Miguel Orozco

Extension versus compression during the Miocene tectonic evolution of the Betic chain. Late folding of normal fault systems

The westernmost part of the Mediterranean Alpine Belt is represented by the Betic-Rif orogenic belt, around the Gibraltar Arc, which in turn surrounds the Alboran Basin. In the Betic Chain, early and middle Miocene crustal thinning of the Alboran basement is well established, as extensional low-angle normal faults and detachment faults, developed in both ductile and brittle conditions, thinned a previously thickened crust. In the Alboran Domain of the central Betics, two main extensional episodes are evidenced: a Langhian one, with a north-northwestward transport direction, followed by a west-southwestward extension, Serravallian in age. Therefore all the units heretofore considered to be thrust nappes are, in reality, extensional units bounded by low-angle normal faults. The cortical segment studied formed the basement of the Miocene Alboran Basin, in which progressively deeper basement units were covered by younger marine sediments as a result of extensional denudation processes. The age of these sediments clearly dates the faulting. The extensional evolution during the Miocene is much more complex than the past models suggest. During the upper Miocene, these extensional systems were folded as the result of a compressive regime, which allowed them to be well exposed. Compression in the Gibraltar Arc is nearly contemporaneous with extension, and the westward migration of the compression through its footwall is related with the extensional spreading.

The Southern Iberian Shear Zone: a major boundary in the Hercynian folded belt

A long ductile shear zone extending across the northern parts of Sevilla and Huelva provinces, southwest Spain, and very probably stretching further west into Portugal, is characterized by a conspicuously developed L-S fabric and the existence of various mylonitic textures. The shear zone, closely associated with amphibolites of tholeiitic affinity, represents an important oceanic suture of the Hercynian belt in Europe. The sense of displacement inferred from microstructures is consistent with southwest-directed upthrusting evolving to a left-lateral shearing movement.

The boundary between the Ossa-Morena and Southportuguese Zones (Southern Iberian Massif): Major suture in the European Hercynian Chain

ZusammenfassungDie Ossa-Morena Zone (OMZ) und die Südportugiesische Zone (SPZ) bauen die südlichsten Anteile des Iberischen Massivs auf (europäisches Variszikum). Sie unterscheiden sich auf lithostratigraphischer, petrographischer und struktureller Basis. Die Grenze zwischen OMZ und SPZ wird vom schmalen Streifen der Acebuches-Amphiboliten gebildet, Meta-Ophiliten tholeiitisch-ozeanischer Prägung (Bard &Moine, 1979;Munha et al. 1986). Sie lassen sich über mehr als 200 km verfolgen. Eine intensive Scherung überprägt sie im Süden. Eine Unterteilung des Südrandes der OMZ und des Nordrandes der SPZ konnte mittels struktureller und lithologischer Kriterien durchgeführt werden. Der südlichste Abschnitt der OMZ längs der Acebuches-Amphibolite, besteht aus hochgradig metamorphen Gesteinen; er ist gegen Norden durch eine weitere, größere Scherzone begrenzt. Die Grenze zwischen OMZ und SPZ muß somit als eine Sutur-Zone zwischen zwei kontinentalen Blöcken betrachtet werden, der OMZ im Norden (heutige Position) und der SPZ im Süden. Diese Sutur wird von einer sinistral transpressiven Konvergenz-Zone mit großräumig liegenden Falten überprägt. Sie kann durch den Ibero-Armorikanischer Bogen mit dem Lizard-Komplex in SW-England korreliert werden.AbstractThe Ossa-Morena Zone (OMZ) and the Southportuguese Zone (SPZ) represent the southernmost domains of the Iberian Massif (European Hercynian Belt). Lithostratigraphic, pétrographic and structural differences exist between both zones. The boundary between the OMZ and the SPZ is marked by a narrow belt of amphibolites of tholeiitic oceanic affinity (Bard &Moine, 1979);Munha et al., 1986), and associated serpentinites, flaser gabbros, pillowed metabasalts (Castro et al., 1987) which are highly sheared along their southern border. These Beja-Acebuches ophiolites (op. cit.) are exposed for over 200 km. In the southernmost part of the OMZ and the northernmost area of the SPZ, several zones have been distinguished on the basis of structural and lithological criteria. The southernmost area of the OMZ which bounds the Acebuches amphibolites, is composed of high grade metamorphic rocks and an another important shear zone mark the OMZ northern boundary. The boundary between the OMZ and the SPZ is considered to be a suture zone between two continental areas represented by the northern OMZ and the southern SPZ. Sinistral transpression associated with large scale recumbent folds are characteristic of the suture, which can be tentatively correlated through the Ibero-Armorican arc with the Lizard complex (SW England).ResumenLa Zona de Ossa-Morena (OMZ) y la Zona Surportuguesa (SPZ) representan los dominios más meridionales del Macizo Ibérico (Cadena hercínica europea). Las diferencias entre ambos dominios son de naturaleza litoestratográfica, petrográfica y estructural. El contacto entre ambas zonas (OMZ y SPZ) está subrayado por una estrecha banda de anfibolitas (»de Acebuches«,Bard, 1969) y rocas asociadas (serpentinitas, flaser gabbros, metabasaltos en pillow,Castro et al., 1987), que se pueden seguir de manera contínua, a lo largo de más de 200 km. Estas anfibolitas tienen afinidades de toleitas oceánicas (Bard &Moine, 1979;Munha et al., 1986) y representan restas de una secuencia ofiolitica (op. cit.). Hacía el sur, están afectadas por un intenso cizallamiento. En la parte meridional de la OMZ y en el sector más septentrional de la SPZ se han diferenciado una serie de zonas en función de sus características litológicas y estructurales. El sector más meridional de la OMZ, directamente en contacto con las anfibolitas de Acebuches, esta constituido por rocas metamórficas de alto grado y esta limitado al N y al S por importantes zonas de cizalla. El contacto entre la OMZ y la SPZ debe ser considerado como una zona de sutura entre dos areas continentales, representadas respectivamente por la OMZ al norte (en su posición actual) y la SPZ, al sur. Una convergencia de tipo transpresiva sinistrorsa, con grandes pliegues recumbentes vergentes hacía el sur, caracteriza esta sutura, que puede correlacionarse con el macizo de Lizard (SW de Inglaterra), a través del arco Ibero-Armoricano.Краткое содержаниеЗона Осса-Морена (OMZ) и юж нопортугальская зона (SPZ) образуют самую южную окраину Иберийского массива — европейски й варисцикум. Но они раз личаются по их литост ратиграфии, петрографии и структ урам. Границу между OMZ и SPZ образует узк ая полоса, состоящая их амфибол итов Acebuches, толеитно-океан ического типа метаофиолитов (Bard и Moine, 1979; Munha и др., 1986). Их можно проследить на более, ч ем 200 км. Интенсивный скол преобразовал их на юге. Южный край OMZ и северный край SPZ можн о различать по их структурным и ли тологическим критер иям. Самый южный отрезок OMZ в доль амфиболитов Acebuches состои т из пород высшей степени метам орфизма; они ограниче ны на севере обширной зо ной сколов. Границу между OMZ и SPZ следует поэт ому рассматривать, как зону шва между дву мя материковыми блоками: на сегодняшн ий день OMZ на севере и SPZ на юге. Этот шов прео бразован левосторон ней трансгрессивной зон ой конвергенции с крупномасштабными с кладками. Ее можно коррелировать с комп лексом Lizard на юго-западе Англии через иберо-ар мориканскую дугу.

