Compositional relations of coexisting orthopyroxene, pigeonite and augite in a tholeiitic andesite from Hakone Volcano
Compositional relations of coexisting orthopyroxene, pigeonite and augite in a tholeiitic andesite from Hakone Volcano
复制标题
箱根火山拉斑斑玄武岩安山岩中共生斜方辉石、红辉石和辉石的成分关系
DOI：
10.1007/bf00390075
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发表时间：
1970
影响因子：
3.5
通讯作者：
I. Kushiro
中科院分区：
文献类型：
--
作者：
Yasuo Nakamura;I. Kushiro
本文用电子探针测定了日本箱根火山拉斑玄武岩安山岩中基质中五种不同类型辉石、紫苏辉石、褐变辉石和普通辉石以及斑晶中古铜岩和普通辉石的成分。结果表明，有一个约25摩尔%的CaSiO 3之间的基质pigeonite和普通辉石，与35%的CaSiO 3之间的斑晶普通辉石和古铜色岩的组成差距。未发现次钙质普通辉石或褐变普通辉石，基质普通辉石仅以褐变辉石和紫苏辉石的薄边出现，其钙含量较斑晶普通辉石低，铁含量较高。它还表明，基质pigeonite是3- 4mol%以上的CaSiO 3-丰富的比共存的基质紫苏辉石。紫苏辉石和褐变岩的Fe/（Mg + Fe）比值分别约为0.31和0.33。这些结果表明，在拉斑玄武岩安山岩基质结晶条件下，普通辉石与Fe/（Mg + Fe）比值至少在0.3附近的褐变岩之间不存在连续固溶体。从镁-铁分配和结构关系可以看出，基质普通辉石的结晶液比基质紫苏辉石和褐变岩的结晶液更富铁。
The compositions of five different coexisting pyroxenes hypersthene, pigeonite and augite in groundmass and bronzite and augite of phenocryst in a tholeiitic andesite from Hakone Volcano, Japan have been determined by the electron probe microanalyser. It is shown that there is a compositional gap of about 25 mole per cent CaSiO3between groundmass pigeonite and augite, compared with 35 per cent CaSiO3between phenocrystic augite and bronzite. Subcalcic augite or pigeonitic augite was not found. The groundmass augite, which occurs only as thin rims of pigeonite and hypersthene, is less calcic and more iron-rich than the phenocryst augite. It is also shown that the groundmass pigeonite is 3–4 mole per cent more CaSiO3-rich than the coexisting groundmass hypersthene. The Fe/(Mg + Fe) ratios of these coexisting hypersthene and pigeonite are about 0.31 and 0.33, respectively. It is suggested from these results that a continuous solid solution does not exist between augite and pigeonite of the Fe/(Mg + Fe) ratio at least near 0.3 under the conditions of crystallization of groundmass of the tholeiitic andesite. It is suggested from the Mg-Fe partition and the textural relation that the groundmass augite crystallized from a liquid more iron-rich than that from which groundmass hypersthene and pigeonite crystallized.