Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina). INGEODAV (Instituto de Geofísica "Daniel A. Valencio")

Menichetti, Marco

Tassone, Alejandro

Diposit Digital de Documents de la UAB

GEOSUR 2004: Mesozoic to Quaternary evolution of Tierra delFuego and neighbouring austral regions IGeologica Acta,  Vol .5 ,  Nº  4 ,  2007,  283-286Avai lable onl ine at  www.geologica-acta.com© UB-ICTJA 283M. MENICHETTI and A. TASSONEIstituto di Scienze della Terra. Università di Urbino.Campus Scientifico Universitario. 61029 Urbino. Italy. E-mail: menichetti@uniurb.itCONICET-Instituto de Geofísica “Daniel A. Valencio” (INGEODAV). Departamento de Geología. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos AiresCiudad Universitaria. Pabellón 2. 1428 Ciudad Autónoma de Buenos Aires. Argentina. E-mail: atassone@gl.fcen.uba.arThe impetus for the publication of thematic issues onTierra del Fuego geology and geophysics born from thewealth of new information presented at Geosur Interna-tional Symposium held in Buenos Aires, Argentina, inNovember 2004. The first aim of the organizing commit-tee of Geosur 2004 was to provide sets of syntheticpapers that could provide a rather comprehensive reviewof the geological and geophysical knowledge of the Tierradel Fuego region; a second aim was to publish more spe-cific papers focused on subjects still under study anddebate, including original contributions from Tierra delFuego and neighbouring areas of the Patagonian Andesand Scotia plate.From the first geographical exploration in the six-teenth century to the modern geophysical researches inthe southern oceans, various approaches to the knowledgeof the Tierra del Fuego have been proposed by differentgeological schools from Argentina, Chile, Italy, Scandi-navia, North America and many others countries. Sincelong time, this remote region of the world has stimulatedthe curiosity and the fantasy of many researches in naturalsciences and in particular in geological sciences. Amongthe pioneering works on Tierra del Fuego geology are thefirst descriptions of Cretaceous “clay-slate broken bydikes” and the recognition by Darwin, during his voyageon the HMS Beagle in 1834, of the metamorphic origin ofthe glacial boulders in the north eastern part of the Island(Darwin, 1845). It must also be mentioned the first geo-logical map of the Island by Bonaraelli (1917; Fig. 1)since it synthesized all the geological information thenavailable and still now it agrees with the modern geologi-cal studies.Tierra del Fuego Island presents a complex geologicaland structural architecture comprised between the Chiletrench in the west and the transform boundaries of thewestern Scotia Sea in the south. The geodinamic historycan be synthetized starting from the Mesozoic in thesouthern margin of the Gondwanaland, when an exten-sional Jurassic-Early Cretaceous phase was followed bythe Late Cretaceous collisional events, with the formationof the Andean Cordillera and the Magallanes and Mal-vinas foredeep basins. The Cenozoic evolution of thisorogen in the southern tip of South America was stronglyinfluenced in the Oligocene by the opening of the ScotiaSea, with the splitting of the Antarctic Peninsula and withthe superposition of important transform faults. The lastglacial events modelled and contributed to the presentlandscape.This first thematic issue in Geologica Acta presentscontributions from a wide disciplinary scope that includesGeodesy, several geophysical techniques (Paleomagne-tism, Gravimetry, Seismic reflection and bathymetricstudies) and Geomorphology. The second thematic issuein the same journal (Menichetti and Tassone, in press2008 ) will include new contributions focused on Strati-1 221GEOSUR 2004: Mesozoic to Quaternary evolution in Tierra del FuegoM. MENICHETTI and A. TASSONE284Geolog ica  Acta ,  Vo l .5 ,  Nº  4 ,  2007,  283-286Reproduction of the first geological map of Tierra del Fuego (Bonarelli, 1917). A) Batholith facies. 1: Diorite to granite batholith facies. B) Batholith roof. 2: Metamorphic schists; 3:Feldspar schists (Lower group); 4: Feldspar schists (Upper group); 5: Microgranulites. C) Ancient eruptive rocks. 6: Propylites. D) Metamorphic series with intrusive and eruptive rocks. 7: (Paleozoic)schists; 8: Granite laccoliths;9: Quartz prophyries, tuffs and associated rocks. E) Mesozoic-Quaternary record. 