我国东部若干地区新生代玄武岩中长石巨晶的特征及成因

本文汇集了中国东部新生代玄武岩中76个长石巨晶的化学成分,并与53个国外长石巨品进行了对比。文中对长石巨晶的产状、物理性质、矿物化学及微量元素进行了研究,并对国际上关于长石巨晶五个有争议的问题进行了讨论。作者同时也提出了自己的观点。     

深源巨晶辉石中“水”的红外光谱研究

深源巨晶辉石中“水”的红外光谱研究彭文世张倩（中国科学院广州地球化学研究所，广州５１０６４０）关键词巨晶辉石结构羟基红外光谱深源地幔岩含水已被许多实验所证实。地幔矿物中少量的水对矿物的诸多性质和许多地幔地质过程的发生和发展，都起着极其重要的作用。近些...     

碱性玄武岩中钛金云母巨晶的研究

钛金云母巨晶产于安徽当涂釜山的碱性玄武岩中,在该岩石中还含有尖晶石二辉橄榄岩包体和辉石、石榴石和歪长石巨晶。 本文提供了钛金云母的光性特征、矿物化学和波谱学等方面的资料。其化学特征是富钛和铁。其折光率显著高于各种产状的金云母。X射线衍射谱的特征是基底奇数层反射强,而偶数层反射不明显。多型为3T型。这些反映了钛金云母在高压条件形成。     

碱性玄武岩中的某些巨晶单斜辉石Ⅱ：穆斯堡尔谱——兼论单斜辉石的异…

本文对辽宁宽甸碱性玄武岩中巨晶单斜辉石进行穆斯堡尔谱研究，应用晶体结构研究结果较合理地解释了单斜辉石的异常穆斯堡尔谱，结合ＸＲＤ讨论了单斜辉石中Ｆｅ结构态的测定以及穆斯堡尔谱的可应用性，巨晶应结晶于相当氧化的环境。     

玄武岩中刚玉巨晶的包体研究：Ⅰ.更长石包体的发现及意义

本文对山东昌乐碱性玄武岩中刚玉巨晶的更长石包体及同一地区产出的歪长石巨晶进行了电子探针、红外吸收光谱测定,讨论了更长石包体与刚玉巨晶、歪长石巨晶间的成因关系,认为刚玉巨品、歪长石巨晶以及玄武岩中的其他巨晶构成了一个结晶序列,歪长石相对较晚结晶。     

福建省新生代玄武岩中辉石巨晶的矿物学研究

本文对我国福建省三条断裂带上产出的辉石巨晶进行了成分、结构、差热及穆斯堡尔谱分析,提出辉石巨晶有黑色和绿色两种类型,每种辉石巨晶均由两个相组成,两个相的存在决定了辉石巨晶的许多特殊性质。黑色辉石巨晶与玄武岩有明显的成因联系,而绿色辉石巨晶则没有。     

福建龙海天马山-牛头山玄武岩中捕虏体和巨晶特征的研究

本文研究了天马山-牛头山新生代玄武岩中二辉橄榄岩和橄辉斜长岩捕虏体的岩石学、矿物学和地球化学等特征并论及碱性玄武岩中单斜辉石和歪长石巨晶。尖晶石二辉橄榄岩存在于碱性玄武岩和橄榄拉斑玄武岩中,由尖晶石、橄榄石、斜方辉石、铬透辉石等组成,与模拟地幔岩相比,具低的MgO含量和不相容元素Ti丰度而富集Co、Ni相容元素。尖晶石二辉橄榄岩具低的稀土总量和平缓的球粒陨石标准化稀土元素分配模式,形成于温度约1000℃、深度为50—80公里的上地幔。橄辉斜长岩具正堆积结构,Al_2O_3、CaO、∑REE和La/Yb明显高于二辉橄榄岩。但MgO含量远低于后者,反映两者成因的不一致性。普通辉石巨晶以富铝为特征,歪长石以富钙为特征。     

