南极西部威廉群岛(Anagram Islands, Wilhelm Archipelago, West Antarctica)长石斛的岩石学

IF 0.5 Q4 MINERALOGY Mineralogical Journal-Ukraine Pub Date : 2020-01-01 DOI:10.15407/mineraljournal.42.04.069
O. Mytrokhyn, V. Bakhmutov, A. Aleksieienko, T. Mytrokhina
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引用次数: 1

摘要

Anagram群岛位于南极洲西部的格雷厄姆海岸附近,距离乌克兰南极站“Akademik Vernadsky”不远。阿格拉姆群岛的地质构造以白垩纪时期的辉长岩为主。在2017年、2019-2020年乌克兰南极考察队的季节性野外工作中,获得了Anagram辉长岩的产状模式及其分层的新数据。通过光学显微镜、电子显微镜、探针分析和岩石磁化率各向异性测量对辉长岩样品进行了研究。研究的目的是明确变形辉长岩的地质位置和岩石学特征,确定造岩矿物的标型特征,明确辉长岩的分层成因。结果表明,在阿格拉姆群岛上,一大型层状辉长岩侵入体的底部是破碎暴露的。预计东北和东南方向的入侵将继续。结果表明,尽管发育变质角闪作用,但辉长岩中仍保留了原始岩浆结构和矿物组成。辉长岩具有典型的岩浆成因累积结构。主要沉积相为斜长石(An70-95)、斜辉石(Wo41-49En34-47)、正辉石(Wo2-4En49-71)、橄榄石(Fo67-69)、钛磁铁矿和钛铁矿。证明了辉长岩中的精细韵律级配是由岩浆库底部积聚的矿物重力沉淀和对流作用下的比重分选作用形成的。隐层是在变位辉长岩中首次发现的,并用结晶分异过程来解释。后者在侵入体底部的层状辉长岩中聚集了最多的钙斜长石和最多的镁质矿物。构造变形导致了变位辉长岩侵入剖面的倾斜,解释了目前的亚垂向分层位置。对辉长岩磁性结构的研究(磁化率数据的各向异性)证实了这一点。
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The Petrology of Gabbroids of the Anagram Islands (Wilhelm Archipelago, West Antarctica)
The Anagram Islands are located near the Graham Coast of West Antarctica not far from the Ukrainian Antarctic Station "Akademik Vernadsky". Gabbroids that are probably Cretaceous in age predominate in the geological structure of the Anagram Islands. New data on the mode of occurrence of the Anagram gabbroids and their layering were obtained during the seasonal field works of the Ukrainian Antarctic Expeditions in 2017, 2019-2020 years. Samples of the gabbroids were examined by optical microscopy, electron microscopy and microprobe analysis as well as by measuring of anisotropy of magnetic susceptibility of rocks. The goal of the research was to clarify the geological position and petrographic features of the Anagram gabbroids, to determine the typomorphic features of rock-forming minerals, and to clarify the origin of the layering in gabbroids. It was determined that the bottom part of a large layered gabbroid intrusion is fragmentarily exposed on the Anagram Islands. The continuation of the intrusion is expected in the northeastern and southeastern directions. It was established that primary magmatic textures and mineral composition are preserved in the gabbroids despite the development of metamorphic amphibolization. The gabbroids show typical cumulative textures of magmatic origin. The main cumulative phases are plagioclase (An70-95), clinopyroxene (Wo41-49En34-47), orthopyroxene (Wo2-4En49-71), olivine (Fo67-69), Ti-magnetite and ilmenite. It is proved that the fine rhythmic-gradational layering in the gabbroids was formed by gravitational precipitation of the cumulative minerals on the bottom of the magma chamber and their further sorting by specific gravity due to convection currents. Cryptic layering is firstly discovered in the Anagram gabbroids and is explained by the processes of crystallization differentiation. The latter caused the accumulation of the most calcium plagioclases and the most magnesian mafic minerals in the layered gabbroids forming the bottom part of the intrusion. The present subvertical position of layering is explained by tectonic deformation that resulted in the tilting of the investigated section of the Anagram gabbroid intrusion. This confirmed by the studying of magnetic texture of the gabbroids (by the anisotropy of magnetic susceptibility data).
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