硼同位素及其地质应用研究

硼的两个稳定同位素（10B 和11B）相对质量差较大,因此,硼同位 素分馏较显著。由于分析测量技术方面的改进和创新, 硼同位素地球化学近年来有了长足 的发展。业已查明,自然界中δ11B值变化为 －37‰～+58‰。其中,较负的 δ11B值见于非海相蒸发硼酸盐矿物和某些电气石,而较正的δ11B值见 于某些盐湖卤水和蒸发海水。现代大洋水的δ11B值十分恒定 (+39,5‰)。原始 地幔的δ11B值估测为－10‰±2‰。陨石的δ11B值很不均一,变化 可达90‰。而月岩的δ11B值变化较小（－6‰～+4‰）。由于硼同位素存在大的 分馏和不同地质体中截然不同的δ11B值,硼同位素地质应用范围十分广泛。目 前,硼同位素在研究星云形成过程和宇宙事件,壳-幔演化和板块俯冲作用过程,判别沉积 环境,研究矿床成因,示踪古海洋和古气候条件,和判断环境污染源区等方面的研究中成效显著。     

安徽庐枞盆地中巴家滩岩体的岩石地球化学特征及成因

巴家滩岩体位于长江中下游庐枞中生代火山岩盆地的中心地带,出露面积约4km2.岩性主要为辉石二长岩和含英辉石二长岩,发育黄铁矿化和黄铜矿化.野外及室内证据表明该岩体可分为两期,第一期表现为闪长质岩石包体;第二期主要为旱阶段的辉石二长岩和晚阶段的含石英辉石二长岩.巴家滩岩体随着由早到晚的演化,其SiO2含量、总碱含量(Na2O K2O)和岩石的氧化度不断增高.稀土配分整体呈右倾趋势,轻稀土富集,重稀土分馏不明显.岩石学、稀土和微量元素地球化学特征表明巴家滩岩体成岩物质来源于富含金云母的富集地幔Ⅱ.巴家滩岩体属于橄榄玄粗岩系,形成于伸展构造环境.巴家滩岩体具有高Al2O2、Sr、St/Y、La/Yb,低Y、Yb、Sr正异常,Eu弱负异常,与沙溪岩体的特征相似,早期包体的Cu含量高达0.8402,推断在其深部可能有可能有类似沙溪岩体的矿化岩浆存在.     

地幔流体的前缘研究

地幔流体是与地幔环境处于平衡的气体和挥发分。其主要化学组分为碳、氢、氧、氮、硫（ＣＨＯＮＳ）。它以富于地球内部原始组分为特征，但也包含部分再循环组分。地幔挥发分在弱还原条件下主要为ＣＯ２－Ｈ２Ｏ，强还原环境则以ＣＨ４－Ｈ２Ｏ－Ｈ２为主。地幔流体地球化学的重要性质为：（１）易溶于硅酸盐熔体；（２）净化作用；（３）再沉淀作用。近年来，有关地幔流体中稀有气体和挥发分的起源、分布及同位素组成等前缘领域的研究已取得重要进展。当前拟优先探索的问题包括气体裂化与金刚石成因，非生物成因地幔烃，地幔流体与成矿作用，以及地幔挥发分注入与地壳重熔等。     

Bulk-rock Major and Trace Element Compositions of Abyssal Peridotites: Implications for Mantle Melting, Melt Extraction and Post-melting Processes Beneath Mid-Ocean Ridges

