Trondhjemites, tonalites and diorites in the South Portuguese Zone and their relations to the vulcanites and mineral deposits of the Iberian Pyrite Belt

Abstract

Zusammenfassungin der Siidportugiesischen Zone treten n6rdlich des Pyritgfirtels enge Vergesellschaftungen von Dioriten, Tonaliten und Trondhjemiten auf. Der Zeitraum ihrer Platznahme ist p~ikarbonisch und nicht, wie bisher allgemein angenommen, variszisch-postorogen. Die trondhjemitische Intrusivsequenz und die unterkarbonische Spilit-Keratophyr-Assoziation sind in weiten Bereichen durch komagmatische Herkunft verbunden. Gemeinsamkeiten beider Abfolgen sind ihre Na-Dominanz, die niedrigen Gehalte an grot~ionigen Elementen, die Anzeichen f~r ein wasserreiches Ausgangsmagma und die mangelhafte Verschlackung des Elementpotentials, das in den Sulfid-und Manganlagerst~itten des Pyritgiirtels w~.hrend postvulkanischer, hydrothermaler Prozef~e angereichert wurde. Die mineralogisch wie geochemisch primitive Zusammensetzung sowohl der Plutonite wie der Vulkanite, ihr Ernptionsmodus von saurer zu basischer Fazies sowie ihre Position im orogenen Ablauf deuten darauf bin, dal~ sie die Produkte einer sukzessiv fortschreitenden Aufschmelzung subduzierender, ozeanischer Kruste darstellen. Die trondhjemitischen Intrusiva sind die Initialite innerhalb der magmatisch-orogenen Entwicklung. AbstractIn the South Portuguese Zone close associations of diorites, tonalites and trondhjemites occur north of the Pyrite Belt. The period of their emplacement is Pre-Carboniferous and not, as has generally been assumed, Variscanpostorogen. The trondhjemitic intrusive suite and the Lower Carboniferous spilite-keratophyre association are related through their comagmatic derivation. Both series share sodium dominance, low concentrations of large-ion lithophile elements, indicators of a water-rich original magma and a deficient scorification of the element potential, which was acummulated in the sulphide and manganese deposits of the Pyrite Belt through post-volcanic hydrothermal processes. The mineralogically and geochemically primitive composition of both plutonites and vulcanites, their mode *) Authors' address: W. SC~IV3TZ, J. EBNETH and K.-D. MEYER, Institut f~ir Angewandte Geologie, Freie Universit~.t Berlin, Wichernstr. 16, 1000 Berlin 33 of eruption from acid to basic facies as well as their position in the orogenic process indicate that they represent products of a successively proceeding partial melting of subducting oceanic crust. The trondhjemitic intrusives are the initialites in the magmatic-orogenic development. R~sum~Dans la zone sud du Portugal, il existe, au nord de la ceinture pyriteuse, des associations &roites de diorites, de tonalyres et de trondhj6mites. Leur raise en place date de la p6-riode pr6-carbonif&e et non, comme on l'avait g~n6rale-ment admis jusqu'fi pr6sent, de la p~riode varisque post-orog6nique. Le faisceau intrusif trondhj6mitique et l'association spilite-k6ratophyre du Carbonif~re inf6rieur sont li~s par une origine comagmatique. Les points communs des deux successions sont leur dominante sodique, les faibles teneurs en ~l~ments ~i gros ions, les indices d'un magma de depart aquif~re et la scorification r6dui...

Geochemistry and U–Pb dating of felsic volcanic rocks in the Riotinto–Nerva unit, Iberian Pyrite Belt, Spain: crustal thinning, progressive crustal melting and massive sulphide genesis

“…Although most of these rocks were emplaced after the main Variscan deformation phase affecting the Volcano-Sedimentary Complex (Simancas 1983;De la Rosa 1992;Quesada 1998), some plutonic rocks, close to the Riotinto mining district, probably intruded earlier (Stein et al 1996). The geochemical similarities between plutonic and volcanic rocks (Schutz et al 1987;Thiéblemont et al 1998) as well as the available U/Pb evidence (Barrie et al 2002;Dunning et al 2002), also suggest that plutonic rocks were at least partly coeval with the VolcanoSedimentary Complex.…”

“…1b) comprise gabbros, diorites, tonalites and granites (Schutz et al 1987;De la Rosa 1992). Although most of these rocks were emplaced after the main Variscan deformation phase affecting the Volcano-Sedimentary Complex (Simancas 1983;De la Rosa 1992;Quesada 1998), some plutonic rocks, close to the Riotinto mining district, probably intruded earlier (Stein et al 1996).…”

Introduction and Geological Setting of the Iberian Pyrite Belt

“…The geochemical similarities between the volcanic rocks of the VSC and the TTG plutonic rocks of the SNB (Schütz et al 1987;Thiéblemont et al 1998; Díez-Montes and Bellido-Mulas 2008; Díez-Montes et al 2011), as well as the available U-Pb geochronology data (Barrie et al 2002;Dunning et al 2002;Valenzuela et al 2011) suggest that the Volcano-Sedimentary Complex was approximately coeval and cogenetic with the TTG plutonic rocks of the Sierra Norte Batholith.…”

“…The SNB includes three types of geochemical associations, mafic rocks (gabbrodiorite) with ultramafic cumulates, subvolcanic TTG intrusions, tonalite, trondhjemite and granodiorite (Schütz et al 1987;Halsall 1989;Díez-Montes and Bellido-Mulas 2008;Díez-Montes et al 2011) with an age range of 335-355 Ma (Dunning et al 2002;Barrie et al 2002;Gladney et al 2014, in press), and aluminopotassic granitoid plutons that intruded the TTG group (Díez-Montes and Bellido-Mulas 2008). There is common evidence of mingling between the TTG and the mafic rocks.…”

The margins of Avalonia

“…This latter zone, which has been correlated with the Rhenohercynian Belt of Germany by, for example, Oczlon (1992, p. 22) and Franke, Dallmeyer & Weber (1995, p. 581) may indeed include fragments which were originally part of Avalonia, but the hypothesis is untestable palaeontologically in the Lower Palaeozoic since the earliest known fossils from the area are of late Givetian age. In addition, most of the rocks seem to have been deposited as calc-alkaline intrusives above a subduction zone (Schütz, Ebneth & Meyer, 1987), and thus it is possible that the whole zone may have only originated after Avalonia ceased to be a separate continent.…”