Spreading center subduction and role of the associated slab window development on intraplate deformations, arc magmatism and craton evolution during associated slab window development: the Chile triple junction area documenting a uniformitarian model

By Jacques Bourgois (PI)

Spreading center subduction is a geodynamic situation that induces strong morphotectonic and magmatic effects along Cordilleran type convergent margins such as the Andes. This includes the forearc, backarc, and foreland areas. The associated development of a slab window at depth induces major tectonic and magmatic imprints on the upper plate, far away from the trench axis. Slab geometry variations referred to explaining inboard tectonic deformation for the upper plate must be questioned since no slab exists at depth at the window. In other words, extensive foreland areas exhibiting pervasive tectonic deformation are considered as resulting from shallow slab (flat slab), horizontal compression being transmitted into the upper plate from high coupling across plate interface. Since no slab exists at slab window, no potential slab dynamics exists.

An active situation of spreading ridge subduction exists at the modern Chile Triple Junction (CTJ) area. Moreover this triple junction is the only one site worlwide where the overriding plate is continental in character. Therefore, the CTJ is a good analog for the past ridge-trench collisions occurring along an Andean-type margin, a situation that likely happened during the subduction of the Tethys Ocean beneath Eurasia plate and Pacific beneath North and South America during the past 200-250 Myr.

During the past three decades, we have conducted tens of field expeditions in the Chile Triple junction area extending from 44 to 49°S from N to S and extend from the Pacific abyssal plain to the Foreland of the Andes. Two major field campaigns were conducted in the Taitao and Tres Montes peninsulas in compliment of the CTJ expedition at sea using the R/V L’Atalante. These works involved tens of colleagues from different countries. Their names appear as authors in the following list of publications. These publications (see reference list) including two major review papers (Bourgois et al., 2016 and 2021) provide uniformitarian constraints for tectonic and magmatic signatures of the upper plate originating from ridge subduction and slab window development.

Main specific results documenting that no slab dynamics exists at 44-47° S latitude include:

(1) The emplacement mode for the Pleistocene Taitao Ridge and the Pliocene Taitao Peninsula ophiolite bodies.

(2) The occurrence of these ophiolitic complexes in association with five adakite-like plutonic and volcanic centers of similar ages at the same restricted locations.

(3) The inferences from the cooccurrence of these sub-coeval rocks originating from the same subducting oceanic lithosphere evolving through drastically different temperature–pressure (P–T) path: low-grade greenschist facies overprint and amphibolite-eclogite transition, respectively.

(4) Evidences that document ridge-jump events and associated microplate individualization during subduction of the SCR1 and SCR-1 segments: the Chonos and Cabo Elena microplates, respectively.

(5) The ridge-jump process associated with the occurrence of several closely spaced transform faults entering subduction is controlling slab fragmentation, ophiolite emplacement, and adakite-like production and location in the CTJ area.

(6) Kinematic reconstruction of South Chile ridge subduction documents the location of the subducted ridge segment -1 beneath the North Patagonia Icefield (NPI). The high relief of the North Patagonia Icefield (NPI) is dynamically sustained by asthenospheric convection.

(7) Between 46°30’ and 47°304S, a right lateral transtensional fault system controlled the 800–1200 m uplift of the Andes at 16.1–18.1 Ma. Our data and analysis indicate that there was no lower Miocene contractile event along the Andean morphotectonic frontline.

(8) The Main Andean Thrust (MAT), which is deeply rooted in the upper crust is a retroarc thrust dipping 10–15◦ westward, and provides evidence for major crustal shortening at ~120 Ma.

(9) Between 45 and 47°S, the processes controlling the dynamic evolution of the two main topographic features of the Andean segment include:

(i) upward convection originating from the subducted South Chile Ridge dynamically sustaining the N-S trending high topography of the North Patagonian Icefield (4070 m at the Mt. San Valentin).

(ii) Collision of the E-W trending MOHO structure against the N-S trending Andean batholith acting as an indenter sustaining the E-W trending Monte Zeballos ridge straddling the Andes and the Foreland.

(10) The dynamic evolution of the two main topographic features, together with the locus of maximum moisture at 47◦S during glacial events has resulted in producing the two largest glacial lobes of Patagonia (General Carrera-Buenos Aires and Cochrane-Peyrredon glacial lakes).

