Petrology of the diamond‐grade eclogite in the Kokchetav Massif, northern Kazakhstan
Petrology of the diamond‐grade eclogite in the Kokchetav Massif, northern Kazakhstan
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DOI：
10.1046/j.1440-1738.2000.00284.x
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发表时间：
2000-09
期刊：
影响因子：
1.5
通讯作者：
Kazuaki Okamoto;J. Liou;Yoshihide Ogasawara
中科院分区：
文献类型：
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作者：
Kazuaki Okamoto;J. Liou;Yoshihide Ogasawara
哈萨克斯坦北方科克切塔夫地块因变质沉积物中石榴石、锆石和单斜辉石中富含微金刚石包裹体而独具特色。为了确定精确的压力-温度（P-T）条件，我们系统地研究了Kumdy-Kol的钛-斜腐植岩-石榴石橄榄岩和金刚石级榴辉岩中的矿物包裹体和主要硅酸盐的成分。结果表明，库姆迪-科尔石榴橄榄岩中含有石榴子石、橄榄石、钛斜齿石和钛铁矿的组合。石榴石包含指示超高压（UHP）和退变质条件的包裹体。超高压后形成了水化相包裹体，如角闪石、闪石和闪石。研究还发现，库姆迪-科尔榴辉岩在绿辉石之后含有钠长石-普通辉石合晶。辉石（钠质普通辉石）的核部含有较高的K2 O（高达1wt%，平均0.24wt%）。多硅白云母包含在核心中。应用基于最近实验的K2 O-in-Augite地质压力计和石榴石-单斜辉石（Grt-Cpx）地质温度计进行峰值变质作用，榴辉岩的P-T估计值为> 6 GPa和> 1000 °C，金刚石级榴辉岩的温度估计值较低，为900-1000 °C和5 GPa。
Abstract The Kokchetav Massif of northern Kazakhstan is unique because of the abundant occurrence of microdiamond inclusions in garnet, zircon and clinopyroxene of metasediments. In order to determine precise pressure–temperature (P–T) conditions, we have systematically investigated mineral inclusions and the compositions of major silicates in Ti–clinohumite–garnet peridotite and diamond‐grade eclogite from Kumdy–Kol. It was found that garnet peridotites from Kumdy–Kol contain assemblages of garnet, olivine, Ti–clinohumite and ilmenite. The garnet contains inclusions that are indicative of both ultrahigh pressure (UHP) and retrograde conditions. Inclusions of hydrous phases such as chlorite, amphibole and zoisite were formed at the post‐UHP stage. The study also found that eclogite from Kumdy–Kol contains albite–augite symplectites after omphacitic pyroxene. The core of pyroxene (sodic augite) contains high K2O (up to 1wt%; average 0.24wt%). Phengite is included in the core. Applying the K2O‐in‐augite geobarometry, which is based on recent experiments, and the garnet–clinopyroxene (Grt–Cpx) geothermometer for peak metamorphism, the eclogites yield P–T estimates of > 6 GPa and > 1000 °C, and the diamond‐grade eclogites yield lower temperature estimates at 900–1000 °C and 5 GPa.