Magmatic andalusite from the migmatite zone of the Aoyama area, Ryoke metamorphic belt, SW Japan, and its importance in constructing the P-T path
Magmatic andalusite from the migmatite zone of the Aoyama area, Ryoke metamorphic belt, SW Japan, and its importance in constructing the P-T path
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日本西南部Ryoke变质带青山地区混合岩带的岩浆红柱石及其在构造P-T路径中的重要性
DOI：
10.2465/jmps.97.241
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发表时间：
2002
影响因子：
0.7
通讯作者：
Tetsuo Kawakami
中科院分区：
文献类型：
--
作者：
Tetsuo Kawakami
红柱石产于日本西南部菱沟变质带青山地区的变质岩和泥质岩中，泥质岩中的石榴石-堇青石（Grt-Crd）带中充满了无色体。一般来说，来自硅线石-钾长石（Sil-Kfs）带和Grt-Crd带低温部分的泥质片岩中不含无色体的红柱石晶体部分转化为硅线石，表明青山地区的峰温条件已达到硅线石品位。另一方面，从Grt-Crd带的低温部分的无色体中发现的红柱石晶体是半自形的，并且根本没有转化为硅线石。红柱石-硅线石转变的证据的缺乏意味着这些晶体没有经历过的红柱石-硅线石转变，因此是退变产物。它们特征性地出现在含有自形斜长石或半自形堇青石晶体的无色体中，并显示出不同于通常在红柱石中观察到的自形的半自形形状。Grt-Crd带低温部分的P-T条件足够高，可使泥质岩部分熔融，含红柱石的无色体具有适当的冻结熔体成分。这些观察结果表明，退变质红柱石是岩浆成因的。硼在熔体中的存在下，添加Al 2 O3的次铝质Qtz-Ab-Or系统中的铝硅酸盐饱和，并优先纳入Fe 2 O3的红柱石的组合效应可能有利于在青山地区的岩浆红柱石的结晶。在Grt-Crd带的低温部分发现岩浆红柱石，表明该带的P-T轨迹穿过过铝质花岗岩的水饱和固相线与红柱石稳定场的重叠区。因此，当采用Holdaway（1971）的铝硅酸盐相图时，Grt-Crd区低温部分的P-T轨迹可能不是发夹形，而是顺时针方向。P-T轨迹的非发夹形性质可能是青山地区部分熔融的结构证据得以保存的部分原因。
Magmatic andalusite is found from the metatexite and from the pelitic rock with boudin necks filled with leucosome in the garnet-cordierite (Grt-Crd) zone of the Aoyama area, Ryoke metamorphic belt, SW Japan. In general, andalusite crystals in the pelitic schist without leucosome from the sillimanite-K-feldspar (Sil-Kfs) zone and low-temperature part of the Grt-Crd zone are partly transformed into sillimanite, suggesting that the peak P-T conditions of the Aoyama area have reached to the sillimanite grade. On the other hand, andalusite crystals found from the leucosome of the low-temperature part of the Grt-Crd zone are subhedral, and have not transformed into sillimanite at all. Absence of an evidence for andalusite-sillimanite transition implies that these crystals did not experience the prograde andalusite-sillimanite transition and thus are retrograde products. They characteristically occur in the leucosome containing euhedral plagioclase or subhedral cordierite crystals and show subhedral shape different from the euhedral shape usually observed in the prograde andalusite. The P-T conditions for the low-temperature part of the Grt-Crd zone is sufficiently high for the partial melting of pelitic rocks, and the andalusite-bearing leucosome has appropriate composition as a frozen melt. These observations suggest that the retrograde andalusite is of magmatic origin. Combining effects of the presence of boron in the melt, addition of Al2O3 to the subaluminous Qtz-Ab-Or system to saturate in aluminosilicates, and preferential incorporation of Fe2O3 into andalusite may have favored the crystallization of magmatic andalusite in the Aoyama area. Finding of the magmatic andalusite from the low-temperature part of the Grt-Crd zone suggests that the P-T path of this zone went through the overlapping region of water-saturated solidus of peraluminous granite and andalusite stability field. The P-T path of the low-temperature part of the Grt-Crd zone may, therefore, not be a hairpin shaped one but a clockwise one when the aluminosilicate phase diagram of Holdaway (1971) is used. Non-hairpin shaped nature of the P-T path may be partly responsible for the preservation of the textural evidences of partial melting in the Aoyama area.
影响因子：
3.4
作者：
Michael Brown
通讯作者：
Michael Brown