我国大陆下地壳的再循环研究取得重大进展

物质的再循环是地球动力学的主要过程之一.大陆下地壳是否能够再循环返回地幔是地球动力学和地球化学一个长期未解决的难题,这一问题对于认识大陆地壳的形成和演化以及壳幔交换作用至关重要.     

地幔岩包体中的Ni，Fe，Au，Mo含量及其意义——以山东和辽宁地区的比较分析为例

目的 探讨华北南北两缘辽宁宽甸及山东临朐两地新生代地幔岩包体中成矿元素含量与矿床分布之间的关系.方法 利用地幔岩包体常量元素、微量元素和稀土元素地球化学分析,结合区域矿产类型及矿产分布进行研究.结果 辽宁宽甸岩石圈地幔经历了较高程度的部分熔融,后期交代作用较之山东临朐较弱;山东临胸部分熔融程度较之辽宁宽甸较低,进行的交代作用较强.辽宁宽甸的地幔岩包体成矿元素Ni,Fe,Au及Mo平均值分别为2 561×10-6g/g,7.07%,4.17×10-9g/g,0.19×10-6g/g;山东临朐的地幔岩包体的成矿元素Ni,Fe,Au及Mo平均值分别为1 967×10-6g/g,6.60%,10.7×10-9g/g,0.37×10-6g/g.中国华北地块南北两缘地幔岩包体中的成矿元素Ni,Fe含量明显表现为北缘高南缘低,而Au,Mo含量则为南缘高北缘低.结论 岩石圈地幔岩Ni,Fe,Au,Mo等成矿元素含量的高低与成矿省情况基本是耦合的.地幔岩包体中Ni,Fe,Au,Mo等含量的高低对地壳矿产分布有指示意义.     

西南天山早白垩世火山岩中发现地幔和下地壳捕虏体

在中国西南天山托云地区早白垩世火山岩中存在地幔和下地壳捕虏体,火山岩的年龄为１２３－１０１Ｍａ,地幔捕虏体既有钛角闪石和韭闪石,长石,云母及辉石等矿物巨晶,也有橄榄岩,辉石岩,角闪石岩和云母岩等岩石碎块,下地壳捕虏体主要是条带状和块状的麻粒岩,火山岩是板内岩浆活动的产物。含水矿物巨晶和地幔岩石碎块中存在含水矿物,表明发生过强烈的地幔交代作用。     

峨眉山大火成岩省中两类岩浆分异趋势及其成因

二叠纪峨眉山大火成岩省存在两种岩浆分异趋势. 攀西古裂谷带内的岩浆显示Bowen分异趋势(即朝富Si贫Fe的流纹质岩浆演化), 在时空上与含V-Ti-Fe矿床的基性-超基性岩体密切相关. 峨眉山岩省东区的玄武岩则具有Fenner分异趋势(即朝富Fe贫Si方向演化), 最终分异产物中Fe₂O₃含量高达23%, SiO₂含量低至44%. 这一成分岩浆的发现为富Fe贫Si岩浆在自然界的客观存在提供了直接的证据. 具Bowen分异趋势的岩浆系列的氧逸度较高, 并经历了较大程度的地壳混染作用, 而具Fenner分异趋势的岩浆的氧逸度较低, 地壳混染不明显. 这暗示地壳混染程度可能是造成幔源岩浆具有不同分异趋势的重要原因. 具不同分异趋势的岩浆的空间分布特征为西南地区V-Ti-Fe矿床的形成机制提供了新的制约.     

下地壳地震深反射的可能载体: 来自层状辉长岩组构和高温高压波速实验的证据

通过对四川攀西地区层状辉长岩中斜长石和普通辉石晶格优选方位(LPO)的测量, 发现矿物定向主要表现在斜长石的[010]极密与辉石的[100]极密分别与面理垂直, 显示出一种与晶体结晶习性有关的生长组构, 与晶体在岩浆中结晶并受到一定的压实作用有联系. 利用矿物组构数据计算的地震波速度结构反映出较强的各向异性, Vp, Vs的各向异性分别为5.81%和5.54%. 高温高压条件下波速的测定结果显示出相似的特征: 层状辉长岩的纵波速度介于6.44~6.97 km/s, 纵波最大各向异性值为5.22%, Poisson比介于0.28~0.31. 通过对攀西层状辉长岩组构和波速结构的研究, 推断该区下地壳可能存在较大规模的层状辉长岩体或类似的层状地质体, 这种具有明显地震波各向异性的层状似层状介质是下地壳地震深反射的可能载体.     

