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首页> 外文期刊>Contributions to Mineralogy and Petrology >Deep crustal anatexis, magma mixing, and the generation of epizonal plutons in the Southern Rocky Mountains, Colorado
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Deep crustal anatexis, magma mixing, and the generation of epizonal plutons in the Southern Rocky Mountains, Colorado

机译：深层地壳anatexis，岩浆混合，以及南岩石山脉的巨髓的一代，科罗拉多州

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The Never Summer Mountains in north-central Colorado, USA, are cored by two Oligocene, epizonal granitic plutons originally emplaced in the shallow levels of a short-lived (similar to 1 m.y.), small-volume continental magmatic system. The younger Mt. Cumulus stock (28.015 +/- 0.012 Ma) is a syenogranite equivalent compositionally to topaz rhyolites. A comparison to the chemical and isotopic composition of crustal xenoliths entrained in nearby Devonian kimberlites demonstrates that the silicic melts parental to the stock were likely derived from anatexis of local Paleoproterozoic, garnet-absent, mafic lower continental crust. In contrast, the older Mt. Richthofen stock is compositionally heterogeneous and ranges from monzodiorite to monzogranite. Major and trace element abundances and Sr, Nd and Pb isotopic ratios in this stock vary regularly with increasing whole rock wt% SiO2. These data suggest that the Mt. Richthofen stock was constructed from mixed mafic and felsic magmas, the former corresponding to lithosphere-derived basaltic magmas similar isotopically to mafic enclaves entrained in the eastern portions of the stock and the latter corresponding to less differentiated versions of the silicic melts parental to the Mt. Cumulus stock. Zircon U-Pb geochronology further reveals that the Mt. Richthofen stock was incrementally emplaced over a time interval from at least 28.975 +/- 0.020 to 28.742 +/- 0.053 Ma. Magma mixing could have occurred either in situ in the upper crust during basaltic underplating and remelting of an antecedent, incrementally emplaced, silicic intrusive body, or at depth in the lower crust prior to periodic magma ascent and emplacement in the shallow crust. Overall, the two stocks demonstrate that magmatism associated with the Never Summer igneous complex was fundamentally bimodal in composition. Highly silicic anatectic melts of the mafic lower crust and basaltic, mantle-derived magmas were the primary melts in the magma system, with mixing of the two producing intermediate composition magmas such as those from which Mt. Richthofen stock was constructed.
机译：美国北部科罗拉多州的夏季山脉从不夏季山脉，由两个寡核苷植物芯，最初被施加在浅水较近（类似于1 M.Y.），小批量大陆岩浆系统。年轻的Mt.腓骨股（28.015 +/- 0.012 mA）是一种同工组成的Syenogranite，Topaz流鼻耳。与附近的德文伯伯莱斯夹带的地壳Xenopiths的化学和同位素组成的比较表明，硅熔化的父母对股票的父母可能来自于局部古普罗佐，石榴石缺席，MAFIC下欧洲地壳的肝脏。相比之下，较旧的MT.Richthofen股票是合成的异质性，与单泽替莫特到Monzogranite的范围。在此股票中，主要和痕量元素丰富和SR，Nd和Pb同位素比率定期随着整个岩石wt％SiO2的增加而变化。这些数据表明，MT. Richthofen股票由混合的MAFIC和FELSIC岩浆构成，前者对应于岩石圈衍生的玄武岩岩浆类似同位素，在股票的东部夹带中夹带的MAFIC环形，后者对应于较少分化的版本硅状融化的父母对山的父母。锆石U-PB地质学进一步揭示了MT.Richthofen股票在至少28.975 +/- 0.020至28.742 +/- 0.053 mA的时间间隔内逐渐增加。在玄武岩底部底壳期间，岩浆混合可以在上层地壳中原位发生，并且在浅层地壳中的周期性岩浆中的下皮中的较低外壳中的较低地壳中的深度。总体而言，这两股股票表明与夏季的黄昏复杂相关的岩浆广告是在构成中的根本双峰。 MAFIC下地壳和玄武岩的高度硅状熔体是岩浆系统中的初级熔体，其两种产生的中间组成岩浆如诸如从中构建的岩浆。

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