摘要
通过青海东昆仑东部沟里地区阿斯哈岩体中寄主闪长岩和暗色微粒包体的岩相学、全岩地球化学研究，确定了岩石成因及其构造属性。阿斯哈岩体中暗色包体广泛分布，包体岩性主要为角闪辉长岩。包体具有岩浆结构，部分包体具有塑性流变特征，包体中可见寄主岩石矿物的捕掳晶和针状磷灰石，表现出岩浆混合的岩相学特征。主岩及暗色包体同属准铝质、高钾钙碱性钾玄岩系列过渡岩石，主量元素在Harker图解及 Al2 O3/K2 O CaO/K2 O和 SiO2/CaO K2 O/CaO的共分母协变图上具良好的线性关系，反映两者成分的变化与岩浆混合作用有关。两者的稀土元素配分模式总体一致，显示二者密切的成因联系。两者都富含大离子亲石元素（Rb、K ），相对亏损高场强元素（Nb、Ta、P、Ti ）。暗色包体具有贫硅（w（SiO2）＝50．70％～53．88％）和富镁、铁、钙的地球化学特征，其 Mg＃值较高（Mg＃＝0．52～0．59），暗示其来源于俯冲带流体交代地幔楔的部分熔融。主岩的 Rb/Sr值为0．22～0．27，接近地壳平均值，Nb/Ta值为14．5～15．2，介于地幔平均值与地壳平均值之间，表明寄主岩石岩浆具有壳源岩浆的性质并经历了幔源岩浆的混合作用。结合区域构造演化及构造判别，认为阿斯哈岩体形成于安第斯型活动大陆边缘的构造环境。早三叠世，阿尼玛卿洋向北俯冲，俯冲带流体交代地幔楔，导致其部分熔融形成基性岩浆，底侵的幔源基性岩浆诱发下地壳部分熔融并与之发生混合形成本区闪长岩，而其中的暗色包体为幔源岩浆混合不彻底的产物。
The authors report petrographical and whole-rock geochemical data of the host diorite and mafic microgranular enclaves（MMEs）within the Asiha diorite pluton at Gouli area in eastern Qinghai East Kunlun,and ascertain their petrogenesis and tectonic setting.The Asiha diorite pluton contains abundant MMEs which are mainly amphibole gabbro.The MMEs display igneous-texture and some of them are characterized by plastic flow deformation.The MMEs have plagioclase,amphibole and quartz xenocrysts and acicular apatite, which belongs to petrographical characteristics of magma mixing. Authors systematically studied petrological and geochemical characteristics of the host rocks and the MMEs,and conclude that both are meta-aluminous,high-K calc-alkaline series-shoshonitic series rocks. The selected major oxides of the MMEs and the host rocks show a linear correlation in Harker diagrams. In addition, Al2 O3/K2 O CaO/K2 O and SiO2/CaO K2 O/CaO identical oxide ratio denominator covariant diagram of the MMEs and their host rocks also show a linear correlation,which indicate their composition change is related to the magma mixing and mingling.Trace elements data show that they are both enriched in large ion lithophile elements （Rb,K）and depleted in high field strength elements （Nb,Ta,P and Ti）.The MMEs are characterized by low SiO2 contents （SiO2=50.70% 53.88%）, high MgO,Fe2O3 and CaO contents,as well as a higher Mg# value （Mg#=0.52 0.59）,which indicates that the primary magma was derived from the partial melting of the mantle wedge.The Rb/Sr ratio of the host rocks varies from 0.22 to 0.27,which is close to but less than average values of the earth crust.The Nb/Ta ratio of the host rocks varies from 14.5 to 15.2,which is between the average values of the crust and mantle,suggesting that the magma of the host rocks is mainly from crust and experienced magma mixing.Combined with regional tectonic evolution and discrimination of tectonic setting,we suggest that the Asiha diorite pluton formed in the Andean-type active continental margin. In Early Triassic,the A’nyemaqen ocean subducted northward,the subduction slab dehydrate led to fluid metasomatism,inducing partial melting of mantle wedge to form the mafic magma.The mafic magma underplated the overlying lower crust,resulting in its partial melting and then mixed with the crustal magma to form the Asiha diorite pluton,while the MMEs are the residually basic part of magma mixing.
出处
《吉林大学学报（地球科学版）》
EI
CAS
CSCD
北大核心
2014年第3期892-904,共13页
Journal of Jilin University：Earth Science Edition
基金
中国地质调查局地质大调查项目(12120111086020)
国家自然科学基金项目(41272093)
关键词
暗色微粒包体
地球化学
岩石成因
岩浆混合作用
沟里地区
东昆仑造山带
mafic microgranular enclaves
geochemistry
petrogenesis
magmatic mixing
Gouli area
Eastern Kunlun orogenic belt
