摘要
吉林双辽地区古近纪玄武岩中一方辉橄榄岩包体记录了上地幔交代作用的信息。原生斜方辉石被交代成因的单斜辉石和橄榄石所围绕,或形成反应边结构,或斜方辉石残留在次生单斜辉石中。这些反应结构仅出现在尖晶石的周围。电子探针分析表明次生单斜辉石具有高Mg#、Cr#和CaO/Al2O3比值,次生橄榄石高Mg#、CaO和Cr2O3,被交代的尖晶石边部高Cr#、CaO。由于交代作用并未影响橄榄岩体系的Mg#,而且熔体-岩石反应结构指示Opx(斜方辉石)+Sp(尖晶石)+熔体(Ⅰ)→Cpx(单斜辉石)+Ol(橄榄石)+熔体(Ⅱ),结合实验以及文献资料,认为双辽地区的岩石圈地幔受到了硅酸盐熔体的交代。这种交代导致橄榄岩中斜方辉石逐渐减少,单斜辉石和橄榄石逐渐增加,从而使方辉橄榄岩渐变成易剥橄榄岩。这种交代现象可能发生在软流圈-岩石圈接触带上的熔-岩反应区,暗示了在古近纪双辽地区岩石圈减薄和软流圈上涌导致的软流圈-岩石圈的相互作用仍在继续。
A harzburgite xenolith sample from Paleogene basalts in Shuangliao area of J ilin Province records the information of upper mantle metasomatism. Primary orthopyroxenes are surrounded by secondary clinopyroxenes and olivine.s, forming reaction texture or existing as residues in secondary clinopyroxenes. These phenomena appear around spinel only. Electronic probe analyses reveal that secondary clinopyroxenes are characterized by high Mg^#, Cr^# and CaO/Al2O3, secondary olivines by high Mg^# , CaO and Cr2O3 content, and the metasomatized rim of spinels by high Cr^# and CaO. As metasomatism had no influence on Mg^# in peridotite, and the melt-rock reaction proceeded in order of Opx ＋ Sp ＋ melt （ Ⅰ ）→Cpx ＋ Ol ＋ melt （ Ⅱ ）, the authors consider that the lithospheric mantle in Shuangliao area was metasomatized by carbonate melt or silicate melt rich in carbonate. This conclusion is based on experiments and literature. The metasomatism resulted in decreasing content of orthopyroxene, increasing contents of clinopyroxene and olivine in peridotite, and the transformation from harzburgites to wehrlites. This metasomatism may occur in the melt-rock reaction zone located in the asthenosphere-lithosphere boundary, suggesting that the asthenosphere-lithosphere interaction resulting from lithosphere thinning and asthenosphere upwelling remained active in Shuangliao area in Early Tertiary.
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2007年第3期213-222,共10页
Acta Petrologica et Mineralogica
基金
国家自然科学基金资助项目(40673038
49925308)
中国科学院百人计划资助项目
关键词
橄榄岩包体
地幔交代作用
反应结构
双辽地区
吉林
peridotite xenoliths
mantle metasomatism
reaction texture
Shuangliao area
J ilin Province
