CAJ | 학술논문

对班公湖-怒江缝合带中段达如错地区侵入于蛇绿岩中的花岗斑岩进行了详细的野外调查及岩石学、地球化学、锆石U-Pb和Hf同位素研究.用LA-ICP-MS技术测得达如错花岗斑岩的锆石U-Pb年龄为110±1Ma,该年龄被解释为达如错花岗斑岩的形成年龄,并且锆石具有明显负的εHf(t)值(-5.5~-2.6).全岩地球化学资料表明,达如错花岗斑岩具有高钾钙碱性系列岩浆岩的特征,且A/CNK>1.1,富集Rb、Ba、Pb、Th,亏损Ta、Nb、Ti,轻稀土元素相对重稀土元素富集,同时具有明显的负Eu异常.以上特征表明,花岗斑岩属于强过铝质S型花岗岩.结合前人资料认为,达如错花岗岩岩体形成于同碰撞的构造环境,是加厚的大陆地壳发生重熔的产物,其形成还可能与同时期拉萨地块底部软流圈热物质上涌有关.班公湖-怒江缝合带中段在110Ma左右已经闭合,并发生了陆-陆碰撞.花岗斑岩侵入于蛇绿岩中,暗示110Ma之前该地区蛇绿岩就已经形成.
대반공호-노강봉합대중단체여착지구침입우사록암중적화강반암진행료상세적야외조사급암석학、지구화학、고석U-Pb화Hf동위소연구.용LA-ICP-MS기술측득체여착화강반암적고석U-Pb년령위110±1Ma,해년령피해석위체여착화강반암적형성년령,병차고석구유명현부적εHf(t)치(-5.5~-2.6).전암지구화학자료표명,체여착화강반암구유고갑개감성계렬암장암적특정,차A/CNK>1.1,부집Rb、Ba、Pb、Th,우손Ta、Nb、Ti,경희토원소상대중희토원소부집,동시구유명현적부Eu이상.이상특정표명,화강반암속우강과려질S형화강암.결합전인자료인위,체여착화강암암체형성우동팽당적구조배경,시가후적대륙지각발생중용적산물,기형성환가능여동시기랍살지괴저부연류권열물질상용유관.반공호-노강봉합대중단재110Ma좌우이경폐합,병발생료륙-륙팽당.화강반암침입우사록암중,암시110Ma지전해지구사록암취이경형성.
Located in the middle part of the Bangong Co-Nujiang River suture zone, the Daru Co granite porphyry was intruded in-to the ophiolite of this suture zone. In this study, the authors performed detailed field investigation, petrological and geochemical study, and zircon U-Pb and Hf isotopic analysis of the Daru Co granite porphyry. Using the LA-ICP-MS technique, the authors obtained the U-Pb age of 110±1Ma for the Daru Co granite porphyry, and this age is interpreted as the formation age of granite por-phyry. The Daru Co granite porphyry has pronounced negative zircon εHf(t) values in the range of-5.5~-2.6. Whole-rock geo-chemical data show that it is characterized by high K calc-alkaline series, A/CNK higher than 1.1, enrichment of LREE, Rb, Ba, Pb and Th, and depletion of Ta, Nb and Ti. All samples show negative Eu anomaly. These features indicate that the Daru Co granite porphyry belongs to the peraluminous S-type granite. It is considered that the Daru Co granite porphyry might have been formed by partial melting of the thickened continental crust in a syn-collision setting, and it was probably related to the hot asthenosphere up-welling under the Lhasa block. The ocean basin had been closed and continental collision started before 110Ma in the middle part of the Bangong Co-Nujiang River suture zone. Furthermore, the ophiolite in this area should be formed before 110Ma in terms of the relationship between the Daru Co granite porphyry and ophiolite.