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首页> 外文期刊>Geosphere >Time scales and processes of Cordilleran batholith construction and high-Sr/Y magmatic pulses: Evidence from the Bald Mountain batholith, northeastern Oregon
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Time scales and processes of Cordilleran batholith construction and high-Sr/Y magmatic pulses: Evidence from the Bald Mountain batholith, northeastern Oregon

机译：堇青石岩床构造和高Sr / Y岩浆脉冲的时间尺度和过程：来自俄勒冈州东北部秃山岩床的证据

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Cordilleran granitic batholiths (sensu lato) preserve information about time scales and processes of upper crustal magmatic arc construction during Mesozoic subduction and mountain building. The Bald Mountain batholith in northeastern Oregon (USA) is a classic example of a composite, incrementally constructed batholith that formed during terrane amalgamation outboard of the western U.S. Cordillera. Whole-rock geochemistry and zircon trace element, U-Pb, Lu-Hf, and O isotopic data reveal that batholith construction occurred over a??15 Ma, commencing with the syncollisional emplacement of small, low-Sr/Y (40) norite-granite plutons from 157 to 155 Ma. The next phase of magmatism was postcollisional and dominated by high-Sr/Y (40) tonalite-granodiorite magmatism that produced the main mass of the batholith, including the granodiorite of Anthony Lake (147 Ma) and the tonalite of Bald Mountain (145a€“141 Ma). Zircons from the norite-granite suite display a narrow range in initial ?μHf of 7.2a€“7.7 and elevated ?′18O (Zrn) ranging from 8.2a€° to 10.0a€° (excluding one outlier). Zircons from the later granodiorite-tonalite suite show a similar range of initial ?μHf values (6.3a€“8.9) and ?′18O (7.1a€°a€“10.0a€°), indicating a similar history of interaction with evolved crustal material. Modeling of whole-rock and zircon geochemistry indicates that both the low- and high-Sr/Y magmas composing the main phase of the batholith were generated by dehydrationa€“partial melting of mafic arc crust (e.g., amphibolite), leaving behind a plagioclase-poor restite, which was garnet granulite in the case of the high-Sr/Y magmas. Final magma compositions in both suites were affected by assimilation of supracrustal material either at depth or during ascent. We suggest that high-Sr/Y magmas in the Bald Mountain batholith were generated by partial melting of thickened arc crust a??10 m.y. after arc-arc collision began at 159a€“154 Ma. Heat to drive lower crustal melting was conveyed by an increase in mantle power input as a result of renewed subduction-related magmatism. Mixing and homogenization in the lower crust involving mantle-derived basalts and crustally derived partial melts can account for the geochemical variation we observe in tonalites and granodiorites in the Bald Mountain batholith.
机译：山脉花岗岩基岩（中苏拉托）保存了中生代俯冲和山区建造过程中上地壳岩浆弧构造时间尺度和过程的信息。美国俄勒冈州东北部的秃山岩基是典型的例子，它是在美国西部山脉外侧的地层合并过程中形成的，复合构造的岩基。全岩地球化学和锆石微量元素，U-Pb，Lu-Hf和O同位素数据表明，岩基构造发生在a ?? 15 Ma以上，始于小，低Sr / Y（<40）的共生沉积。 157至155 Ma的红土花岗岩花岗岩体。下一阶段的岩浆作用是碰撞后，由高Sr / Y（> 40）的斜纹岩-闪长闪长岩岩浆作用主导，形成了岩基岩的主体，包括安东尼湖的花岗闪长岩（147 Ma）和秃头山的斜纹岩（145a） €“ 141 Ma）。来自红土-花岗岩套件的锆石的初始μμHf范围很窄，为7.2a-7.7，升高的α'18O（Zrn）范围为8.2a- 10.0a（不包括一个异常值）。后来的花岗闪石-tonalite套件中的锆石显示出相似的初始？μHf值范围（6.3a？8.9）和？'18O（7.1a？a？10.0a？°），表明与演化的相互作用历史相似。地壳材料。整个岩石和锆石地球化学模型表明，构成岩基主相的低和高Sr / Y岩浆都是通过脱水作用产生的：“镁铁质弧形地壳（例如，角闪石）的部分融化，留下了斜长石-较差的重晶石，在高Sr / Y岩浆中为石榴石花岗石。两组中的最终岩浆成分在深度或上升过程中均受到表壳物质同化的影响。我们认为，秃山基岩中的高Sr / Y岩浆是由加厚的地壳a ?? 10 m.y的部分融化产生的。弧弧碰撞开始于159a€154 Ma。由于俯冲相关的岩浆作用的更新，地幔动力输入的增加传递了驱动下地壳熔融的热量。在下地壳中的混合和均质化涉及地幔衍生的玄武岩和地壳衍生的部分熔体，这可以解释我们在秃头山岩床的同色岩和花岗闪长岩中观察到的地球化学变化。

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