(11) The Patagonia Slab Window and South America asthenospheric dynamics (upward and corner flows, respectively) and their in–depth interaction appear to control the morphotectonic evolution of the whole studied segment through a powerful feedback loop between tectonics, morphology, and climate, at least for the past 3–4 Myr.

References related to the CTJ Project (Full texts available from Research Gate)

Main references, journal in bold characters

Bourgois, J., Frutos, J., Cisternas, M.E., 2021, The internal versus external dynamics in buiding the Andes (46°30’-47°30’S) at the Patagonia slab window, with special references to the lower Miocene morphotectonic frontline : a review, Earth-Science Reviews, 223, 103822, https://doi.1016/j.earscirev.2021.103822.

Bourgois, J., Frutos, J., Cisternas, M.E., 2021, The internal versus external dynamics in buiding the Andes (46°30’-47°30’S) at the Patagonia slab window, with special references to the lower Miocene morphotectonic frontline : a review, Earth-Science Reviews, 223, 103822, https://doi.1016/j.earscirev.2021.103822. Supplemental Data

Bourgois, J., Cisternas, M.E., Frutos, J., 2019, Comments on :« Glacial lake evolution and Atlantic-Pacific drainage reversals during deglaciation of the Patagonia ice sheet » by Thorndycraft et al., Quaternary Science Reviews, 203,102-127.

Bourgois, J., Cisternas, M.E., Braucher, R., Bourles, D., Frutos, J., 2016, Geomorphic records along the General Carrera (Chile)-Buenos Aires (Argentina) glacial lake (46-48°S), climate inferences and glacial rebound for the past 7-9 ka, A Reply, The Journal of Geology 124, p. 637-642, DOI: 10.1086/687551

Bourgois, J., Lagabrielle, Y., Martin, H., Dyment, J., Frutos, J., Cisternas, M.E., 2016, A review on forearc ophiolite obduction, adakite-like generation, and slab window development at the Chile Triple Junction area: uniformitarian framework for spreading-ridge subduction, Pure and Applied Geophysics 173, 3217-3246, DOI: 10.1007/s00024-016-1317-9 http://rdcu.be/nd50

Bourgois, J., Cisternas, M.E., Braucher, R., Bourles, D., Frutos, J., 2016, Geomorphic records along the General Carrera (Chile)-Buenos Aires (Argentina) glacial lake (46-48°S), climate inferences and glacial rebound for the past 7-9 ka, The Journal of Geology 124, p. 27-53. DOI: 10.1086/684252

Lagabrielle, Y., Bourgois, J., Dyment, J., Pelletier, B., 2015, Lower plate deformation at the Chile Triple Junction from the paleomagnetic record (45°30'S-46°S), Tectonics 34, p. 1646-1660, doi:10.1002/2014TC003773.

Guivel, C., Lagabrielle, Y., Bourgois, J., Martin, H., Fourcade, S., Cotten, J., Maury, R., 2003, Very shallow melting of oceanic crust during spreading subduction: origin of near trench Quaternary volcanism at the Chile triple junction, Journal of Geophysical Research, 108, 2345-2463.

Bourgois, J., Michaud, F., 2002, Comparison between the Chile and Mexico triple junctions areas substantiates slab window development beneath northwestern Mexico during the past 12-10 Myr, Earth and Planetary Science Letters, 201,35-44.

Corgne, A., Maury, C., Lagabrielle , Y., Bourgois, J., Suarez, M., 2001, La diversité des basaltes de Patagonie à la latitude du point triple du Chili (46°-47° lat. S) : données complémentaires et implications sur les conditions de la subduction, C.R.Acad.Sci. Paris, 333, p 363--371.

Lagabrielle, Y., Guivel, C., Maury, R., Bourgois, J., Fourcade, S., Martin, H., 2000, Magmatic-tectonic effects of high thermal regime at the site of active ridge subduction: the Chile triple junction model, Tectonophysics, 326, 255-268.

Bourgois, J., Guivel, C., Lagabrielle, Y., Calmus, T., Boulègue, J., Daux, V., 2000 Glacial-interglacial trench supply variation, spreading-ridge subduction, and feedback controls on the Andean margin development at the Chile triple junction area (45-48° S), Journal of Geophysical Research, 105, 8355-8386.

Guivel, C., Lagabrielle, Y., Bourgois, J., Maury, R.C., Fourcade, S., Martin, H., and Arnaud, N., 1999, New geochemical constraints for the origin of ridge-subduction-related plutonic and volcanic suites from the Chile triple junction (Taitao Peninsula and Site 862, Leg ODP 141 on the Taitao ridge), Tectonophysics, 311, 83-111.

