Variations in andean andesite compositions and their petrogenetic significance
Variations in andean andesite compositions and their petrogenetic significance
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安第斯安山岩成分变化及其成岩意义
DOI：
10.1016/0040-1951(79)90101-x
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发表时间：
1979
期刊：
影响因子：
2.9
通讯作者：
P. Francis
中科院分区：
文献类型：
--
作者：
R. Thorpe;P. Francis
安第斯山脉存在三个活动安山岩火山带--哥伦比亚和厄瓜多尔的北部带(5°N-2°S)，主要位于秘鲁南部和智利北部的中部带(16°S-28°S)和主要位于智利南部的南部带(33°S-52°S)。北带以玄武岩安山岩为主，中部以安山岩-英安岩和点火岩为主，南带以高铝玄武岩、玄武岩和安山岩为主。苏珊岩和碱性玄武岩-粗面岩组合火山岩分布在活动火山链以东的零星地区，北部和中部火山带位于向东倾斜的贝尼奥夫带上方140公里，而南部火山带仅位于贝尼奥夫带上方90公里处。大陆地壳厚度在中部以下约70公里，但在北部和南部火山带下方30-45公里。微量元素和同位素数据支持火山产物与其构造环境之间的相关性。中带安山岩熔岩的Si、K、Rb、Sr、Ba值和初始锶同位素比值均高于北带和南带熔岩。南部地区高铝玄武岩的Ce/Yb比值低于其他地区的火山岩。安第斯安山岩岩浆是部分熔融、分离结晶和地幔深部“混染”过程以及地壳混染和分离结晶作用综合作用的结果。安第斯山脉中部安山岩成分的变化反映了部分熔融程度的减小，或分离结晶的增加，或向东传递的“污染”的增加。安第斯链上的变化表明中央带安山岩的地壳贡献很大，南部带的高铝玄武岩和玄武岩来自于比其他火山岩更浅的地幔源区。中央带英安岩-流纹岩点火岩与安山岩同源，可能是安山岩岩浆在厚陆壳隆升过程中分离结晶的结果。活动火山链中橄榄岩和碱性玄武岩的产出是由于远离俯冲带的地幔橄榄岩部分熔融所致。
Three linear zones of active andesite volcanism are present in the Andes — a northern zone (5°N–2°S) in Colombia and Ecuador, a central zone (16°S–28°S) largely in south Peru and north Chile and a southern zone (33°S–52°S) largely in south Chile. The northern zone is characterized by basaltic andesites, the central zone by andesite—dacite lavas and ignimbrites and the southern zone by high-alumina basalts, basaltic andesites and andesites. Shoshonites and volcanic rocks of the alkali basalt—trachyte association occur at scattered localities east of the active volcanic chain,The northern and central volcanic zones are 140 km above an eastward-dipping Benioff zone, while the southern zone lies only 90 km above a Benioff zone. Continental crust is ca. 70 km in thickness below the central zone, but is 30–45 km thick below northern and southern volcanic zones. The correlation between volcanic products and their structural setting is supported by trace element and isotope data. The central zone andesite lavas have higher Si, K, Rb, Sr and Ba, and higher initial Sr isotope ratios than the northern or southern zone lavas. The southern zone high-alumina basalts have lower Ce/Yb ratios than volcanics from the other zones. In addition, the central zone andesite lavas show a well-defined eastward increase in K, Rb and Ba and a decrease in Sr.Andean andesite magmas are a result of a complex interplay of partial melting, fractional crystallization and “contamination” processes at mantle depths, and contamination and fractional crystallization in the crust. Variations in andesite composition across the central Andean chain reflect a diminishing degree of partial melting or an increase in fractional crystallization or an increase in “contamination” passing eastwards. Variationsalongthe Andean chain indicate a significant crustal contribution for andesites in the central zone, and indicate that the high-alumina basalts and basaltic andesites of the southern zone are from a shallower mantle source region than other volcanic rocks. The dacite-rhyolite ignimbrites of the central zone share a common source with the andesites and might result from fractional crystallization of andesite magma during uprise through thick continental crust. The occurrence of shoshonites and alkali basalts eat of the active volcanic chain is attributed to partial melting of mantle peridotite distant from the subduction zone.