The System MgrSiOn-SiO2 at Pressures Up to 25 Kilobars'
The System MgrSiOn-SiO2 at Pressures Up to 25 Kilobars'
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压力高达 25 公斤的 MgrSiOn-SiO2 系统
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C. PnBsNnrl
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CssNc;2. E. DnnN;C. PnBsNnrl
利用活塞筒装置，在25kbar压力下测量了镁橄榄岩+顽辉石相和顽火辉石硅相两条单变量固相线。原顽火辉石-正顽辉石的反转曲线在8kbar和1313‘~14I7“C处发生了反转，确定了三个不变点。一种为镁橄榄岩相、原顽辉岩相、斜辉辉石相和液态相，温度为15.2kbar，温度为1700oC。第二个涉及高石英、原顽辉石、正顽辉石和液体相，位于15.6kbar，1720“C。第三个涉及原顽辉石、正顽辉石和液体，放置在15.8kbar，1730‘C。第四个不变点，包括方石英、高石英、原顽辉石和液体，没有被紧密地包围，但大约出现在4.1kbar，1620”C。二氧化硅和顽辉石之间的等压共晶的组成不随压力至少高达25kbar而发生显著变化。在约1.3kbar的压力下，与镁橄榄岩和顽辉石平衡的单气氛方镁石液体转变为共晶液体，其成分随着压力的增加而逐渐向镁橄榄岩移动。然而，二元体系的这一结果并不一定意味着在类似的压力下，天然岩浆中的镁橄榄岩、顽辉石和液体的反应关系一定会消失。
Using piston-cylinder apparatus, two univariant solidus curves involving the phases forsterite + enstatite * liquid and enstatite * silica * liquid have been bracketed at pressures up to 25 kbar. Also, the protoenstatite-orthoenstatite inversion curve has been reversed at 8 kbar and l3l3' to l4I7"C. Three invariant points have been located. One involves the phases forsterite, protoenstatite, orthoenstatite, and liquid and is located at 15.2 kbar, l700oC. The second involves the phases high quartz, protoenstatite, orthoenstatite, and liquid and is located at 15.6 kbar, 1720"C. The third involves protoenstatite, orthoenstatite, and liquid and is placed at 15.8 kbar, 1730'C. A fourth invariant point involving the phases cristobalite, high quartz, protoenstatite, and liquid has not been bracketed closely but occurs approximately at 4.1 kbar, 1620"C. The composition of the isobaric eutectic between silica and enstatite does not change measurably with pressure at least up to 25 kbar. The one-atmosphere peritec-tic liquid in equilibrium with forsterite and enstatite changes to a eutectic liquid at a pressure of approximately 1.3 kbar and its composition moves progressively toward forsterite as pressure increases. However, this result for the binary system does not necessarily mean that the reaction relation involving forsterite, enstatite, and liquid in a natural magma must disappear at a similar pressure.