Variability of Metamorphic P-T-t Paths in Compressional Magmatic Arcs and the Relationship Between Magmatism, Metamorphism, and Crustal Loading: Example from the North Cascades, WA

拟议中的研究将提供关键的约束收缩岩浆弧的加载/高压变质作用的性质，并大大提高数据可用于破译北瀑布的构造历史。研究将整合来自华盛顿瀑布结晶核（CCC）韦纳奇区块（WB）的新的高精度地质年代学、温压学和变质相平衡数据。出版的温压，地质年代学和构造数据的WB已被用来提出构造模型，但是，变质数据在很大程度上是不足以解决一些重要的问题。例如，构造解释取决于整个WB是否经历了同步加载和高压变质作用，以及WB中部火成岩侵入体的高压变质作用的时间。然而，有几个可靠的年龄峰变质和少数的P-T-t路径确定的中部和北方WB。现有的数据包括基于矿物边缘化学的P-T估计值、基于分带的石榴石核生长的P-T估计值和基于角闪石中Al的岩体侵位的P估计值（Ague布兰登，1996年）。详细的数据可用于东北边缘的山。Stuart岩基（Stowell Tinkham，1999; Tinkham Stowell，2000 a，2000 b; Tinkham in prep. 2）。PI的初步定量P-T-t路径变质作用表明，区域石榴石的生长晚于山。史都华地质年代学和岩石学数据是兼容的后侵入变质可能涉及一个小的P增加。研究将结合石榴石Sm-Nd年龄和石榴石生长条件的山北部。斯图尔特·巴特利斯。 这些数据将被用来开发定量的P-T-t路径，将补充现有的数据东北边缘的岩石。梨湖正片麻岩和韦纳奇岭条带状片麻岩的变质P-T-t轨迹和新的锆石U-Pb年龄将被用来限制变质作用的热源。石榴石的年龄将由石榴石岩石的Sm-Nd等时线估算。P和T的初始石榴石生长将估计从矿物成分和伪截面，补充P和T从平衡温压。锆石U-Pb年代学将为带状片麻岩和梨湖正片麻岩中的岩浆体提供临界年龄，这些岩浆体可能在变质作用期间提供了大量的热量。地质年代学和温压数据将在结构数据的背景下进行解释，以限制变形的条件和时间。这些数据的整合将有助于确定WB变质历史，并阐明变质作用和随后的冷却如何与岩浆弧深成岩作用和变形。它还将记录如何详细的石榴石温压和年代学技术可以用来提取复杂的构造历史。描述岩浆弧中变质/造山过程的构造模型只有在详细描述了变质P-T-t路径之后才能进行批判性评价，这些路径在空间和时间上与深成岩作用和变形有关。这一研究结果将有助于区分岩体对流热传递引起的变质作用和地壳增厚后的传导热传递。

Proposed research will provide critical constraints on the nature of loading/high pressure metamorphism in contractional magmatic arcs, and greatly enhance data available for deciphering the tectonic history of the North Cascades. Research will integrate new high precision geochronologic, thermobarometric, and metamorphic phase equilibria data from theWenatchee Block (WB), Cascades Crystalline Core (CCC) of Washington. Published thermobarometric, geochronologic, and structural data for the WB have been used to propose tectonic models; however, the metamorphic data are largely inadequate to resolve some of theimportant problems. For example, tectonic interpretations hinge on whether the entire WB experienced synchronous loading and high-pressure metamorphism, and the timing of high-pressure metamorphism with respect to igneous intrusions in the central WB. Yet, there are few reliable ages for peak metamorphism and few P-T-t path determinations for the central and northern WB. Available data comprise P-T estimates based on mineral rim chemistry, P-T estimates for growth of garnet cores based on zoning, and P estimates for pluton emplacement based on Al in hornblende (Ague & Brandon, 1996). Detailed data are available for the NE margin of the Mt. Stuart batholith (Stowell & Tinkham, 1999; Tinkham & Stowell, 2000a, 2000b; Tinkham in prep. 2). The PI's preliminary quantitative P-T-t paths for metamorphism indicate that regional garnet growth postdates the Mt. Stuart. Geochronologic and petrologic data are compatible with post intrusion metamorphism likely involving a small P increase. Research will integrate garnet Sm-Nd ages and garnet growth conditions north of the Mt. Stuart batholith. These data will be used to develop quantitative P-T-t paths that will complement existing data for the NE edge of the Batholith. Metamorphic P-T-t paths and new U-Pb zircon ages for orthogneisses at Pear Lake and within the Banded Gneiss on Wenatchee Ridge will be used to constrain the heat source for metamorphism. Ages for garnet will be estimated from garnet - rock Sm-Nd isochrons. P and T of initial garnet growth will be estimated from mineral compositions and pseudosections, supplemented with P and T from equilibrium thermobarometry. U-Pb zircon geochronology will provide critical ages for magmatic bodies in the Banded Gneiss and the Pear Lake orthogneiss that may have provided significant heat during metamorphism. Geochronologicand thermobarometric data will be interpreted in the context of structural data to place constraints on the conditions and timing of deformation. Integration of these data will help define the WB metamorphic history, and elucidate how metamorphism and subsequent cooling relates to magmatic arc plutonism and deformation. It will also document how detailed garnet thermobarometric and chronologic techniques can be used to extract complex tectonic histories. Tectonic models describing metamorphic/orogenic processes in a magmatic arc can only be critically evaluated after details of metamorphic P-T-t paths have been described, and these paths spatially and temporally related to plutonism and deformation. The results of this study will help to distinguish between metamorphism resulting from advective heat transfer by plutons and conductive heat transfer after crustal thickening.