P-T-D Evolution of the Higashi-akaishi Ultramafic Mass in the Sanbagawa Metamorphic Belt, Central Shikoku, Japan
P-T-D Evolution of the Higashi-akaishi Ultramafic Mass in the Sanbagawa Metamorphic Belt, Central Shikoku, Japan
复制标题
日本四国中部三波川变质带东明石超镁铁质体的 P-T-D 演化
DOI：
10.5026/jgeography.113.5_617
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发表时间：
2004
影响因子：
3.1
通讯作者：
T. Mizukami
中科院分区：
文献类型：
--
作者：
M. Enami;T. Mizukami
在三八川变质带百志地区的东赤石橄榄岩中局部出露含石榴子石的超镁铁质岩，包括单斜辉石岩、硅镁石和镁橄榄石。这些岩石类型以透镜体、石香肠或厚度从几厘米到1米的层的形式出现在纯橄榄岩中。大规模的岩石成分和整体层状结构的广泛和系统的变化意味着超镁铁杂岩起源于堆积序列。石榴石和其他主要的硅酸盐含有罕见的包体的退变质角闪石，石榴石，磁铁矿，这意味着平衡在相对较低的温度和含水条件下，在变质作用。与石榴石共生的斜方辉石具有钟形铝分带，铝含量从核部向边缘逐渐降低，边缘记录了峰期变质条件。估计的P-T条件意味着在逆冲变质作用期间从1.5-2.4 GPa/700-800 °C到2.9-3.8 GPa/700 - 810°C的高P/T梯度（> 3.1 GPa/100 ° C）。高P/T变质阶段再结晶的橄榄石具有B型晶格择优取向，a轴浓度垂直于拉伸线理。B型LPO的存在表明，俯冲变质阶段的变形可能是在俯冲板片附近的楔状地幔的含水和高应力条件下进行的。东赤石橄榄岩是一个很好地记录了俯冲超镁铁质岩演化的独特实例。
Garnet-bearing ultramafic rocks including clinopyroxenite, wehrlite, and websterite locally crop out in the Higashi-akaishi peridotite of the Besshi region in the Sanbagawa metamorphic belt. These rock types occur within dunite as lenses, boudins, or layers with a thickness ranging from a few centimeters to 1 meter. The wide and systematic variations of bulk-rock composition and overall layered structure imply that the ultramafic complex originated as a cumulate sequence. Garnet and other major silicates contain rare inclusions of edenitic amphibole, chlorite, and magnetite, implying equilibrium at relatively low T and hydrous conditions during prograde metamorphism. Orthopyroxene coexisting with garnet shows bell-shaped Al zoning with a continuous decrease of Al from the core towards the rim, and its rim records peak metamorphic conditions. Estimated P-T conditions imply a high P/T gradient (> 3.1 GPa/100 °C) from 1.5-2.4 GPa/700-800 °C to 2.9-3.8 GPa/700-810°C during prograde metamorphism. Olivines recrystallized at the high P/T prograde metamorphic stage show a B-type lattice preferred orientation (LPO) with a-axis concentrations normal to the stretching lineation. The presence of B-type LPO indicates that deformation of the prograde metamorphic stage possibly progressed under hydrous and high-stress conditions at the wedge mantle adjacent to the subducted slab. The Higashi-akaishi peridotite is a unique example that well records the prograde evolution of subducted ultramafic rocks.
影响因子：
64.8
作者：
T. Mizukami;S. Wallis;J. Yamamoto
通讯作者：
T. Mizukami;S. Wallis;J. Yamamoto
影响因子：
3.9
作者：
Aoya, M
通讯作者：
Aoya, M
影响因子：
3.9
作者：
BREY, GP;KOHLER, T
通讯作者：
KOHLER, T