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Spatio-temporal variation of the strain field in the southern Central Andes broken-foreland (27°30′S) during the late cenozoic
Journal of South American Earth Sciences ( IF 1.7 ) Pub Date : 2021-03-01 , DOI: 10.1016/j.jsames.2020.102981
R. Quiroga , M. Peña , F. Poblete , L. Giambiagi , J. Mescua , I. Gómez , A. Echaurren , S. Perroud , J. Suriano , F. Martínez , D. Espinoza

Abstract We present an integrated structural and Anisotropy of Magnetic Susceptibility (AMS) study focused on the characterization of the spatio-temporal variation of the strain field during the main Neogene deformation, of the Argentine Precordillera and the northern Sierras Pampeanas, immediately to the south of the Puna plateau (27°30′S). The AMS from 43 sites and fault-slip data analysis from mesoscale faults (n = 540) were carried out in Early Miocene to Middle Pliocene sedimentary and volcaniclastic rocks. The AMS results show moderate values of anisotropy degree near to deformation zones, and low and high values of bulk susceptibility. The most predominant magnetic fabric is sedimentary type I and II, with a weak magnetic lineation. In areas where the rocks are deformed, the incipient magnetic lineation are subparallel to the regional structural trend and present a main N–S orientation in the Precordillera and Fiambala basin, while in the Sierras Pampeanas they are mostly NE-oriented. Combining these results with kinematic analysis from fault-slip data, we identify, in the Precordillera and Fiambala basin areas, a contractional event with E-W main direction, from ∼23 Ma to 5 Ma, mostly active from the onset of deposition of Neogene sequences. During this period, in the NW Sierras Pampeanas, the contraction directions follow a NW orientation. The onset of N–S to NNW contraction, mostly recognized in rocks younger than 5 Ma, exposed in the northern areas of Precordillera and Sierra Pampeanas, documents a change of the strain field during the early-to-middle Pliocene, associated with a shift in the contractional direction from E-W to N–S. We relate the change to the rapid uplift of the southern Puna, generating a juxtaposition of an area under N–S extension, affecting the topographically-higher Puna, with the other area under N–S contraction in the adjacent Precordillera and Sierras Pampeanas. We associate these two events as part of the evolution of this segment of the Andes, where the broken foreland setting is active during this time. By combining the AMS and kinematic analysis results, we obtain a timing for the spatio-temporal change of contraction directions, which allows us to compare both the broken-foreland and foreland basins to understand spatio-temporal strain variations.

中文翻译:

晚新生代中安第斯破碎前陆南部(27°30′S)应变场时空变化

摘要 我们提出了一项综合结构和磁化率各向异性 (AMS) 研究,重点是新近纪主要变形期间应变场的时空变化特征,即阿根廷前科迪勒拉山脉和潘佩纳山脉北部,紧邻普纳高原(27°30'S)。在早中新世至中新世沉积岩和火山碎屑岩中进行了 43 个站点的 AMS 和中尺度断层(n = 540)的断层滑动数据分析。AMS 结果显示变形区附近的各向异性度值适中,体磁化率低值和高值。最主要的磁性组构是沉积型Ⅰ和Ⅱ型,磁性线状较弱。在岩石变形的区域,初期磁力线与区域构造趋势不平行,并在 Precordillera 和 Fiambala 盆地呈现主要的 N-S 取向,而在 Sierras Pampeanas,它们大多是 NE 取向。将这些结果与断层滑动数据的运动学分析相结合,我们在 Precordillera 和 Fiambala 盆地地区确定了一个具有 EW 主方向的收缩事件,从~23 Ma 到 5 Ma,主要从新近纪序列沉积开始时开始活跃。在此期间,在 NW Sierras Pampeanas 中,收缩方向遵循 NW 方向。N-S 到 NNW 收缩的开始,主要在小于 5 Ma 的岩石中发现,暴露在 Precordillera 和 Sierra Pampeanas 北部地区,记录了上新世早中期应变场的变化,与收缩方向从 EW 到 N-S 的转变有关。我们将这种变化与普纳南部的快速抬升联系起来,产生了一个在 N-S 延伸下的区域并置,影响了地形较高的 Puna,另一个区域在相邻的 Precordillera 和 Sierras Pampeanas 中处于 N-S 收缩下。我们将这两个事件作为安第斯山脉这一部分演化的一部分,在这段时间内,破碎的前陆环境活跃。通过结合 AMS 和运动学分析结果,我们获得了收缩方向时空变化的时间,这使我们能够比较破碎前陆和前陆盆地,以了解时空应变变化。产生一个在 N-S 延伸下的区域的并置,影响地形较高的 Puna,另一个区域在相邻的 Precordillera 和 Sierras Pampeanas 中处于 N-S 收缩下。我们将这两个事件作为安第斯山脉这一部分演化的一部分,在这段时间内,破碎的前陆环境活跃。通过结合 AMS 和运动学分析结果,我们获得了收缩方向时空变化的时间,这使我们能够比较破碎前陆和前陆盆地,以了解时空应变变化。产生一个在 N-S 延伸下的区域的并置,影响地形较高的 Puna,另一个区域在相邻的 Precordillera 和 Sierras Pampeanas 中处于 N-S 收缩下。我们将这两个事件作为安第斯山脉这一部分演化的一部分,在这段时间内,破碎的前陆环境活跃。通过结合 AMS 和运动学分析结果,我们获得了收缩方向时空变化的时间,这使我们能够比较破碎前陆和前陆盆地,以了解时空应变变化。在此期间,破碎的前陆环境处于活动状态。通过结合 AMS 和运动学分析结果,我们获得了收缩方向时空变化的时间,这使我们能够比较破碎前陆和前陆盆地,以了解时空应变变化。在此期间,破碎的前陆环境处于活动状态。通过结合 AMS 和运动学分析结果,我们获得了收缩方向时空变化的时间,这使我们能够比较破碎前陆和前陆盆地,以了解时空应变变化。
更新日期:2021-03-01
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