中国东部新生代玄武岩中巨晶矿物的地球化学

本文对安徽女山、河北汉诺坝和广东普宁碱性玄武岩中的单斜辉石和角闪石巨晶进行了主要元素、稀土元素、微量元天和Ｓｒ＿Ｎｄ同位素的综合分析。数据显示产出于３个研究区的单斜辉石巨晶有３类：Ａｌ普通辉石、透辉石和Ｆｅ＿Ｎａ透辉石。普宁地区的角闪石巨晶乃世界上罕见的绿钙闪石巨晶。女山和普宁的单斜辉石和角闪石巨晶是碱性玄武岩浆在幔源高压下的结晶产物；汉诺坝的单斜辉石巨晶既可以是碱性玄武岩浆又可以是拉斑玄武岩浆的高压结晶体。所有巨晶相对于寄主岩者属于偶然捕掳晶。巨晶的形成符合“流动结晶模式”。它们与共存的橄榄岩色体无成因     

河北汉诺坝玄武岩中深源包体和巨晶分布的动力学机理

汉诺坝碱性玄武岩是深源包体和巨晶的主要寄主岩,同时,也有不含包体的碱性玄武岩和含包体的拉斑玄武岩。本文基于理论计算,探讨了包体和巨晶分布的动力学机理。     

汉诺坝玄武岩的主要特征及其形成的T、P、fo_2条件

汉诺坝玄武岩主要为由拉斑玄武岩系列与碱性玄武岩系列岩石组成的高原玄武岩。喷发时代为晚第三纪,喷发类型为裂隙式。一、玄武岩、巨晶、包体的组成常见的玄武岩种属为石英拉斑玄武岩、橄榄拉斑玄武岩、碱性橄榄玄武岩及碧玄岩,以碱性玄武岩系列较为少见。在碱性玄武岩系列中,常见巨晶及包体。巨晶有镁铝榴石、普通     

延边地区中生代火山岩的岩浆源区:来自Sr-Nd同位素和深源捕虏体(晶)的证据

延边地区中侏罗世和早白垩世火山岩中包含有较多的辉石岩捕虏体和角闪石捕虏晶,前者为普通辉石变种,其化学成分类似于中国东部新生代玄武岩中单斜辉石巨晶的成分,具有岩浆堆积成因特征;后者为韭闪石和镁质绿钠闪石变种,其成分类似于中生代晚期玄武岩中角闪二辉石岩包体里的角闪石和新生代玄武岩中的角闪石巨晶.矿物温压计算结果显示,它们形成深度介于25～37km.延边地区中生代火山岩的(87Sr/86Sr)i值介于0.704 3～0.705 0,εNd(t)值介于2.33～4.71,表明岩浆源区应是一套具有亏损性质的新增生的地幔物质.综合上述结果,可以判定延边地区中生代火山岩的原始岩浆应来源于新增生的壳幔过渡带物质的部分熔融,地壳增生事件的时间为新元古代.     

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。     

内蒙古集宁新生代玄武岩中橄榄岩包体和巨晶的发现及意义

内蒙古集宁新生代玄武岩产于华北克拉通北缘，属于广义的“汉诺坝玄武岩”。首次在三义堂附近的碱性玄武岩中发现了大量的橄榄岩包体、辉石和长石以及少量的含钛磁铁矿巨晶。包体主要是尖晶石二辉橄榄岩，造岩矿物为橄榄石＋斜方辉石＋单斜辉石＋尖晶石，辉石巨晶主要为透辉石和普通辉石，长石巨晶主要是歪长石和少量斜长石。1．5GPa条件下，尖晶石二辉橄榄岩样品所记录的平衡温度与汉诺坝相近，集中于950℃左右，大体上反映了华北克拉通北缘大陆岩石圈地幔尖晶石相部分的温度状态。单斜辉石巨晶的结晶温压大于幔源包体的平衡温压，表明巨晶的来源深度可能大于包体。包体的结构及矿物成分分析表明，这些包体是玄武质岩浆上升过程中偶然捕获岩石圈地幔的岩石碎块。二辉橄榄岩包体中橄榄石高Mg#值（89．5～91．7）和较高的NiO含量（0．29％～0．55％），暗示集宁玄武岩中的橄榄岩包体来自较高熔融程度的岩石圈地幔。     

延边明月沟盆地中生代火山岩深源捕虏体和捕虏晶的发现及矿物化学

在延边地区明月沟盆地中侏罗世屯田营组火山岩中发现含有较多的辉石岩捕虏体及单斜辉石和角闪石捕虏晶。单斜辉石相对富含Al2O3、FeO和TiO2,与中国东部新生代玄武岩中单斜辉石巨晶的成分相当。角闪石巨晶的成分明显不同于地幔橄榄岩包体中的韭闪石。从矿物化学所获得的温度-压力计算结果表明：岩浆来源应位于壳幔过渡带。     

