Collaborative Research: Contrasting Styles of Ca. 1.4 Ga Tectonism in the Southern Rockies: Evidence for a Fossil Rheologic Transition in a Deeply Exhumed Intracontinental Orogen

合作研究：Ca 的风格对比。

• 批准号: 0101314
• 负责人: Christine Siddoway
• 金额: $ 2.52万
• 依托单位: Colorado College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-01-01 至 2003-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0101314&HistoricalAwards=false
• 关键词: Collaborative; Research; Contrasting; Styles; Ca.

Karlstrom 0003500Connelly 0003528Williams 0003569Siddoway 0101314Proterozoic rocks in central Colorado preserve a transition, from semi-brittle upper crust to pervasively ductile middle crust, that was frozen in at about 1.4 Ga. This rheologic transition is expressed as a regionally significant change in the style of ca. 1.4 Ga intracratonic tectonism. Field observations suggest that a subhorizontal boundary separates a domain in northern and central Colorado (exemplified by the Colorado Mineral Belt), where 1.4 Ga deformation is characterized by discrete mylonite zones, from a domain in southern Colorado and northern New Mexico dominated by penetrative ductile deformation. Geodynamic models developed for intracontinental orogens such as Tibet, Altiplano-Puna, and the Sevier-Laramdie indicate that such mechanical decoupling may be a critical factor in controlling the tectonic evolution of intracontinental deformation. Like some of its younger analogs, the structural transition of central Colorado apparently corresponds with a magma- and fluid-rich, high-strain layer. These deeply exhumed rocks present intriguing opportunities to directly investigate deep-crustal processes that are inaccessible in younger orogens. Issues of general impact include characterization of: (1) the controls on the depth and thickness of the brittle/ductile transition (e.g. temperature, lithology, fluids), (2) the kinematics and dynamics of deformation near the rheological transition, (3) mechanisms of accommodating strain incompatibility between different deformation regimes, and (4) the role of granitoid melts and/or a widespread melt-fluid layer, in localizing middle crustal flow and structural decoupling of upper and lower crust. In addition to exploiting the deep crustal exposures of central Colorado to study general processes of intracontinental deformation, this study is contributing to the understanding of the Proterozoic tectonic evolution of the southwestern United States. In particular, alternate models for "anorogenic" (extensional) versus "orogenic" (transpressional) tectonic settings for 1.4 Ga tectonism can perhaps be reconciled in an orogenic plateau model where regional horizontal contraction is balanced by more localized gravitational collapse. The study uses an integrated data set involving structural, petrologic, and U-Pb geochronologic data to evaluate the kinematics and evolution of this important structural transition. Focus is on a well exposed transect across the structural transition. Specifically, studies of the Black Canyon of the Gunnison and adjacent areas within the Colorado Mineral Belt are characterizing the style, extent, and P-T conditions of mylonite shear zones and emplacement of syn-kinematic 1.4 Ga plutons above the transition. Work in the Wet Mountains and Sangre de Cristo Range is characterizing pervasively ductile deformation and fabric reactivation within and below the transition. The geochronology is emphasizing both U/Pb zircon dating of critical syn-kinematic plutons in central Colorado and microprobe monazite dating of high-grade metamorphism along the transect.

Karlstrom 0003500 Connelly 0003528Williams 0003569Siddoway 0101314 Proterozoic岩石中心的岩石保留了从半脆性上皮到普遍延性的中壳的过渡，在大约1.4 ga的情况下，它是在大约1.4 ga的情况下进行的。 1.4 ga内部构造。 现场观察表明，下侧边界将北部和中部科罗拉多州的一个域分开（以科罗拉多州矿物带的例证），其中1.4 GA变形的特征在于离散的mylonite区与科罗拉多州南部和北部新墨西哥的一个领域，由渗透性粘液性粘液性粘液性粘液粘膜变形主导。 为肠内牛根（例如西藏，altiplano-puna和Sevier-laramdie）开发的地球动力学模型表明，这种机械解耦可能是控制内部内部变形的构造演化的关键因素。 像某些年轻的类似物一样，科罗拉多州中部的结构过渡显然与岩浆和流体富含岩石的高应变层相对应。这些深挖的岩石为直接研究年轻烤树脂中无法访问的深层过程提供了有趣的机会。 一般影响的问题包括：（1）对脆性/延性过渡的深度和厚度的控制（例如温度，岩性，流体），（2）流变学过渡附近的变形和动态，（3）在不同的变形状态和（4）或（4）的作用机制的机制（3）融化的融合层，将上层和下地壳的中层地壳流量和结构脱钩。 除了利用科罗拉多州中部的深层地壳暴露以研究末期变形的一般过程外，这项研究还有助于理解美国西南部的proterokoic构造演化。 特别是，在造基高原模型中，可以对区域水平收缩通过更局部的重力崩溃平衡的造型高原模型，以对付“厌食”（延伸）（延伸）（延伸）与“造山学”（转染）构造设置的替代模型。该研究使用涉及结构，岩石学和U-PB地质数据的综合数据集来评估这一重要结构过渡的运动学和演变。 重点放在整个结构过渡的外样良好的横断面上。具体而言，对科罗拉多州矿物带内的黑峡谷和邻近区域的黑峡谷表征了肌lon虫剪切区的样式，范围和P-T条件，以及在过渡上方的Syn-Kinematic 1.4 Ga Plutons的安置。 在湿山和Sangre de Cristo范围内的工作表征了延性的延性变形和织物在过渡内外的重新激活。 地年学强调了科罗拉多州中部临界合成型岩体的U/Pb锆石的日期和沿该样带的高级变质的微探针构造。