Paleomagnetism in Extremadura (Central Iberian Zone, Spain) Paleozoic Rocks: Extensive Remagnetizations and Further Constraints
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Paleomagnetism in Extremadura (Central Iberian zone, Spain) Paleozoic rocks: extensive remagnetizations and further constraints on the extent of the Cantabrian orocline Daniel Pastor-Galán, Gabriel Gutiérrez- Alonso, Mark J. Dekkers & Cor G. Langereis Journal of Iberian Geology Including Latin America and the Mediterranean ISSN 1698-6180 Volume 43 Number 4 J Iber Geol (2017) 43:583-600 DOI 10.1007/s41513-017-0039-x 1 23 Your article is protected by copyright and all rights are held exclusively by Springer International Publishing AG. This e-offprint is for personal use only and shall not be self- archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy J Iber Geol (2017) 43:583–600 https://doi.org/10.1007/s41513-017-0039-x RESEARCH PAPER Paleomagnetism in Extremadura (Central Iberian zone, Spain) Paleozoic rocks: extensive remagnetizations and further constraints on the extent of the Cantabrian orocline 1 2,3 4 Daniel Pastor-Gala´n • Gabriel Gutie´rrez-Alonso • Mark J. Dekkers • Cor G. Langereis4 Received: 5 June 2017 / Accepted: 14 October 2017 / Published online: 2 November 2017 Ó Springer International Publishing AG 2017 Abstract show two distinct remagnetization events in Paleozoic rocks Introduction The winding Variscan belt in Iberia, featuring in Extremadura: (1) Mesozoic or Cenozoic remagnetization the Cantabrian orocline (NW Iberia) and the Central Ibe- occurring in dolomitized limestones and (2) late Carbonifer- rian curve, is a foremost expression of the late Carbonif- ous remagnetization in limestones, characterized by consis- erous amalgamation of Pangea, which produced tent shallow inclinations, but largely scattered declinations remagnetizations spanning almost the entire globe. indicating a counter clockwise (CCW) vertical axis rotation. Geological settings Also in Iberia, late Carboniferous Pyrrhotite is documented as magnetic carrier in the limestones remagnetizations are widespread often hindering paleo- which testifies a remagnetization under anchimetamorphic magnetic interpretations in terms of pre-Pangean geologic conditions, i.e. during the Variscan orogeny. history. In contrast, such remagnetizations facilitated the Interpretation We interpret the declination scattering as a kinematic study of the Cantabrian orocline. Immediately to remagnetization coeval to the vertical axis rotation. The its south is located the Central Iberian curve whose described CCW rotations are those expected for the geometry and kinematics are under debate. Recent studies southern limb of the Cantabrian orocline and are in dis- suggest that this putative structure cannot have formed in agreement with a late Carboniferous secondary origin for the same process as the Cantabrian orocline. the Central Iberian bend, extending the Cantabrian orocline Results Here we present a paleomagnetic and rock magnetic to at least most of the Iberian peninsula. study from Extremadura, a region in the utmost west of the southern limb of the Central Iberian curve. Our new results Keywords Paleomagnetism Á Central Iberian zone Á Remagnetization Á Cantabrian orocline Á Carboniferous tectonics Electronic supplementary material The online version of this article (doi:10.1007/s41513-017-0039-x) contains supplementary Resumen material, which is available to authorized users. Introduccio´n El oro´geno Varisco, que en la penı´nsula & Daniel Pastor-Gala´n Ibe´rica esta´ curvado y contiene el Oroclinal Canta´brico [email protected] (NO de Iberia) y la curva oroge´nica Centro Ibe´rica, es el ´ ´ 1 resultado mas visible de la amalgamacion de Pangea en el Center for North East Asia Studies, Tohoku University, 41 Carbonı´fero superior. Durante ese tiempo, la formacio´nde Kawauchi, Aoba-ku, Sendai 980-8576, Japan Pangea produjo remagnetizaciones en todos los continen- 2 ´ Departamento de Geologıa, Universidad de Salamanca, Pza. tes. En Iberia, las remagnetiaciones del Carbonı´fero supe- de los caı´dos s/n, 37008 Salamanca, Spain 3 rior son muy extensas y afectan a casi todas las rocas Geology and Geography Department, Tomsk State ocultando y dificultando cualquier interpretacio´n paleo- University, Lenin Street 36, Tomsk, Russian Federation 634050 magne´tica de la historia geolo´gica anterior al Pe´rmico. Parado´jicamente, dichas remagnetizaciones facilitaron el 4 Paleomagnetic Laboratory ‘‘Fort Hoofddijk’’, Department of Earth Sciences, Universiteit Utrecht, Budapestlaan 17, estudio de la cinema´tica del Oroclinal Canta´brico. Inme- 3584, CD, Utrecht, The Netherlands diatamente al sur de este oroclinal se situ´a la curva 123 Author's personal copy 584 J Iber Geol (2017) 43:583–600 oroge´nica Centro Ibe´rica cuya geometrı´a y cinema´tica recognized as having caused