大别山沙村辉长岩中长石的结构水及其对岩浆演化的指示

本文报道了大别山沙村地区碰撞后辉长岩的化学组成和其中斜长石的傅立叶变换红外光谱(FTIR)分析结果。10个辉长岩从化学组成上分为两组,代表了两个不同的岩浆。斜长石普遍含有结构水,以OH-的形式存在,含量为213×10-6~658×10-6(H2O的质量分数)。结合大别山榴辉岩的数据来看,由长石中结构水含量推测的原始岩浆的富水特征可能与其源区中含有俯冲断离的榴辉岩有关。两组辉长岩中的长石都表现出水含量与全岩Mg#值的负相关关系,即随着结晶分异的进行,岩浆中的水含量在逐渐减少。这可能是由于角闪石的连续结晶和/或岩浆的去气作用造成的。沙村长石水含量与全岩Mg#值之间的相关性说明后期热液蚀变事件没有改变长石中的水,它们依然有效地保存了原始信息。     

碱性玄武岩中的某些巨晶单斜辉石──Ⅱ:穆斯堡尔谱──兼论单斜辉石的异常穆斯堡尔谱和铁结构态的测定

本文对辽宁宽甸碱性玄武岩中巨晶单斜辉石进行穆斯堡尔谱研究。应用晶体结构研究结果较合理地解释了单斜辉石的异常穆斯堡尔谱。结合XRD讨论了单斜辉石中Fe结构态的测定以及穆斯堡尔谱的可应用性。巨晶应结晶于相当氧化的环境。     

山东昌乐新生代碧玄岩中歪长石巨晶特征及成因

山东昌乐新生代玄武岩中发育大量长石、辉石和刚玉巨晶。前人的研究多集中在辉石和刚玉上,而长石巨晶的来源仍存在争议。本文对新生代玄武岩岩石学、地球化学,以及长石巨晶矿物特征、包裹体成分和原位主微量元素进行了系统分析,结果显示：长石巨晶主要存在于K₂O和Na₂O含量较高、SiO₂含量较低的碧玄岩中。背散射图像下长石巨晶无环带,存在长石、辉石微晶及玻璃质组成的反应边。巨晶原位主量元素分析表明：长石为歪长石,An值为4.76%～5.62%,Ab值为49.81%～71.89%,巨晶核部Mg、Fe、Na、Al、K等元素及An、Ab的含量处于小范围内的无序波动状态,无明显的变化规律,可能为地幔环境下结晶的高温无序矿物;长石巨晶富集轻稀土元素（LREE）,亏损重稀土元素（HREE）,具有明显的Eu正异常（δEu=12.37～26.22）,Sm、Nd、Gd相对亏损,核部稀土元素总量较低,ΣREE=1.98×10^-6～2.46×10^-6,LREE/HREE=21.71～76.51,（La/Yb）_N为18.14～36.70,长石巨晶与碧玄岩的稀土元素总量比值在0.006～0.015之间,暗示两者无演化联系。综合歪长石巨晶以及寄主岩浆的成因特征,本文认为歪长石巨晶结晶于含有洋壳俯冲流体组分的地幔环境,后期被来源于软流圈地幔的玄武质岩浆捕获,带出地表。     

西伯利亚雅库特金伯利岩中四颗古老锆石巨晶的微量元素和Hf同位素特征——对区分金伯利岩中锆石巨晶的启示

金伯利岩中的锆石按照颗粒大小可以分为细粒锆石（一般小于200μm）和巨晶锆石（一般大于500μm）。前人的研究结果显示在金伯利岩中粒径较大的巨晶锆石的U-Pb体系在高温的地幔中一直保持着开放状态,直到寄主金伯利岩浆的喷发才使地幔锆石的U-Pb体系封闭,因此这些巨晶锆石是确定金伯利岩年龄的重要矿物之一。然而,近年来的研究表明,金伯利岩中还存在一些时代远老于金伯利岩年龄的锆石,也具有较大的粒径（以下称古老锆石巨晶）。它们的存在无疑影响了利用锆石U-Pb方法确定金伯利岩年龄的准确性。本文以西伯利亚雅库特（Yakutia）金伯利岩省中的四颗古老锆石巨晶为研究对象,通过形态学、年代学、微量元素和Hf同位素组成,讨论古老锆石巨晶的来源。同时,我们统计和对比了全球多个金伯利岩中能够确定金伯利岩年龄的锆石和古老锆石巨晶的形态学、U、Th含量和微量元素组成、Hf-O同位素等特征。研究结果显示,金伯利岩中的古老锆石巨晶的t_DM年龄和O同位素组成与可以用来确定金伯利岩年龄的锆石巨晶具有明显的差别。这些手段在未来的研究中可以用来区分可确定金伯利岩年龄的锆石巨晶和古老的锆石巨晶。