10: Jurassic-Cretaceous Series; 11: Lower Cenozoic marine horizon 12: Upper Ceno-zoic marine horizon 13: Basal Cenozoic continental conglomerate; 14: Sands, tuffaceous clays and true tuffs (Santacruceana Series)- continental Cenozoic; 15: Basalts; 16: Distal moraines; 17: Qua-ternary deposits; 18: Monte Burney volcano.FIGURE 1graphy, Structural Geology, Petrology, Seismostratigraphyand Hydrocarbon exploration.The long-lasting debate about the orogene vs. oroclinenature of the Fuegian Andes is addressed on paleomag-netic grounds (Rapalini, this issue). The revision of theavailable paleomagnetic data in the southern Patagonianand Fuegian Andes reveals systematic counterclockwiserotations, which might indicate the secondary orogen cur-vature. However, the variable quality of these revisedpaleomagnetic data hinders a conclusive definition of thesouthernmost Andean curvature.New insights into the dynamics and evolution of theChile trench between 50°S and 56°S are provided by seis-mic reflection profiles combined with satellite derivedgravity maps (Polonia and Torelli, this issue), whichreveal varying frontal wedge morphology, different ratesof accretion and underthrusting and a high degree ofstructural diversity within the accretionary wedge. Takinginto account structural style, internal deformation, andseafloor morphology, the authors distinguish fourdomains within the studied portion of the Antarctic/Scotiaplate boundary. The segmented character of the continen-tal margin would be controlled by oblique structuraltrends belonging to the Scotia/South America plateboundary.A synthetic picture of the onshore anatomy of theMagallanes-Fagnano deformation zone is provided bymeans of gravity and bathymetric data of the central-east-ern part of the Isla Grande de Tierra del Fuego (Lodolo etal., this issue). The regional gravity anomaly trend showsa progressive southward negative gradient over whichbroadly E-W-trending gravity minima are superimposed.The authors interpret these relative minima as represent-ing elongated and narrow sedimentary basins formedwithin the principal displacement zone of the Magallanes-Fagnano transform system. The presented bathymetricmap of the Lago Fagnano, in turn, reveals a partitionedasymmetric lake basin with flat depocenters as generallyfound in similar pull-apart settings developed withintransform systems. Del Cogliano et al. (this issue) present an improve-ment of the previously known regional geoid (based onclassical GPS levelling and gravimetric data) of Tierra delFuego. The authors expose the results of a successfulexperiment directed to determine the equilibrium watersurface topography of Lago Fagnano -inaccessible forclassical GPS levelling and gravimetric data acquisition.The employed method measured the ellipsoidal mean sur-face heights of the water body using a GPS buoy and tidegauges and the achieved accuracy is comparable with thatof GPS levelling. Moreover, the derived geoid undula-tions show a strong correlation with the local mountainsand the lake floor topography.Combined bathymetry and gravity data allowed mo-delling the crust-mantle interface of the Early MiocenePowell Basin (Chávez et al., this issue). This is a smallocean basin located within the Antarctic Plate close to thelimit with the Scotia Plate. Mean depth of the crust-man-tle interface in the Powell Basin is estimated in 13.5 km.The modeled 3D geometry -computed by numericalinversion methods- of the crust-mantle interface providesevidence of a NW-SE oriented axis, which supports theinferred existence of inactive spreading ridges within thebasin. Increase in the modeled crustal thickness towardthe continental margins is considered as resulting fromthe asymmetric nature of the basin.The Quaternary evolution of two contrasting coastalareas of Tierra del Fuego is provided by Bujalesky (thisissue): the northeastern Atlantic coast and the Beagle Chan-nel. The former is located at the extra Andean lowlandswithin the South-American Plate where the southernmostPliocene and Pleistocene beaches recorded in the worldoccur. This area was a free-ice area since 1.8 Ma B.P. Dur-ing the Holocene gravel barriers plugged the inner estuariesof the palaeoembayments suggesting a relative sea level fallof 0.214 m each 1,000 years. The Beagle Channel is a 300m depth basin running between the Pacific and Atlanticoceans, located at the active seismic-tectonic setting of theFuegian Andes within the Scotia Plate. This 5 km wide tec-tonic valley was covered by ice during the Last Glaciationand was rapidly flooded by the sea immediately after theYounger Dryas, 11,000 year B.P. Holocene raised beachesalong the channel allow estimating the average tectonicuplift for this period ranging from 1.5 to 2.0 mm/year.As a final linguistic note, it must be emphasized thatin the papers presented here the terms Fuegian andFueguian are synonymous and both are used as adjectivesmeaning “of Tierra del Fuego” or “pertaining to Tierra delFuego”.ACKNOWLEDGEMENTSMost of the papers presented in this volume have resultedfrom researches carried out in the last decade under the sponsor-ing and the financial support of Antarctic national scientific pro-grams that have been jointly managed by Argentinean and Ita-lian Institutions. The continuous scientific cooperation betweenArgentinean and Italian researchers was developed within