Structure of Synnyr alkalic rock massif

There are five intrusive complexes in the Synnyr range, one of which is the complex of alkalic igneous rocks discussed. It consists of several phases, some of which have been more or less completely rnetasomatized. These metasomatic rocks are considered by the author as a separate “complex.” K-A determinations on biotite from the syenites of these two complexes indicate an age of between 300 and 350 m.y. The alkalic rocks and their metasomatic equivalents form the equant Synnyr massif, situated at the intersection of two regional faults of northeast and northwest strike. The former is considered to have been the “magma channel.” The periphery of the massif is coarse alkalic syenites that underlie a ring-like erosional depression within which occur finer (trachytoid) Ne-bearing syenites and pulaskites. Contact zones consist of skarn, hornfels, and fenite. Within the intrusive the overall mineral composition of the metasomatized facies is not greatly different from that of the original rocks, but the texture has been changed by neocrystallization and recrystallization and the porosity is distinctly higher. Plagioclase has been replaced by almost pure albite and some of the potassium feldspar by intergrowths with kaliophylite. Fluorite and analcite occur as new minerals. In the late, low-temperature stage scapolite, zeolites, epidote-zoisite, and sparse quartz are found in some places. The other three complexes of the range are described very briefly: subalkalic syenite complex, a complex of silicic intrusive rocks, and a series of late lamprophyric dikes. – E. Ingerson.     

赤峰地区中生代火山岩中非金属成矿系列研究

研究表明,满克头鄂博组、玛尼吐组、白音高老组和义县组中酸性火山岩是赤峰地区珍珠岩、沸石、膨润土、叶腊石、高岭石等非金属矿床的重要赋矿层位,并形成珍珠岩—沸石—膨润土成矿系列和叶腊石—高岭石成矿系列.在矿床特征和成因研究后认为,矿床的时空分布主要受控于区域性NNE向断裂和中生代火山岩建造,成矿作用对矿床成因类型及组合关系...     

Jebel al Abyad: A recent alkalic volcanic complex in western Saudi Arabia

Arabia, a supposedly aseismic plate, has been the site of extensive alkalic volcanism during the past 10 m.y. The products of this activity, which extend intermittently from Syria to south central Saudi Arabia, are strongly alkalic and primarily basic in composition. Examination of specimens from the Jebel al Abyad area in Saudi Arabia, which displays a particularly wide variety of rock types, suggests the parental melt moved rapidly from depth to high level chambers where most of the chemical variation was produced by crystal fractionation. N-S dilational fissures of regional extent seem to have allowed the melt easy and rapid egress and a low degree of partial melting in the mantle could account for the high total alkalis content. The high K/Rb ratio, which also characterizes the granitic rocks of the underlying Precambrian basement, is thought to reflect a source mantle particularly low in rubidium.     

Petrogenesis of alkalic and calcalkalic volcanic rocks of Mormon Mountain Volcanic Field,Arizona

The Cenozoic Mormon Mountain Volcanic Field (MMVF) of northern Arizona is situated in the transition zone between the Basin and Range and the Colorado Plateau. It is composed of alkalic to sub-alkalic basalts and calcalkalic andesites, dacites, and rhyodacites. Despite their spatial and temporal association, the basalts and the calcalkalic suite do not seem to be co-genetic. The petrogenesis of primitive MMVF basalts can be explained as the result of different degrees of partial melting of a relatively homogenous, incompatible element-enriched peridotitic source. The variety of evolved basalt types was the result of subsequent fractional crystallization of olivine, spinel, and clinopyroxene from the range of primitive basalts. Crustal contamination seems to have occurred, but affected only the highly incompatible element abundances. The formation of MMVF calcalkalic rocks is most readily explained by small to moderate amounts of partial melting of an amphibolitic lower crust. This source is LREE-enriched but depleted in Rb and relatively unradiogenic Sr (⁸⁷Sr/⁸⁶Sr 0.7040). Calcalkalic rhyodacites may also be derived from andesitic parents by fractional crystallization. The overall petrogenesis of the MMVF complex is the result of intra-plate volcanism where mantle-derived magmas intrude and pass through thick continental crust.     