     

安徽铜陵地区中生代幔源岩浆底侵作用——来自矿物巨晶和岩石包体的证据

安徽铜陵地区中生代的岩浆岩岩体中产有多种矿物巨晶和岩石包体。笔者对产于曹山辉石冈长玢岩和鸡冠石花岗闪长岩中的辉石和角闪石巨晶及其堆积岩或堆积晶进行了详细的岩相学和矿物化学研究，并在此基础上估算了矿物平衡结晶的温压条件，讨论了安徽铜陵地区中生代幔源岩浆底侵作用问题。研究表明，铜陵地区大约在140Ma以前发生了碱性橄榄玄武质岩浆的底侵作用，辉石巨晶和角闪石巨晶及其堆积晶是由底侵的碱性橄榄玄武质岩浆在28～33km深处的深位岩浆房中与下地壳发生同化混染作用形成的中基性岩浆经结晶分异作用形成的，而辉石堆积岩是由中基性岩浆在19～21km深处的浅位岩浆房中与中地壳的浅变质岩系发生同化混染作用形成的中性岩浆经结晶分异作用形成的。     

Water solubility in nominally anhydrous minerals measured by FTIR and 1H MAS NMR: the effect of sample preparation

Samples of enstatite and forsterite were crystallized in the presence of a hydrous fluid at 15 kbar and 1100 °C. Water contents in quenched samples were measured by ¹H MAS NMR and by FTIR. If the samples were prepared in the same way, similar water concentrations were obtained by both methods. There is no evidence that one or the other method would severely over or underestimate water contents in nominally anhydrous minerals. However, measured water contents vary by orders of magnitude depending on sample preparation. The lowest water contents are measured by polarized FTIR spectroscopy on clear, inclusion-free single crystals. These water contents probably reflect the real point defect solubility in the crystals. Polycrystalline material shows much higher total water concentrations, presumably due to hydrous species on grain boundaries, growth defects, and in submicroscopic fluid inclusions. Grinding the sample in air further increases water concentration. This effect is even more pronounced if the sample is ground in water and subsequently dried at 150 °C. Polarized FTIR measurements on clear single crystals of enstatite saturated at 15 kbar and 1100 °C give 199 ± 25 ppm by weight of water. The spectra show sharp and strongly polarized bands. These bands are also present in spectra measured through turbid, polycrystalline aggregates of enstatite. However, in these spectra, they are superimposed on much broader, nearly isotropic bands resulting from hydrous species in grain boundaries, growth defects, and submicroscopic fluid or melt inclusions. Total water contents for these polycrystalline aggregates are between 2000 and 4000 ppm. Water contents measured by FTIR on enstatite powders are 5300 ppm after grinding in air and 12 600 ppm after grinding under water und subsequent drying at 150 °C. Received: 25 June 1999 / Revised, accepted: 4 October 1999     

Zircon megacrysts from basalts of the Venetian Volcanic Province (NE Italy): U–Pb ages, oxygen isotopes and REE data

Mafic alkaline lavas from the Venetian Volcanic Province (NE Italy) contain orange–brown zircon megacrysts up to 15 mm long, subhedral to subrounded and showing equant morphology, with width-to-length ratios of 1:2–1:2.5. U–Pb ages of zircon (51.1 ± 1.5 to 30.5 ± 0.51 Ma) fit the stratigraphic age of the host lava (Middle Eocene and Oligocene) and their oxygen isotope composition (δ¹⁸O = 5.31–5.51‰) is similar to that of zircon formed in the upper mantle. Cathodoluminescence images and crystal chemical features, e.g. depletion of incompatible elements such as REE, Y, U and Th at constant Hf content, indicate that centre-to-edge zircon zoning is not consistent with evolution of the melt by fractional crystallization. All the above features, together with the fact that zircon and host basalts are coeval, indicate that the studied Zr megacrysts crystallised from a primitive alkaline mafic magma, which later evolved to the less alkaline host magma.     

