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| 1 | 俄罗斯极地乌拉尔硬玉岩成因矿物学研究显示文摘俯冲带是壳-幔物质循环的重要场所,硬玉岩可以记录这一循环过程。文中总结了俄罗斯极地乌拉尔硬玉岩的研究进展。硬玉岩呈脉状或透镜状产在蛇纹石化的方辉橄榄岩中,主要由硬玉和绿辉石组成。根据结构和颜色,硬玉可识别出两个世代。硬玉韵律环带发育,含有H2O和CH4流体包裹体,显示从流体中结晶的特征。硬玉岩中的锆石为热液锆石,锆石稀土元素中LaN/YbN=0.001~0.01,LuN/GdN=10~83,Ce/Ce*=2.8~72,显示正异常,δ^Eu=0.53~1.02,类似于岩浆锆石。锆石的^176Hf/^177Hf=0.282708~0.283017,εHf(t)=+6^+17,类似于N-MORB的Hf同位素组成,锆石δ^18O组成为5.03‰~6.04‰,平均δ^18 O为(5.45±0.11)‰,类似于岩浆热液和地幔的氧同位素组成。这可能反映了锆石是被俯冲带流体从途经火成岩中捕获的或者形成锆石的流体与寄主岩(方辉橄榄岩)达到了平衡。硬玉岩稀土元素配分模式近平坦或轻稀土元素略显富集,LaN/YbN比值为0.82~2.42,δEu为1.2~1.6,显示正异常,这与寄主岩稀土元素配分模式相似。富集Sr、Ba、Zr、Hf,Nb为负异常,与岛弧岩浆特征类似。(^87Sr/^86Sr)t为0.703400~0.703519(t=368 Ma),变化较小,与古海水差别明显;εNd(t)值为+0.77^+5.61,变化较大,与寄主岩(方辉橄榄岩)的Nd同位素组成类似,但不同于海水及沉积物的Nd同位素组成,表明硬玉岩的物质来源与寄主岩有明显继承关系,海水与沉积物的贡献不是主要的。矿物学和岩石学证据支持极地乌拉尔的硬玉岩主要是俯冲带流体与橄榄岩相互作用后并在其中结晶的产物。 | 孟繁聪 白盛锦 Alexander B.MAKEYEV Ksenia V.KULIKOVA | 2020 | 地学前缘2020，27，5： | 2 |
| 2 | Preface: Metamorphism and Orogenic Belts——Response from Micro-to Macro-Scale显示文摘The geological toolbox for the analysis of orogenic processes has seen substantial additions over the recent decades.Major advances have been made in the ability to simulate geological conditions and processes by computer modeling,we have a much improved knowledge of geochemical processes(trace elements and isotopes in particular),and,last but not least,the range and versatility of micro-analytical methods and instrumentation available to us has been expanded dramatically.The latter aspect has had a particular impact on metamorphic petrology as the conventional tools to determine pressure-temperaturetime paths via rock and mineral analysis combined with isotope geochronology have generally gained in precision and accuracy through a much improved resolution.Geochronology has moved from whole-grain analysis to spot analyses on zoned single grains while analyzing trace elements and isotopes at the same time.It is therefore possible to recognize complex multi-stage orogenic events in single samples or single grains.Diffusion profiles in minerals provide us with time-scales of metamorphic and magmatic processes.Major and trace elements as well as isotope profiles of mineral grains give us insight into changing ambient conditions during mineral growth.This special issue focuses on pressure-temperature conditions and geochronology of metamorphic rocks,isotope studies of magmatic rocks,partial melting and metasomatic processes,all with a view at tectonic implications and orogeny.Much of the evidence has been gained from small-scale observation and analysis.Diligent field work and detailed microscopic examination remain indispensable,though,as demonstrated clearly by the'expansion'of the P-T space as applicable to crustal metamorphic processes towards extreme pressures and temperatures.As a