摘要
内蒙古中部地区晚古生代花岗岩类侵入岩分布广泛,在空间上构成一条巨大的东西向花岗岩带,是研究花岗岩成因和地壳演化的天然实验室。四子王旗北大庙岩体作为一个典型代表,以花岗闪长岩为主,其内部普遍发育镁铁质微粒包体,对理解花岗岩石成因和演化有重要意义。对包体及其寄主岩进行岩相学研究及矿物化学分析,结果显示:包体具塑性外形及岩浆结构,存在多种不平衡矿物组合,是岩浆混合的重要证据;MME中斜长石斑晶边部与核部An值较低,幔部An值较高,黑云母斑晶MgO边部与核部较低,幔部较高,两种矿物相似的成分变化指示结晶环境的改变,从矿物学角度证实存在基性岩浆的反复注入。黑云母及角闪石化学成分上也显示出岩体形成于造山带背景下,岩浆具壳幔混合的特点。岩体形成温度为650℃～700℃左右,压力为1.5×108Pa左右,氧逸度lgfO2较高,约-10～-15。
A large number of late Paleozoic granitoids occurred in the middle part of Inner Mongolia,which formed a large granite belt from west to east. It was a natural laboratory for the study of genesis of granite and evolution of crust. As a representative intrusion, the Damiao granitoids mainly consisted of mid-course grained granodiorite with abundant mafic microgranular enclaves （MMEs） in the north of Siziwangqi area and the MMEs provided important information for the genesis and evolvement of the granite. The results of petrologic and mineralogical study on the MMEs were indicated that the MMEs commonly showed ellipsoidal shapes with igneous textures, and exhibited obvious disequilibrium textures in mineralogy, suggesting magma mixing. Plagioclase crystals had lower An in the core and rim, higher An in the mantle. While biotite crystals had lower MgO content in the core and rim, higher MgO content in the mantle. The similar compositional oscillatory variations of plagioclase and biotite crystals indicated the change of crystal environment, suggesting the repeating injection of basic magma in mineralogy. The compositions of biotite and hornblende also revealed that the Damiao granodirorite formed under an orogenic background, and the magma might undergo the process of crust-mantle mixing. Biotite-amphibole diagrams showed that the temperature of magma was about 650 ℃～700℃, and pressure was about 1.5 × 10^8 Pa, the oxygen fugacity was relatively higher and lgfo2 was about - 10～-15
出处
《矿物岩石》
EI
CAS
CSCD
北大核心
2008年第2期28-38,共11页
Mineralogy and Petrology
基金
国土资源部地质调查局1∶25×104补力太(K49C002003)
四子王旗幅区调修测项目(K49C003003)
博士后基金(20060390508)
