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首页> 外文期刊>Journal of Asian earth sciences >Oriented kokchetavite compound rods in clinopyroxene of Kokchetav ultrahigh-pressure rocks
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Oriented kokchetavite compound rods in clinopyroxene of Kokchetav ultrahigh-pressure rocks

机译：Kokchetav超高压岩石的斜辉石中定向的Kokchetavite复合棒

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摘要

Two microdiamond-bearing samples, a dolomite marble and a garnet-clinopyroxene rock, from the Kokchetav ultrahigh-pressure metamorphic terrane were selected in the present study to explore the possible origin of KAISi_3O_8 rod inclusions oriented along the c-axis of clinopyroxene host. The KAlSi_3O_8 rod inclusions at clinopyroxene cores, where K_2O content is high in the range of 0.5-1.0 wt.%, are mostly fine-grained with a rod width less than 1 um. AEM studies showed that the KAIS1_3O_8 phase in most rod inclusions is kokchetavite. K-feldspar is present only in a few cases, probably the result of phase transformation/recrystallization from kokchetavite during rock exhumation. Electron diffractions further showed that kokchetavite rods are oriented parallel to clinopyroxene [001] direction and they exhibit the same epitaxial relation with the clinopyroxene host in both samples with the (Al, Si)O_4 tetrahedra chains along the hexagonal a-axis of kokchetavite parallel to the single SiO_4 chain along the c axis of clinopyroxene; i.e., [1 210]_(Ko)//[001]_(Cpx) and (0001)_(Ko)//(100)_(Cpx). It is interesting to note that kokchetavite is always in association with phengite, tremolite, p-cristobalite, Si-rich (Al, K, Ca-bearing) low crystallinity phase, ±Si-Ca (Cl, As) phase, ±calcite, ±apatite, ±lollingite (FeAs_2), forming compound rods. Furthermore, all these phases are also present within submicron-scale polyphase inclusion pockets in garnet within garnet-clinopyroxene rock sample. These kokchetavite compound rods are therefore most likely to have resulted from melt/fluid-clinopyroxene interactions leading to epitaxial deposition rather than exsolution sensu stricto from the clinopyroxene host. The suggested melt/fluid would have an "external" and/or an "internal" origin related to rock partial melting involving phengite breakdown. Discrete phlogopite and phengite needle-like inclusions with a needle width less than 1 μm, as well as phlogopite-phengite and kokchetavite-mica intergrowth needles, are also not uncommon in clinopyroxene cores. There are specific crystallographic orientation relationships among phases. These micas might have formed earlier than kokchetavite and have exsolved from clinopyroxene host, although the mass balance issue during exsolution and the temporal relation between phlogopite and phengite needles remain to be settled. Clinopyroxene rims generally contain mica needles only. Domains near fractures with coarse-grained kokchetavite compound rods or with coarse-grained phlogopite + quartz needles are not uncommon. These clinopyroxene rims/domains are low in K_2O (<0.5 wt.%) and their inclusions are most probably a result of precipitation/recrystallization from late-stage(s) infiltrated fluid-clinopyroxene interactions.
机译：在本研究中，从科科切夫超高压变质地层中选出了两个含微金刚石的样品，即白云岩大理石和石榴石-斜辉石岩，以探索沿斜辉石基质c轴取向的KAISi_3O_8棒状夹杂物的可能来源。在斜辉石芯处的KAlSi_3O_8棒状夹杂物（其中K_2O含量在0.5-1.0 wt。％的范围内较高）大多是细晶粒的，棒宽小于1 um。 AEM研究表明，大多数棒状夹杂物中的KAIS1_3O_8相都是kokchetavite。钾长石仅在少数情况下存在，这很可能是岩石发掘过程中科科切维（Kokchetavite）发生相变/重结晶的结果。电子衍射进一步表明，kokchetavite棒的取向平行于clinopyroxene [001]方向，并且在两个样品中，其（cl，Al）O_4四面体链沿kokchetavite的六边形a轴平行于clinopyroxene主体，具有相同的外延关系。沿亚次氯环烯c轴的单SiO_4链;即[1210] _（Ko）// [001] _（Cpx）和（0001）_（Ko）//（100）_（Cpx）。有趣的是，kokchetavite总是与亚辉石，透闪石，对方英石，富硅（含Al，K，Ca的低结晶度相），±Si-Ca（Cl，As）相，±方解石， ±磷灰石，±硅钙石（FeAs_2），形成复合棒。此外，所有这些相也都存在于石榴石-斜柏石样品中的石榴石的亚微米级多相夹杂物囊中。因此，这些kokchetavite化合物棒极有可能是由熔融/流体-斜吡咯烷酮相互作用导致外延沉积，而不是从斜吡咯烷酮中严格析出。所建议的熔体/流体将具有“外部”和/或“内部”起源，与岩石的局部变质有关，涉及到陨石的分解。在斜辉石岩芯中，针宽度小于1μm的离散金云母和扁钢针状夹杂物，以及金云母-辉石和科克塔维特-云母共生针也很常见。在各相之间存在特定的晶体取向关系。这些云母可能早于kokchetavite形成，并已从斜辉石宿主中溶出，尽管溶出过程中的质量平衡问题以及金云母和锂铁矿针之间的时间关系尚待解决。 Clinopyroxene轮辋通常只包含云母针。用粗粒角铁矿复合棒或粗粒金云母+石英针在裂缝附近的区域并不罕见。这些斜方铁环的边缘/区域的K_2O含量低（<0.5 wt。％），它们的夹杂物很可能是由于后期渗透流体与斜方铁的相互作用而沉淀/重结晶的结果。

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  • 来源
    《Journal of Asian earth sciences》 |2013年第15期|56-69|共14页
  • 作者

    S.L. Hwang; T.F. Yui; H.T. Chu; P. Shen; J.G. Liou; N.V. Sobolev;

  • 作者单位

    Department of Materials Science and Engineering, National Dong Hwa University, Hualien, Taiwan, ROC;

    Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan, ROC;

    Central Geological Survey, P.O. Box 968, Taipei, Taiwan, ROC;

    Department of Materials and Optoelectronic Science, National Sun Yat-sen University, Kaohsiung, Taiwan, ROC;

    Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, USA;

    Institute of Geology and Mineralogy, Siberian Branch of Russian Academy of Sciences, 630090 Novosibirsk 90, Russia;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    kokchetavite; oriented inclusions; kokchetav UHP terrane; AEM; exsolution; fluid/melt infiltration;

    机译：kokchetavite定向夹杂物;kokchetav UHP地形;AEM;出庭流体/熔体渗透;

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