碱性玄武岩中巨晶辉石的出溶结构

人们在研究玄武岩浆的起源和演化时,对碱性玄武岩中的巨晶辉石产生了越来越大的兴趣。这些巨晶辉石具下列特点:个体大;常与来自上地幔的橄榄岩包体伴生;其氧化铝含量,特别是Al(?)的含量远高于寄主玄武岩中的辉石斑晶和橄榄岩包体中的单斜辉石;与寄主     

吉林伊通新生代玄武岩中的高压巨晶组合及其岩石学意义

新生代碱性玄武岩中,高压巨晶分布比较广泛,它们常与二辉橄榄岩包体伴生。研究这些巨晶,对了解玄武岩浆形成和演化历史,解决深部成岩作用和岩浆结晶分离过程具有很大意义。伊通火山群[1]含上地幔包体的玄武岩火山锥普遍含高压巨晶,它们是普通辉石、钠透长石和铁黑云母。小孤山火山锥含巨晶达1％,为钠透长石和普通辉石组合,尖山火山锥含巨晶2％,为钠透长石+普通辉石+铁黑云母组合。大孤山东山、     

中国夕卡岩矿床中的角闪石

文章综合分析研究了中国21个夕卡岩矿床中的130个角闪石的成分分析数据。根据夕卡岩类型及其伴生金属矿化的不同，把角闪石分为4大类：钙夕卡岩中的角闪石多属钙角闪石，包括绿钙闪石、铁角闪石、镁绿钙闪石、铁浅闪石、阳起石、铁阳起石、铁镁钙闪石和铁韭闪石等；镁夕卡岩中的角闪石以透闪石为主，局部有浅闪石或韭闪石；锰质夕卡岩中的角闪石有锰质阳起石、锰质透闪石、锰直闪石和锰镁闪石；碱质夕卡岩中的角闪石属钠-钙角闪石或钠角闪石类，包括钠透闪石、镁亚铁钠闪石、亚铁钠闪石、镁铝钠闪石和镁钠闪石。碳酸盐围岩和有关侵入岩的成分对角闪石的类型、成分及其伴生金属矿化起重要的作用。     

How late are K-feldspar megacrysts in granites?

Various petrologists have suggested that K-feldspar megacrysts grow in granites that are extensively crystallized, even at subsolidus conditions. However, experimental evidence indicates that, though K-feldspar nucleates relatively late in the crystallization history, abundant liquid is available for development of large crystals. A great deal of evidence, involving many different factors, favours a magmatic/phenocrystic origin for K-feldspar megacrysts in granites, namely simple twinning, oscillatory zoning, euhedral plagioclase inclusions, and concentric, crystallographically controlled arrangements of inclusions. In addition, abundant evidence has been presented of (1) mechanical accumulation of K-feldspar megacrysts in granites, (2) alignment of megacrysts and megacryst concentrations in magmatic flow foliations, (3) involvement of megacrysts in zones of magma mixing in granite plutons, and (4) occurrence of megacrysts in some volcanic rocks, implying that the megacrysts were suspended in enough liquid to be moved without fracturing or plastic deformation. Detailed trace element and isotopic data also indicate that megacrysts can move between coexisting felsic and more mafic magmas. Irregular overgrowths on megacrysts are consistent with continued magmatic growth after euhedral megacrystic growth ceased, the overgrowths being impeded by simultaneously crystallizing quartz and feldspar grains.     

Ultramafic inclusions and high pressure megacrysts from a nephelinite sill,Nandewar Mountains,north-eastern New South Wales,and their bearing on the origin of certain ultramafic inclusions in alkaline volcanic rocks

Ultramafic inclusions and megacrysts are unusually abundant in a nephelinite sill in the Nandewar Mountains in north-eastern New South Wales. The inclusions are divisible into a Cr-diopside group and a Ti-augite group, the former being dominated by Cr-spinel Iherzolites of restricted modal composition, the latter by olivine and titaniferous Al-rich clinopyroxene assemblages which vary widely in their modal proportions. The principal megacryst species are olivine and black, titaniferous Al-rich clinopyroxene; additional but comparatively rare megacrysts include titanphlogopite, kaersutitic amphibole, and deep green, relatively Fe-rich clinopyroxene. The Cr-spinel Iherzolites conform closely in mineralogy and chemistry with the spinel lherzolites which dominate upper mantle xenolith assemblages in alkaline mafic volcanic rocks from other provinces. Megacrysts and Ti-augite inclusion mineral assemblages are consistently more Fe-rich than analogous phases in the Cr-diopside xenoliths and also display more extensive cryptic variation. The available experimental data on the high pressure liquidus or near-liquidus phases in olivine nephelinite and related compositions indicate that the olivine and black clinopyroxene megacrysts were precipitated at pressures in the vicinity of 15–20 kb. The similarity in the nature and compositions of the principal megacryst species to analogous phases in the Tiaugite group of inclusions indicates that the latter also represent cognate cumulates derived from the olivine nephelinite at broadly comparable pressures. High pressure fractionation of the host olivine nephelinite liquid, controlled mainly by the separation of olivine and aluminous clinopyroxene, produced only comparatively minor compositional changes in the derivative liquid. The hiatus in olivine compositions at approximately Fo_86–88, apparently characteristic of the olivines in coexisting Cr-diopside and Ti-augite inclusions, is assessed in terms of the compositions of olivine in equilibrium with alkali basaltic liquids at high pressures.     