Crystal bending in metamorphic calcite, and its relations to associated twinning

This paper deals with the incidence and geometry of lattice bending in calcite of naturally strained marble and possible relations in time to associated {01¯12} twinning, as revealed by microscopic examination with a universal stage. Microscopic technique and graphic treatment of data with a view to identifying the relation in time of bending to twinning, and possible glide mechanisms involved in the bending process are reviewed as a basis for present and subsequent investigation of this general topic.In most instances development of surviving thin e twins postdates bending of the host crystal (such twins everywhere are rationally oriented). Rarely (in contrast with experimental experience) some thin twins are slightly irrational (Le lamellae) and apparently developed in the final stages of bending. Thick twins (a few tens of microns wide) on the other hand rather commonly predate or are synchronous with bending.The geometry of bending (external rotation) — especially for rotation less than 25° —commonly is compatible with models (based on experimental experience) of simple translation in the strained domains. The commonest translation system so identified is on {10¯11}, with sense of shear, where recognizable, either negative or positive. Translation on {02¯21} is relatively rare. Unexpectedly there is rather strong but not conclusive evidence of translation on {0001} parallel to an a axis. This mechanism, hitherto never identified with certainty, is now here documented unequivocally in a crystal of calcite experimentally strained at 300° C, 5 kb.

Mediterranean spotted fever with encephalitis.

Rickettsia conorii infection is endemic in the Mediterranean basin, where it is known as Mediterranean spotted fever, also known as Boutonneuse fever and Marseilles fever. We report the case of a 66-year-old diabetic man who presented a severe form of the disease, complicated by acute renal failure, thrombocytopenia and encephalitis. Diagnosis was confirmed by indirect immunofluorescence assay. Despite appropriate treatment, severe neurological sequelae have remained. Medical literature on encephalitis caused by R. conorii is also reviewed.

The development of folds in bedded chert and related rocks in the Malaguide Complex, southern Spain

Abstract Folds and folding mechanism in a chert sequence and related rocks of the Malaguide Complex (the uppermost tectonic unit of the Betic Zone) have been investigated. The geometric study shows that folds that developed in the chert sequence are usually angular in shape and asymmetric. Chevron and conjugate folds are common. Folding in bedded chert is explained in terms of a suggested model: 1. (1) Development of folds by kink and conjugate kinking. 2. (2) As the shortening increases, the interlimb angles decrease; in the kink folds this is caused by a reduction of the angle between the layers within the kink and the kink boundaries. There seems to be a relationship between this angle and the asymmetrical thinning-out in the limbs of many folds: the smaller is the angle between the kink boundary and the layers within the kink band, the larger is the reduction of the thickness in these layers. Single limestone layers embedded in slate deform very probably by a buckling mechanism, implying tangential longitudinal strain and an additional flattening.