浙江新昌复合式火成杂岩的岩石学、地球化学及其地质意义

浙江新昌复合式火成杂岩包括复合火山岩流和复合侵入杂岩。复合火山岩流由玄武岩和流纹岩/流纹质熔结凝灰岩组成,有的含少量安山质-英安质岩流和岩石包体;复合侵入杂岩由辉绿岩和花岗岩复合而成,含闪长质-石英闪长质岩石包体。它们在空间上紧密伴生,同位素年龄为96~113 Ma;地球化学上,它们统属钙碱性岩系,具有轻稀土元素和大离子亲石元素富集、高场强元素亏损等特点,稀土元素、微量元素配分型式基本相同,Sr=0.7069~0.7079,εNd (t ) = -2.3~-5.3,指示它们的微量元素和同位素发生过充分的交换。这些特点与浙闽沿海其他复合岩流和复合侵入杂岩的特点基本一致。它们形成在伸展构造背景,由起源于受消减作用影响的岩石圈地幔部分熔融而产生的玄武岩岩浆底侵,并与深熔的壳源花岗岩浆发生不同程度的岩浆混合而形成。新昌复合式火成杂岩的研究,为更深入研究中国东南部沿海地区晚中生代地球动力学环境变化和构造-岩浆作用提供了一个典型实例。     

从31届国际地质大会分析前寒武纪地质研究进展和走向

第31届国际地质大会于2000年8月6日至17日在巴西里约热内卢市召开,有关大会的一般概况已由记者们在《国土资源报》上作了报道。我作为前寒武纪地质研究人员主要参加了与专业有关的学术会议和野外考察。像这样的大型国际会议,作为一名参会     

Petrology of the Betulia Igneous Complex,Cauca, Colombia

The Betulia Igneous Complex (BIC) is a group of Late-Miocene (11.8 ± 0.2 Ma) hypabyssal intrusions of intermediate to felsic composition located in the SW of the Colombian Andes. These bodies have a calc-alkaline tendency and are related to the subduction of the Nazca plate under the South American plate. Diorites, quartz diorites and tonalities have porphyritic and phaneritic textures and are composed of plagioclase, amphibole, quartz, biotite, and orthoclase. Plagioclase is mainly of andesine-type and the amphiboles were classified mainly as magnesiohornblendes, actinolites, and tschermakites.BIC rocks have a narrow range of SiO₂ content (59–67wt%) and exhibit an enrichment of LILE and LREE relative to HFSE and HREE, respectively. These features are attributed to enrichment of LILE from the source and retention of HFSE (mainly Nb, Ta, and Ti) by refractory phases within the same source. The depletion of HREE is explained by fractionation of mineral phases that have a high partition coefficients for these elements, especially amphiboles, the major mafic phase in the rocks. Nevertheless, the fractionation of garnet in early stages of crystallization is not unlikely. Probably all BIC units were generated by the same magma chamber or at least by the same petrologic mechanism as shown by the similar patterns in spider and REE diagrams; fractional crystallization and differentiation processes controlled the final composition of the rocks, and crystallization stages determined the texture.Isotopic compositions of BIC rocks (⁸⁷Sr/⁸⁶Sr: 0.70435–0.70511; ¹⁴³Nd/¹⁴⁴Nd: 0.51258–0.51280; ²⁰⁶Pb/²⁰⁴Pb: 19.13–19.31; ²⁰⁷Pb/²⁰⁴Pb: 15.67–15.76; ²⁰⁸Pb/²⁰⁴Pb: 38.93–39.20) indicate a source derived from the mantle with crustal contamination. The model proposed for the BIC consists of fluids from the dehydration of the subducted slab (Nazca plate) and subducted sediments that generated partial melting of the mantle wedge. These basaltic melts ascended to the mantle–crust boundary where they were retained due to density differences and began to produce processes of melting, assimilation, storage, and homogenization (MASH zone). At this depth (∼40–45 km), fractional crystallization and differentiation processes began to produce more felsic magmas that were able to ascend through the crust and be emplaced at shallow depths.     

Petrology of Igneous Rocks in Northern Golpayegan, Iran

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21世纪地质科学展望——31届国际地质大会学术启示

第31届国际地质大会于2000年8月6～17日在巴西里约热内卢举行，共103个国家和地区3705名代表出席。第31届国际地质大会的主题是：地质学与可持续发展——第三个千年的挑战。中国代表团共180余人出席了大会，在不同的领域和学科参加交流。作者有幸参加了大会，现根据交流资料和领会的感受，对新世纪地质科学发展的趋向及面临的挑战作一归纳，与同仁讨论。文中简单回顾过去100年地质科学发展的特征，强调了技术进步推动地质科学进步的决定性作用；提出了21世纪地质科学面临的若干方面任务，包括：矿产资源持续供给、水资源短缺、减轻自然灾害、溶入社会和政治等。     

Petrology of the Guadalupe Igneous Complex South-western Sierra Nevada Foothills California

The Guadalupe igneous complex is one of several late Jurassic,mesozonal plutons in the foothills of the Sierra Nevada. Severallines of evidence suggest that the different rock types, rangingfrom eucrite to leucogranophyre, originated mainly through fractionalcrystallization of a parent basaltic magma. Important differencesbetween this complex and other large differentiated basic intrusionsinclude the presence of steeply inclined but weak layering inthe gabbroic rocks and an abundance of hydrous mafic mineralsrelative to olivine and pyroxene, which are not representedby iron-rich end-members in the granitic differentiates. Chemically,the differentiation trend is marked by a large variation infelsic parameters and only a weak enrichment in iron. This trend,which is similar to that of calc-alkaline suites of orogenicregions, may have been influenced by abnormally high pressuresof water and oxygen for a crystallizing basaltic magma.     

