Why the Rio Quente Is a Special Spring Within the Caldas Novas Thermal Aquifer, Central Brazil?
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1st WSEAS International Conference on ENVIRONMENTAL and GEOLOGICAL SCIENCE and ENGINEERING (EG'08) Malta, September 11-13, 2008 Why the Rio Quente is a special spring within The Caldas Novas Thermal Aquifer, central Brazil? LUIZ JOSÉ HOMEM D´EL-REY SILVA, DETLEF HANS-GERD WALDE, JOSÉ ELÓI GUIMARÃES CAMPOS RODRIGO ÁVILA CIPULLO Instituto de Geociências Universidade de Brasília Campus Darcy Ribeiro, Asa Norte, CEP 70910-900, Brasília, DF BRAZIL Abstract: - Thermal waters up-rise through Precambrian rocks in the inner part of the Neoproterozoic Brasília Belt (Tocantins Province, central Brazil) and make of the town of Caldas Novas an outstanding tourism place. They have fed a boom in the economy of the region around the Caldas Novas dome, a tectonic structural window ~20 km-long and ~12 km-wide cored by sub- greenschist facies quartzite, metasiltite, meta-argillite, slate, phyllite, and metarhythmite (Paranoá Group) and mantled by a nappe of biotite-quartz schist and garnet-bearing chlorite-muscovite schist (Araxá Group). Multidisciplinary geology studies have been supported from the local community of tourism entrepreneurs concerned with environmental issues, the quality of the underground aquifers, and with the possibility of artificial recharge. Rocks of the Paranoá Group record a passive margin-like basin developed 1300 – 900 Ma ago along the western coast of the São Francisco paleo-continent, and rocks of the Araxá Group record sedimentation/volcanism in a 900-800 Ma back arc basin developed between the paleo-continental margin and an intra-oceanic island arc to the west. Amalgamation of the arc and back-arc rocks to this margin led to ESE- driven transport of a nappe of Araxá Group rocks over the Paranoá Group rocks. All these rocks exhibit evidence of D1-D2 ductile deformation and metamorphism according to regional contraction in the WNW-ESE direction, during the first (~750-650 Ma old) stage of the Brasiliano orogeny. A new tectonic pulse (D3) shortened all D1-D2 tectonites, 630-620 Ma ago, and developed, in the southern segment of the belt, km-scale and NNW-trending F3 folds, such as the Caldas Novas dome F3 braquiantiform. The anomalous thickness of 1,000 m of quartzite in the core of the dome (geophysical evidence) is likely due to a duplex of basal quartzite layers of the Paranoá Group. In the western margin of the dome the thermal waters flow within Paranoá basal quartzite at a rate of 1.6 m3/s and reach surface as hot as 50 0C, forming a true river of hot waters. To the E-NE of the dome, in the Araxá schist flooring the town of Caldas Novas, the water flows at a much smaller rate. Hydrogen, carbon and oxygen isotopes data point to the thermal waters as being meteoric in origin, and the temperature indicates up-rise from depths of about 1,000 m. Data from detailed structural studies strongly suggest that the path for up-rise is controlled by a net of open surfaces that include the S3 axial planar foliation and fractures associated mostly to the D3 compression, combined with the stiffness of basal rocks of both the Paranoá and Araxá Groups. The 1.6 m3/s flow of thermal waters in the western margin of the dome relates to a combination of the thickness and asymmetry of the D3 duplex with the effects of late-D3 gravity slide in the area. Key-words: - Thermal water aquifer; Caldas Novas dome, Brasília Belt, Neoproterozoic, Brasiliano orogeny, central Brazil. 1 Introduction The province is bounded by the Parnaíba The area of Caldas Novas, Goiás State – and Paraná Phanerozoic sedimentary basins, central Brazil, is part of the Internal Zone of and results from the collision of the paleo- the Brasília Belt. This one forms, together with continents precursors of the Amazonian and the Araguaia and Paraguay belts, a São Francisco cratons, as recorded by poly- Neoproterozoic geotectonic unit known as the deformed and metamorphosed Archean- Tocantins Province (Fig. 1). Neoproterozoic rocks. ISSN: 1790-5095 70 ISBN: 978-960-474-001-7 1st WSEAS International Conference on ENVIRONMENTAL and GEOLOGICAL SCIENCE and ENGINEERING (EG'08) Malta, September 11-13, 2008 460W Neoproterozoic Phanerozoic sedimentary cover within the belts A Belts and in the Paraná and Parnaíba Basins T O C A N T I N S P R O V I N C E A 0 Phanerozoic 16 S T Time OTHER BELTS BRASÍLIA BELT T = cover Tocantins SF PARAGUAY High-PT nappes (southern part of the belt) Province Eo- Cratons Paleozoic Cuiabá and A = Amazon Alto Paraguay a SF = São Francisco Groups Anápolis-Itauçu complex o o Araxá, Ibiá, and 50 W46W N Bambuí Groups Neo- Tonalitic orthogneiss (arc), Parnaíba Proterozoic Basin volc-sed sequences, and slices of Archean gneiss Amazon Belt RBF Mafic-Ultramafic layered Araguaia 12oS Craton MRT ARAGUAIA complexes + volc sequences Meso- to Paranoá Canastra São Estrondo Neo- and Group Group Proterozoic Pt Tocantins Araí and Serra da Mesa Francisco Groups Groups CV Ct P Craton SDF Paleo- A Proterozoic ParaguayBelt Paleoproterozoic F gneisses, orthogneisses, and