Bourgois, J., and the Scientific crew, 1997, Unpublished report of the CTJ cruise, Chile trench (45° to 49°S), from Puerto Montt to Puerto Montt. 150 pages.

Bourgois, J., Martin, H., Lagabrielle, Y., Le Moigne, J., and Frutos Jara, J., 1996, Subduction-erosion related to spreading-ridge subduction: Taitao peninsula (Chile margin triple junction area), Geology, 24, 723-726.

Le Moigne, J., Lagabrielle, Y., Whitechurch, H., Bourgois, J., et al., 1996, Petrology and geochemistry of the ophiolitic and volcanic suites of the Taitao peninsula, Chile triple junction area. Journal of South American Earth Sciences, 9, p.43-58.

Lagabrielle, Y., Le Moigne, J., Maury, R.C., Cotten, J., and Bourgois, J., 1994, Volcanic record of the subduction of an active spreading ridge, Taitao Peninsula (Southern Chile), Geology, 22, 515-518.

Le Moigne, J., Lagabrielle,Y., et Bourgois, J., 1993, Ophiolites en contextes de dorsale en subduction : nouvelles données sur la péninsule de Taitao (sud Chili). C.R.Acad.Sci., Paris, t. 317, Sér.II, p. 403-410.

Bourgois, J., Lagabrielle, Y., Le Moigne, J., Urbina, O. Janin, M.-C., and Beuzart, P., 1993, Preliminary results of a fiels study of the Taitao ophiolite (Southern Chile) : Implications for the evolution of the Chile triple junction. Ofioliti , v. 18, n°2, p. 113-129.

Corgne, A., Maury, C., Lagabrielle , Y., Bourgois, J., Suarez, M., 2001, La diversité des basaltes de Patagonie à la latitude du point triple du Chili (46°-47° lat. S) : données complémentaires et implications sur les conditions de la subduction, C.R.Acad.Sci. Paris, 333, p 363--371.

Deruelle, B., et Bourgois, J., 1993, Sur la dernière éruption du volcan Hudson (Sud Chili, août 1991). C.R.Acad.Sci., Paris, t. 316, Sér. II, p. 1399-1405.

Guivel, C., Martin, H., Lagabrielle, Maury, R.C., Y., Fourcade, S., Bourgois, J., 1999, Activité magmatique liée à la subduction d’une dorsale océanique active: origine des dacites du point triple du Chili. Réunion  Spécialisée de La SGF, Villefranche sur Mer.

Guivel, C., Lagabrielle, Y., Bourgois, J., Martin, H., Maury, R.C., and Fourcade, S., 1998, Subduction d’une dorsale océanique active : le point triple du Chili (46°S). Réunion des Sciences de la Terre Brest. p. 126.

Guivel, C., Lagabrielle, Y., Bourgois, J., Maury, R., Martin, H., Arnaud, N., and Cotten, J., 1996, Magmatic responses to active spreading ridge subduction: multiple magma sources in the Taitoa peninsula region (46°-47°S, Chile triple junction). Third ISAG, St Malo (France). Géodynamique Andine, ORSTOM éditions, p. 575-578.

Le Moigne, J., Lagabrielle, Y., Maury, R., et Bourgois, J., 1993, Le volcanisme associé à l'ophiolite de Taitao (région du point triple du Sud du Chili) : conséquence de la subduction d'une ride océanique active. Coll. Géosciences Marines, S.G.F., Paris, Décembre 1993.

Le Moigne, J., Lagabrielle, Y., Maury, R., Bourgois, J., and Juteau, T., 1993, Petrology and geochemistry of the Taitao Ophiolite volcanic-plutonic suite (Chile Triple Junction region). Second International Symposium on Andean Geodynamics. ISAG 93, Oxford 21-23 Septembre 93, v. , p.

Bourgois, J. et l'équipe de programme : Lagabrielle, Y., Maury, R., Le Moigne, J., Vidal, P., Cantagrel, J.-M., Martin, H., et Urbina, O., 1992, Géologie de la Péninsule de Taitao (Point Triple du Chili, 46°-47°S) : Obduction de l'ophiolite de Bahia Barrientos entre le Miocène et le Pléistocène. Colloque DBT- INSU, Toulon, Novembre 1992.