雷州英峰岭玄武岩中单斜辉石巨晶的地球化学和地幔交代作用

雷州半岛英峰岭火山岩中单斜辉石巨晶以低Mg^#值(0．62—0．47)、贫重稀土(HREE)和富Al2O3、TiO2、Na2O和中稀土(MREE)为特征，并具有明显的成分变化。随着Mg^#降低，单斜辉石的Al：O，(11．58～6．97％，)、TiO，(2．28～1．06％)和HREE逐渐降低。这种变化特征不同于世界上大多数辉石巨晶的变化规律。随着演化辉石巨晶的大多数不相容元素，如Nb、Sr、Zr、Hf和LREE—MREE逐渐增加。低的Mg^#值和Ni、Co、Cr含量指示巨晶母岩浆是一种强烈演化的残余岩浆(Mg^#=0．27～0．35)。分离结晶模拟表明本研究最富镁的巨晶(Lz-54)的母岩浆很可能是由拉斑玄武质岩浆经70～80％，以单斜辉石为主的结晶分异后形成。而本研究的其它辉石巨晶是该母岩浆在不同演化阶段(25～80％)分离结晶的产物。分离矿物中除了单斜辉石还包含了大量的石榴子石、斜长石和钛铁矿。温压计算表明英峰岭巨晶是高温岩浆在56～60km深的上地幔的结晶产物(r=1290℃～1130℃，P=1.73～1．83GPa)，这一深度有利于石榴子石结晶。对比不同地区辉石巨晶的成分特征和形成条件，作者指出不同地区单斜辉石巨晶各种元素的不同变化规律主要受母岩浆成分和结晶条件控制。巨晶母岩浆在地幔结晶时对围岩橄榄岩进行了不同程度的交代作用。早期贫流体的岩浆对橄榄岩的交代作用较弱，只有Sr，La等强活动性元素被明显改变；晚期富流体(F，P，H2O)岩浆对橄榄岩的交代作用强烈，大多数元素被明显改变。因此，可以推断交代熔体中流体的含量是影响地幔橄榄岩交代作用的关键。     

长白山天池火山千年大喷发岩浆含水量研究——熔融包裹体含水量的红外光谱测试

长白山天池火山在公元一千年左右曾发生过大规模喷发,其产物为大面积分布的灰白色碱流质浮岩和碎屑流,在其斑晶矿物橄榄石、钙铁辉石和碱性长石中均可见到熔融包裹体。在最主要的斑晶矿物——碱性长石中含有数量众多且个体也较大的熔融包裹体,多数含有一个以上的气泡,其中部分含有子晶,根据形貌特征的不同可分为截然不同的两组包裹体。这些熔融包裹体带有大量喷发前地下岩浆的信息,成为研究地下深部的岩浆在复杂的溢流-爆炸喷发中所发生变化的最好媒介。也是本文的研究对象,通过其中挥发份尤其是水的含量,可以推知天池火山发生大喷发的原因。经Nicolet Magna-IR 550红外光谱仪测定,这些熔融包裹体的含水量较高,达1．6％-3．6％,为当时天池火山发生了巨大规模爆炸喷发的原因提供了强有力的证据。但目前红外光谱仪的应用范围还比较有限,有待今后拓宽其应用领域。     

The origin of K-feldspar megacrysts hosted in alkaline potassic rocks from central Italy: a track for low-pressure processes in mafic magmas

In situ Sr-isotope and microchemical studies were used to determine the provenance of K-feldspar megacrysts hosted in mafic alkaline potassic, ultrapotassic rocks and in differentiated rocks from two nearby volcanic apparatus in central Italy.

At Monte Cimino volcanic complex, mafic leucite-free ultrapotassic megacryst-bearing rocks of olivine latitic composition are associated with evolved latite and trachyte. Here, latites and trachytes straddle the sub-alkaline field. Age-corrected ⁸⁷Sr/⁸⁶Sr values (Sr_i) of the analysed Cimino olivine latites vary from 0.71330 and 0.71578 and strongly increase at constant Mg value. Latite and trachyte have lower Sr_i than olivine latites ranging between 0.71331 and 0.71361. Sr_i of K-feldspar megacrysts from olivine latites are between 0.71352 and 0.71397, but core and rim ⁸⁷Sr/⁸⁶Sr ratios within individual megacryst are indistinguishable. In all the mafic rocks, the megacrysts are not in isotopic equilibrium with the hosts. K-feldspar megacrysts from both the latite and trachyte have similar Sr-isotope compositions (Sr_i=0.71357–0.71401) to those in the olivine latites. However, Sr_i of megacryst in the trachyte vary significantly from core to rim (Sr_i from 0.71401 to 0.71383). As with the olivine latites, the K-feldspar megacrysts are not in isotopic equilibrium with bulk rock compositions of the latite or trachyte.

