9 research outputs found
Preliminary petrological inferences on the high-grade metamorphic rocks exhumed by the South Rif Thrust, Prerif, Northern Morocco
The exhumation of deep crustal rocks along major shear zones is common, yet a highly debated subject, particularly when occurring during recent tectonic events. This is the case of the South Rif Thrust (SRT), a significant shear zone analogous to those described at the Betic Cordillera in Spain.
The SRT separates two major geodynamic domains in Northern Morocco: a) the Prerif, to the North, mostly composed of Miocenic sedimentary units on top of a stratigraphic sequence continuously deposited since the Triassic; and b) the Western Meseta, to the South, mostly composed of Paleozoic metasedimentary units, correlated with the Iberian Variscan Belt [1]. Associated to the SRT, and exhumed by its activity, there is a dismembered and exotic high-grade metamorphic belt representative of the middle and lower crust. Also in this region, several thermo-mineral waters occur, whose deep circulation can be traced back to the SRT [2].
Detailed geological mapping, structural, stratigraphic and petrographic analyses on this dismembered and highly deformed exotic sequence reveal the presence of low- to high-grade metasediments (including migmatites and felsic granulites), but mostly high-grade metabasic and basic rocks, including amphibolites, mafic granulites and gabbros. Preliminary geothermobarometry in the mafic granulites provides an important characterization of the infra-crustal conditions of the pre-Alpine geodynamics and of the activity and exhumation along the SRT since the Miocene: a) the mafic granulites endured M1 metamorphic peak conditions of T
= 1030 ÂșC at P = 8.5 kbar, which is consistent with typical conductive continental crust geothermal gradients (~30 ÂșC.km-1); b) M2 retrogression occurred by near isothermal decompression at T = 820 ÂșC and P = 3.5 kbar, implying an initial vertical uplift of >18 km of the granulite-facies rocks to very shallow levels; c) during this period, the geothermal gradient in the region surpassed 60 ÂșC.km-1; d) exhumation and retrogression continued by almost isobaric cooling at T < 750 ÂșC and P = 1.7 â 3.0 kbar with an M3 amphibolitization of the granulites after late water inflow.
The overall metamorphic evolution of these deep crustal rocks is compatible with a clockwise P-T path, involving initial fast tectonic exhumation, followed by thermal readjustment to shallower levels. This is consistent with the currently observed geothermal gradients in the area (†42 ÂșC.km-1) [2] which may still be a reflection of the events during the Miocene. These petrological constrains on the tectonic processes associated with the exhumation of this lower crust segment and the activity of the SRT during the closure of the Alboran Basin are key to understanding the circulation of deep hot waters, which are an important part of the economy of this region in Northern Morocco.publishe
North-Gondwana assembly, break-up and paleogeography: UâPb isotope evidence from detrital and igneous zircons of Ediacaran and Cambrian rocks of SW Iberia
The Estremoz Anticline in the Ossa-Morena Zone (SW Iberia) includes upper Ediacaran detrital rocks uncon-
formably overlain by lower Cambrian detrital and carbonate rocks. The spectra of detrital zircon UâPb ages
dominated by Cryogenian and Ediacaran ages (with a typical gap in Mesoproterozoic ages) of the upper Edi-
acaran greywackes and lower Cambrian arkosic sandstones indicate provenance from sources placed near or
at the North-Gondwana margin. These late Ediacaran and early Cambrian basins developed in a paleoposition
close to the West African Craton and related to a long-lived Neoproterozoic magmatism (c. 850â700 Ma â
Pan-African suture; c. 700â635 Ma â early Cadomian arc; and c. 635â545 Ma â late Cadomian arc).
