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

Ducea和Chesley Ear-0229470有强有力的证据表明，主要的大陆岩浆弧是在被岩浆静止期隔开的间歇性“爆发”中建立的，尽管造成高岩浆流量的机制尚未解决。此外，耀斑事件似乎是由镁铁质输入推动的，人们认为镁铁质输入主要来自大陆岩石圈地幔。这就要求存在一个比地幔楔形和构造模型中观测到的厚度大一个数量级的地幔岩石圈。然而，这些证据大多来自石器时代地体浅部裸露中发现的次要镁铁质岩石。要么是在高岩浆通量期间，大量的镁铁质输入到弧形下地壳中，而不是(主要)来自岩石圈地幔，要么是如果是，我们需要修改我们对大陆之下俯冲动力学和大陆盖子偶尔向地幔楔体提供熔融-肥沃物质的能力的看法。这些问题将在加利福尼亚州中部沿海圣卢西亚山脉大苏尔地区地壳中弧暴露的镁铁质岩石岩石学研究中得到解决。暴露在那里的基底岩代表了一个倾斜的岩浆弧暴露，代表了从25公里到10公里的古深度。在弧下约25公里处，有从大型英云闪长岩侵入到花岗闪长岩成分的转变，这些成分由典型的内华达山脉基岩的陡峭屏幕分隔，到近水平的面片麻状岩石，其中有大量的镁铁质侵入体。镁铁质侵入岩，现在要么是角闪岩，要么是麻粒岩，在这一水平上非常丰富，由于浮力的原因，它们在那里停滞不前。我们的填图、岩石学、化学和同位素结果将被用来解决大陆弧岩浆作用涉及的地壳与次地壳、岩石圈与软流圈的储集层，并为大型基岩的形成机制提供新的制约因素。

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.