Insights into the tectonomagmatic evolution of NW Mexico: Geochronology and geochemistry of the Miocene volcanic rocks from the Pinacate area, Sonora
Insights into the tectonomagmatic evolution of NW Mexico: Geochronology and geochemistry of the Miocene volcanic rocks from the Pinacate area, Sonora
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DOI：
10.1130/b26053.1
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发表时间：
2008-05
影响因子：
4.9
通讯作者：
J. Vidal-Solano;A. Demant;F. P. Moreno;H. Lapierre;M. Ortega-Rivera;James K. W. Lee
中科院分区：
文献类型：
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作者：
J. Vidal-Solano;A. Demant;F. P. Moreno;H. Lapierre;M. Ortega-Rivera;James K. W. Lee
索诺拉皮纳卡特地区中新世火山岩记录了软流圈上涌和岩石圈减薄导致岩浆源区的渐进变化。40 Ar/ 39 Ar年龄数据，矿物化学，以及主要和微量元素含量允许识别两个火山序列：最古老的玄武岩幕（约。中中新世（12 - 15.5 Ma）序列，由具有过渡碱性特征的梅萨玄武岩、钙碱性英安岩和向过碱性液体演化的高硅流纹岩组成。Sr、Nd和Pb同位素比值揭示了中新世玄武岩的不同源区。最东部的玄武岩具有指示前寒武纪岩石圈地幔源的特征，而最西部的拉斑玄武岩到过渡玄武岩与岩石圈和软流圈地幔的混合有关。流纹是过渡型玄武岩岩浆分离结晶的结果，并受到前寒武纪地壳的轻微混染。化学模拟表明，过碱性流纹与其在上地壳居住期间的同化作用稍高有关，但也与母玄武岩地幔来源的变化有关。同位素特征的时空演化表明：（1）火山活动位于岩石圈主边界之上，（2）岩石圈逐渐变薄，使得大量碱性玄武岩在第四纪期间能够到达地表，形成了Pinacate火山场。地球化学特征与北美板块西缘构造演化之间的相关性表明，岩浆活动源的渐进变化可能与中新世板窗的发育有关。
Miocene volcanic rocks in the Pinacate area, Sonora, record a progressive change in the source of magmatism induced by asthenospheric upwelling and lithospheric thinning. 40 Ar/ 39 Ar age data, mineral chemistry, and major- and trace-element contents allow the identifi cation of two volcanic sequences: an oldest basaltic episode (ca. 20 Ma), and a middle Miocene (12‐15.5 Ma) sequence that consists of mesa basalts with transitional alkali character, calc-alkaline dacites, and high-silica rhyolites evolving toward peralkaline liquids. Sr, Nd, and Pb isotope ratios reveal different sources for the Miocene basalts. The easternmost basalts have signatures indicating a Precambrian lithospheric mantle source, while the westernmost tholeiitic to transitional basalts are related to mixing of lithospheric and asthenospheric mantle. Rhyolites are the result of fractional crystallization of transitional basalt magmas with slight contamination by Precambrian crust. Chemical modeling shows that peralkaline rhyolites are related to slightly higher assimilation during their residence in the upper crust but also to a change in the mantle source of the parent basalt. The evolution of the isotopic signatures in space and time indicates that: (1) the volcanic activity is located over a major lithospheric boundary, i.e., the western limit of the North American Craton; (2) the lithosphere was progressively thinned so that huge volumes of alkalic basalts could access the surface during the Quaternary, building the Pinacate Volcanic Field. Correlation between geochemical signatures and the tectonic evolution of the western margin of the North American Craton shows that a progressive change in the source of magmatism can be related to the development of a slab window during the Miocene.