At Vico volcano, megacryst-bearing rocks are mafic leucite-free potassic rocks, mafic leucite-bearing ultrapotassic rocks and old trachytic rocks. The mafic leucite-bearing and leucite-free rocks are a tephri-phonolite and an olivine latite, respectively. A megacryst in Vico trachyte is isotopically homogeneous (Sr_i CORE=0.71129, RIM=0.71128) and in equilibrium with the host rock (Sr_i bulk ROCK=0.71125). Sr_i of megacryst from tephri-phonolite is clearly not in isotopic equilibrium with its host (Sr_i bulk ROCK=0.71158), and it increases from core (Sr_i=0.71063) to rim (Sr_i=0.71077). A megacryst in Vico olivine latite is isotopically homogeneous (Sr_i CORE=0.71066, RIM=0.71065), but not in equilibrium with the host rock (Sr_i bulk ROCK=0.71013).

The Sr isotope microdrilling technique reveals that Cimino megacrysts were crystallised in a Cimino trachytic magma and were subsequently incorporated by mixing/mingling processes in the latitic and olivine latitic melts. A model invoking the presence of a mafic sub-alkaline magma, which was mixed with the olivine latite, is proposed to justify the lack of simple geochemical mixing relation between Cimino trachytes and olivine latites. This magmatological model is able to explain the geochemical characteristics of Cimino olivine latites, otherwise ascribed to mantle heterogeneity.

The similarity of core Sr_i of megacrysts hosted in Vico tephri-phonolite and olivine latite suggests that the K-feldspar megacrysts are co-genetic. Isotopic equilibrium between megacryst and Vico host trachyte indicates that the trachyte is the parent of this megacryst. On the contrary, the megacrysts hosted in tephri-phonolite and olivine latite do not derive from the old trachytic magma because no diffusion process may explain the core to rim Sr isotope increase of the xenocryst hosted in the tephri-phonolite. The megacrysts hosted in the Vico mafic rocks might derive from a trachytic melt similar in composition to the old Vico trachytes.     

REE Abundaces in Megacrysts and Host Basalts：REE Behavior of Magma at High Pressures

Based on REE abundances in megacrysts and host basalts and their equilibrium conditions,it has proved that megacrysts may have been produced from the magma derived from the host rocks or of more basic composition.The REE ratios of megacrysts to host rocks may be taken as partition coefficients when both are equilibrium with each other.The crystal fractionation of megacrysts has caused the evolution of REE in the magma.It is obvious that some host basalts are the product of magma evolution after crystal fractionation.According to REE abundances in the host rocks and the partition coefficients between crystal and liquid,the history of crystal fractionation of magma can be traced.     

Garnet inclusions in alkali basalts of Primorye: Deep-seated xenoliths or cognate megacrysts?

Detailed study of garnet and garnet-pyroxene inclusions from alkali basalts of Primorye allowed us to distinguish two heterogeneous mineral assemblages: early (primary) and late (secondary) ones. The former reflects the initial stage of rock formation and consists of garnet, clinopyroxene, orthopyroxene, plagioclase, and ilmenite. The latter, orthopyroxene-plagioclase-spinel assemblage replaces garnet. The transformation of garnet typically accompanies the change in the garnet assemblage to a higher temperature pyroxene-plagioclase-spinel assemblage owing to its entrainment in high temperature magma. The study of the chemical composition and textural relationships of minerals, together with the examination of similar mineral assemblages from alkali basalts around the world and mafic-ultramafic intrusions, led us to the conclusion that the garnet inclusions of Primorye are typical xenoliths and xenocrysts representing fragments of tholeiite intrusions of an ophiolite complex that were transformed in the host basaltic magma.