Reaction textures and metamorphic evolution of sapphirine–spinel-bearing and associated granulites from Diguva Sonaba, Eastern Ghats Mobile Belt, India
Reaction textures and metamorphic evolution of sapphirine–spinel-bearing and associated granulites from Diguva Sonaba, Eastern Ghats Mobile Belt, India
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印度东高止山脉迪古瓦索纳巴含蓝宝石尖晶石及伴生麻粒岩的反应结构和变质演化
DOI：
10.1017/s0016756814000399
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发表时间：
2015
影响因子：
2.3
通讯作者：
Frimmel
中科院分区：
文献类型：
--
作者：
Prakash;Deepak;Frimmel
Diguva Sonaba地区（印度南部安得拉邦Vishakhapatnam区）代表了东高止山脉移动的带麻粒岩相地形的一部分。该区前寒武纪变质岩石主要由镁铁质麻粒岩（±石榴石）、孔兹岩、变粒岩（±石榴石、黑云母）、紫苏花岗岩、长角闪岩、钙质麻粒岩、混合片麻岩和含镁铁尖晶石麻粒岩组成。后一种岩石类型以透镜体形式出现在孔兹岩、变粒岩和钙麻粒岩中。结构的关系，如腐蚀的黑云母内石榴石和斜方辉石，再吸收的辉石内的角闪石，粗粒板条的硅线石，大概是蓝晶石后的假晶，提供证据的早期发作的上角闪岩相变质作用，或他们代表的遗迹，导致麻粒岩相变质作用。在麻粒岩相变质作用的热峰期，含镁橄榄石-尖晶石的麻粒岩中，除镁橄榄石、尖晶石和石英外，还存在稳定的镁橄榄石组合，但在退变质叠加期，该组合被Crd-Opx-Qtz-Kfs-合晶岩和各种反应冕所取代。不同量的黑云母或黑云母+石英合晶岩取代斜方辉石，堇青石和Opx-Crd-Kfs-Qtz合晶岩在更晚的退变质阶段。C峰变质条件。1000°C和C.根据石榴石中XMg和斜方辉石中XAl的等值线计算了12 kbar。从日冕和合晶岩组合推断的反应序列，以及成岩网格和假剖面模拟，记录了顺时针P-T演化。P-T路径的特征是T凸，表明等温减压路径，并反映了快速隆升，然后冷却的构造增厚的地壳。
The Diguva Sonaba area (Vishakhapatnam district, Andhra Pradesh, South India) represents part of the granulite-facies terrain of the Eastern Ghats Mobile Belt. The Precambrian metamorphic rocks of the area predominantly consist of mafic granulite (±garnet), khondalite, leptynite (±garnet, biotite), charnockite, enderbite, calc-granulite, migmatic gneisses and sapphirine–spinel-bearing granulite. The latter rock type occurs as lenticular bodies in khondalite, leptynite and calc-granulite. Textural relations, such as corroded inclusions of biotite within garnet and orthopyroxene, resorbed hornblende within pyroxenes, and coarse-grained laths of sillimanite, presumably pseudomorphs after kyanite, provide evidence of either an earlier episode of upper-amphibolite-facies metamorphism or they represent relics of the prograde path that led to granulite-facies metamorphism. In the sapphirine–spinel-bearing granulite, osumilite was stable in addition to sapphirine, spinel and quartz during the thermal peak of granulite-facies metamorphism but the assemblage was later replaced by Crd–Opx–Qtz–Kfs-symplectite and a variety of reaction coronas during retrograde overprint. Variable amounts of biotite or biotite+quartz symplectite replaced orthopyroxene, cordierite and Opx–Crd–Kfs–Qtz-symplectite at an even later retrograde stage. Peak metamorphic conditions of c. 1000°C and c. 12 kbar were computed by isopleths of XMg in garnet and XAl in orthopyroxene. The sequence of reactions as deduced from the corona and symplectite assemblages, together with petrogenetic grid and pseudosection modelling, records a clockwise P–T evolution. The P–T path is characteristically T-convex suggesting an isothermal decompression path and reflects rapid uplift followed by cooling of a tectonically thickened crust.
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