Quaternary volcanism near the Valley of Mexico: implications for subduction zone magmatism and the effects of crustal thickness variations on primitive magma compositions
Quaternary volcanism near the Valley of Mexico: implications for subduction zone magmatism and the effects of crustal thickness variations on primitive magma compositions
复制标题
墨西哥谷附近的第四纪火山活动：对俯冲带岩浆作用的影响以及地壳厚度变化对原始岩浆成分的影响
DOI：
10.1007/s004100050513
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发表时间：
1999
影响因子：
3.5
通讯作者：
I. Carmichael
中科院分区：
文献类型：
--
作者：
P. Wallace;I. Carmichael
摘要墨西哥山谷和墨西哥周围地区以及墨西哥中部的莫雷洛斯州，除了波波卡特佩特、伊兹塔奇瓦特尔和内瓦多德托卢卡等大型复合火山外，还有250多个第四纪喷发喷口。喷发的喷口包括煤渣和熔岩锥，盾形火山，以及孤立的安山岩和英安质熔岩流，在形成墨西哥山谷南端的奇奇纳津山脉中数量最多。奇奇纳津火山田(CVF)是东西走向的墨西哥火山带(MVB)的一部分，MVB是一条横跨墨西哥的与俯冲有关的火山弧。CVF(∼50 Km)之下的地壳厚度是MVB中最大的，也是世界上发现的任何弧形中最大的区域之一。从CVF喷口喷发的熔岩和火山岩包括碱性玄武岩和钙碱性玄武岩安山岩、安山岩和英安岩。碱性群和钙碱性群都含有原始品种，其全岩镁、镁、镍含量和液态橄榄石成分(≤FO90)接近地幔橄榄岩部分熔融的预期。原始品种还表现出广泛的不相容微量元素丰度(如Ba210-1080 ppm；Ce25-100 ppm；Zr130-280 ppm)。来自CVF和MVB以西其他地区的原始钙碱性岩的数据与下伏地幔楔体中的岩浆生成一致，该地幔楔体亏损钛、锆和Nb，富含大离子亲石元素(K、BA、Rb)和轻稀土(La、Ce)元素。根据钛和锆数据估计的CVF原始钙碱性岩浆的部分熔融程度低于MVB以西地壳较薄地区的部分熔融程度。CVF中原始钙碱性岩浆独特的主量元素组成(低CaO和Al_2O_3，高SiO_2)表明，在这一厚地壳区域之下有更难熔的地幔来源。相反，来自CVF和MVB其他地区的原始碱性岩浆的成分与墨西哥盆地和山脉省弧后喷发的板内型碱性玄武岩的成分相似。这些相似之处与MVB下地幔楔体中板条诱导的对流导致软流圈地幔从弧后平流到岩浆产生区的假设相一致。MVB原始岩浆的微量元素系统学显示，俯冲过程中地幔楔体的富集度和与先前提取的碱性至亚碱性玄武岩熔体有关的地幔不均匀成分都具有很大的变异性。
Abstract The Valley of Mexico and surrounding regions of Mexico and Morelos states in central Mexico contain more than 250 Quaternary eruptive vents in addition to the large, composite volcanoes of Popocatépetl, Iztaccíhuatl, and Nevado de Toluca. The eruptive vents include cinder and lava cones, shield volcanoes, and isolated andesitic and dacitic lava flows, and are most numerous in the Sierra Chichináutzin that forms the southern terminus of the Valley of Mexico. The Chichináutzin volcanic field (CVF) is part of the E-W-trending Mexican Volcanic Belt (MVB), a subduction-related volcanic arc that extends across Mexico. The crustal thickness beneath the CVF (∼50 km) is the greatest of any region in the MVB and one of the greatest found in any arc worldwide. Lavas and scoriae erupted from vents in the CVF include alkaline basalts and calc-alkaline basaltic andesites, andesites, and dacites. Both alkaline and calc-alkaline groups contain primitive varieties that have whole rock Mg#, MgO, and Ni contents, and liquidus olivine compositions (≤Fo90) that are close to those expected of partial melts from mantle peridotite. Primitive varieties also show a wide range of incompatible trace element abundances (e.g. Ba 210–1080 ppm; Ce 25–100 ppm; Zr 130–280 ppm). Data for primitive calc-alkaline rocks from both the CVF and other regions of the MVB to the west are consistent with magma generation in an underlying mantle wedge that is depleted in Ti, Zr, and Nb and enriched in large ion lithophile (K, Ba, Rb) and light rare earth (La, Ce) elements. Extents of partial melting estimated from Ti and Zr data are lower for primitive calc-alkaline magmas in the CVF than for those from the regions of the MVB to the west where the crust is thinner. The distinctive major element compositions (low CaO and Al2O3, high SiO2) of the primitive calc-alkaline magmas in the CVF indicate a more refractory mantle source beneath this region of thick crust. In contrast, primitive alkaline magmas from the CVF and other regions of the MVB show compositional similarities to intraplate-type alkali basalts erupted behind the arc in the Mexican Basin and Range province. These similarities are consistent with the hypothesis that slab-induced convection in the mantle wedge beneath the MVB causes advection of asthenospheric mantle from behind the arc to the region of magma generation. Trace element systematics of primitive magmas in the MVB reveal substantial variability in both the extent of mantle wedge enrichment by subduction processes and in the composition of mantle heterogeneities that are related to previous extraction of alkaline to sub-alkaline basaltic melts.