Igniting Continental Arcs; A Petrologic Study Of Mafic Rocks And Peridotites From The Coast Ridge Belt, Santa Lucia Mountains (California)

点燃大陆弧；

• 批准号: 0229470
• 负责人: Mihai Ducea
• 金额: $ 22.17万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-01-01 至 2005-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0229470&HistoricalAwards=false
• 关键词: Igniting; Continental; Arcs; Petrologic; Study

Ducea and Chesley EAR-0229470 There is strong evidence that major continental magmatic arcs are being built in episodic "flare-ups" separated by periods of magmatic quiescence, although the mechanisms responsible for the high magmatic fluxes are not resolved. Moreover, flare- up events appears to be fueled by a mafic input, thought to be largely derived from continental lithospheric mantle. This requires the existence of a mantle lithosphere an order of magnitude thicker than allowed by observations in mantle wedges and tectonic models. However, most of this evidence comes from subordinate mafic rocks found in shallow exposures of batholithic terranes. Either the voluminous mafic input to the arc lower crust is not (predominantly) from the lithospheric mantle during high magmatic fluxes, or if it is, we need to revise our thinking regarding the dynamics of subduction beneath continents and the ability of continental lids to episodically feed melt-fertile mass to the mantle wedge. These issues will be addressed in a petrologic study of mafic rocks from a mid-crustal arc exposure in the Big Sur area of the Santa Lucia Mountains, central coastal California. The basement rocks exposed there represent a tilted exposure of a magmatic arc representing paleo-depths ranging from 25 km to 10 km. At about 25 km beneath the arc there is a transition from large intrusions of tonalite to granodiorite composition separated by steeply dipping screens typical of the Sierra Nevada batholith to near horizontal, foliated gneissic rocks with numerous mafic intrusions. Mafic intrusions, now either amphibolites or granulites, are abundant at this level, where they stalled due to buoyancy reasons. Our mapping, petrographic, chemical and isotopic results will be used to resolve crustal vs. sub-crustal, and lithospheric vs. asthenospheric reservoirs involved in continental arc magmatism and provide new constraints for the mechanisms of generation of large batholiths.

强有力的证据表明，主要的大陆岩浆弧是在由岩浆静止期分开的间歇性“爆发”中形成的，尽管造成高岩浆通量的机制尚未解决。此外，爆发事件似乎是由一种被认为主要来自大陆岩石圈地幔的岩浆输入所推动的。这要求地幔岩石圈的存在比在地幔楔和构造模型中观测到的要厚一个数量级。然而，这些证据大多来自于在底石器时代地体的浅层暴露中发现的次级基性岩石。在岩浆高通量时期，流入弧下地壳的大量镁质要么不是（主要）来自岩石圈地幔，要么就是如此，我们就需要修正我们对大陆俯冲动力学的看法，以及大陆盖偶尔向地幔楔提供熔融肥沃物质的能力。这些问题将在加利福尼亚中部沿海圣卢西亚山脉大苏尔地区中地壳弧暴露的基性岩石的岩石学研究中得到解决。暴露在那里的基底岩石代表了岩浆弧的倾斜暴露，代表了古深度从25公里到10公里不等。在弧下约25公里处，有一个从大型的闪长岩侵入体过渡到花岗闪长岩组成的过渡，由内华达山脉典型的陡倾筛屏分隔，到近水平的片理片麻岩，其中有许多基性侵入体。镁质侵入岩，现在要么是角闪岩，要么是麻粒岩，在这一水平丰富，由于浮力的原因，它们停滞不前。我们的填图、岩石学、化学和同位素结果将用于解决大陆弧岩浆作用下的地壳与次地壳、岩石圈与软流圈储层，并为大型岩基的形成机制提供新的约束条件。