Abstract

This study is concerned with the mineralogical composition of volcanic ejecta in the Central Kamchatka Depression: the plateau basalts of the Ozernaya Kamchatka, Kunch, and Nikolka Stratovolcano. These data were compared with rock compositions for some volcanoes in the Klyuchevskoi Group, the plateau basalts of Bakening Volcano, and data on xenoliths of two types, viz., the “island-arc” type (Klyuchevskoi, Kharchinsky, and Sheveluch volcanoes) and the “intraplate” type (the plateau of Bakening Volcano). We have identified complementary vulcanite–xenolith pairs for which we propose a concept of dynamic evolution that envisages the ascent of melts to the ground surface accompanied by nearly synchronous change in the mineralogical composition of rocks in both pairs, while we are merely able to detect some fragments of the process. Mineralogically, the CKD riftogenic vulcanites differ from the island-arc rocks of the Klyuchevskoi Group in (1) a greater iron content of the olivines and greater concentrations of MnO and CaO in these, (2) greater titanium concentrations (over 1 wt % in the former and below 1 wt % in the latter) in clinopyroxenes, their high sodium concentration (over 0.5 wt % in the former and below 0.5 wt % in the latter), and greater (occasionally reaching 9 wt %) alumina content, and (3) the appearance of high titanium chromous spinellids, anorthoclase, and sanidine. These differences are controlled by differences in alkalinities of the melts, in the depth, composition, and the degree of melting in the mantle substrate. The compositions of the CKD rocks that we have studied, considering that the depression is a riftogenic feature, could arise in connection with a low degree of melting in the mantle sources similar to those which gave rise to intraplate subalkaline basalts in the Bakening plateau, which we treated as the standard of riftogenic volcanic occurrence.

中文翻译：

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关于堪察加半岛中部凹陷（CKD）的年龄，物质组成和地质结构的新数据。第2部分。火山岩和地幔异种岩的矿物学组成。走向岩石学模型

摘要

这项研究与堪察加半岛中部凹陷火山喷出物的矿物学组成有关：Ozernaya Kamchatka，Kunch和Nikolka Stratovolcano的高原玄武岩。将这些数据与Klyuchevskoi组中某些火山的岩石组成，Bakening火山的高原玄武岩以及两种类型的异岩的数据进行了比较，即“岛-弧”型（Klyuchevskoi，Kharchinsky和Sheveluch火山）和“板内”型（Bakinging火山的高原）。我们已经确定了互补的沃肯岩-异种岩对，我们提出了一种动态演化的概念，设想了熔体上升到地表的过程，伴随着两对岩石的矿物组成几乎同步变化，而我们仅能够探测到一些过程的碎片。矿物学上 CKD裂谷生火山岩与Klyuchevskoi组的岛弧岩石不同之处在于：（1）橄榄石中铁含量较高，其中MnO和CaO含量较高，（2）钛含量较高（前者超过1 wt％并在次生辉石中含量低于1 wt％），高钠浓度（前者超过0.5 wt％而后者低于0.5 wt％）和更高的氧化铝含量（有时达到9 wt％），以及（3）高钛铬尖晶石，正长石和山梨糖苷的外观。这些差异由熔体的碱度，深度，组成和地幔底物中的融化度的差异控制。考虑到凹陷是造成裂谷的特征，我们研究了CKD岩石的成分，