赣中盛源盆地及邻区橄榄玄粗岩系列火山岩中黑云母化学成分特征

本文利用电子探针技术对赣中盛源盆地及邻区橄榄玄粗岩系列火山岩中黑云母的类型、化学成分及结晶时的温度和氧逸度条件等进行了研究.黑云母为镁质黑云母;结晶时温度的大致范围为1 060°C~1 100°C,氧逸度大致范围为10-7bar~10-9 bar.本文研究表明,黑云母的化学成分研究是揭示岩石成因类型的一种有效途径,可为研究岩体成因类型以及成岩时的物理化学条件提供依据,并对成岩具有重要的指示意义.     

安徽庐枞地区中生代火山岩系的时代及其意义

<正> 庐枞地区的中生代火山岩系自老而新分为:龙门院组、砖桥组、双庙组、浮山组。按古生物证据,砖桥组所含瓣鳃类和腹足类化石属晚侏罗世,叶肢介、轮藻、植物与孢粉多为早白垩世组合,介形虫类化石为晚侏罗—早白垩世。地质力学所(1979)、安徽区调队(1979)、南京地矿所岩石组(1978)、地科院地矿所(1978)、贵阳地化所(1977)、安徽地矿局327地质队(1977)等单位均将砖桥组、龙门院组及与其相应地层划归侏罗系上统。刘鸿     

Paleomagnetic dating of younger volcanic series

Summary Paleomagnetic dating of younger volcanic series is based on the thermoremanent magnetism of these rocks. This fossilises the periodic reversals of the earth's magnetic field over 180°. The slower a-periodic drifting of the magnetic pole is not considered.Magnetic orientation of younger extrusive rocks, either N(ormal) or R(eversed), can normally be measured in the field with a geologic hand compass. This gives us a simple method, which can be valuable to every field geologist working in volcanic series. It should, however, preferably be used in relation with geologic mapping, as magnetic correlation of sections taken far apart, easily lead to false conclusions.Paleomagnetic stratigraphy has until now been based only on the detailed studies of the french physicist A.Roche. In the Auvergne in Central France he studied the sequence of magnetic periods on geologically dated extrusives. It is expected that paleomagnetic studies of this type will yield many results in the years to come.

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Zusammenfassung Paläomagnetische Datierung junger Ergußgesteine stützt sich auf den thermoremanenten Magnetismus dieser Gesteine. Hierdurch wird der wiederholte Umschlag des erdmagnetischen Feldes über 180° festgelegt. Es bleiben bei dieser Art Untersuchungen die langfristigen Verschiebungen des magnetischen Poles außer Betrachtung.Die magnetische Orientierung junger Ergußgesteine, entweder N(ormal) oder R(eversed), läßt sich im Terrain mit einem geologischen Kompaß meistens festlegen. Hieraus folgt eine einfache Methode zur Charakterisierung junger Ergußgesteine, welche jedem Geologen, der in vulkanischem Gebiet arbeitet, eine Stütze sein kann. Die Methode darf aber nur in Zusammenhang mit geologischen Kartierarbeiten angewandt werden, da sonst leicht Fehlschlüsse gezogen werden können.Die paläomagnetische Stratigraphie stützt sich bis jetzt nur auf genaue Untersuchungen an geologisch datierten Ergußgesteinen in der Auvergne seitens des französischen Physikers A.Roche. Voraussichtlich wird diese Methode in den kommenden Jahren große Erfolge erzielen.

     

五大连池火山岩带的地幔富集作用

小古里河-科洛-五大连池-二克山新生代火山岩带是一条富钾火山岩带,本文选择科洛荡子山新近纪的白榴碧玄岩和其中的方辉橄榄岩地幔包体和白榴霓霞岩岩浆包体为重点研究对象,通过岩相学和地球化学研究发现大量地幔交代的证据,从而认识到以方辉橄榄岩代表的岩石圈地幔在来自软流圈富含不相容元素的流体交代作用下,形成了富集地幔,白榴霓霞岩包体和富钾的火山岩则来自这类交代型地幔不同阶段部分熔融的岩浆,因此火山岩具有低Nd、低Pb和高Sr的同位素特征。富钾火山岩带的K2O／Na2O等值线图表明长400km,宽50km的幔源富钾的火山岩带是受新生代陆内NNW走向的裂谷控制。     

Nature of the clinopyroxene and iron enrichment in alkalic and transitional basaltic magmas

Iron enrichment and clinopyroxene composition are considered to be good indicators of the magmatic parentage of volcanic series produced by fractionation of basaltic magma. Tholeiitic series are in fact believed to be constantly more iron enriched than alkalic series and systematic differences in the clinopyroxene mineralogy of the two suites seem also to be well established. The aim of this paper is to demonstrate that such generalization cannot be accepted, as natural conditions can be realized under which the fractionation of alkalic or mildly alkalic basalts may produce series with strong iron enrichment and with clinopyroxene mineralogy atypical for basalts of alkaline affinity.In the Erta'Ale volcanic range (Northern Danakil Depression, Ethiopia), an example of such a serie is found, with a mildly alkalic basaltic magma fractionating under low and falling oxygen fugacity and giving rise to a series with some tholeiitic chemical and mineralogical features.     

