Collaborative Research: Milankovitch-Scale Time Resolution to Determine Rates and Kinematics of Folding

利用轨道强迫气候变化产生的沉积旋回(持续约20,000-400,000年的Milankovitch韵律)，PI试图阐明滑脱褶皱的复杂运动学，改进评估生长结构的方法，并通过多学科的构造、地层学和磁学研究确定高分辨率变形年代学。滑脱褶皱是大多数造山带中的一种重要构造样式，在变形地层层序中主要分布在竞争力强对比和厚而弱的层序中。构造构造的解释、评价和重建需要了解运动学和几何学，单靠几何学不能限制变形、褶皱运动学或褶皱力学的分布。生长构造为解旋造山景观的变形和沉积过程提供了独特的机会。PI‘s建议评估变形模式的空间变化，作为构造几何、岩性和地层位置的函数，遍及两个暴露良好的反斜构造；一个在墨西哥东北部的Fraile山脉，另一个在西班牙中北部的中外部塞拉利昂。这两个地区都有大规模的蒸发岩岩芯同沉积滑塌褶皱。褶皱的长期生长发生在不同的水深和沉积环境中，并通过不同的不整合几何形状和生长地层厚度的变化来记录。这些关系将能够比较变形地形和沉积过程之间的复杂相互作用，并成为评估对生长地层几何形状的运动学控制的手段。PI将绘制岩石磁化率、磁化率各向异性(AMS)和方解石孪生测量的地图，并对岩石进行取样。生长前地层中的AMS测量将被用作变形组构的替代，并将通过孪生研究来加强，以约束褶皱运动学。生长地层几何学将被用来区分固定的和可移动的轴面，作为一种完全独立的方法来评估褶皱运动学。将利用磁化率变化和绝对年龄的Milankovitch尺度相关性来建立年代地层学，以便在约20,000年的时间内控制Fraile山脉和塞拉利昂外部生长地层的沉积和变形速率。在这两个领域的侦察调查提供了试点数据，证实了产生褶皱运动学高分辨率空间和时间分析的无与伦比的机会。这两个地区气候控制的旋回地层和同沉积变形的良好暴露相结合，为确定大规模滑脱褶皱的运动学提供了一个难得的机会，这是大多数造山带中的一种重要构造样式。

Using sedimentary cycles generated from orbitally forced climatic changes(~20,000-400,000 year duration Milankovitch rhythms), the PI's seek to elucidate thecomplex kinematics of decollement folds, refine methodological approaches forevaluating growth structures, and determine high-resolution deformation chronologieswith a multidisciplinary structural, stratigraphic, and magnetic study. Decollement foldsare an important structural style in most orogenic belts and dominate where strongcompetency contrasts and thick, weak layers characterize deformed stratigraphicsequences. The interpretation, evaluation, and reconstruction of tectonic structuresrequires an understanding of kinematics and geometry alone cannot constrain thedistribution of deformation, fold kinematics, or fold mechanics. Growth structuresprovide a unique opportunity to deconvolute the deformational and depositionalprocesses of orogenic landscapes. The PI's propose to evaluate spatial variations in deformation patterns as a function of structural geometry, lithology, and stratigraphic position throughout two well-exposed anticlinoria; one at Sierra del Fraile, northeastern Mexico and another in the central External Sierra, north central Spain. Both field areas contain large-scale, evaporite-cored, synsedimentary decollement folds. Prolonged fold growth occurred in varying water depths and depositional environments at each site and were recorded by a variety of unconformity geometries and changes in growth strata thickness. These relationships will allow comparison of the complex interaction between deformational topography and depositional processes and a means to evaluate kinematic controls on growth strata geometries. The PI's will map and sample rocks for magnetic susceptibility, anisotropy of magnetic susceptibility (AMS), and calcite twinning measurements. AMS measurements in pregrowth strata will be used as a proxy for deformation fabric and will be augmented by twinning studies to constrain fold kinematics. Growth strata geometry will be used to distinguish between fixed and migrating axial surfaces as a fully independent means of assessing fold kinematics. Milankovitch-scale correlation of magnetic susceptibility variations and absolute ages will be used to establish a chronostratigraphy allowing for ~20,000 year temporal control on depositional and deformational rates within both the Sierra del Fraile and External Sierra growth strata. Reconnaissance investigations in both field areas provided pilot data confirming unparalleled opportunities to generate high-resolution spatial and temporal analysis of fold kinematics. The combination of excellent exposures of climatically controlled cyclic stratigraphy and synsedimentary deformation in the two field areas provide an exceptional opportunity to determine the kinematics of large-scale decollement folding, an important structural style in most orogenic belts.