Dehydration melting and the granulite transition in metapelites from southern Namaqualand, S. Africa
Dehydration melting and the granulite transition in metapelites from southern Namaqualand, S. Africa
复制标题
南非纳马夸兰南部变泥岩中的脱水熔融和麻粒岩转变
DOI：
10.1007/bf00380171
复制
发表时间：
1984
影响因子：
3.5
通讯作者：
C. Whales
中科院分区：
文献类型：
--
作者：
D. Waters;C. Whales
在纳马夸兰变质杂岩的斜长角闪岩-麻粒岩过渡带中，变岩显示出角闪岩相组合黑云母+硅线石+石英与麻粒岩相组合石榴石+堇青石+钾长石的互带。残留的粒序层理表明成分条带是沉积成因的。石榴子石-堇青石-钾长石片麻岩中含有围绕石榴子石的石英长石质分凝体，比黑云母-硅线石片岩具有更多的富Fe体相成分，如果石榴子石-堇青石-钾长石层中的H_2O系统性地较低，则在相同的压力和温度下可以形成对比鲜明的镶嵌体。SiO_2（H_2O）的还原作用是由硅酸盐熔体在无蒸汽熔融作用下的连续Fe-Mg反应（如黑云母+硅线石+石英=石榴石+钾长石+液体）产生的，这一过程影响了更多富镁岩石在无蒸汽熔融作用前的富铁组成。这些分凝物代表了反应的固体和液体产物，这种过程意味着a（H2O）的局部控制，并表明这种麻粒岩转变不是由于交代流体的区域性流入。
In a prograde amphibolite-granulite transition zone in the Namaqualand Metamorphic Complex, metapelites show an interbanding of the amphibolite facies association biotite+sillimanite+quartz with the granulite facies association garnet+cordierite+K-feldspar. Relict graded bedding shows that compositional banding is of sedimentary origin. The garnet-cordierite-K-feldspar gneisses contain quartzofeldspathic segregations surrounding garnets, and have more Fe-rich bulk compositions than the biotite-sillimanite schists.The contrasting asemblages could have formed at the same pressure and temperature provided thata(H2O) was systematically lower in the garnet-cordierite-K-feldspar layers. Thea(H2O) reduction resulted from the production of silicate melt by a vapour-absent continuous Fe-Mg reaction such as biotite+sillimanite+quartz=garnet+K-feldspar+liquid which affects Fe-rich compositions before vapour-absent melting occurs in more Mg-rich rocks. The segregations represent the solid and liquid products of the reaction.Such processes imply local control ofa(H2O), and indicate that this granulite transition did not result from a regional influx of metasomatising fluids.