Oblique-to-the-orogen fault systems and it causal relationship with volcanism and geothermal activity in Central Southern Chile: Insights on ENE and NW regional lineaments

Major crustal faults systems at convergent margins are commonly organized into margin-parallel, high-strain domains that appear to be continuous over hundreds of kilometers. This major architecture shapes the structural grain of a given mountain belt and is thought to represent the long-term record of its deformation history. However, second-order transverse structures, cross-cutting the orogen main structural grain, also are common. In the Andes they play a key role in the tectonic, magmatic and hydrothermal history. Although the relevance of these oblique-to-the-orogen structures is widely recognized, little is known regarding their nature, kinematics and timing and also their long and short-term tectono-magmatic role. The present work address the tectono-magmatic significance of WNW and ENE-striking basement structures, through a combination of field geology and geophysics. Our working hypothesis is that WNW and ENE-striking structures correspond to long-lived fault zones that play a fundamental tectono-magmatic role in Andean evolution. They have accommodated part of the upper plate deformation arising from the ~ ENE-WNW-trending shortening and -at the same time- they have provided episodic pathways for magma and hydrothermal fluid transport in the lithosphere. Furthermore, we speculate that because WNW-striking fault zones are severely misoriented with respect to the prevailing stress field, they reactivate under supra-lithostatic fluid pressures. ENE-striking faults, in turn, are favorably oriented and do not require supra-lithostatic fluid pressures to reactivate. The problem is being tackled by selecting two outstanding case studies in the Andes of Central Chile: the ENE-oriented Tatara-San Pedro-Pellado volcanic complex - Laguna del Maule volcanic field alignment (TPMA) and the WNW-oriented Cortaderas-Chillán lineament (CChL). Observations on satellite images combined with preliminary field studies suggest that WNW-striking faults and ENE striking faults show sinistral-reverse and dextral-normal displacement respectively. Both systems crosscut each other and their activity is younger than Late Pleistocene. Furthermore, Late Pleistocene mafic dikes, vein systems and fault-controlled fumaroles appear to be synkinematic with both transverse crustal faults.