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首页> 外文期刊>International Geology Review >Reappraisal of the Geology and Geochemistry of Volcan Zamorano, Central Mexico: Implications for Discriminating the Sierra Madre Occidental and Mexican Volcanic Belt Provinces
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Reappraisal of the Geology and Geochemistry of Volcan Zamorano, Central Mexico: Implications for Discriminating the Sierra Madre Occidental and Mexican Volcanic Belt Provinces

机译:墨西哥中部萨莫拉诺火山的地质和地球化学的重新评估:区分马德雷山脉西部和墨西哥火山带省份的含义

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We report new geological, ~(40)Ar/~(39)Ar geochronology, and geochemical data (major and trace dements, and Sr, Nd, and Pb isotopic ratios) on andesitic to dacitic rocks collected from Volcan Zamorano and on rhyolitic ignimbrites from the surrounding area. These data better constrain the relationship of two major volcanic provinces of Mexico: the mid-Tertiary Sierra Madre Occidental (SMO) and the Miocene to Recent Mexican Volcanic Belt (MVB). Structurally, the SMO and MVB show different extensional styles. The SMO was affected by east-west extension mainly during the Oligocene and middle Miocene, whereas the MVB was affected by extensional deformation during middle-to-late Miocene and Plio-Quaternary times, although reactivation of the older structural systems, such as the NNW-SSE system, has occurred in more recent times. The new geological data from the study area are consistent with the ~(40)Ar/~(39)Ar dates. The andesitic and dacitic rocks from Volcan Zamorano are about 10 Ma. These rocks, along with nearby andesitic and basaltic volcanoes, mark a relatively early phase of the MVB. The basaltic to dacitic rocks show the following ranges for Sr, Nd, and Pb isotopic ratios: (~(87)Sr/~(86)Sr)_i 0.70362-0.70474; (~(143)Nd/~(144)Nd)_i 0.51258-0.51286; ~(206)Pb/~(204)Pb 18.38-18.81; ~(207)Pb/~(204)Pb 15.57-15.63; and ~(208)Pb/~(204)Pb 38.27-38.70. For SMO ignimbrites (approx 30-28 Ma) cropping out in the Zamorano area, (~(87)Sr/~(86)Sr)_i are slightly higher (0.70407-0.70557), and (~(143)Nd/~(144)Nd) are somewhat lower (0.51250-0.51253). Pb-isotope ratios for these ignimbrites are also higher (about 18.84-18.87, 15.65, and 38.78-38.82, respectively) than for basaltic to dacitic rocks from Volcan Zamorano and the surrounding area. Most studied rocks from both provinces seem to contain a crustal component. The ignimbrites are chemically and isotopically similar to rhyolitic and ignimbritic rocks sampled from other areas of the SMO. Our study of Volcan Zamorano shows that the transition from SMO to MVB was rather sudden and not a gradual process.
机译:我们报告了从Volcan Zamorano和流纹岩火成岩上收集的安山岩到大晶岩的新地质学,〜(40)Ar /〜(39)Ar地质年代学和地球化学数据(主要和微量元素,以及Sr,Nd和Pb同位素比)。从周围地区。这些数据更好地限制了墨西哥两个主要火山省的关系:第三纪中西部的马德雷山脉(SMO)和中新世与最近的墨西哥火山带(MVB)。在结构上,SMO和MVB显示不同的扩展样式。 SMO主要在渐新世和中新世中期受东西向伸展的影响,而MVB受中新世晚期至上新世和上新世时期的伸展变形的影响,尽管较老的结构系统(如NNW)被重新激活了。 -SSE系统,是最近发生的。研究区的新地质数据与〜(40)Ar /〜(39)Ar日期一致。 Volcan Zamorano的安山岩和大晶岩约10 Ma。这些岩石以及附近的安第斯和玄武岩火山标志着MVB的相对早期。玄武岩到大晶岩的Sr,Nd和Pb同位素比范围如下:(〜(87)Sr /〜(86)Sr)_i 0.70362-0.70474; (〜(143)Nd /〜(144)Nd)_i 0.51258-0.51286; 〜(206)Pb /〜(204)Pb 18.38-18.81; 〜(207)Pb /〜(204)Pb 15.57-15.63;和〜(208)Pb /〜(204)Pb 38.27-38.70。对于Zamorano地区播种的SMO火成岩(大约30-28 Ma),(〜(87)Sr /〜(86)Sr)_i稍高(0.70407-0.70557),和(〜(143)Nd /〜( 144)Nd)稍低(0.51250-0.51253)。这些火成岩的铅-同位素比率也比沃尔坎·扎莫拉诺火山和周围地区的玄武岩到大晶岩更高,分别为18.84-18.87、15.65和38.78-38.82。来自这两个省的大多数研究过的岩石似乎都含有地壳成分。这些火成岩在化学和同位素上类似于从SMO其他地区采样的流纹岩和火成岩。我们对Volcan Zamorano的研究表明,从SMO到MVB的过渡相当突然,而不是一个渐进过程。

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