CAJ | 학술논문

野外地质调查工作表明,阿尔金地区西起且末河到茫崖长达300 km范围内的"阿尔金山岩群"中多处出露榴辉岩透镜体.榴辉岩在产状和岩石学特征上可以分为两种: 第1种是中细粒结构,块状构造,退化变质较弱,围岩多与片麻状花岗岩或花岗闪长岩关系密切;第2种是细粒结构,片麻状构造,具有透入性片麻理,有明显退化变质现象,围岩多与大理岩、黑云变粒岩、石英片岩等关系密切.在分布上,榴辉岩限于古元古代"阿尔金山岩群"中,含有榴辉岩的阿尔金构造杂岩带是柴达木盆地北缘碰撞杂岩带的西延部分.
야외지질조사공작표명,아이금지구서기차말하도망애장체300 km범위내적"아이금산암군"중다처출로류휘암투경체.류휘암재산상화암석학특정상가이분위량충: 제1충시중세립결구,괴상구조,퇴화변질교약,위암다여편마상화강암혹화강섬장암관계밀절;제2충시세립결구,편마상구조,구유투입성편마리,유명현퇴화변질현상,위암다여대리암、흑운변립암、석영편암등관계밀절.재분포상,류휘암한우고원고대"아이금산암군"중,함유류휘암적아이금구조잡암대시시체목분지북연팽당잡암대적서연부분.
Field geological survey shows that there are many eclogite lenses outcropped in the Altun Mountains Rock Group which extends for 300 km from the Qiemo River in the west to Mangya in Altun area. Eclogite can be divided into two types according to its modes of occurrence and petrologic characteristics. One is characterized by medium-fine grained texture, massive structure, no gneissosity, weak retrogressive metamorphism, and a close relation to gneissic granite or granodiorite;mineral assembly of the early period is garnet + omphacite + quartz, and that of the late period is amphibole (or pyroxene) + plagioclase + quartz;omphacite has remarkably different Al_2O_3 and FeO content, while its CaO, MgO and Na_2O content is relatively stable: Al_2O_3 is generally 5.55%～9.50%, FeO 4.33%～7.53%, and NaO 3.05%～5.54%;jadeite content is 15.39～27.49% with an average of 22.22%;the end member compositions of pyroxene are between those of kyanite eclogite and gneiss eclogite;Chemical composition of garnet varies a lot with ∑FeO 18.82%～30.58%, MgO 2.38%～13.67%, and CaO 4.65%～10.26%, while SiO_2 and Al_2O_3 change insignificantly, being 35.63%～39.57% and 20.92%～23.65% respectively;the average end member composition of eclogite (mostly being Mg- and Ca-rich almandine) is assigned to C type eclogite in Coleman's classification diagram (1965). The other is characterized by fine-grained texture, gneissic structure, penetrative geissosity, and obvious retrogressive metamorphism, with its wall rocks mostly related to marble, biotite granulite, quartz schist etc;a majority of this type of eclogite has been changed into garnet amphibolites with obvious retrogressive metamorphism;the eclogite is confined to Palaeoproterozoic Altun Mountains Rock Group and is comparable to the eclogite on the nortern margin of Qaidam Basin in the aspect of either wall rock characteristics or eclogite property, suggesting similar geneses;moreover, granitic gneisses as the wall rocks of eclogite have basically the same diagenetic ages[(930±42)～(686±20) Ma] and metamorphic ages[(525±31)～(434±29) Ma]as the eclogite. These similarities show that these two types of eclogite were both formed in Early Paleozoic by deep subduction of Late Proterozoic crust materials. The eclogite-bearing Altun structural complex belt is the westward extending part of the northern Qaidam Basin collision complex belt.