黑龙江省科洛—二克山富钾火山岩的辉石和长石巨晶

本文对富钾火山岩中单斜辉石、斜方辉石、长石巨晶的物理性质、化学成分、微量元素等特征进行了研究。文中还对巨晶的成因及对岩浆的影响问题,提出了作者自己的观点。

PYROXENE AND FELDSPAR MEGACRYSTS OF K-RICH VOL- CANICS FROM KELUO-ERKESHAN, HEILONGJIANG PROVINCE

The clinopyroxene megacrysts are endiopside and augite. Their rims are salite. The or-thopyroxene megacrysts are bronzite and hypersthene. The main distinction between thess pyroxene megacrysts in this area and the pyroxene megacrysts in sodic alkali basalts is that the former is low in Al. This may imply that the depth of crystallization of the pyroxene megacrysts in this area is relatively shallow, although they still are the products under middle pressure.The feldspar megacrysts in this area are Na-sanidine that are higher in K than those in sodic alkali basalts which is consistent with the richment of the magma in K in this area.The studies suggest that the megacrysts are the products of crystallization from host magma. The rims of the megacrysts which have lower Al than the megacrysts are the products of equilibrium crystallization under lower pressure during their ascending.The calculation of fractional crystallization of the megacrysts indicates that the main difference between mother magma and host magma in chemical composition is that the acid degree of the later is lower, from basic to ultrabasic; the alkali degree of the later is higher, the value of a of the later is 100 times higher than the former. Therefore, the influence of fractional crystallization of the megacrysts for mother magma composition can not be considered negligible. The host magma bearing megacrysts can not be considered of mother magma composition, since it is, in fact, an evolutionary or residual magma after the megacrysts had fractionally crystallized from the mother magma. Under middle pressure (1-2GPa), as Al-rich pyroxene megacrysts crystallized first, the magma evolved towards alkali-rich direction. It is different from that under ordinary pressure, as olivine crystallized first, the magma evolved towards silica-rich direction.