theframe of several joint projects dealing with Tierra del Fuegogeology and geophysics (PNRA-FORTE Project), onshore/off-shore geophysical data acquisition (PNRA-TESAC Project) andthe installation in 1994 of the broad-band seismological networkGEOSUR 2004: Mesozoic to Quaternary evolution in Tierra del FuegoM. MENICHETTI and A. TASSONE285Geolog ica  Acta ,  Vo l .5 ,  Nº  4 ,  2007,  283-286Alejandro A. Tassone graduated in 1989from the Buenos Aires University (Argen-tine) and in 1998 obtained his PhD fromBarcelona University (Spain). He ispresently a researcher of the CONICET,the national council of scientific andtechnological research of Argentine,working at the the D. Valencio Institute ofGeophysics of the Department of Geology(Buenos Aires University). His main research interest is related to theapplication of several geophysical methodologies (seismic reflection,gravimetry, magnetometry, etc.) in deciphering the tectonostratigraphicand geodynamic evolution of the Patagonian and Antarctic continentalmargins.Marco Menichetti received PhD in struc-tural geology from the University ofPerugia, Italy, in 1991. He spent thepostdoctoral fellowship working on thecrustal seismic survey project in CentralApennines. From 1995 to 1997 he was aconsultant for oil and water companies.He joined Urbino University, Italy, in 1998 where he is currently incharge of the degree courses on Structural geology and Tectonics.His research interest focus on field geology and structural conceptsand methods for interpretation of mountain chains.in the Scotia Arc region, among other activities. We mustexpress our deep gratitude to all the colleagues and friends thatin many different ways helped us in Tierra del Fuego duringthese years. We particularly thank the Italian Embassy inArgentina for its encouragement and financial support in theorganization of the Geosur 2004 International Symposium. Theeditors thank the following colleagues and friends who kindlyhelped with the papers’ review submitted to this Geologica Actaissue: C. Ayala (Spain), P. Colantoni (Italy), R. Chávez (Mexico),M. Fernández (Spain), M. Garcés (Spain), R. López (Argentina),V. Ramos (Argentina), M. Sevilla (Spain), R. Somoza (Argenti-na), J.F. Vilas (Argentina) and T. Zapata (Argentina). We are par-ticular grateful to the Bonarelli family for allowing us to publishthe original of the first geological map of the Tierra del FuegoIsland. Our special acknowledgement addressed to Lluís Cabreraand Ángeles Santos (Scientific and Managing Editors of Geolo-gica Acta, respectively) and to the whole Managing ScientificCommittee of the journal for their constant support during theeditorial process. Finally, thanks are also due to Miquel Canalswho encouraged us to edit this thematic issue.REFERENCESBonarelli, G., 1917. Tierra del Fuego y sus turberas. Anales delMinisterio de Agricultura de la Nación. Sección Geología,Mineralogía, Mineria. Buenos Aires, Tomo 12, 3, 1-119. Bujalesky, G.G. 2007. Coastal geomorphology and evolution ofTierra del Fuego (Southern Argentina). Geologica Acta, 5(4),337-362.Chávez, R.E., Flores-Márquez, E.L., Suriñach, E., Galindo-Zaldívar, J.G., Rodríguez- Fernández, J.R., Maldonado, A.,2007. Combined use of the GGSFT data base and on boardmarine collected data to model the Moho beneath the PowellBasin, Antarctica. Geologica Acta, 5(4), 323-335.Darwin, C.R., 1845. Journal of researches into the natural histo-ry and geology of the countries visited during the voyage ofH.M.S. Be agle round the world, under the Command ofCapt. Fitz Roy, R.N. 2d edition. London, John Murray.Del Cogliano, D., Dietrich, R., Richter, A., Perdomo, R., Hor-maechea, J.L., Liebsch, G, Fritsche, M., 2007. Regionalgeoid determination in Tierra del Fuego including GPS lev-elling. Geologica Acta, 5(4), 315-322.Lodolo, E., Lippai, H., Tassone, A., Zanolla, C., Menichetti, M.,Hormaechea, J.L., 2007. Gravity map of the Isla Grande deTierra del Fuego, and Morphology of Lago Fagnano. Geo-logica Acta, 5(4), 307-314.Menichetti, M., Tassone, A. (eds.), in press 2008. GEOSUR2004: Mesozoic to Quaternary evolution of Tierra del Fuegoand neighbouring austral regions (II). Geologica Acta, 6(1).Polonia A., Torelli, L., 2007. Antarctic/Scotia plate convergenceoff southernmost Chile. Geologica Acta, 5(4), 295-306.Rapalini, A. 2007. A paleomagnetic analysis of the PatagonianOrocline. Geologica Acta, 5(4), 287-294.GEOSUR 2004: Mesozoic to Quaternary evolution in Tierra del FuegoM. MENICHETTI and A. TASSONE286Geolog ica  Acta ,  Vo l .5 ,  Nº  4 ,  2007,  283-286

GEOSUR 2004 : Mesozoic to Quaternary evolution of Tierra del Fuego and neighbouring austral regions I

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GEOSUR 2004 : Mesozoic to Quaternary evolution of Tierra del Fuego and neighbouring austral regions I

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