Fore arc tectonothermal evolution of the El Oro metamorphic province (Ecuador) during the Mesozoic

Abstract

The El Oro metamorphic province of SW Ecuador is a composite massif made of juxtaposed terranes of both continental and oceanic affinity that has been located in a fore-arc position since Late Paleozoic times. Various geochemical, geochronological, and metamorphic studies have been undertaken on the El Oro metamorphic province, providing an understanding of the origin and age of the distinct units. However, the internal structures and geodynamic evolution of this area remain poorly understood. Our structural analysis and thermal modeling in the El Oro metamorphic province show that this fore-arc zone underwent four main geological events. (1) During Triassic times (230-225 Ma), the emplacement of the Piedras gabbroic unit at crustal-root level (~9 kbar) triggered partial melting of the metasedimentary sequence under an E-W extensional regime at pressure-temperature conditions ranging from 4.5 to 8.5 kbar and from 650 to 900°C for the migmatitic unit. (2) At 226 Ma, the tectonic underplating of the Arenillas-Panupalí oceanic unit (9 kbar and 300°C) thermally sealed the fore-arc region. (3) Around the Jurassic-Cretaceous boundary, the shift from trench-normal to trench-parallel subduction triggered the exhumation and underplating of the high-pressure, oceanic Raspas Ophiolitic Complex (18 kbar and 600°C) beneath the El Oro Group (130-120 Ma). This was followed by the opening of a NE-SW pull-apart basin, which tilted the massif along an E-W subhorizontal axis (110 Ma). (4) In Late Cretaceous times, an N-S compressional event generated heterogeneous deformation due to the presence of the Cretaceous Celica volcanic arc, which acted as a buttress and predominantly affected the central and eastern part of the massif.

Deciphering the Late Cretaceous‐Cenozoic Structural Evolution of the North Peruvian Forearc System

“…The Amotape basement is interpreted to form a continental block accreted onto the South American margin in the Early Permian (Ramos, ) or Early Cretaceous (Mourier et al, ; Winter et al, ). It is also interpreted as a rifted fragment of South America (western Pangaea) within a back‐arc setting in the Triassic (Riel et al, ; Spikings et al, ; Witt et al, ).…”

“…Although the onshore area was affected by post‐Oligocene rotation (Mitouard et al, ), no clear field evidence of strike‐slip faulting over the Talara‐Lancones area is found (Laj et al, ). Major strike‐slip faulting is described in the arc and more to the north (e.g., Alvarado et al, ; Riel et al, ; Witt et al, ). Finally, the sequential restoration respects paleobathymetries of the sedimentary units (Fernández et al, ; Fildani et al, ; Vega, ) and paleo‐sea levels (Haq et al, ).…”

Quantitative and Qualitative Assessment of the “El Sexmo” Tourist Gold Mine (Zaruma, Ecuador) as A Geosite and Mining Site

“…Within the Azuay-El Oro district, there are several epithermal mineral deposits of the Miocene, such as Zaruma-Portovelo [51,52] (Figure 3b), where there is important structural control of the Palestina and Piñas dextral faults. The faults have a NW-SE trend, where the Palestina fault marks the northern limit of the Zaruma-Portovelo mineral field, and the Piñas fault comprises the southern limit and separates the Saraguro group from the El Oro metamorphic complex [53,54]. Consequently, the structural dynamics have favored the formation of dilating spaces for the location of vein assemblages (Figure 3b), where gold mineralization occurs [46,55] and associated minerals (pyrite, chalcopyrite, sphalerite, galena, bornite, hematite, tetrahedrite, molybdenite, quartz, and calcite) identified in different studies [55][56][57].…”

“…The process consisted of the collection of historical and cultural information (e.g., [15,30,32,[35][36][37]39,41,43,45]). In addition, the mining geological context of the mine and its setting was defined based on previous studies [31,42,46,[49][50][51][52][53][54][55] as a basis for subsequent assessment. The potential geotouristic interest presented by the study area was described.…”

Celebrating Alexander von Humboldt’s 250 th anniversary: Exploring bio- and geodiversity in the Andes (IBS Quito 2019)

“…The Andes of Ecuador is part of the Northern Andes, which is limited to the south by a complex geological structure called the Huancabamba Deflection (Riel et al 2014; Fig. 2).…”