Strontium isotope evidence for petrogenesis of Mexican andesites
Strontium isotope evidence for petrogenesis of Mexican andesites
复制标题
墨西哥安山岩岩石成因的锶同位素证据
作者：
S. Moorbath;R. Thorpe;I. Gibson
墨西哥火山带(MVB)由几座非活火山和活火山组成(图1)。活火山包括太平洋海岸附近的Colima1，2和Ceboruco3，墨西哥中部的Popocatépetl和Izattcihuatl，以及靠近加勒比海海岸的San Martin4。MVB位于厚约40公里的陆壳5，6上，与墨西哥中部下方的科科斯板块俯冲有关。板块俯冲与MVB的部署之间的联系并不简单，因为后者与中美洲海沟3成约20°的夹角。这种复杂性可能与大陆地壳的结构5有关，也可能与俯冲作用和伸展作用4的结合有关。MVB火山作用最突出的产物是由中级熔岩和火山碎屑岩连续喷发形成的大型复合火山3，8。图1所示的活火山熔岩主要是钙碱性安山岩和英安岩3，8-10。相反，最东端的活火山San Martin是由苦味玄武岩-玄武岩-碱性玄武岩-夏威夷岩组合4，11，12建造的熔岩。这个火山区发生在MVB方向的变化，因此可能与与MVB破坏性边缘背景有关的伸展或断裂有关。4)。在这里，我们报道了来自Ceboruco、Colima和San Martin的熔岩的新的锶同位素数据。这些数据和已发表的墨西哥中部新生代火山岩的锶同位素数据13构成了墨西哥火山岩成因的证据。
THE Mexican volcanic belt (MVB) consists of several inactive and active volcanoes1 (Fig. 1). The active volcanoes include Colima1,2 and Ceboruco3 near the Pacific coast, Popocatépetl and Iztaccihuatl in central Mexico, and San Martin4 close to the Caribbean coast. The MVB rests on continental crust approximately 40 km thick5,6, and is associated with subduction of the Cocos plate below central Mexico3,7. The link between plate subduction and the disposition of the MVB is not simple since the latter makes an angle of about 20° with the Middle America Trench3. This complexity might be related to the structure of the continental crust5, or to a combination of subduction and extensional processes4. The most prominent products of volcanism of the MVB are the large composite volcanoes built up from successive eruptions of intermediate lavas and pyroclastic rocks3,8. The lavas of the active volcanoes shown in Fig. 1 are dominantly calc-alkaline andesite and dacite3,8–10. In contrast, the easternmost active volcano, San Martin, is built from lavas of a picritic basalt–basanitoid–alkali basalt–hawaiite association4,11,12. This volcanic area occurs at a change in direction of the MVB and might therefore be linked with extension or fracturing associated with the destructive margin setting of the MVB (ref. 4). Here we report new Sr isotope data for lavas from Ceboruco, Colima, and San Martin. These data, and published Sr isotope data for Cainozoic volcanics from central Mexico13 constitute evidence for petrogenesis of Mexican volcanic rocks.