Deciphering the Tectonic History of Slowly Cooled Precambrian Polymetamorphic Terranes in the American Southwest

破译美国西南部缓慢冷却的前寒武纪多变质地体的构造历史

• 批准号: 0126148
• 负责人: Christopher Andronicos
• 金额: $ 2.66万
• 依托单位: University of Texas at El Paso
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-03-01 至 2003-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0126148&HistoricalAwards=false
• 关键词: Deciphering; Tectonic; History; Slowly; Cooled

The Proterozoic tectonic history of the American southwest is the subject of considerable controversy. Controversy revolves around the nature of ~1.4 Ga plutonism and tectonism and its relationship to Paleoproterozoic (1.8-1.6 Ga) crustal accretion. To help resolve this question The P.I. will investigate the Cimarron Mountains of northern New Mexico and the Needle Mountains of southwestern Colorado. These two regions preserve deformation and plutonic histories that record both Paleoproterozoic accretion and subsequent Mesoproterozoic reactivation. 1.4 Ga metamorphism has erased the Paleoproterozoic thermal signature in most of northern New Mexico and southern Colorado. Therefore, these two proposed study areas may provide the only opportunity to decipher the Paleoproterozoic metamorphic and cooling history in northern New Mexico and southern Colorado.The Cimarron Mountains contain an upper amphibolite grade block and a greenschist grade block separated by the Fowler Pass Shear Zone (FPSZ). Metamorphic mineral assemblages across the shear zone suggest up to 10 km of vertical separation. Cooling ages from the high-grade block suggest high-grade metamorphism occurred at ~1.4 Ga. In contrast, rocks in the low-grade block record a 1678 Ar 40 /Ar 39 cooling age: this is the oldest cooling age reported in northern New Mexico. Detailed structural analysis of the two blocks and the F.P.S.Z. will be undertaken to clarify the deformation history and tectonic significance of this structure and its relationship to the metamorphic evolution of the region.The Needle Mountains record a much different history. Paleoproterozoic supracrustal rocks in this region are divided into two packages. The Uncompahgre Formation, consisting of quartzites and schists, is regionally metamorphosed to the greenschist facies. These rocks rest on a sheared unconformity above the second package, which is composed of amphibolite facies gneiss, migmatite, and schist. The 1.46 Ga Eolus granite intrudes both packages and has a well-developed contact aureole with peak metamorphic assemblages including sillimanite and K-feldspar. However, many of the rocks far from the granite have assemblages that appear to be unaffected by 1.4 Ga metamorphism. This situation may provide the opportunity to determine the thermal structure of the crust during Paleoproterozic orogenesis as well as during the 1.4 Ga overprint. In order to better understand the role of 1.4 Ga tectonics in the evolution of southwest North America, the P.I. will undertake a structural, metamorphic, and geochronologic study of the two ranges. Both of these areas are similar in having 1.4 Ga metamorphic features and Paleoproterozoic thermal and metamorphic signatures. These regions are therefore well suited to determine which deformational and metamorphic features belong to each of the two events. The preservation of Paleoproterozic metamorphic features makes these areas ideal for testing of models for slow cooling and long-term residence in the middle crust in newly formed lithosphere.

美国西南部的原始构造历史是引起极大争议的主题。争议围绕〜1.4 ga plutonism和构造的性质及其与古元古代（1.8-1.6 ga）的地壳积聚的关系。为了帮助解决这个问题。将调查新墨西哥州北部的西马隆山脉和西南科罗拉多州的针线。这两个区域保留了记录古元古代积聚和随后的中元元重新激活的变形和柱形历史。 1.4 GA变质性在新墨西哥州北部和科罗拉多州南部的大部分地区删除了古元热签名。因此，这两个提出的研究区域可能会提供唯一的机会，可以破译新墨西哥州北部和科罗拉多州南部的古代古代变质和冷却历史。西马隆山脉含有上闪石级的块和一个被Fowler Pass Shear shear shear shear Zone（FPSZ）隔开的绿色山脉坡度。整个剪切带的变质矿物组合表明，垂直分离最多10 km。高度块的冷却年龄表明高级变质发生在〜1.4 ga。相比之下，低级块中的岩石记录1678 AR 40 /AR 39冷却年龄：这是新墨西哥州北部报道的最古老的冷却年龄。两个块和F.P.S.Z的详细结构分析将进行阐明这种结构的变形历史和构造意义及其与该地区变质演变的关系。针山记录了截然不同的历史。该区域的古元中古生代岩石被分为两个包装。由石英岩和片岩组成的不易植物形成在区域变形为绿党相。这些岩石位于第二条包装上方的剪切不整合面上，该包由闪石相片麻岩，migmatite和Schist组成。 1.46 Ga Eolus花岗岩侵入了两个包装，并具有发达的触点金黄色葡萄球菌，其峰值变质组合包括sillimanite和k-feldspar。但是，许多距离花岗岩远处的岩石的组合似乎不受1.4 GA变质的影响。这种情况可能会提供机会，以确定古质造成造成过程中以及1.4 GA覆盖过程中地壳的热结构。为了更好地了解1.4 GA构造在西南北美的进化中的作用，P.I。将对这两个范围进行结构性，变质和地质研究。这两个区域都具有1.4 GA变质特征以及古元古代的热和变质标志相似。因此，这些区域非常适合确定两个事件中的每个事件的变形和变质特征。古龙物变质特征的保存使这些区域非常适合测试模型，以缓慢冷却和在新形成的岩石圈中的中层地壳中进行缓慢的冷却和长期居住。