Late Miocene to recent morphotectonic evolution and potential seismic hazard of the northern Lerma valley: Clues from Lomas de Medeiros, Cordillera Oriental, NW Argentina
Late Miocene to recent morphotectonic evolution and potential seismic hazard of the northern Lerma valley: Clues from Lomas de Medeiros, Cordillera Oriental, NW Argentina
复制标题
晚中新世到近期的地貌构造演化和莱尔马山谷北部潜在的地震危险：来自阿根廷西北部东科迪勒拉山脉洛马斯德梅代罗斯的线索
DOI：
10.1016/j.tecto.2013.06.021
复制
发表时间：
2013
期刊：
影响因子：
2.9
通讯作者：
E. Cristallini
中科院分区：
文献类型：
--
作者：
V. García;F. Hongn;E. Cristallini
Loma de Medeiros是位于Lerma谷地最北端的低起伏丘陵，收集了新的构造、地貌和地形关键数据，并与现有的地层和年代学数据相结合，以阐明该地区近10 Ma以来的地貌构造演化。本区上新世至下更新世砾岩和粉砂岩(皮克特组)变形，形成向东发散、轴向N10°E的非对称背斜，后肢呈递进不整合。同构造沉积作用也与北S向褶皱轴线附近的正断层运动有关。中更新世至全新世厚的河流砾岩不整合地覆盖皮克特组，形成几米厚的层状阶地。最高和最古老的阶地相对于Calvimonte组砾岩的顶部已经抬升了160多米(约0.33 Ma)，其地层对比在未变形的Lerma山谷。阶地的详细地形剖面显示了褶皱递进抬升的证据，以及与反向断裂有关的陡坎的存在。背斜采用断层扩展褶皱机制模拟，在新生代盖层与古生代基底接触处，背斜向西倾斜32°，滑脱面位于地表以下2.7公里处。这些观测数据与之前公布的数据相结合，可以建立该地区在过去10 Ma期间的地形构造演化。Loma de Medeiros的中更新世至全新世阶地的褶皱和断裂，以及Mojotoro山脉抬升的上更新世沉积，是与这些地貌构造有关的断层具有孕震潜力的有力证据。应用地下破裂长度的关系，估计了Medeiros断裂、小断裂和Mojotoro断裂的最大力矩震级(MW)分别为6.5、7.0和7.1。
The Lomas de Medeiros are low relief hills located at the northern extreme of the Lerma valley, where new structural, morphological and topographic key data have been collected and integrated with the available stratigraphic and geochronological data in order to elucidate the morphotectonic evolution of the region during the last ~ 10 Ma. In this area, Pliocene to Lower Pleistocene conglomerates and siltstones (Piquete Formation) are deformed delineating an asymmetrical anticline with eastward vergence, axial plane trending N10°E, and progressive unconformities at the backlimb. Syntectonic sedimentation has been documented as related to N–S trending normal faulting near the fold axis as well. Middle Pleistocene to Holocene thick fluvial conglomerates cover unconformably the Piquete Formation as strath terraces with a few meters of thickness. The higher and oldest terrace has been uplifted more than 160 m respect to the top of Calvimonte Formation conglomerates (~ 0.33 Ma), its stratigraphic correlate at the undeformed Lerma valley. Detailed topographic profiles of the terraces show evidences of progressive uplifting by folding and the presence of scarps related with reverse faulting. The anticline has been modeled using the fault propagation folding mechanism with a blind ramp dipping 32° to the west and a decollement level located 2.7 km below the surface, at the contact between the Cenozoic cover and the Paleozoic basement. The integration of these observations with previously published data allowed to establish the morphotectonic evolution of this region during the last 10 Ma. Folded and faulted Middle Pleistocene to Holocene terraces at Lomas de Medeiros and Upper Pleistocene deposits uplifted at Mojotoro range are strong evidences of the seismogenic potential of the faults related with these morphostructures. Applying relationships with the subsurface rupture length, earthquakes with maximum moment magnitudes (Mw) of 6.5, 7.0 and 7.1 have been estimated for Medeiros, Lesser and Mojotoro faults respectively.