辽西中侏罗统海房沟组埃达克质岩的确认及地质意义

海房沟组火山岩是辽西中生代火山岩的重要成员，其岩石共生组合为粗安岩—安山岩—英安岩—粗面英安岩，属于高钾钙碱性—钙碱性火山岩系。火山岩主量元素、稀土元素和微量元素研究表明：海房沟组火山岩属埃达克质岩；这些火山岩的源岩较深，可能为古老的下地壳玄武质岩石部分熔融产物。海房沟组埃达克质岩的确认对探讨辽西地区火山岩浆起源、壳幔相互作用、中生代构造应力场的重大转换及大规模断陷盆地群的形成具有重要意义。     

闽台区域地球动力学及地震活动效应研究

该文主要依据近30多年以来对福建地块的地震地质背景、地壳变形观测、构造应力场、地震活动性以及震源动力学参数等资料,结合台湾学者对台湾岛弧地球动力学、强震构造等的研究成果,探索海陆板块俯冲一碰撞地球动力学特征及其对板内活动地块影响,进而揭示板间-板缘-板内强震活动关联性和动力学性状的异同,以期为闽台区域的强震预测和防震减灾对策提供新思路.     

Identification and analysis of shear waves recorded by three-component OBSs in northeastern South China Sea

Structure models associated with P- and S-wave velocities contain considerable amount of information on lithology and geophysical properties, which can be used to better understand the complexity of the deep crustal structure. However, records of converted shear waves are less due to the speciality of seismic survey at sea and the rigorous generated conditions. The study on shear waves has always been a weakness for studying the deep crustal structures of South China Sea （SCS）. In this paper, eleven three-component OBSs were deployed along the Profile OBS-2001 in northeastern SCS. After the data processing of polarization and band-pass filter, converted S-wave phases were identified in the radical component records of nine OBSs. Taking the OBS7 as an example, identification and analysis of converted shear waves were presented and discussed in detail. A few phase groups, such as PwSc, PgSs, PnSc, ProS, and PwSn, were found coming from the deep crust or Moho interface by simple theoretical model calculation and ray-tracing simulation. The results not only provide the underlying basis for studies of S-wave velocity structure and Poisson＇s ratio structure, but also reveal the relationship between crustal petrology and seismology, which will be of importance for making full use of S-wave information in the future.     

Partial melting of deeply subducted continental crust and the formation of quartzofeldspathic polyphase inclusions in the Sulu UHP eclogites

Two types of quartzofeldspathic inclusions hosted by omphacite and garnet were identified in the Sulu UHP eclogites. The first consists of albite, quartz, and various amounts of K-feldspar. In contrast, the second consists predominantly of K-feldspar and quartz without any albite. The presence of quartzofeldspathic inclusions within the UHP mafic eclogites indicates that partial melting occurred in deeply subducted continental crust via mica dehydration melting reactions at an early stage of rapid exhumation. Such a melting event generated hydrous Na-K-Al-Si melts. These melts infiltrated into the mafic eclogite and were captured by recrystallizing garnet or omphacite, which together followed by dehydration and crystallization to form feldspar-bearing polyphase inclusions. Formation of silicate melts within the deeply subducted continental slab not only provides an excellent medium to transport both mobile （LILE） and immobile （HFSE） elements over a large distance, but also induces effective changes in the physical properties of the UHP slab. This process could be a major factor that enhances rapid exhumation of a deeply subducted continental slab.     

地球最迷人之七大温泉

当地下水激烈运动,冲出地壳,便形成了温泉。有些是在2000万年和4500万年前剧烈火山活动形成的。最高温度可达350℃。它们遍布地球的各个角落,每个大陆上,甚至在海洋中都有分布。下面就让我们走进地球上最著名的七大温泉。