从玄武岩铸石论月球玄武岩的冷却史

一、引言铸石是利用天然岩石,如玄武岩、辉绿岩或某些工业废渣为原料,经配料或直接熔化、浇铸成型、结晶、退火而成的一种工艺岩石。它的矿物组分主要为单斜辉石,磁铁矿的量很少,在个别情况下可有少量橄榄石。从生产技术来看,铸石就是把天然玄武岩类所含的复杂矿物相用人工转变为单一矿物相,也就是将原料中大量的斜长石和相当量的橄榄石

A DISCUSSION ON THE COOLING HISTORY OF SOME LUNAR BASALT FROM THE BASALT PETRURGY

The writer first notes some similarity in morphology of quenching crystals between terrestrial basalt and casting stone, and then descries more similarity in composition and morphology of quenching pyroxene between casting stone and some lunar basalt. The relationship between the composition and trend of crystallization of pyroxene in various basalt and its cooling history are discussed in turn. In basalt petrurgy, the morphology and high A12O3 content of pyroxene are controlled by definite degree of undercooling, say, under the cooling rate of about 30°-40℃/minute, in the non-equilibrium condition. Under theis condition, the plagioclase molecular can enter into the pyroxene structure in the form of Ca-tsch molecular+SiO2. Some lunar basalt is a pyroxene vitrophyre consisting primarily of accicular pyroxene phenocrysts and glass matrix. The pyroxene always shows zonal structure with high Al2O3 and TiO2 contents increasing to a maximum of 14.0 and 3.5wt.% respectively toward the rim. This fact argued that there is an analogy between the quenching augite of the casting stone and ihe pyroxene of some lunar basalt in their crystallization process. It is postulated that the zoning trend and the high A12O3 content of pyroxene in some lunar basalt may be attributed to the crystallization in the absence of co-crystallization plagioclase under much rapid cooling condition, which never occurs in the terrestrial circumstance.