Geomorphological AND gEOPHYSICAL EVIDENCESFORNEOTECTONICS, cENTRAL AND Southern Brazil

Paulo César Soares1, Silvana Bressan Riffel2, Alberto P. Fiori 3

1 FUNPAR/UFPR,Projeto Falhas, Curitiba,

2 School of Earth Sciences, The University of Queensland,

3 UFPR,Projeto Falhas, Curitiba,

Abstract

Paleosurfaces, correlative deposits, ages, lineaments, heat flow and Curie surface are used in an integrated way to reach some conclusions about the complex histories of uplift, denudation and tectonic movements in the Meridional plateau region, including coastal ranges. The South American peneplane is taken as reference surface and contoured showing differential uplift. Transcurrent faults in correlative deposits, recorded in field indicate concentrated zones of deformation. Heat flows and low depth of estimated Curie surface confirms heat transfer in narrow zones. The Lancinha lineament (Cubatão - Alem Paraiba) is the focused fault in the work area. Active tectonics and heat flux are associated with crustal flexural deformation, modified by differential movement along fault zones.

INTRODUCTION -The Late Cretaceous stable conditions recorded from fission-track ages (90-60 Ma, Gallagher et al., 1994; Hiruma et al., 2010) refer to the Bauru sedimentation cycle in SE South America. It is followed by Paleocene uplift ages(60-40 Ma)denudation and cooling. A late Eocene age for South ameriacan peneplane is concluded based in geological record of Chaco Paraná and Santos basins and FTA.

Fig. 1 – Location of investigated region with Paraná basin coastal ranges and Miocene interior sea.

METHODS - Data and information from tectonic events, geoforms associated to correlative residual weathering and sediments over paleosurfaces from southeastern South America (fig. 1) are compared to potential correlative sequences either in interior (Chaco Parana) as marginal basin (Santos) and to regional rifting basins (Taubaté, Curitiba). Uplift and quiescence times are interpreted from fission track ages (FTA) in literature. Heat flow (HF) results are regionally extended bounded by lineaments in a region of more dense information (PR, SC). Deepness of Curie (DC) surface was estimated from magnetic data.

RESULTS - South American Peneplane, as a surface of minimum hydraulic erosion with maximum chemical erosion processes, needs a long time of tectonic quiescence. The record of Paleocene to late Eocene erosion and weathering in the continent is indicative of extensive erosion ander warm climate and uplift. In mid Eocene uplift slown down and climate become warmer, from Central Brazil to south down to 34oS longitude as seen in Paraná and Uruguay; fossil termites nests is a common feature. Correlative reddish siliclastic deposits occur in Chaco-Parana interior and Santos and Pelotas basin (Pereira & Macedo 1990).In Paraná, the Fe-laterite peneplane precedes Curitiba plateau and Serra do Mar formation. In Uruguay, the Fe-lateritic paleosurface precedes the calcrete-silcrete paleosurface and Fray Bento Fm of Late Oligocene age (Ubilla, 2004). Both precede the Miocene transgression (Camacho Fm; Perea & Martinez 2004).

First pediplanation (Pd2, Bigarella and Ab Saber 1956) and Curitiba rift basin fill (Salamuni et all. 2003) are pene-contemporaneous. High plateaus pediplanes as Japi and Campos are considered as result o extensive pediplanation (Pd2), in view of remaining insebergs and of Fe poor and Al-silica rich residual weathering mantle (Modenesi-Gautieri et al 2011). In similar way kaolin residual deposits are found over Pd2 remnants over gneiss and volcanic rocks in Serra do Mar.A second pediplane is preserved locally everywhere in region, and referred as Pd1, probably Miocene. These deposits are faulted in Curitiba plateau. The big escarpment from Serra do Mar to coastal plain is the result of back strip of this PD1 paleosurface.

