辽宁榴辉岩包体的石榴石中金云母出溶片晶的发现

THE DISCOVERY OF PHLOGOPITE EXSOLUTION LAMELLAE IN GARNETS OF ECLOGITE ENCLAVES, LIAONING PROVINCE

在辽宁复县50号金伯利岩岩筒中,发现了罕见的榴辉岩包体,在该包体的主要组成矿物石榴石中发现了金云母出溶片晶。通过显微镜、透射电镜及其能谱观察分析测定与研究,确认该片晶为金云母。金云母无色,断面呈针状,一般宽0.5—5μm,长10—100μm;但宽0.05—0.1μm,长1—2μm的细小片晶也较发育。金云母片晶沿石榴石[111]晶带大致呈夹角为60°—70°的三组定向排列,表明它是由于榴辉岩从地幔深处上升到较浅部时释压作用从石榴石中出溶的产物。世界各地金伯利岩中榴辉岩包体的石榴石、辉石中微小针状出溶矿物(或包裹体)普遍存在,据文献报道,已经鉴定的出溶物有辉石和金红石。迄今为止,金云母出溶片晶的发现尚属首次。

In No. 50 kimberlite pipe of Fuxian County, Liaoning Province, eclogite enclaves, which are extremely rare in the world, were discoveried. Being rounded in form and 10 cm in diameter, these enclaves comprise mainly garnet, pyroxene (pseudomorph) and, subordinately, phlogopite and rutile. In garnets (pyrope-almandine) of these enclaves, exsolution lamellae of phlogopite were discovered for the first time. Microscopic, TEM and energy spectral observations and studies prove that these lamellae are phlogopite. The lamellae are colorless and acicualr in section, generally 0. 5 -5 μm in width and 10 - 100 μm in length. Nevertheless, fine lamellae 0. 05 -0. 1 μm wide and 1-2 μm long are also well developed. Along [111] of garnet, three sets of phlogopite lamellae show oriented arrangement approximately at angles of 60°-70°, and the lamellae oriented in the same direction have the same extinction position, suggesting that these lamellae might be the product of exsolution from garnet as a result of pressure-release when eclogite ascended from the relatively deep level of the mantle to the relatively shallow level.