Crust-formaticn processes in the Kontum Massif, Vietnam

越南中部的Kontum地块由低品位片岩和角闪岩-麻粒岩相变质岩组成，曾被s型和i型花岗岩侵入。该地体以前被认为主要由太古界麻粒岩（坎纳克杂岩）、元古代角闪岩相变质岩（玉林杂岩）和低品位片岩（坎德杂岩）组成。它们被认为是东南亚印度支那克拉通的基底。坎纳克杂岩以泥质-半泥质片麻岩为主，在高温至超高温（UHT）条件下变质为麻粒岩相。片麻岩中也嵌有少量镁铁质和钙硅酸盐岩。变质程度最高的是石榴石-正辉石-硅线石-堇青石片麻岩，说明逆行阶段多期正辉岩形成始于UHT条件下（1000℃<）等温减压。另一方面，新发现的Ngoc - Linh杂岩石榴石-斜辉石-正辉石麻粒岩（榴辉岩超高温基性麻粒岩）显示出从石榴石-斜辉石-石英到角闪石-石英，再到斜辉石-正辉石-斜长石-石榴石的一系列不同组合变化。确定了这些岩石是等温减压和近等压冷却的变质演化的结果。孔屯地块超高温变质岩沿Dac—Kan剪切带出露，呈现顺时针压力—温度路径，峰值变质条件约1.2 GPa，约1050℃（M1变质）。高压M0变质作用（约1.7 GPa<，约1000℃）为进阶变质作用的一部分，低压（但仍超高温）M2变质作用（0.9-1.0 GPa，约1000℃）为进阶变质作用的一部分。1000℃)为顺时针压力-温度演化过程中的逆行变质作用的一部分。广泛报道的二叠纪-三叠纪变质事件（约240-260 Ma）表明，东亚大陆碰撞过程中发生了从M0期到低压低温逆行期（M2期后期）的快速变质演化。新测定的Kannak和Ngoc Linh杂岩Sm-Nd内部等时线和SHRIMP年龄也表明Kontum地块也经历了泛非变质事件（约2.5、1.0和0.5 Ga）。目前关于Kontum地块变质演化的研究成果，包括41篇学术论文，表明考虑东亚大陆演化过程具有很强的局限性。少

The Kontum massif in central Vietnam consists of low-grade schists and amphibolite- to granulite-facies metamorphic rocks, that have been intruded by S-type and I-type granites. This terrane was formerly considered to be composed mainly of Archean granulites (the Kannak Complex), Proterozoic amphibolite-facies metamorphic rocks (the Ngoc Linh Complex) and low-grade schists (the Kham Duc Complex). They were thought to be the basement of the Indochina Craton in south-east Asia. The Kannak Complex is dominated by pelitic-semipelitic gneisses metamorphosed under high- to ultrahigh-temperature (UHT) conditions into granulite-facies. A minor amount of mafic and calcsilicate rocks are also intercalated within the gneisses. The highest-grade metamorphic condition is determined from garnet-orthopyroxene-sillimanite-cordierite gneiss, which indicates that multi-stage symplectite formation during retrograde stage started from isothermal decompression in UHT condition (1000 ℃<). On the other hand, … More the newly found garnet-clinopyroxene-orthopyroxene granulites (eclogitic ultrahigh-temperature mafic granulite) from the Ngoc Linh Complex shows a series of changes in divariant assemblages from garnet-clinopyroxene-quartz to hornblende-quartz through clinopyroxene-orthopyroxene- plagioclase-(garnet). It was identified that these rocks were formed as a result of their metamorphic evolution of isothermal decompression followed by nearly isobaric cooling.The ultrahigh-temperature metamorphic rocks in the Kontum massif, which are exposed along the Dac To Kan shear zone, show a clockwise pressure-temperature path with the peak metamorphic condition of ca. 1.2 GPa and ca. 1050 ℃ (M1 metamorphism). High-pressure M0 metamorphism (ca. 1.7 GPa<, ca. 1000 ℃) as part of the prograde metamorphism and low-pressure (but still ultrahigh-temperature) M2 metamorphism (0.9-1.0 GPa,ca. 1000 ℃) as part of the retrograde metamorphism during the clockwise pressure-temperature evolution are also recognized. The widely reported Permo-Triassic metamorphic event (ca. 240-260 Ma) from the ultrahigh-temperature metamorphic rocks would indicate a rapid metamorphic evolution from M0 stage to low-pressure and low-temperature retrograde stage (later M2 stage) during the continents collision in eastern Asia. The newly determined Sm-Nd internal isochron and SHRIMP ages from the Kannak and Ngoc Linh Complexes would also indicate that the Kontum massif had also undergone the Pan African metamorphic event (ca. 2.5,1.0 and 0.5 Ga). The present results of the metamorphic evolution of the Kontum massif including 41 journal papers indicate a strong constraint to consider the coninental evolution process in Eastern Asia. Less