PZHS B Bu Reworked: V-S sequences 16oS Archean gneisses and EZ orthogneisses Amazonian Archean Gneisses, São Francisco Paleo-continent MA IZ Paleo-continent orthogneisses, and Brasília Belt greenstone belt CN sequences P Brasília A = Araxá, Bu = Buritis, CN = Caldas Novas, a Towns B (Federal Ct = Cavalcante, CV= Campos Verdes, r District) a n F = Formosa, Pt = Porangatu á B Fig. 2 a MRT = Maranhão River Thrust, RBF = Rio dos Bois Fault, s b i A SDF = São Domingos Fault, PZHS = Pirineus Zone of High Strain n 20oS 50oW 0 Km 500 Thrusts, D -D Maximum D regional Domain boundary 1 2 3 Nappes compression shortening Fig. 1: Summary map displaying the main tectonic For this reason, since about two years ago, provinces in Brazil (a) and the central part of the the local association of entrepreneurs that Tocantins Province, as well as the three main explore the thermal waters (AMAT) has lithotectonic units of the Brasília Belt (b; legend to supported an international and multi- the right): the Magmatic Arc – MA; the Internal disciplinary scientific project destined to study Zone – IZ; and the External Zone – EZ. The EZ includes part of the Neoproterozoic sedimentary the area and understand better the geological cover of the São Francisco craton. A = Araxá, and controls of the thermal aquifer, aiming to find P = Paranoá. Adapted from [1] and [2]. alternatives for future planning. The Caldas Novas dome is an elliptical structure with a NNW-trending axis as long as The relevance of the Caldas Novas area 20 km, and minor axis of ~10 km. Since [3] rests on a structural dome and on the Rio the dome is known as a structural window, as Quente, Caldas Termas Clube, and Lagoa it exhibits a core of sub-greenschist facies Quente springs of thermal waters (Fig. 2). The quartzite and finer grained siliciclastics rocks exploration of the thermal waters for tourism of the Meso-Neoproterozoic Paranoá Group and leisure purposes has improved tectonically juxtaposed by a nappe of dramatically the economy in Caldas Novas and greenschist-amphibolite facies mica schist of other two towns in the surroundings (Fig. 2a). the Neoproterozoic Araxá Group. A boom in the economy of the area has Nevertheless, solely more recently the area been possible in the last twenty years because has been the locus of detailed geological of an exponential growth in the volume of studies: [4] described the Paranoá Group pumped thermal waters from artificial wells, lithostratigraphy units; [5] and [6] described but also brought to light a crescent concern the rocks of the Araxá Group, as well as the about the capacity of the underground tectonic structures and the structural-tectonic reservoir to maintain the current volume and evolution of the whole area surrounding the temperature of the thermal waters. Caldas Novas dome, whereas [7], [8], and [9] ISSN: 1790-5095 71 ISBN: 978-960-474-001-7 1st WSEAS International Conference on ENVIRONMENTAL and GEOLOGICAL SCIENCE and ENGINEERING (EG'08) Malta, September 11-13, 2008 have studied the main physical and chemical Among them, the Rio Quente (or Hot parameters and other aspects directly linked to River) is a 10 m-wide natural stream that starts the thermal waters and underground aquifers. to flow in the upper part of the western flank of the Caldas Novas dome. The TWs rise on 736000 738 740 742 744 746 748 750 752 754 756 758000 0 Brasília 32 20 22 surface at a temperature of ~50 C and total 8042000 3 17 LQ 27 rate of 1 m /s, from a series of open spaces Morrinhos ETE Y DR 20 14 8040 30 33 (described ahead) in the basal layers of 15 17 25 15 60 30 8038 quartzite of the Paranoá Group, within the 27 66 53 30 CTC Airport 8036 artificial pools of the Pousada Park (Fig. 3). ESPLANADA 25 22 C A L D A S 25 22 N O V A S 21 14 8034 PESCAN Neoproterozoic Pousada N o v a s Araxá Group 8032 20 X C a l d a s Schist with lenses of quartzite, metapelite, metasiltite, and 20 ultramafic rocks RIO D o m e 8030 QUENTE Meso-Neoproterozoic Corumbá 1 17 8028 Paranoá Group dam 10 45 Metasiltite, meta-argilite, argillaceous metasiltite Eastern limit 8026 20 of the area Metarhythmite: intercalated layers of quartzite and 25 05 affected by metasiltite the late-D3 8024 extension Quartzite: argilaceous, laminated, immature, 15 bronwish-red colour 17 15 recorded by 02km foliation d´ 8022 Ortoquartzite: silicified, wave ripples, crossed (see text) stratification, white colour São Paulo a 8020000 Bedding (S ) Main tectonic foliation Nappe D -D 0 17 1 2 20 and dip (S /S ) and dip 1 0 Horizontal Axial trace of km-scale F folds Pre-D3 dip 3 Braquiantiform F Araxá Group (dashed = inferred) 3 D2 nappe b Paranoá Group Future dome Lineaments in aerial photographs Future D3 thrust Paved road PESCAN = Parque Estadual da Non-paved road Serra de Caldas Novas D2 nappe D3 thrust c CTC = Caldas Termas Clube, DR = Di ROMA Future duplex Natural show of ETE = Estação Tratamento Esgoto, thermal waters LQ = Lagoa Quente D nappe Dome surface (eroded) Foliation d´ 2 X Rio Quente CTC LQ Y The Rio Quente is unique, and there is not another natural spring of TWs in Paranoá quartzite layers elsewhere around the dome.