The rhyolites of the VolcanicâSedimentary Complex of Estremoz whose stratigraphic position so far has been
a controversy, yielded an upper Cambrian age (Furongian) at about 499 Ma indicating that carbonate produc-
tion was episodic in SW Iberia during the Cambrian. This new evidence should be taken into account in the
reshaping of paleogeographic reconstruction models that have erroneously insisted on placing Iberia at
southerly cold water higher latitudes (>60°S) during the Furongian
Deciphering a multi-event in a non-complex set of detrital zircon UâPb ages from Carboniferous graywackes of SW Iberia
The provenance of Late Ediacaran and Early Ordovician siliciclastic rocks in the Southwest Central Iberian Zone: constraints from detrital zircon data on northern Gondwana margin evolution during the late Neoproterozoic
UâPb geochronology of detrital zircon from Late Ediacaran (Beiras Group greywackes) and Early Ordovician
(Sarnelhas arkosic quartzites and Armorican quartzites of Penacova) sedimentary rocks of the
southwest Central Iberian Zone (SW CIZ) constrain the evolution of northern Gondwana active-passive
margin transition. The LA-ICP-MS UâPb data set (375 detrital zircons with 90â110% concordant ages) is
dominated by Neoproterozoic ages (75% for the greywakes and 60% for the quartzites), among which the
main age cluster (more significant for Beiras Group greywackes) is Cryogenian (c.840â750 Ma), while a
few Mesoproterozoic and Tonian ages are also present (percentages <8%). These two features, and the
predominance of Cryogenian ages over Ediacaran ages, distinguish the Beiras Group greywackes (SW
CIZ) from the time-equivalent Serie Negra (Ossa-Morena Zone â OMZ), with which they are in inferred
contact. The age spectra of the Beiras Group greywackes also reveal three major episodes of zircon crystallisation
in the source area during the Neoproterozoic that are probably associated with a long-lived
system of magmatism that developed either along or in the vicinity of the northern Gondwana margin
at: (1) c. 850â700 Ma â Pan-African suture (not well represented in OMZ); (2) c. 700â635 Ma â early
Cadomian arc; and (3) c. 635â545 Ma â late Cadomian arc. Comparison of Neoproterozoic ages and those
of the Paleoproterozoic (c. 2â1.8 Ga) and Archean (mainly Neoarchean â 2.8â2.6 Ga, but also older) in the
Beiras Group greywackes with UâPb ages of Cadomian correlatives shows that: (1) SW CIZ, OMZ, Saxo-
Thuringian Zone, North Armorican Cadomian Belt and Anti-Atlas) evolved together during the formation
of back-arc basins on the northern Gondwana active margin and (2) all recorded synorogenic basins that
were filled during the Ediacaran by detritus resulting from erosion of the West African craton, the Pan-
African suture and a long-lived Cadomian magmatic arc. Differences in detrital zircon age populations in
the greywackes of the Beiras Group (SW CIZ Cadomian basement) and the Serie Negra (OMZ Cadomian
basement) are also observed in their respective overlying Early Ordovician quartzites. Since both these
SW Iberia Cadomian basements evolved together along the active margin of Gondwana (but sufficiently
separated to account for the differences in their detrital zircon content), this continuation of differing
zircon populations into the Early Ordovician suggests that the inferred contact presently juxtaposing
the Beiras Group and the Serie Negra is not pre-Early Ordovician and so is unlikely to demonstrate a
Cadomian suture
North-Gondwana assembly, break-up and paleogeography: UâPb isotope evidence from detrital and igneous zircons of Ediacaran and Cambrian rocks of SW Iberia
Tracing the Cadomian magmatism with detrital/inherited zircon ages by in-situ UâPb SHRIMP geochronology (Ossa-Morena Zone, SW Iberian Massif)
Uncommon Association Between Diabetic Ketoacidosis, Thyrotoxicosis, Cutaneous Abscess and Acute Pericarditis in an Immunocompetent Patient: A Single Case Report and Literature Review
Variscan Magmatism
This chapter aims to identify, characterize and locate the main facts/events related to orogenesis in the Iberian Peninsula. Its succession in space and time determines the geodynamic environment of the broader geological phenomenon corresponding to the Variscan cycle. In this sense, this section comprises two parts: IâThe Iberian orogenic magmatism seen through a space-time approach of its westernmost regionâfocus on the enormous complexity of the inherited basement, its nature, age and distribution in space. Establishes a space-time sequence of geodynamic environments correlated with the obtained data and tries to identify the agents responsible for its genesis. Some case studies are presented to illustrated significant regional aspects of the magmatic process and IIâAn overview of the petrogenesis of the great batholiths and of the basic, intermediate and mantle-related rocksâidentify and analyze a great amount of these rocks intruding and extruded from 400 to 280 Ma and to better understanding the large-scale process involving the whole lithosphere during Variscan cycle.publishe
Variscan Metamorphism
Various segments of Variscan crust are currently exposed in Iberia in response to successive tectonic events during the Variscan orogeny itself and subsequent extensional and compressive events during the Alpine cycle, all accompanied by surface erosion, and collectively contributing to their exhumation. We review the main characteristics and geodynamic contexts of the metamorphic complexes developed in Iberia during the Variscan cycle, which include: (i) LP-HT complexes associated to the Cambrian-Early Ordovician rift stage; (ii) HP-LT complexes associated to subduction; and (iii) syn-to-post-collisional, MP and LP/HT complexes from the hinterland to the foreland fold-and thrust belts. All the above contexts are illustrated with case studies. Finally, a review of Variscan metamorphism in the Pyrenees and Catalan Coastal Ranges, located far away from the Rheic suture is also presented