和歌山県潮岬の塩基性貫入岩中の単斜輝石の累帯構造に見られるCa増加経路(<特集>造岩鉱物研究の現状と展望-地団研第33回総会鉱物学ミニシンポジウム-)

抄録

Zoned clinopyroxene and orthopyroxene found in the hornblende-dolerites of the Shiono-misaki Igneous Complex were examined. In the case of the clinopyroxene, the core part and the mantle part have contrasting Ca-content. In the core, Ca/Ca+Mg+Fe ratio is within the range from 0.42 to 0.39. On the other hand, in the mantle, this ratio is within 0.46 to 0.44. Both the core and the mantle part of the clinopyroxene can be concluded to have coprecipitated with the core and the mantle part of the zoned orthopyroxene, respectively. Such a Ca-enrichment trend of zoned clinopyroxene that have coprecipitated with orthopyroxene can be attributed to the abrupt increase of P_H2O in the magma chamber, and to the resorption of the existing crystal to a certain degree, followed by the formation of new pyroxene being stable under the higher P_H2O and somewhat lowered temperature. Some of the zoned clinopyroxene show idiomorphic shapes. Accordingly, above-mentioned increase of P_H2O was the event not restricted in the trapped liquid but yielded wholly in the magma chamber.