汉诺坝玄武岩及其超镁铁质岩包体的成因岩石学研究

本文提出的超镁铁质岩包体的全岩成分,矿物化学和微量元素地球化学的全部资料表明,大部分二辉橄榄岩包体代表饱满的地幔样品,而黑色二辉岩包体代表来自下部地壳的麻粒岩样品。二辉橄榄岩包体在980—1120℃有限的温度范围内平衡,但是平衡压力在计算的温度下变化相当大(12.5—24千巴)。黑色二辉岩包体有相对低的平衡条件(850—950℃,8千巴)。和大洋、地盾地温相比,在深度小于100公里时,由二辉橄榄岩体包体所确定的古地温有陡得多的斜率。可以推断最少亏损的地幔可能直接位于被研究的地区之下。     

CENOZOIC VOLCANIC ROCK SERIES IN SOUTHEASTERN CHINA——PETROCHEMISTRY

In this paper, the age, spatial distribution and petrochemistry of Cenozoic volcanic rocks of southeastern China are discussed. They are subalkalic and alkalic. Except for the Pleistocene calc-alkalic volcanic rocks of northern Taiwan and the Late Tertiary tholeiitic rocks of Eastern Coastal Range of Taiwan, the alkalic basaltic rocks form the majority. Only alkalic and strongly alkalic basaltic and ultrabasic volcanic rocks occur in the inland to the west of the Haifeng-Zhenghe-Shangyu fracture zone. It follows that the petrochemical nature of the Cenozoic volcanics studied exhibits a marked trend of variation with time and space, implying that their formation was obviously controlled by the geotectonic setting.     

CENOZOIC VOLCANIC ROCK SERIES IN SOUTHEASTERN CHINA (Ⅱ)——TRACE ELEMENT GEOCHEMISTRY

On the premise of the sister paper, the trace element geochemistry of Cenozoic volcanic rocks of southeastern China is discussed in detail in this paper. The data presented in this paper indicate that the upper mantle beneath the area studied is enriched in the strongly HYG elements as compared with the chondritic mantle, and that the depth of Cenozoic basaltic magma sources progressively increases from the coast to the inland. The Cenozoic basaltic volcanism has occurred in a geotectonic setting of rifting continental margin; on the contrary, the Mesozoic volcanic rocks are predominated by the felsic volcanics erupting in a geotectonic setting of active continental margin. It can be inferred from the studies of ultramafic inclusion-derived geotherm that the Cenozoic rifting of eastern China continent has been mainly controlled by the thermal mantle diapirism.     

MINERALOGY AND T-P CONDITIONS OF CRYSTALLIZATION OF EARLY ARCHAEAN GRANULITES FROM QIANXI COUNTY, NE CHINA

This paper presents new wet chemical analyses of proxeue, garnet, amphibole and bio-tite from the Early Archaean granulites of Qianxi county, NE China. The mineralogy anddistribution coefficients of Fe and Mg between coexisting ferromagnesian minerals are discussedin detail. The narrow K_D(Fe) range and the close clustering of the intersections on the Wo-Enjoin for the pyroxene pairs may be suggestive of the attainment of uniform equilibrium condi-tions. From petrographic observations and geothermobarometric calculation, it is concluded thatthe P-T conditions of metamorphic recrystallization of the granulites are 11--13 Kb and800--850℃ during an intermediate pressue granulite facies metamorphism at a geothermalgradient of 18--23℃/km.     

滇西蓝片岩及其构造意义

滇西蓝片岩作为夹层产在澜沧江和哀牢山变质带里的绿片岩和云母片岩中。原岩是碱性玄武岩和泥砂质岩石,其代表性的矿物组合分别为Cr(或Win)±Ab±Q_2+Chl+Ph+Ep+Sph和Gl±Act+Ph+Tc+Ep+Alm+Q_2+Sph+Do。蓝片岩变质作用的p-T范围为170—390℃,4—6.7 kbar,相应的地热梯度为10—16℃/km。澜沦江带蓝片岩的形成与古特提斯洋盆的消减和封闭有关。哀牢山蓝片岩的形成可能与陆块之间的碰撞和动力变质作用有关。     

PETROGENESIS OF HANOBA AND THEIR ULTRAMAFIC INCLUSIONS

All the data presented in this paper for the bulk compositions, mineral chemistry and trace element geochemistry of ultramafic inclusions suggest that the most lherzolite inclusions represent fertile mantle samples, and the black websterite inclusions represent granulite samples from the lower crust. The lherzolito inclusions equilibrate at the temperature in the restricted range from 980 to 1120℃ and have a considerable variation in equilibrium pressure (i. e. between 12.5 to 24 kb) at calculated temperatures, and the black websterite inclusions have the relatively low equilibrium P-T conditions (850-950℃. 8 kb). As compared with both ocean and shield geotherms, the paleogeotherm defined by the lherzolite inclusions has much steeper slope at depths less than 100 km. It may be inferred that the least depleted mantle is probably located immediately beneath the region studied.     

中国东南部新生代火山岩系——Ⅰ.岩石化学

本文详细地讨论了我国东南部新生代火山岩的时代和空间分布,以及它们的岩石化学特征。它们是碱质的和非碱质的。除了台湾北部更新世钙碱性火山岩和台湾东海岸山脉晚第三纪拉斑玄武质岩石以外,以碱性玄武质岩石形成主体。海丰-政和-上虞断裂带以西的内陆只有碱性和强碱性玄武岩和超基性火山岩。新生代火山岩的岩石化学性质显示了随时间和空间明显变化的趋势这表明它们的形成明显地受大地构造环境所控制。     

冀东迁西地区早太古代麻粒岩的矿物学和结晶的P-T条件

本文提供了冀东迁西地区早太古代麻粒岩辉石、石榴石、角闪石和黑云母的大量新的湿化学分析结果。详细地讨论了共存铁镁矿物之间铁和镁的分配系数。辉石对的K_D(Fe)值变化不大以及在Wo-En结上的交点十分接近,暗示达到了均一的平衡条件。根据岩相学观察和各种地质温度计和地质压力计的计算,在遭受地热梯度为18—23℃/公里的中压麻粒岩相变质作用时,麻粒岩变质重结晶的P-T条件是11—13千巴和800—850℃。     

中国滇西腾冲新生代火山岩的成因

腾冲上新—全新世火山岩属高钾的钙碱性岩系,以强亏损高场强元素、富集大离子亲石元素和轻稀土为特征,明显具岛弧或活动陆缘属性。其形成与新特提斯演化有关,即:印度微大陆与东南亚微大陆间的洋盆于晚白垩—古新世向东消减,伴以岛弧形成,始新世开始印度板块与该岛弧碰撞;作为弧后盆地的安达曼海及内缅甸盆地于中新世晚期扩张。腾冲的独特之处是岛弧型火山活动迟后于消减作用。     

中国东南部新生代火山岩系——Ⅱ.微量元素地球化学

本文详细地讨论了新生代火山岩的微量元素地球化学特征。研究表明,中国东南部之下的上地幔,相对球粒陨石质地幔,富集强HYG元素,以及从沿海向内陆玄武岩浆源的深度变大。新生代玄武岩质火山作用发生于张裂的大陆边缘构造环境中。相反,以长英质为主的中生代火山岩喷发于活动大陆边缘的构造环境中。由超镁铁质岩包体推导的地温分布表明,中国东部新生代张裂作用主要受热地幔底辟作用所控制。