A review of the Pikes Peak batholith, Front Range, central Colorado A “type example” of A-type granitic magmatism
A review of the Pikes Peak batholith, Front Range, central Colorado A “type example” of A-type granitic magmatism
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科罗拉多州中部前岭派克峰岩基回顾 A 型花岗质岩浆作用的“典型实例”
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发表时间：
1999
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影响因子：
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通讯作者：
K. Chamberlain
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作者：
Diane R. Smith;J. Noblett;R. Wobus;D. Unruh;K. Chamberlain
科罗拉多中部1.08 Ga的派克峰复合岩基是A型花岗岩系统的典型实例。从20世纪70年代到90年代，详细的现场关系，矿物学，主要和微量元素成分，以及同位素地球化学的派克峰岩石被记录下来，他们揭示了两个化学组的存在，钾和钠系列。钾质系列（SiO2含量64-78 wt %）包括派克峰花岗岩，主要是粗粒黑云母±角闪石正长花岗岩和少量二长花岗岩，占岩基的主导地位。钾质岩系还包括在整个岩基中的许多小的晚期侵入岩中发现的细至中等粒度的黑云母花岗岩。钠质系列存在于7个岩体中，包括辉长岩、闪长岩、正长岩/石英正长岩、铁橄榄石和钠质角闪石花岗岩等多种岩石类型（SiO2含量为44%-78%）。钠质系列和钾质系列的岩石学和地球化学特征的差异表明不同的成岩历史。一些工作者利用主量和微量元素以及锶和氧同位素数据假设，幔源碱性玄武岩经历了晶体分馏，并与下地壳岩石反应，生成钠质系列的正长岩浆，随后进一步分馏，生成钠质花岗岩。最近的研究涉及氧逸度的估计，沿着额外的微量元素和钕同位素数据，也支持钠质系列的玄武岩分馏模型，但建议只有轻微的地壳参与。辉长岩和Different脉与钠质系列似乎已经来自地幔来源，以前已受到俯冲事件的影响，钕同位素和微量元素数据的基础上。一些学者认为钾质岩系也是由正长岩和/或玄武质岩浆的分馏作用以及与中地壳而不是下地壳的反应形成的。其他工作者提出了一个模型，其中成因的钾质系列占主导地位的部分熔融涉及英云闪长岩来源，分馏和岩浆混合发挥次要作用，在钾质花岗岩类之间产生成分多样性。因此，派克峰岩基是由至少两种岩石成因不同的花岗岩类型侵位而形成的，这两种花岗岩类型在空间和时间上紧密地侵位在一起，并表现出典型的A型花岗岩的地球化学特征。
The ∼1.08-Ga Pikes Peak composite batholith of central Colorado is a type example of an A-type granitic system. From the 1970s through the 1990s, details of the field relations, mineralogy, major and trace element compositions, and isotopic geochemistry of Pikes Peak rocks were documented, and they reveal the existence of two chemical groups, a potassic and a sodic series. The potassic series (∼64–78 wt % SiO 2 ) includes the Pikes Peak Granite, which is mostly coarse-grained biotite ± hornblende syenogranite and minor monzogranite that dominates the batholith. The potassic series also includes fine- to medium-grained biotite granite found in numerous, small, late-stage plutons throughout the batholith. The sodic series is found in seven plutons comprised of a wide range of rock types (∼44–78 wt % SiO 2 ), including gabbro, diabase, syenite/quartz syenite, and fayalite and sodic amphibole granite. Differences in petrologic and geochemical characteristics between the sodic and potassic series indicate different petrogenetic histories. Major and trace element and strontium and oxygen isotopic data were used by some workers to hypothesize that mantle-derived alkali basalt underwent crystal fractionation and reaction with lower crustal rocks to generate syenitic magmas of the sodic series, which subsequently underwent further fractionation to produce sodic granites. Recent studies involving estimates of oxygen fugacities, along with additional trace element and neodymium isotopic data, also support a basalt fractionation model for the sodic series, but suggest only minor crustal involvement. Gabbros and diabase dikes associated with the sodic series appear to have been derived from mantle sources that previously had been affected by a subduction event, based on neodymium isotopic and trace element data. Some workers propose that the potassic series also formed by fractionation of syenitic and/or basaltic magmas coupled with reaction with intermediate rather than lower crust. Other workers propose a model in which genesis of the potassic series was dominated by partial melting involving tonalitic sources, with fractionation and perhaps magma mixing playing subordinate roles in generating compositional diversity among the potassic granitoids. The Pikes Peak batholith thus formed by emplacement of at least two petrogenetically different granite types, which were emplaced close together in space and time and which exhibit geochemical characteristics typical of A-type granites.