Seismically active fracture zones and distribution of large accumulations of metals in the central part of Andean South America

摘要

The analysis of the geometry of distribution ofearthquake foci in the central part of Andean South Americabetween 18 deg and 34 deg Smade the delineation of severalseismically active fracture zones in the continental wedgeoverlying the subducting Nazca plate possible. Correlation oftheir position with the distribution of hypogene accumulationsof metals revealed that the majority of large mineral depositsand mining districts are situated in the outcrops of these fracturezones. We present geometrical documentation (map ofepicentres, vertical and longitudinal cross sections) of the mostimportant fracture zones and data on mineralogical composition,genetic type and available radio-metric ages of mineral deposits.Sixteen mining districts in Chile, and 24 in Argentina, wereattributed to the seismically active fracture zones. Major miningdistricts and individual large mineral deposits occur in sixseismically active fracture zones roughly parallel to the axis ofthe Peru-Chile trench (Carachas-Portillo, Choqu-elimpie,Iquique, Domeyko, Río Blanco-Los Bayos and Farellones F.Z.),in six fracture zones roughly perpendicular to the trench (ElSalvador, Maricunga, Jaroma, Ujina, Tumbaya and Incahuasi-León Muerto F.Z.) and in two fracture zones oriented at an angleof about 45 deg in relation to the direction of the presentlyactive Andean subduction (Aconcagua and Sierra del VolcanF.Z.). The occurrences of large mineral deposits of different agesshow that these fracture zones were also active in the geologicalpast and represent sites of permanent reopening of pathsallowing ore-bearing solutions and long-term accumulation oflarge amounts of metals to occur in relatively restricted domainsof the Earth's crust. The mining districts with dated mineraldeposits are arranged into four periods of hypogenemineralization: Upper Miocene-Pliocene, Upper Oligocent-Middle Miocene, Upper Eocene-Middle Oligocene, LowerPaleocene-Upper Eocene. These periods of metallogenic activitycorrelate well with four supposed Andean subduction cyclesactive in the Tertiary. The occurrence of mineral deposits ofdifferent ages in recently active fracture zones can be used as animportant evidence in favour of long-term spatial permanenceand activity of these zones and as a guide for the discovery offurther mineral deposits hidden volcanic cover in the fracture zones.