合,参与基因的转录调控。本研究采用同源克隆和RACE技术,获得单环刺螠的Sp8的全长cDNA,该序列长1 913bp,开放阅读框1 521bp,编码506个氨基酸;将其开放阅读框cDNA克隆到原核表达载体pET28a中,并转化大肠杆菌BL21(DE3)感受态细胞,在37℃条件下,经1mmol/L IPTG诱导表达4h,获得以包涵体形式存在的重组蛋白pET28a-SP,使用8mol/L尿素溶解包涵体,并通过镍离子金属螯合柱纯化获得重组蛋白,SDS-PAGE分析该蛋白的分子量约为50kD。Sp8蛋白体外表达的成功将为研究单环刺螠相关基因的转录调控打下基础。     

Exsolution lamellae in a clinopyroxene megacryst aggregate from Cenozoic basalt,Leizhou Peninsula,South China: petrography and chemical evolution

Petrographic investigations and electron microprobe analyses have been performed on a rare aggregate of clinopyroxene megacrysts collected from Cenozoic basalts in Yinfengling, Leizhou Peninsula of South China. The aggregate, composed of several clinopyroxene megacrysts, shows abundant exsolution lamellae of garnet (Grt) and orthopyroxene (Opx), and granular texture. Cr- and Ti-poor spinels are also present in this sample. They occur predominantly as Sp–Opx–Grt clusters (Cr# = 0.025–0.034) at the interspace between different megacrysts, and subordinately as bleb-shaped (Cr# = 0.025–0.034) or thin-lamella crystals (Cr# = 0.006–0.021) in clinopyroxene. Three different assemblages of exsolution are identified, namely (1) Sp (high Cr/Al) and Opx; (2) Grt–Opx; (3) Sp (low Cr/Al) and Opx. In addition, some garnets were likely developed as response to breakdown of the high-Cr/Al Sp. The homogeneous compositions in all constituent minerals and the good agreement between calculated Cpx/Grt partition coefficients (K _d’s) for trace elements and reference data strongly suggest a chemical equilibrium among coexisting minerals, probably attained by diffusion after the exsolution. Thermobarometric calculation based on exsolved assemblage yields a temperature of 900 ± 30°C and a pressure of 12 ± 2.2 kbar, corresponding to the present-day thermal gradient in the region. Much higher P–T estimates (T = 1,210 ± 30°C, P = 16.2 ± 3.5 kbar) are obtained for the reconstructed composition of cpx prior to exsolution. The contrast in thermal state before and after the exsolution might reflect the thermal evolution of the lithosphere beneath South China during the Cenozoic. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

2012年南海西北陆架冬季水文特征的观测分析

本文基于2012年12月南海西北部陆架海区的温盐和流速实测资料,分析了粤西和琼东陆架海区冬季三维温、盐结构和流场特征,给出沿陆架和跨陆架方向的水体和热盐通量。结果表明：（1）在50m以浅,粤西和琼东海区温度均由近岸向外海递增,深层则相反;冬季近岸海区混合层较深,外海密度跃层位于60—120m深度且层结较强,浮力频率大于10^–2/s;（2）海流大致沿等深线向西南流动,30m以深流速大小在0.03—0.40m/s之间,且随着深度增加而略有减小;琼东海区100m等深线附近在60m以浅水层观测到水体辐聚并有明显温度锋面存在;（3）沿陆架方向的水体和热盐输送均大于跨陆架方向,其中粤西单位面积沿/跨陆架水体通量平均值为0.13×10^–6/0.03×10^–6Sv/m²,低于琼东海区的0.91×10^–6/0.56×10^–6Sv/m²。