Browsing by Author "Veloso, Eugenio E."

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    Magma flow directions in the sheeted dike complex at superfast spreading mid-ocean ridges: Insights from IODP Hole 1256D, Eastern Pacific
    (2014) Veloso, Eugenio E.; Hayman, Nicholas W.; Anma, Ryo; Tominaga, Masako; Gonzalez, Rodrigo T.; Yamazaki, Toshitsugu; Astudillo, Natalia
    Integrated Ocean Drilling Program (IODP) Hole 1256D successfully sampled a complete section of an intact oceanic crustal sheeted dike complex (SDC) (from 1061 to 1320 meters below seafloor; mbsf) on a 15 Ma old Cocos Plate. A series of rock magnetic measurements were carried out to understand the magmatic processes that accreted this end-member, superfast-spread (200 mm/yr full rate) oceanic crust. Results indicate that main ferromagnetic minerals are predominantly pseudo single-domain (titano)magnetite crystals, responsible for both anisotropy of magnetic susceptibility (AMS) and magnetic remanence signals. AMS fabrics were reoriented into a geographic reference frame using magnetic remanence data, and corrected for a counterclockwise rotation of the Cocos Plate relative to the East Pacific Rise (EPR) ca. 15 Ma. Corrected AMS fabrics were then compared with the orientations of chilled margins previously obtained from Formation MicroScanner (FMS) images of the SDC at Hole 1256D. For some samples taken from close to dike margins, a dike-normal orientation of the minimum AMS axes (K-min) of prolate AMS ellipsoids mean that the long axis (K-max) can be used to infer magma flow directions. Subvertical K-min orientations in the interior of the dikes, however, may have required settling or compaction of the magma shortly after intrusion, thus rearranging the AMS fabric. Despite this orientation of K-min axes, orientation of K-max axes indicate a rather constant subhorizontal paleo-flow direction, suggesting that magmas most probably traveled to the surface considerable distances from source regions within the EPR system.
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    Multi-scale flow structure of a strike-slip tectonic setting: A self-similar model for the Liquine-Ofqui Fault System and the Andean Transverse Faults, Southern Andes (39-40 degrees S)
    (PERGAMON-ELSEVIER SCIENCE LTD, 2022) Roquer, Tomas; Arancibia, Gloria; Crempien, Jorge G. F.; Mery, Domingo; Rowland, Julie; Sepulveda, Josefa; Veloso, Eugenio E.; Nehler, Mathias; Bracke, Rolf; Morata, Diego
    The flow structure of a brittle crustal volume is defined by the multi-scale geometric and hydraulic properties of its fracture meshes. The length density distribution n(L,l) and the transmissivity distribution K(L,l) control the hydrologic scaling, where l is fracture length and L is the system size. The flow structure might display at most three key hydrologic scales: the connection scale, above which flow is focused in few critical paths; the channeling scale, above which flow is distributed in several paths; and the homogenization scale, above which permeability approaches a constant value. According to these scales, the hydrological structure could be distributed or clustered, thus having a clear impact in geothermal exploration campaigns and reservoir modeling. In this work, we determine the multi-scale flow structure for the Liquine-Ofqui Fault System (LOFS) and the Andean Transverse Faults (ATF) in the Southern Andes, by establishing the hydrologic scaling they follow. Using fractal statistics, we integrated geological data at the regional, meso-and micro-scale, including image analysis from X-ray microtomography. Our results suggest a self-similar, dense network with n(L,l)similar to l(-a) and a = 2.6-2.9, from the regional scale where the LOFS and ATF interact to the meso-and micro-scale within highly fractured areas of the LOFS. Scaling models are constrained by the length distribution, and other power-law functions reflecting the geometric arrangement of fractures, as well as the spatial distribution of superficial geothermal occurrences. Thus, we expect the hydrologic scaling to depend on the transmissivity distribution. Lognormal transmissivity distribution yields a permeability increase with scale, from the connection to the homogenization scales; whereas power-law transmissivity distribution yields a permeability increase from the connection scale without a limiting value. Approximations of the connection scale are around 10(-3)-10(0) m; the channeling scale, around 100-104 m; and if the homogenization scale exists, it should be equal or greater than 10(3)-10(4) m. Finally, the results presented here could to define the internal architecture of fracture meshes in fault-controlled fluid flow, and be used to select an appropriate hydrologic model according to the analyzed scale. Therefore, these findings must be taken into consideration in future geothermal prospecting, modeling and exploitation.