中国东部碱性玄武质岩石中的辉石和角闪石巨晶

在中国东部,北起黑龙江、南到海南岛,广泛地分布着新生代碱性玄武质岩石,例如碱性橄榄玄武岩、碧玄岩、霞石玄武岩等。它们含有丰富的超镁铁岩包体和各种巨晶。已发现的有辉石、角闪石、石榴石、歪长石、钛铁矿和云母等巨晶。Harte(1978)把巨晶定义为大的单矿物单个晶体,它比超镁铁岩团块中的矿物粗得多(2—20cm)。然而有的地质学家把巨晶的粒度下限定在1cm(Eggler 等,1979)。笔者遵循这一定义和采纳后一界线,在此基础上着重对中国东部部分地区的辉石和角闪石巨晶进行研究,研究情况见表1。     

Corundum from basaltic terrains: a mineral inclusion approach to the enigma

 This paper investigates the origin of corundum megacrysts that occur in many basaltic terrains, and which are considered to be eroded from basaltic rocks. Geochemical data for over 80 primary mineral inclusions within corundum megacrysts are used to gain a new insight into the petrogenetic history of the corundum megacrysts. A wide spectrum of minerals is present as inclusions in the corundum; the most common are Nb−Ta oxides (such as titaniferous columbite and uranpyrochlore), alkali feldspar, low-Ca plagioclase (albite-oligoclase) and zircon. Rare inclusions include Fe,Cu-sulphide (low in Ni), cobalt-rich spinel, Th,Ce-rich phosphate and uraninite. The similar chemistry of some inclusion minerals from corundum occurring in widely separated areas suggests that the corundum megacrysts in basalts have a similar petrogenesis. Geochemical characteristics of the inclusions indicate a bimodal grouping, which is best explained by a mixing-hybridisation process. This study indicates that the corundum megacrysts are not cogenetic with their basaltic hosts but are crustal fragments accidentally incorporated into the erupting magma. It is suggested that interactions between a silicic component and an intruding carbonatitic or similar Si-poor magma is responsible for Al-oversaturation, resulting in locally distributed lenses of corundum-bearing rock of mixed paragenesis (“hybrid rock hypothesis”). Feldspar exsolution textures provide strong evidence that this hybridisation occurred at mid-crustal levels. Subsequent volcanic eruptions brought the corundum-bearing rocks (later disintegrated in the magma) up to the Earth's surface. This petrogenetic model for corundum megacrysts is experimentally testable. Received: 15 March 1995 / Accepted: 30 June 1995     

An Al-spinel ultramafic-mafic inclusion suite and high pressure megacrysts in an analcimite and their bearing on basaltic magma fractionation at elevated pressures

An analcimite sill, which intrudes Carboniferous sedimentary rocks northwest of the township of Barraba in northeastern New South Wales, is exceedingly rich in ultramafic and mafic inclusions and also contains a varied megacryst assemblage. The majority of inclusions belong to an ultramafic-mafic granulite suite whose members generally contain a Cr-poor green spinel. Layering is preserved in many inclusions and their textures are appropriate to those arising from recrystallization at subsolidus temperatures. Ultramafic granulites of the Al-spinel suite are mainly pyroxenites, with rarer lherzolites, and mafic granulites usually consist of the assemblage plagioclasea-luminous pyroxenes-spinel. Ca-rich tschermakitic clinopyroxenes and coexisting aluminous Ca-poor orthopyroxenes define a trend of moderate iron enrichment. Spinels also display significant Fe²⁺ → Mg substitution. Plagioclase in some plagioclase-bearing pyroxenites and mafic granulites contains numerous rod-like inclusions of spinel, compositionally similar to the discrete spinels unassociated with plagioclase. The formation of spinel in plagioclase is believed to have resulted largely from the migration of (Mg, Fe²⁺) to Al-rich nucleation sites in the feldspar. Other inclusion types include Cr-spinel lherzolites —more Fe-rich than Cr-diopside lherzolite inclusions in alkaline volcanics — and rare wehrlite heteradcumulates, probably cognate with the host analcimite. The megacryst assemblage is dominated by anorthoclase megacrysts, which are accompanied, in order of decreasing abundance, by megacrysts of tschermakitic clinopyroxene, titanbiotite, kaersutite, and aluminous titanomagnetite. The Al-spinel mafic granulites have low Ti, K and P contents and their petrochemical affinities are high-alumina mafic alkaline to transitional. They compare closely in major and minor element chemistry with some ocean ridge basalts. The Al-spinel ultramafic-mafic inclusions suite is interpreted as the remnants of a layered ultramafic-mafic “pluton ” which initially crystallized at pressures in the vicinity of 10 kb and subsequently re-equilibrated at subsolidus temperatures (ca 950° C) and comparable pressures. The parent magma was K-poor, ol-normative subalkaline and its fractionation at moderate pressures, controlled mainly by olivine and subcalcic clinopyroxene, resulted in decreases in the derivative liquids in their saturation levels and ol contents, and increases in Al and Ca. These trends are reflected in the compositions of the mafic granulites. The pressure regime of megacryst formation apparently was greater than 10–12 kb i.e. the megacrysts precipitated before acquisition of xenoliths of the Al-spinel granulite suite by the analcimite host. Anorthoclase fractionation produced only limited compositional changes in the original alkali basaltic melt.     