安徽庐枞火山岩矿集区东南部成矿系列及成矿规律

安徽庐枞火山岩矿集区是长江中下游成矿带重要的铁铜硫多金属成矿区.文章基于近年来在该矿集区东南部取得的找矿成果,提出该区有4个成矿系列:与高钾钙碱性系列侵入岩有关的矽卡岩型铁铜、金硫成矿系列,与橄榄安粗岩系有关的火山—次火山热液脉状铜多金属、铁成矿系列,与岩浆作用有关的沉积—叠加改造铁铜成矿系列和与富碱侵入岩有关的铁、铜铅锌、铀成矿系列.分别论述了4个典型矿床地质特征及成矿规律,认为成矿时间为两期三阶段成矿,成矿空间受盆地基底地层石炭系—侏罗系、基底断裂、火山机构及东南部"A型"花岗岩带和高钾钙碱性侵入岩带的控制,提出了区域成矿模式.     

火山岩储层含气性预测

针对目前火山岩储层难以进行含气性预测的现状,本文完整论述了采用叠前反演为基础来解决此问题的方法。具体说明了火山岩储层含气性预测的原理和主要工作步骤。累积厚度预测的方法图示。将其应用于松南气田火山岩的储层预测研究中,其预测结果与实际钻井吻合较好,对于本地区的勘探开发具有一定的指导意义和参考价值。     

演化中的裂谷带——五大连池火山岩带

小古里河—科洛—五大连池—二克山新生代火山岩带是一条富钾火山岩带。文中重点论述了以下4点内容:(1)火山岩及其包体中存在典型的地幔交代作用;(2)根据火山岩K2O/Na2O比值勾画出富钾火山岩带范围;(3)地幔气体的绝热膨胀导致"冷泉和冻土现象";(4)地震活动的现状。论证了NNW走向的五大连池火山岩带是新生代初始的大陆裂谷,它们切穿了大兴安岭北北东向构造带。进一步从岩浆演化的趋势认为五大连池裂谷带将持续演化而不会夭折。     

Petrology of some volcanic rock series of the Aeolian arc,Southern Tyrrhenian Sea: Calc-alkaline and shoshonitic associations

In the Aeolian island arc two different magmatological associations, calc-alkaline andesite series and shoshonites, occur in close vicinity. Although both associations erupted simultaneously during the last glaciation, there is a general tendency for the calc-alkaline rocks to be older. Shoshonitic activity is still going on.Calc-alkaline lavas include high-Al basalts, andesites and dacites, with the general characteristics of the island-arc type andesite series. Large cation trace elements (Rb, Ba, Sr) however are distinctly enriched.Shoshonite series include trachybasalts and latites, with which potassium-rich rhyolites can be associated. Leucite tephrites and potassic trachytes form a different evolution trend of the shoshonitic association.Petrology relates both associations of the Aeolian Islands to the island arc dynamics which is presently characterized by deep-focus earthquakes in the depth range of 200–350 km. The present-day gap in seismic activity from 50–200 km coincides with the present-day lack of calc-alkaline volcanic activity and is explained by the model of a detached slab which continues to sink into the mantle.     

熊耳群火山岩系金银多金属矿床热水成矿作用

在华北板块南缘熊耳群火山岩系地层内部，已发现金、银多金属矿床多处，但对其成因机制的解释，不同学者往往存在不同认识。笔者通过对已知矿床产出地质特征、成矿热水流体特征和来源以及矿化、蚀变围岩系统研究后提出熊耳期后火山热液是控制金、银多金属矿床形成的主要因素，成矿作用以热水流体的沉积、充填作用为主，主成矿期应为熊耳群火山活动后期等新认识。     