consequence,much interest has thus focused on UHP and UHT rocks and the orogenic processes that generate them.There is petrological evidence for subduction to,and subsequent exhumation from,depths in excess of 250 km.While this impacts substantially on the large-scale geodynamic models of orogenic processes,the evidence is gathered primarily from small-scale petrological observation.The same applies in principle to UHT granulites.To generate temperatures in the 900 to 1100℃range within the sillimanite stability field in orogenic heat budget models remains a serious challenge,however.The large overlap of solid-state metamorphism,partial anatexis and magmatic crystallization in P-T space suggests close interrelationships,and the role and contribution of the diverse magmatic activities in forming orogenic belts,from the onset of subduction to late-orogenic delamination or slab-break-off is crucial for our understanding of geodynamics,with focus on geochemistry and geochronology.Aspects of metasomatism in the framework of orogeny are given some special consideration in this issue.The topics include the formation of sagvandite,pyrope quartzite(or whiteschist),jadeitite and rodingite.One of the key questions addressed is the source and the nature of the fluids that triggered the different types of metasomatic events.Finally,it is shown how small-scale methods contribute to a better understanding of the formation of deep-seated mantle xenoliths. | Xu-Ping Li Hans-Peter Schertl Jürgen Reinhardt | 2019 | Journal of Earth Science2019，30，6： | 1 |
| 3 | 变质矿物内部结构研究——彩色阴极发光研究的地质意义显示文摘阴极发光(CL)方法主要应用于原位离子探针和激光剥蚀技术进行年龄测定之前的锆石研究,以及碳酸盐、长石和石英等矿物结构的分析。本研究介绍了采用热阴极发光方法分析变质矿物内部结构的优势,并结合不同岩类各变质相的常见代表性变质矿物,介绍了利用彩色阴极发光研究矿物结构的实例。一般来说,CL的产生是由激发元素如Mn、稀土元素(REE)和晶格缺陷引起的。像Fe这样的CL抑制元素的存在可以减少发光甚至完全不发光。变质矿物内部的CL彩色环带生长特征,在偏光显微镜的薄片研究中无法看到,但用彩色阴极发光方法在几秒钟内就可以识别出来。稀土元素的含量往往低于电子探针的检测限,对此,配之以分光计,阴极发光显微镜甚至可以提供化学成分的数据信息。本研究精选典型的具有彩色阴极发光结构的变质矿物,如大理岩中的橄榄石、镁铝榴石、钙铝榴石、镁铝榴石和钙铝榴石固溶体、锆石、矽线石、红柱石、蓝晶石、灰硅钙石、粒硅钙石、硬柱石、黝帘石/斜黝帘石、透辉石、硬玉/绿辉石、硅灰石、透闪石、葡萄石、绿泥石、钾长石、斜长石、石英、柯石英、玉髓等,展示了其CL显微镜下的结构特征。上述变质矿物来自不同地质环境的岩石中,如Margarita岛的高压(HP)变质岩,Dora-Maira地块(意大利)、苏鲁(中国)、Kokchetav地块(哈萨克斯坦)、西部片麻岩地区(挪威)和Pohorje(斯洛文尼亚)的超高压(UHP)变质岩,罗马尼亚的矽卡岩矿床和接触变质岩,美国内华达州的Twin Lakes和Bushveld杂岩,多米尼加共和国里约热内卢圣胡安杂岩,中国日喀则的交代岩,南非的Namaqualand、中国内蒙古的高温(HT)-超高温(UHT)变质岩,意大利Monzoni、坦桑尼亚Merelani的亚绿片岩和宝石级的黝帘石样品以及来自瑞士Campolungo的钙硅酸盐样品。矿物的内部特征主要指具有不同颜色分布的均匀无带状结构、同心环状分带结构(反映从核到边缘的元素逐渐增加或减少)、振荡环带结构、不均匀生长结构和生长过程中晶体形态变化的结构。进一步研究表明,变质结构还包括矿物的出溶结构、放射性损伤结构、变形结构、不同晶粒域出现的流体通道闭合结构以及细粒矿物的分布结构。CL方法用于薄片研究的优点之一是可以在较低放大倍数下较全面地观察各种矿物之间及其内部的结构。此外,CL记录的是清晰的彩色图像,而不像常规使用的U/Pb年龄测定前的电子探针CL系统,只能记录锆石的黑白图像。尽管上述讨论的CL信息主要是描述性的,但在使用电子探针、离子探针、激光剥蚀以及其他光谱学或矿物流体包裹体等研究之前,可作为重要的辅助研究方法。 | SCHERTL Hans-Peter 李旭平 | 2022 | 山东科技大学学报(自然科学版)2022，41，6： | 0 |
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