A transient fault-valve mechanism operating in upper crustal level, Sierras Pampeanas, Argentina

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• 作者：Marí ; a Silvia Japas^a ; ^{msjapas@gl.fcen.uba.ar" class="auth_mail" title="E-mail the corresponding author} ; Nilda Esther Urbina^b ; ^{urbina@unsl.edu.ar" class="auth_mail" title="E-mail the corresponding author} ; Patricia Sruoga^c ; ^{patysruoga@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; José ; Matí ; as Garro^b ; ¹ ; ^{jomaga007@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; Oscar Ibañ ; es^b ; ^{oscaribanes@gmail.com" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Fault-valve behaviour ; Crack and seal vein growth ; Calcareous onyx ; Tertiary volcanic belt ; Sierra de San Luis ; Sierras Pampeanas broken-foreland
• 刊名：Journal of Geodynamics
• 出版年：2016
• 出版时间：November 2016
• 年：2016
• 卷：101
• 期：Complete
• 页码：142-154
• 全文大小：5432 K

文摘

Located in the Sierras Pampeanas (the broken-foreland of the Pampean flat slab segment in the southern Central Andes), the Cerro Tiporco volcanic field shows Neogene hydrothermal activity linked to migration of arc-magmatism into the foreland. Late Neogene deposits comprise epithermal vein systems emplaced in Precambrian—Early Palaeozoic igneous-metamorphic basement, Late Miocene sedimentary rocks and Early Pliocene volcaniclastic rocks. Mineralization consists of calcareous onyx, aragonite and calcite veins as well as travertine deposits. Onyx and aragonite occur as fill of low-displacement nearly vertical reverse-sinistral faults striking NW, and nearly horizontal dilatant fractures. The latter consist of load-removal induced fractures affecting the igneous-metamorphic rocks, as well as bedding planes in the Late Miocene sediments. The presence of veins recording multiple fracture episodes and crack-and-seal growth of veins suggests relatively low differential stress and supralithostatic fluid pressure, as well as cyclic changes in pore pressure and high mineral-deposition/fracture-opening ratio. These conditions support a mechanism of fault-valve behaviour during onyx and aragonite vein emplacement. The fault-valve mechanism involves fractures associated with impermeable barriers between environments with different fluid pressure. Faulting generated an appreciable directional permeability triggering fluid migration from the highest to the lowest pressure region, with subsequent deposition and sealing that started a new pressurization-faulting-sealing cycle. Late aragonite and calcite veins suggest a change in kinematics indicating the onset of tectonic-load conditions.