This paper presents the first comprehensive major and traceelement data for 130 abyssal peridotite samples from the Pacificand Indian ocean ridge–transform systems. The data revealimportant features about the petrogenesis of these rocks, mantlemelting and melt extraction processes beneath ocean ridges,and elemental behaviours. Although abyssal peridotites are serpentinized,and have also experienced seafloor weathering, magmatic signaturesremain well preserved in the bulk-rock compositions. The betterinverse correlation of MgO with progressively heavier rare earthelements (REE) reflects varying amounts of melt depletion. Thismelt depletion may result from recent sub-ridge mantle melting,but could also be inherited from previous melt extraction eventsfrom the fertile mantle source. Light REE (LREE) in bulk-rocksamples are more enriched, not more depleted, than in the constituentclinopyroxenes (cpx) of the same sample suites. If the cpx LREErecord sub-ridge mantle melting processes, then the bulk-rockLREE must reflect post-melting refertilization. The significantcorrelations of LREE (e.g. La, Ce, Pr, Nd) with immobile highfield strength elements (HFSE, e.g. Nb and Zr) suggest thatenrichments of both LREE and HFSE resulted from a common magmaticprocess. The refertilization takes place in the ‘cold’thermal boundary layer (TBL) beneath ridges through which theascending melts migrate and interact with the advanced residues.The refertilization apparently did not affect the cpx relicsanalyzed for trace elements. This observation suggests grain-boundaryporous melt migration in the TBL. The ascending melts may notbe thermally ‘reactive’, and thus may have affectedonly cpx rims, which, together with precipitated olivine, entrappedmelt, and the rest of the rock, were subsequently serpentinized.Very large variations in bulk-rock Zr/Hf and Nb/Ta ratios areobserved, which are unexpected. The correlation between thetwo ratios is consistent with observations on basalts that D_Zr/D_Hf< 1 and D_Nb/D_Ta < 1. Given the identical charges (5⁺ forNb and Ta; 4⁺ for Zr and Hf) and essentially the same ionicradii (R_Nb/R_Ta = 1·000 and R_Zr/R_Hf = 1·006–1·026),yet a factor of 2 mass differences (M_Zr/M_Hf = 0·511 andM_Nb/M_Ta = 0·513), it is hypothesized that mass-dependentD values, or diffusion or mass-transfer rates may be importantin causing elemental fractionations during porous melt migrationin the TBL. It is also possible that some ‘exotic’phases with highly fractionated Zr/Hf and Nb/Ta ratios may existin these rocks, thus having ‘nugget’ effects onthe bulk-rock analyses. All these hypotheses need testing byconstraining the storage and distribution of all the incompatibletrace elements in mantle peridotite. As serpentine containsup to 13 wt % H₂O, and is stable up to 7 GPa before it is transformedto dense hydrous magnesium silicate phases that are stable atpressures of 5–50 GPa, it is possible that the serpentinizedperidotites may survive, at least partly, subduction-zone dehydration,and transport large amounts of H₂O (also Ba, Rb, Cs, K, U, Sr,Pb, etc. with elevated U/Pb ratios) into the deep mantle. Thelatter may contribute to the HIMU component in the source regionsof some oceanic basalts. KEY WORDS: abyssal peridotites; serpentinization; seafloor weathering; bulk-rock major and trace element compositions; mantle melting; melt extraction; melt–residue interaction; porous flows; Nb/Ta and Zr/Hf fractionations; HIMU mantle sources     

滇西北保山核桃坪铅锌矿床成矿流体来源的同位素地球化学证据

滇西北核桃坪铅锌矿是保山地块内沿澜沧江断裂带发育的一个大型铅锌多金属矿床,矿体严格受近SN向的断裂带及层间破碎带控制,赋存于上寒武统核桃坪组和沙河厂组大理岩化灰岩及矽卡岩中。文章在分析矿床地质特征的基础上,通过对V1矿体的氢、氧、碳、硫、硅和铅同位素地球化学的示踪研究,探讨了成矿溶液中水、碳、硅、硫和铅的来源以及成矿流体的演化问题。研究表明,V1矿体中矿石的石英δ18O水值变化范围为6·1‰~7·6‰,平均为6·7‰,其δDV-SMOW值变化范围为-100‰~-108‰,平均为-104‰,说明成矿流体主要来自深部岩浆分异水,并在后期成矿作用过程中有地层建造水和大气降水的加入;矿石中方解石的δ13CV-PDB和δ18O水值分别为-6·6‰~-5·9‰和5·0‰~5·2‰,反映成矿流体的碳、氧具有深部流体与围岩发生交代反应的特征。硅、硫和铅同位素具深部岩浆或地幔来源的特点,但遭受后期壳源物质的混染。据此提出该矿床是与深部岩浆热液或幔源流体贯入有关的构造热液脉型矿床,其成矿作用受控于深部过程的驱动和控制,可为指导地质找矿提供依据。     

利用加强水平方向总水平导数对位场全张量数据进行边界识别

位场全张量梯度数据以其信息量大、含有更高频的信号成分,能更好地描述小的异常特征等优点在地球物理领域中得到广泛应用.边界检测是位场解释中不可缺少的任务,需要新的边界探测器来处理位场梯度张量数据.为了充分利用位场梯度张量数据的多信息成分,本文定义了方向总水平导数和加强方向总水平导数,并利用其定义新的边界检测器.为了能同时显示不同振幅大小异常的边界,本文对其进行了归一化处理.通过模型试验,证明了归一化方法能更加清晰准确地显示浅部和深部的地质体边界信息.最后将该边界检测方法用于加拿大圣乔治湾实际测得全张量重力梯度数据和中国朱日和地区的磁异常数据中,并得到了较好的边界检测结果.     