Uplift from Oligocene - This uplift and erosion cycle have two main step: mid Oligocene (Santos platform erosion and faulting) and Pliocene (Late Miocene) to present (platform prograding wedge). Fission track analysis(Gallagher et al., 1994; Franco-Magalhaes 2010) indicate that East Paraná larger upliftwas preceding SAP (40-60 Ma) and during late Miocene and Pliocene (last 20 Ma). This means that the main uplift was after Pd2 pediplanation and even more recent, after PS1, which agrees very well with geomorphologic and field observation of altimeric position of paleosurface and deposits, including the prominent escarpment sculptured on PS1 and their inselbergs. Faulting affecting both are recovered in field.

Structural contour of PSA and heat flow - Contour map (figure ) shows a high bulge in Central Paraná and Santa Catarina, mainly forced by points in SantosBasin and in continent interior.Heat flow map (from Soares et al 2011) shows high values associated with higher uplift.

/ / Figure 2 Left - Uplift of South America peneplane (SAP) during Neogene (grey <100m; green/brown=600m;pale=over 1300 m) Along coastal range SAP altitudes are underestimated by absence of remains (SP and PR> 2000m; SC>1700). Right - Heat flow from oil wells in Parana basin estimated by many authors ( mainly Hurter and Pollack 1996). The colored area north of SC is detailedin next figure)

The South American paleosurface is characterized by intense planation, chemical leaching, Fe-laterization crust, summit positioning, implying a long time of tectonic quiescence during warm and semi humid climate. In some place it is covered by ferruginous quartz conglomerate; other places, gravel, sands and gray clays cover the surface.

Figure 2 Left- Lineaments from many sources (Soares et al. 2009), the two main correspond to Lancinha (NE-SW) and Itapirapuã (NNE) faults in basement (at the extreme northeast of the area (green line); Center – Depth of Curie surface oscillating from 10 (red/purple) to 40 (green/blue) km indicating narrow zones of high heat flow; right – contour of heat flow estimates from deep wells (mainly from Hurter .&Pollack 1996), showing heat flow in the range 40 to 80 mW/m2 (blue/purple = 56 mW/m2); high heat flow are associated to fault zones (square delineates the area of left figures)(partial maps from Soares et al. 2011).

DISCUSSION AND CONCLUSIONS- In the continental interior,lateritic South American peneplane surface are documented in isolated inselbergs and plateaus with warm climate indicator untilUruguay and Chaco. In coastal ranges it was uplifted and eroded before and during the emplacement of the rift basins (Oligocene), because was not preserved as basement. The subsequent large erosion event, mostly under semi-arid and cold climate, have constructed extensive pediplane surfaces in Serra da Mantiqueira (Campos Surface) and Serra do Mar (PD2 in Paraná).At this time climate changed abruptly, depositing feldspatic sands and green muds with caliche paleosoils (Guabirotuba Fm inCuritiba basin, and Taubaté Group) toward coastal ranges. Toward Paraná basin interior, records of Late Oligocene have similar lithologies and a rich fossil record inFray Bentos Fm in Uruguay (Ubilla, 2004). The larger uplift event may have been after Pd1 pediplanation, Miocene transgression and Pd2 pediplanation, during late Miocene to Pliocene, feeding the prograding clastic wedge in Santos and documented in FTA and annealing zone. At the low Paraná-Paraguay-Uruguay basin, early to mid Miocene sea cover continental cold and semiarid deposits, up to 10 Ma. They are extensively exposed and transitional to mid Pleistocene alluvial deposits (Perea & Martinez 2004). This is considered the main time of neotectonic activity which maintain active heat flow in narrow zones along crustal discontinuities.

CONCLUSIONS - Tectonic activity are powerful generator of heat in faults associated with continental uplift. The heat flow may double in narrow fault zones. Paraná basin and neighbor regions presents active uplift and faulting as deduced from paleosurfaces succession and altimetry positioning, mainly during Pliocene and Quaternary, contemporaneous to Quechua Andean activity, continental plate flexures and marginal basin clastic wedge.

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