| 埃达克岩的原义、特征与成因 |
| |
| 引用本文： | 董申保,田伟.埃达克岩的原义、特征与成因[J].地学前缘,2004,11(4):585-594. |
| |
| 作者姓名： | 董申保 田伟 |
| |
| 作者单位： | 北京大学,地质学系,北京,100871;北京大学,地质学系,北京,100871 |
| |
| 基金项目： | 教育部博士点基金项目 ( 2 0 0 10 0 0 10 15 ) |
| |
| 摘 要： | 论述了埃达克岩的原义与综合特征 ,并针对其与太古宙TTG之间的区别和联系及今后研究埃达克岩的建议提出了自己的见解。埃达克岩 (adakite)的原义是指一类具有镁铁质斑晶的隐晶质火山岩 ,属于岛弧型岩浆钙碱性岩系 ,一般形成于年轻的 (<2 5Ma)、地热高的岛弧环境 ,是俯冲板块和上覆地幔相互作用产生的杂化熔液通过结晶分异形成的。综合总结埃达克岩 (原义 )的地球化学特征如下 :(1)原生标志 ,高Mg# 、低FeO /MgO、高Cr及Ni;(2 )微量元素标志 ,高LILE、高LREE、低HREE、低HFSE以及高分异的REE型式等。对实验岩石学研究资料的总结可知杂化 (hybridized)熔液是由小数量的板块熔液与地幔楔反应经交代作用、同化作用形成的 ,可分异直至出现酸性岩浆 ,这一过程称为“地幔同化及分离结晶作用 (mantle AFC)”。在橄榄岩的同化作用中 ,原有熔液Mg# 迅速上升 ,并在熔液成分加多后 ,向高Mg# 区迅速发展。在近代一些埃达克岩及相关岩石研究中 ,部分学者认为太古宙TTG与新生代板块 (榴辉岩 )重熔的TTD岩系类似。同时 ,亦有学者认为太古宙“绿岩带”中与TTG有关的深成岩系是一类Mg质花岗闪长岩Mg质二长闪长岩 ,成因与Sanukite相似 (太古宙sanuk itoid岩系 ) ,相当于富集橄榄岩重熔形成的岩系。这些研究重新引发了太古宙
|
| 关 键 词： | 埃达克岩 Mg质安山岩 杂化熔液对板块熔液 太古宙TTG对近代埃达克岩系列 |
| 文章编号： | 1005-2321(2004)04-0585-10 |
| 修稿时间： | 2004年9月8日 |
The nomenclature, characteristics and petrogenesis of adakite |
| |
| DONG Shen-bao,TIAN Wei.The nomenclature, characteristics and petrogenesis of adakite[J].Earth Science Frontiers,2004,11(4):585-594. |
| |
| Authors: | DONG Shen-bao TIAN Wei |
| |
| Abstract: | Adakite is a group of mafic phenocryst-bearing aphanitic andesites, which belong to the arc magmatic series. It occurs in some modern arcs where relatively young(<25 Ma) and high-geotherm lithosphere is being subducted, and is mainly generated from the partially melting due to the interaction of subducted slab (eclogite facies) and overlying mantle peridotite, forming a hybridized melt successively fractionated to evolve different adakite suites distinguished as the calc-alkline rocks. The geochemical characteristics of adakite can be shown as the primitive characters such as high Mg~#, low FeO~*/MgO, high Cr, Ni, derived from the mantle source; the trace elements as high LILE and LREE, low HFSE and HREE, with high fractionated REE pattern, and the isotopic ratio as low I(Sr) and~(206)Pb/~(204)Pb ratio. Experimental studies show that the hybridized melt can be modally expressed as a small amount of slab melt reacting with mantle wedge through the metasomatic reaction, the assimilation reaction and finally to the fractionated melt of high silicic content. It is known as “mantle-AFC”. The effect of peridotite assimilation causes a sharp increase in the Mg~# of the melt, and extends the melt composition towards the field for high Mg~# adakites.In the recent researches of adakite, it is claimed that the Archean TTG is similar to those adakite—the Cenozoic TTD derived by the slab melting (eclogite facies). Meanwhile, the Mg-granodiorite Mg-monzonite series related to TTG in the Archean “greenstone belt” is known as “Archean Sanukitoid”, which can be compared to the Sanukitoid from Setouchi Belt, Japan in consistence with the melting of enriched peridotite. Thus, a new controversy has been rejuvenated among the tectonic styles between the Archean and modern subduction array. However, the geological documents show that most Mg~# of Archean TTG is higher than the experimental liquids on account of more Mg-rich tholeiites during the Archean. While the dominance of the komatiite rocks in the “greenstone belt” may be the source of the Archean sanukitoids. So they are nothing to do with the subduction environment. Anyhow, it is to be expected that further progress can be achieved in the light of the secular change of the heat dissipation in the Earth, to explain the intrinsic reasoning of this puzzle. |
| |
| Keywords: | adakite magnesian andesite hybridized melt vs slab melt Archean TTG vs Cenozoic TTD |
| 本文献已被 CNKI 维普 万方数据 等数据库收录！ |
|
