Ophiolite Emplacement and the Effects of the Subduction of the Active Chile Ridge System: Heterogeneous Paleostress Regimes Recorded in the Taitao Ophiolite (Southern Chile)

Abstract

ABSTRACT. The repeated north and southward migration of the Chile Triple junction, offshore the Península de Taitao, is expected to have imposed contrasting stress fi elds in the forearc for the last 6 Ma because of changes in convergence direction and rate of subducting plates. NNW-SSE to E-W and minor NE-SW striking brittle faults developed in the plutonic units of the Mio-Pliocene Taitao Ophiolite, whereas NNE-SSW and minor NW-SE trending faults developed in its eastern border (Bahía Barrientos fault-zone). These brittle faults are studied to elucidate the style of ophiolite emplacement and the tectonic effects resulting from the alternated migration of the Chile Triple junction in the area. Analyses of heterogeneous fault-slip data on both areas suggest that faults were activated by different stress fi elds. Two different compressional stress fi elds were identifi ed in the plutonic units (A and B), whereas three different stress fi elds, ranging from compressional to strike-slip, were identifi ed in the Bahía Barrientos fault-zone (C, D and E). Calculated directions of σ 1 axes for A, C, D and E solutions are mostly E-W trending, roughly similar to the convergence direction of subducting plates, whereas that for B solution is counterclockwise rotated ca. 60° with respect to the previous E-W trend. Brittle structures related to solution B were attributed to an early deformation of the ophiolite, most probably developed shortly after its emplacement (ca. 6 Ma). These structures were further counterclockwise rotated, while new structures (related to solution A) developed in the plutonic units in order to absorb the continuous deformation. In the eastern margin of the ophiolite, the stress fi eld divided into compressional and strike-slip components. During periods of relatively strong compression (fast subduction of the Nazca plate), the fault-zone experienced well defi ned compressional and strike-slip movements (solutions C and D). In contrast, during periods of relatively weak compression (slow subduction of the Antarctic plate), the fault-zone experienced a complex mixture of thrust and strike-slip movements (solution E). Thus, the wide range of calculated stress ratios for all solutions could be attributed to the alternated change in convergent velocity of the subducting plates beneath the Taitao area. RESUMEN.Emplazamiento de ofi olitas y los efectos de la subducción de la dorsal activa de Chile: Regímenes heterogéneos de paleostress registrados en la Ofi olita Taitao (Sur de Chile). Es esperable que la repetida migración norte-sur del Punto Triple de Chile cercana a la costa de la Península de Taitao haya impuesto campos de esfuerzos distintos en el antearco por los últimos 6 Ma debido a cambios en la dirección de convergencia y tasa de subducción. Fallas con rumbos NNO-SSE y E-O y otras menores con rumbos NE-SO se desarrollaron en las unidades plutónicas de la Ofi olita Miocena-Pliocena de Taitao, mientras que fallas con rumbos NNE-SSO y otras menores con rumbos NO-SE se desarrollaron en el borde Est...

Geochemical characterization and petrogenesis of intermediate to silicic rocks in ophiolites: A global synthesis

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Shallow-depth melt eduction due to ridge subduction: LA-ICPMS U-Pb igneous and detrital zircon ages from the Chile Triple Junction and the Taitao Peninsula, Chilean Patagonia

“…9c). This inflection could be attributed to the block rotation of the Taitao ophiolite during its final emplacement (Veloso et al, 2005(Veloso et al, , 2009. If so, the inflection implies that the original trend of the Chile Margin Unit magmatism was EW, subTaitao ophiolite (5.7 to 5.2 Ma: Anma et al, 2006) and after synchronous intrusions of Tres Montes (TM in Fig.…”

The Taitao ophiolite-granite complex, Chile: Emplacement of ridge-trench intersection oceanic lithosphere on land and the origin of calc-alkaline I-type granites

“…The gabbros continued to fold even below their Curie temperature, as evidenced by macroscopic folding and Z-shaped demagnetization paths in the layered gabbros (Anma et al, 2005;Veloso et al, 2005), whereas the sheeted dike complex and the MVU rotated as rigid blocks as deformation proceeded (Veloso et al, 2005(Veloso et al, , 2009. It was the eastern part of the subducted segment of the Chile ridge that was emplaced as the plutonic section of the Taitao ophiolite Anma et al, 2005Anma et al, , 2006.…”