Mineral chemistry and petrogenesis of an ultrapotassic-ultramafic volcanic rock

Compositions of the major phenocryst minerals (olivine, phlogopite) and groundmass minerals (olivine, phlogopite, kalsilite), and a glass phase have been determined from a biotite mafurite occurring as an ejected block in the highly K-rich ultramafic rocks of south west Uganda. Comparison of the phenocryst mineral compositions with those determined from recent high pressure experiments on biotite mafurite composition suggests this rock may have formed by partial melting of a K-enriched mantle source containing both H₂O and CO₂ at approximately 1,250 ° C and 30 kb. The absence of crystalline leucite but its presence as a major component of the glass phase and textural relations in the groundmass indicate that the final consolidation of the biotite mafurite took place at pressures greater than atmospheric. The presence of phlogopite, olivine, kalsilite, and glass mainly of leucite composition may suggest that consolidation took place under the conditions where these phases were in equilibrium. Based on the experimentally determined conditions for the reaction of phlogopite break down to olivine+kalsilite +liquid+vapor, a crude estimation of the consolidation conditions for ejected blocks of biotite mafurite are 1,150 °–1,180 ° C at a of 1–2 kb.     

Dating of a volcanic rock by electron spin resonance

The age of a volcanic rock has been determined by ESR dating using the Ge center in quartz. The total dose of natural radiation and the age obtained from the Ge center are 460 krad and 2.07 ± 0.50 Ma, respectively, and those from the unidentified defect at g = 2.011 are 484 krad and 2.16 ± 0.21 Ma, respectively. These dates agree well with the age of 2.0 ± 0.5 Ma determined by the fission-track method. High stress or temperature destroy these accumulated defects but, in the same time, produce a lot of new diamagnetic precursors which enable us to observe the clear ESR signal.     

利用测井方法识别火山岩岩相方法

利用实际岩石薄片数据及测井数据,通过GR-TH 及GR-AC 交会图方法将松南气田营城组岩石结构划分为熔岩结构、熔结结构和凝灰结构3 种。凝灰结构和熔结结构对应爆发相,熔岩结构对应喷溢相。结合次生孔隙度的大小及岩心、录井信息对出现的6 种亚相: 热碎屑流亚相、热基浪亚相、空落亚相、上部亚相、中部亚相和下部亚相进一步划分,其结果与地质上的岩相亚相基本一致。     

青藏高原北羌塘新生代高钾钙碱岩系火山岩角闪石类型有痕量元素地球化学

利用电子探针和激光探针剥蚀系统（LA－ICP－MS）对北羌塘新第三纪高钾钙碱岩系英安岩中角闪石的主元素和微量、角闪石强烈富集Sc、Ti、V、Cr、Co、Ni等不相容亲铁元素，而相对亏损Th、U、Pb、Rb等强不相容的大离子亲石元素。稀土元素丰度高，且无Eu异常，批示北羌塘这套高钾钙碱岩系火山岩可能是青藏高原加厚的相当于榴辉岩相物质组成的下部陆壳脱水熔融的产物。     

Nature and cause of compositional variation among the alkalic cap lavas of Mauna Kea Volcano,Hawaii

Most Hawaiian basaltic shield volcanoes are capped by moderately to strongly evolved alkalic lavas (MgO<4.5 wt.%). On Mauna Kea Volcano the cap is dominantly composed of hawaiite with minor mugearite. Although these lavas contain dunite and gabbroic xenoliths, they are nearly aphyric with rare olivine and plagioclase phenocrysts and xenocrysts. The hawaiites are nearly homogeneous in radiogenic isotope ratios (Sr, Nd, Pb) and they define coherent major and trace element abundance trends. These compositional trends are consistent with segregation of a plagioclase-rich cumulate containing significant clinopyroxene and Fe-Ti oxides plus minor olivine. Elements which are usually highly incompatible, e.g., Rb, Ba, Nb, are only moderately incompatible within the hawaiite suite because these elements are incorporated into feldspar (Rb, Ba) and oxides (Nb). However, in the most evolved lavas abundances of the most incompatible elements (P, La, Ce, Th) exceed (by 5–10%) the maximum enrichments expected from models based on major elements. Apparently, the crystal fractionation process was more complex than simple, closed system fractionation. The large amounts of clinopyroxene in the fractionating assemblage and the presence of dense dunite xenoliths with CO₂ inclusions formed at minimum pressures of 2 kb are consistent with fractionation occurring at moderate depths. Crystal segregation along conduit or magma chamber walls is a possible mechanism for explaining compositional variations within these alkalic cap lavas.