太行山中生代岩浆作用过程中的壳幔岩浆混合作用:岩石学和地球化学证据  

Magma-mixing between mantle- and crustal-derived melts in the process of Mesozoic magmatism, Taihangshan: constraints from petrology and geochemistry.

作　　者：陈斌[1] 刘超群[1] 田伟[1] 

机构地区：[1]北京大学地球与空间科学学院造山带与地壳演化教育部重点实验室,北京100871

出　　处：《地学前缘》2006年第2期140-147,共8页Earth Science Frontiers

基　　金：国家自然科学基金委员会资助项目(40372033;40502009)

摘　　要：太行山中生代岩浆岩的主体——石英二长岩中常见闪长质包体。无论包体还是寄主岩石中均可见斜长石具有成分和结构的不平衡现象，即斜长石具有富钙的核（An=57～65）和富钠的幔部（An=20-35），而且两者变化截然。这是壳幔岩浆发生混合作用的记录：核部代表基性岩浆中早期结晶的斜长石（或代表花岗岩中斜长石由于高温基性岩浆的注入而发生部分熔融形成的残留核？），而幔部代表从混浆中结晶的斜长石。与此类似，角闪石也发育成分环带，其核部为相对富Al和Ti的黄褐色的韭闪石，而边部为贫Al和Ti的绿色调的浅闪石。韭闪石形成于较高的温度，浅闪石形成于较低的温度，也反映了壳幔岩浆混合的过程。壳幔岩浆混合模式同样得到地球化学数据的支持，太行山中生代岩浆岩的高K2O和MgO、高分异稀土模式（和Eu异常不明显）、高Sr-Ba和富集的Sr-Nd同位素特征等均与来自富集地幔的基性岩浆的混合有关。Mafic enclaves are widespread in the Mesozoic monzonitic batholiths of the Taihang mountains. Compositional and textural disequilibrium can be found in plagioclase crystals from both mafic enclaves and host rocks. Normally, plagioclase has a calcium-rich core with An=57-65, mantled by a sodium-rich rim with An=20-35. This abrupt change from a high-anorthite core to a low-anorthite rim in single plagioclase crystals is likely an indication of magma mixing between mantle- and crustal-derived melts. The cores represent plagioclase crystallized from a mantle-derived mafic magma, and the rims represent plagioclase from hybrid magma sources. Similarly, compositional zoning can be observed in hornblende crystals in which aluminum and titanium contents are high in the core （yellow- to brown in color） and low in the rim （green in color） ; these zones fall in the compositional fields of pargasite and edenite, respectively. Pargasite crystallized at significantly higher temperatures than edenite, which is consistent with our model of magma mixing. In addition, the magma-mixing model is supported by geochemical data. The characteristic geochemical signatures of high-K and Mg^# , highly fractionated REE patterns （with minor Eu anomalies）, high Sr-Ba abundances, and enriched Sr-Nd isotopic compositions are believed to originate from the hybridization of enriched mantle-derived mafic magma with granitic melts of crustal origin.

关 键 词：斜长石 角闪石 成分和结构不平衡 地球化学 岩浆混合 富集地幔 太行山 

分 类 号：P588.1[天文地球—岩石学]