Amphibole-rich xenoliths and host alkali basalts: petrogenetic constraints and implications on the recent evolution of the upper mantle beneath Ahaggar (Central Sahara,Southern Algeria)

Quaternary basanitic to nephelinitic volcanoes from Tahalra (western Ahaggar, southern Algeria) contain numerous Mg-ilmenite and amphibole-rich inclusions (±olivine, ±salite) and spinel lherzolite (±pargasite) inclusions associated with kaersutite megacrysts. On the basis of petrological, geochemical and Sr isotopic study of representative xenoliths (including a composite nodule defined as a vein cross-cutting peridotite) and lavas, we attribute the series of amphibole-rich xenoliths and megacrysts to segregation under upper mantle conditions from a hydrous high Ti and LREE melt geochemically similar to the Quaternary basanite but isotopically different. Amphibole-rich rocks and megacrysts are the results of magmatic events (less than 40 Ma) probably contemporaneous with the various pre-Quaternary volcanic phases recognized in Ahaggar. The amphibole-rich veins and the Quaternary lavas have a garnet lherzolitic source enriched in REE (7 to 9 times chondritic in LREE, 2 times in HREE). This enrichment probably results from former metasomatic events unrelated to the recent magmatic history. Melts from which these veins precipitated within upper mantle peridotite also account for mantle enrichment processes; they induced a local partial melting and contact metasomatism (pargasitization). The upper mantle beneath the volcanic areas of Ahaggar is veined and hydrous, and consequently lightened: thus, the uplift of basement may be the isostatic response to magmatism and related metasomatism and therefore the result of the Cenozoïc igneous activity.     

Myrmekite associated with alkali feldspar megacrysts in felsic rocks from New South Wales

Comparison of myrmekites in undeformed and deformed ‘porphyritic’ felsic rocks shows that they have different morphologies and spatial distributions within their megacrysts. In particular, plagioclase inclusions in the undeformed megacrysts carry myrmekite rims which may be explained by solid-state exsolution, as may the quartz blebs in associated perthitic plagioclase. Myrmekite at the rims of the megacrysts may be due to an interaction between exsolution and metasomatic processes. Stress concentrated at the margins of pre-existing megacrysts in the deformed rocks and the occurrence here of random non-coherent plagioclase nuclei will explain the preponderance of myrmekite at this location.     

中国山东昌乐地区碱性玄武岩刚玉中记录的岩浆不混溶作用

Abundant melt-and fluid inclusions occur in corundum megacrysts of alkaline basalt from the Changle area,Shandong province,eastern China.One type of melt inclusions,i.e.muhiphase melt inclusions(glass bubbles daughter minerals)were identified,which occur along growth zones of host corundum megacrysts.Microthermometry and laser Raman microprobe analysis were performed on the melt inclusions.The bubbles within the melt inclusions are confirmed to be CO_2-rich phase and the daughter minerals are probably silicates,such as augite and okenite.The results of high temperature homogenization experiment strongly suggest that two immiscible melts,i.e.a H_2O-and CO_2-rich melt and an anhydrous and CO_2-poor melt were trapped by melt inclusions in corundum megacryst.     

Andesine megacrysts in alkali basalts from Japan

Andesine megacrysts up to 3 cm in size occur sporadically in certain alkali basalts and allied mafic rocks in southwestern Japan. They are sometimes accompanied by megacrysts of mafic minerals and ultramafic and mafic inclusions. Nine andesines have been chemically analysed.From the petrography and chemistry and the results of high pressure experimental work, it is suggested that andesine megacrysts crystallized from alkali basalt magma under dry conditions at a depth of about 30 to 60 km.