中国东部几个地区新生代玄武岩中单斜辉石-熔体平衡温压——兼论幔源包体的成因  

Clinopyroxene-melt equilibrium temperature and pressure of Cenozoic basalts with special reference to the genesis of mantle xenoliths in some areas of eastern China

作　　者：李天福[1] 马鸿文[2] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质大学材料科学与工程学院,北京100083

出　　处：《岩石矿物学杂志》2002年第1期11-23,共13页Acta Petrologica et Mineralogica

基　　金：国家教委 跨世纪优秀人才计划 "基金资助项目;国家自然科学基金资助项目(4 973 3 110)

摘　　要：以中国东部宽甸、汉诺坝和明溪含有幔源包体的新生代玄武岩中的单斜辉石斑 (巨 )晶为研究对象 ,采用最新的单斜辉石 -熔体平衡温压计对单斜辉石斑 (巨 )晶 -熔体进行了平衡温压计算。结果表明 ,碱性玄武岩中的单斜辉石斑晶结晶温度和压力高于共生的亚碱性玄武岩中的单斜辉石斑晶 ,单斜辉石巨晶的结晶温度和压力高于单斜辉石斑晶。这说明碱性玄武岩的形成深度大于亚碱性玄武岩 ,单斜辉石巨晶是更高压力下的结晶产物 ,单斜辉石斑晶在岩浆上升的不同深度均有晶出。回归分析表明 ,尽管携带幔源包体的玄武岩浆上升速度较快 ,但并不是绝热上升。单斜辉石斑 (巨 )晶的结晶温压条件与同一地点幔源包体平衡温压条件的对比表明 ,单斜辉石巨晶和碱性玄武岩中的部分单斜辉石斑 (巨 )晶的结晶温压大于幔源包体的平衡温压 ,表明了包体寄主岩浆的来源深度大于包体的深度。因此 ,幔源包体是寄主岩浆上升途中捕虏的上地幔碎块 ,而非寄主岩浆形成源区的残留体。On the basis of the newly published clinopyroxene-melt equilibrium thermobarometer, the authors calculated the clinopyroxene-melt equilibium temperature and pressure of mantle xenoliths_bearing basalts at Kuandian, Hannuoba and Mingxi in eastern China. The res_ ults show that the crystallization temperature and pressure of cpx porphyritic crystals in alkali basalts are generally higher than those in subalkali basalts, and the crystallization temperature and pressure of cpx megacrysts are higher than those of phenocrysts, which further proves that the cpx megacrysts crystallize at higher pressure than cpx porphyritic crystals. The existence of cpx phenocrysts at various pressures indicates that the cpx can crystallize continually along the way through which the magma moves upward. Regression analysis shows that although the basalts which bear mantle xenoliths move up so fast, they are not adiabatic but have heat diffusion. The comparison of temperatures and pressures between the crystallization of cpx phenocrysts (or megacrysts) and that of xenolith in alkali basalts indicates that host magma exists originally deeper than the mantle xenoliths in terms of pressure and so the xenoliths are fragments of the upper mantle captured by magma along the ascending way instead of being the source residues of host magma as considered previously.

关 键 词：中国东部 新生代 玄武岩 单斜辉石斑晶 幔源包体 单斜辉石-熔体平衡 温压计 

分 类 号：P588.145[天文地球—岩石学] P59[天文地球—地质学]