摘要
埃达克岩 ( adakite)是一种特殊的岛弧安山岩、英安岩、流纹岩 (以英安岩最常见 )或英云闪长岩和奥长花岗岩。其地球化学特征表现为 Si O2 56% ,高铝 ( Al2 O3 1 5% ) ,Mg O常小于 3% (很少超过 6% ) ,富钠 ,一般 Na2 O>K2 O,Na2 O含量一般在 4%± ,K2 O含量大多在 1 - 2 %± ,Y和 Yb含量较低 (分别为 1 8μg/g和 1 . 9μg/g) ,Sr含量较高( >40 0 μg/g) ,具正 Eu、正 Sr异常。 87Sr/86 Sr比值常常小于 0 .70 4。埃达克岩是由年轻的( <2 5Ma,因此是热的 )俯冲板片以小角度俯冲、并在 75- 85km深处 (相当于角闪岩 -榴辉岩过渡带 )发生板片部分深融作用形成的。它是板片俯冲作用开始的一种标志。
Adakite is a special kind of island arc andesite, dacite and rhyolite (mainly dacite) or tonalite and trondhjemite. The main geochemical characteristics of adakite are SiO 256%, high Al content (Al 2O 315%), MgO<3% (rarely higher than 6%), Na enrichment with Na 2O>K 2O (Na 2O-4%±; K 2O-1-2%±), very low Y and Yb content (18μg/g and 1.9μg/g, respectively),relatively high Sr content (>400μg/g),and positive Eu and Sr analomy, and 87 Sr/ 86 Sr<0.704. Adakite is generated by young (<25Ma, thus hot) subducted slab dipping continuously at a shallow angle and partial melting at the depth of 75-85 km (amphibolite eclogite transition zone). Adakite may represent the start of subduction of the oceanic crust.
出处
《地质科学》
CAS
CSCD
北大核心
2000年第2期251-256,共6页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
国家自然科学基金资助项目!(编号 4 9872 0 2 7
4 9672 1 4 1 )