火成岩的10年研究进展和未来的挑战

文中简要列举了近年在火成岩领域的研究进展及今后发展方向,主要涉及7个方面内容：①新元古代末期大陆裂谷火山作用与Rodinia超级联合大陆裂解;②中亚石炭纪—早二叠世大规模裂谷火山事件的深部地球动力学背景及其与古特提斯裂解和晚古生代中亚大规模成矿事件的关系;③中—新生代东亚火山作用与岩石圈巨量减薄;④新生代印度—亚洲大陆碰撞与高原隆升的火山作用响应;⑤大火成岩省和地幔柱;⑥花岗岩与地球动力学环境;⑦铁镁—超铁镁岩与蛇绿岩。提出在下一个10年里,需要继续开展岩浆成因和演变、岩浆作用和构造环境的关系,变质岩石的P—T—t轨迹,以及变质作用、岩浆作用和大地构造的关系等方面的研究;需要研究更深层次的地壳和上地幔,以了解岩浆形成和运移的过程;海洋钻探有可能取得深部地壳或上地幔的样品,大陆钻探将钻到10 km及更深;将使用地震层析来描述地壳和上地幔的结构,确定俯冲带或地幔柱的位置,以及部分熔融的分布面积,等等。此外,分析和测试等方面的高新技术的开发和运用,以及实验岩石学的发展都对岩石学领域的发展起到至关重要的作用。     

关于我国地质岩心钻机发展方向的分析

对立轴式钻机和全液压动力头钻机进行了全面的对比分析,重点对2种钻机进行了技术经济对比。结果表明,动力头钻机不仅在搬迁和运移性方面要优于立轴式钻机,而且在钻进施工的技术经济指标方面也优于立轴式钻机。钻孔深度加大后,动力头钻机在钻进施工效率方面的对比优势会逐渐减弱,应该考虑采取加大钻杆立根长度,从而加大起下钻速度的措施。     

Igneous Petrology of the Synorogenic Fongen-Hyllingen Layered Basic Complex, South-Central Scandinavian Caledonides

The 160 km² Caledonian Fongen-Hyllingen complex is an extremelydifferentiated, layered, basic intrusion, synorogenically emplacedat 5–6 kb in the allochthonous Trondheim nappe complex,situated in the Trondheim region of Norway. A zone of gabbroic rocks without rythmic layering usually occursalong the margin and a supposed feeder to at least part of thecomplex is preserved. A wide variety of magmatic sedimentarystructures are present in the c. 10,000 m thick sequence ofrhythmically layered rocks which vary from olivine-picotitecumulates at the base to quartz-bearing ferrosyenites at thetop. Mineral compositions, fractionation trends, and the compositionof feeder rocks suggest a tholeiitic parent. Mineral compositions cover extreme ranges. Olivine varies fromFo_86·2 to Fo_0·2 with a hiatus between about Fo₇₁and Fo₆₁. Plagioclase ranges from An_79·5 to An_1·5,albite coexisting with orthoclase microperthite in the finaldifferentiates. Cumulus Ca-poor pyroxene (Wo_2.4En_66.8Fs_30.8-Wo_2·0En_17·0Fs_81·0)first shows sporadic inversion from pigeonite at the Fe-richcomposition of Fs₆₇ and the final Ca-poor pyroxenes are replacedby magmatic grunerite which reaches an Mg: Fe ratio of 12:88.Ca-rich pyroxenes (Wo_44·7En_43·8Fs_11·5-Wo_47·0En₀Fs_53·0)are highly calcic and have a slight Ca-minimum in the earlystages, unrelated to the disappearance of Ca-poor pyroxene.Calcic amphibole, a constant intercumulus phase in most of thecomplex, becomes a cumulus phase in the later stages and variesfrom titanian-pargasite to ferro-edenite. Magnetite and ilmenitejoin the cumulate assemblage at Fo₅₅ and ilmenite persists intothe final quartz-bearing ferrosyenite where it shows replacementby sphene. Apatite, biotite, zircon, quartz, K-feldspar andallanite join the final extreme differentiates in the namedsequence. The fractionation trend is, in many respects, transitionalbetween those typical of the tholeiitic and calc-alkaline series,and is interpreted as reflecting crystallization under moderate,increasing P_H2O. Cryptic layering shows several reversals to higher temperatureassemblages with increasing stratigraphic height. Successivereversals are to irregular compositions and measured in termsof olivine composition, can be up to about 30 mole per centFo. The minimum stratigraphic thickness to include the entirefractionation range is reduced to about 2200 m after ‘removal’of the compositional overlaps due to the reversals. Thus roughlythree-quarters of the present cumulate stratigraphic sequencerepresents magma replenishment. A mechanism involving the mixingof fresh magma batches with the residual, differentiated magmafrom the previous influx, is envisaged. The periodic influxof fresh magma took place into a chamber which was probablyclosed to the exit of material.     

耗散结构理论及其在火成岩岩石学中的意义

本文简要介绍了耗散结构理论及其研究方法,以及它在火成岩中的应用,其中包括以下几个方面:(1)基性杂岩体的层状构造;)2)花岗岩中的球状构造;(3)斜长石的环带;(4)花岗岩体的成分分带。并讨论了这四种耗散结构的形成机理。这些耗散结构都是在远离平衡的条件下,通过内部不可逆的非线性过程,由于外界的扰动和内部的涨落造成定态的失稳而形成的。其形成的根本原因是其内部反馈机制作用的结果。斜长石的环带是时间耗散结构——极限环。利用耗散结构理论简要地解释了辽宁二道沟花岗闪长岩的成因。