Mineral chemistry of spinel peridotite xenoliths from Baengnyeong Island, South Korea, and its implications for the paleogeotherm of the uppermost mantle

Abstract   The mantle-derived xenoliths entrained in the Pliocene basanite from Baengnyeong Island, South Korea, are spinel lherzolites and spinel harzburgites. The overall compositional range of the Baengnyeong xenoliths matches that of the post-Archean xenoliths of lithospheric mantle origin from eastern China, but without any compositional evidence for a refractory Archean mantle root. Mineral compositions of the xenoliths have been used to estimate the equilibrium temperatures and pressures, and to construct a paleogeothermal gradient of the source region. The xenolith-derived paleogeotherm is constrained from about 820°C at 7.3 kbar to 1000°C at 20.6 kbar. Like those from the post-Archean Chinese xenoliths of lithospheric mantle origin, the Baengnyeong geotherm is considerably elevated relative to the conductive models at the depth of the crust–mantle boundary, reflecting a thermal perturbation probably related to lithospheric thinning. There is no significant P / T difference between harzburgite and lherzolite, which suggests that the harzburgites are interlayered with lherzolites within the depth interval beneath Baengnyeong Island.     

华北地区地壳上地幔三维P波速度结构

利用华北地震科学台阵和首都圈地震台网记录的4511次近震和625次远震的P 波到时数据,采用纬度和经度方向分别为0.5deg;times;0.5deg;的网格划分,反演得到了华北北部地区（111deg;E——120deg;E,37deg;N——42deg;N）深至400km 的地壳上地幔三维P 波速度结构.层析成像结果表明,研究区的速度存在明显的横向不均匀性,随着深度增加横向不均匀性总体呈现减弱趋势.燕山隆起带在60——120km 深度内存在明显的高速异常,这与较大的岩石圈厚度有关;山西裂陷盆地、华北平原下方60km 深度存在明显低速异常,与软流圈的出现有关.燕山隆起带岩石圈厚度在120km 以上,明显比太行山隆起的岩石圈厚度大,与稳定大陆地区的岩石圈厚度一致.太行山山前断裂已切穿莫霍面,贯入岩石圈.研究区上地幔顶部大范围的低速异常反映了软流圈上隆的特点.在华北平原及燕山隆起下方200——300km 存在高速异常可能与太古代大陆板块岩石圈的残留体有关.     

垂直地电场观测新技术的数据研究——基于坪城观测点的分析

结合同台观测的水平地电场数据,研究坪城垂直地电场观测数据,结果表明:(1)采用固体不极化电极进行垂直地电场观测,同一极距的观测结果基本一致,而铅板电极与固体不极化电极之间存在较大的电位差;(2)垂直地电场日变化形态清晰,长极距测道(A1C1、A2C1和A3C1测道)日变幅为5.85 mV/km左右,短极距(B1C1、B2C1和B3C1测道)日变幅为10.02 mV/km左右;(3)垂直向观测的地电场日变化优势周期在12 h和24 h。     

辉南新生代玄武岩中捕虏体橄榄岩矿物化学与华北岩石圈地幔演化

内容提要：在对吉林辉南新生代玄武岩中捕虏体橄榄岩详细的岩相学和矿物主量元素研究基础上,重点分析了单斜辉石激光原位微量元素,并讨论了辉南陆下岩石圈地幔的性质及其在华北克拉通破坏过程中的意义。橄榄石、单斜辉石和尖晶石的Mg#和Cr#均表明该区陆下岩石圈地幔主体是饱满的,同时也存在少量过渡和难熔型地幔。单斜辉石REE配分形式包括LREE亏损、倒U字型REE和LREE富集等不同类型。这些橄榄岩是地幔经历不同程度的部分熔融作用(低于10%)和复杂地幔交代作用的产物。交代介质主体是硅酸盐熔体,但个别样品有碳酸岩熔体交代的残留。橄榄石Mg#和平衡温度无相关性,说明辉南陆下岩石圈地幔不存在明显的分层而是交叉的。这些地幔特征和华北东部其他地区新生代的主体地幔性质相似,是熔-岩反应、侵蚀作用和上涌软流圈物质冷却转变置换的综合结果。