摘要
本文对西藏丁青玻安岩类深成岩的辉石和新喀里多尼亚玻安岩的斜顽辉石进行了矿物学工作及高分辨电镜观察。丁青斜方辉石堆晶岩辉石的超微结构包括:单斜辉石的(100)双晶、斜方辉石a/4平移畴结构及斜方辉石—单斜辉石相转变。玻安岩斜顽辉石典型超微结构是(100)双晶。由矿物的碎裂、错动以及斜方辉石—单斜辉石相变中只出现偶数倍单斜辉石等表明:矿物结晶及成岩过程中曾受应力作用、后者可能与岩石所处的构造位置有关。由辉石成分计算的地质温度表明,丁青堆晶斜方辉石岩的辉石是在高温下晶出、岩石固结温度是1013～1111℃,当它们在～1000℃下稳定时,斜方辉石出溶了单斜辉石片晶。将玻安岩斜顽辉石加热至1100℃后淬冷及按120℃/h速度冷却均未得到纯的斜顽辉石,可能斜顽辉石是原顽火辉石在应力环境中高温淬冷所成。
The chemical compositions and ultrastructures of cumulate orthopyroxenite from Dingqing, Tibet and clinoenstatite in boninite from Nepoui, New Caledonia have been investlgated. The ultrastructures of pyroxenes include twin, domain structure of translation with a/4 of orthopyroxene and orthopyroxene-clinopyroxene phase transformation. The clinopyroxenes, measuring 2n×0.9nm in width, in orthopyroxenes and the strain-slip cleavages and cracking of pyroxenes show the effects of stress during the formation of the rock, which might be related to plate subductton and the convection and circulation of boninite magma.
The two-pyroxene geothermometry data show that the crystallization of orthopyroxenes in cumulate orthopyroxenite from Dingqing happened at high temperatures (>1100℃), and rock condensation at 1013～1111℃. The cumulate orthopyroxenss were exsolved the lamellae of diopsides while the rock remained in the environment with a temperature of～1000℃.
Heating experiments on clinoenstatites in boninite from New Caledonia have been made. Neither the quenching products nor the cooling ones at the speed of 120℃/h are similar to natural clinoenstatites, and they are the mixture of orthopyroxenes, clinopyroxenes and (2n+1 )×0.45nm lamellae. It is suggested that the clinoenstatites in boninite might be formed as a result of quenching of protoenstatites at the high temperature(1200℃). In addition, the effect of stress should be taken into consideration.
出处
《矿物学报》
CAS
CSCD
北大核心
1993年第2期115-123,T002,共10页
Acta Mineralogica Sinica
基金
国家自然科学基金
关键词
玻安岩
辉石
结构
蛇绿岩
深成岩
boninite
pyroxene
ultrastructure
Dingqing ophiolite
Tibet