global-scale remagnetizations esta´n bajo debate. Algunos estudios recientes apuntan a la (e.g. Stamatakos et al. 1996; Zegers et al. 2003; Elmore posibilidad de que la curva Centro Ibe´rica se formase a la et al. 2012). In the Iberian peninsula the studies of the vez que el Oroclinal Canta´brico. widespread late Carboniferous remagnetizations (e.g. Weil Resultados En este artı´culo presentamos los resultados and van der Voo 2002; Tohver et al. 2008) were crucial to paleomagne´ticos obtenidos rocas Paleozoicas de Extrema- constrain the kinematics of the Cantabrian ‘‘arc’’, a dura, regio´n que contiene la seccio´n sur-occidental de la strongly bent section of the Variscan orogen in Northern curva Centro Ibe´rica. Nuestros resultados muestran dos Iberia interpreted as a secondary orocline (Hirt et al. 1992; remagnetizaciones separadas en el tiempo: 1) Una remag- van der Voo et al. 1997; Weil et al. 2000, 2001, 2013; Weil netizaciio´n Mesozoica o Cenozoica que aparece en calizas 2006). More recently, the late Carboniferous remagneti- dolomitizadas y 2) Una remagnetizacio´n del Carbonı´fero zations delivered pivotal input for Pastor-Gala´n et al. tardı´o cuyas caracterı´sticas incluyen inclinaciones subho- (2015a, 2016) and Ferna´ndez-Lozano et al. (2016) to dis- rizontales y declinaciones dispersas que indican una rota- cuss and discard a coeval secondary origin for the alleged cio´n de eje vertical en sentido horario. Adema´s, hemos curvature in Central Iberia (e.g. Martı´nez Catala´n 2011; identificado pirrotina como mineral magne´tico en las Shaw et al. 2012). The extent and boundaries of the Can- calizas. Este mineral solo aparece en calizas remagnetiza- tabrian orocline are now considered to include the two das durante metamorfismo de bajo grado (anquizona). Paleozoic continents, Gondwana and Laurussia (Pastor- Discusio´n Interpretamos que la dispersio´n en la decli- Gala´n et al. 2015b), involved in the Carboniferous Var- nacio´n registra una remagnetizacio´n que ocurrio´ a la vez iscan collision in western Europe. que la rotacio´n de ejes verticales. La rotacio´n horaria que In this paper we investigate the paleomagnetism and sugieren nuestros resultados coincide con la esperada para rock magnetism in rocks from Extremadura (southern el flanco sur del Oroclinal Canta´brico. Estos resultados Central Iberian zone), which provide new insights into the contradicen la posibilidad de que la curva Centro Ibe´rica y expression of the late Carboniferous remagnetization event el Oroclinal Canta´brico ocurriesen al mismo tiempo y con in the Iberian hinterland of the Variscan orogen. In addi- cara´cter secundario respecto a la orogenia Varisca, y tion, our results help to further constrain the extent and extienden las rotaciones de eje vertical ligadas al Oroclinal kinematics of the Cantabrian orocline and its relationship Canta´brico a todo el sur oeste de la Penı´nsula Ibe´rica. with the putative Central Iberian curve and assess the extensive hydrothermal activity occurred in Iberia during Palabras clave Paleomagnetismo Á Zona Centro-Ibe´rica Á post-Paleozoic times. remagnetizacio´n Á Oroclina Canta´brico Á Tecto´nica del Carbonı´fero 2 Geological background 1 Introduction The collision between Laurussia and Gondwana and sev- eral microplates resulted in the late Paleozoic orogen in Remagnetizations are ubiquitous in most orogens on Earth, central and western Europe, known as the Variscan orogen from the Alps (e.g. Pueyo et al. 2007) to the Himalayas (e.g. Nance et al. 2010). The earliest record of Variscan (e.g. Huang et al. 2017) and the Rocky Mountains (e.g. deformation in Iberia dates ca. 400 Ma (e.g. Dallmeyer and Enkin et al. 2000). In a remagnetized rock, the original Ibarguchi 1990;Go´mez Barreiro et al. 2006), while the natural remanent magnetization (NRM) is replaced or continent–continent collision ocurred later, at ca. overprinted due a set of geologic processes acting alone or 365–370 Ma (e.g. Dallmeyer et al. 1997;Lo´pez-Carmona in concert. Although sometimes disregarded because of the et al. 2014). At 325–318 Ma, NW Iberia was extensively implied information loss—the rock record before the oro- intruded by anatectic leucogranites and granodiorites, often genesis cannot be recovered-, remagnetized rocks have interpreted as a product of extensional collapse (e.g. Bea proven to be an excellent tool to unravel orogenic kine- et al. 2006; Castin˜eiras et al. 2008;Lo´pez-Moro et al. matics., They are capable of constraining vertical axis 2017). From 310 to 295 Ma the originally quasi-linear rotations (e.g. Gong et al. 2009; Izquierdo-Llavall et al. Variscan orogen buckled around a vertical axis forming the 2015) or evaluating subsequent deformation phases coeval Cantabrian orocline (a.k.a. Ibero-Armorican Arc; Gutie´r- to or postdating the remagnetization event (e.g. Calvı´n rez-Alonso et al. 2012; Weil et al.