The metamorphic evolution of the high pressure mafic granulites of the Bacariza Formation (Cabo Ortegal Complex, Hercynian belt, NW Spain)

Galán, Gumer; Marcos, A.

doi:10.1016/s0024-4937(00)00020-7

Cited by 30 publications

(29 citation statements)

References 61 publications

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“…Peucat et al, 1990;Santos-Zalduegui et al, 1996;Ordóñez-Casado et al, 2001) and zircon, monazite, and titanite U-Pb ages from the mafic granulite and the qz-fsp gneisses (Santos-Zalduegui et al, 1996;Fernández-Suárez et al, 2002. This event reached metamorphic conditions above 800 • C and 1.7 GPa Fernández, 1997;Galán and Marcos, 2000). The eclogitic and granulitic rocks registered partial anatexis during the initiation of decompression at peak temperature conditions, which was followed by partial retrogression and amphibolitization.…”

Section: Tectonic Evolution Of the High-grade Cabo Ortegal Nappementioning

confidence: 95%

“…Some authors interpret inclusion trails as representing a distinct earliest event (D 1 structures) formed during the prograde path related to the subduction stage (i.e. Ábalos et al, 2003); even though only the fabric elements of the retrograde Pressure-Temperature-time (P-T-t) path have been unequivocally recognized Fernández, 1997;Galán and Marcos, 2000). All units of the high-grade nappe show a pervasive blastomylonitic tectonic fabric, which locally is highly heterogeneously developed (Fernández, 1997;Marcos et al, 2002).…”

Section: Tectonic Evolution Of the High-grade Cabo Ortegal Nappementioning

confidence: 99%

“…P-T path in the gneisses proposed is in grey. Detailed metamorphic work by Galán and Marcos (2000) traced the P-T-t path (thick dashed line) of the underlying Mafic granulites (after Galán and Marcos, 2000) is also plotted. Thin dashed lines trace sub-parallel retrograde paths for metasedimentary and migmatitic qz-fsp gneisses ently have recorded an early intrusive event related to the injection of the pre-D 2 dioritic/granodioritic dykes in the gneisses, and a latter anatectic melting event that produced the migmatitic layering, which is preserved within the less deformed lozenges bodies surrounded by anastomosing D 2 -shear bands.…”

Section: Migmatitic Gneissesmentioning

confidence: 99%

“…HP-HT metamorphism followed by rapid decompression leading to the formation of the D 2 tectonic fabric, based on the M 2 metamorphic assemblages defining the main foliation in the qz-fsp migmatites, eclogites and mafic granulites Fernández, 1997;Galán and Marcos, 2000;Ábalos et al, 2003).…”

Section: Metamorphic Evolution In the Gneissesmentioning

confidence: 99%

“…The development of the main tectonic foliation in Cabo Ortegal nappe rocks, defined by mineral assemblages from eclogite facies to greenschist facies, indicates that the structure formed during the progressive exhumation from highpressure conditions to mid-crustal depths (Galán and Marcos, 2000;Marcos et al, 2002) (Fig. 5).…”

Section: Characteristics Of the Exhumation Of Cabo Ortegal Nappe Rocksmentioning

confidence: 99%

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Insights on high-grade deformation in quartzo-feldspathic gneisses during the early Variscan exhumation of the Cabo Ortegal nappe, NW Iberia

et al. 2016

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Abstract. High-grade, highly deformed gneisses crop out continuously along the Masanteo peninsula and constitute the upper part of the lower crustal section in the Cabo Ortegal nappe (NW Spain). The rock sequence formed by migmatitic quartzo-feldspathic (qz-fsp) gneisses and mafic rocks records the early Ordovician (ca. 480-488 Ma) injection of felsic dioritic/granodioritic dykes at the base of the qz-fsp gneisses, and Devonian eclogitization (ca. 390.4 ± 1.2 Ma), prior to its exhumation. A SE-vergent ductile thrust constitutes the base of quartzo-feldspathic gneissic unit, incorporating mafic eclogite blocks within migmatitic gneisses. A NW-vergent detachment displaced metasedimentary qz-fsp gneisses over the migmatites. A difference in metamorphic pressure of ca. 0.5 GPa is estimated between both gneissic units. The tectono-metamorphic relationships of the basal ductile thrust and the normal detachment bounding the top of the migmatites indicate that both discrete mechanical contacts were active before the recumbent folding affecting the sequence of gneisses during their final emplacement. The progressive tectonic exhumation from eclogite to greenschist facies conditions occurred over ca. 10 Ma and involved bulk thinning of the high-grade rock sequence in the high pressure and high temperature (HP-HT) Cabo Ortegal nappe. The necessary strain was accommodated by the development of a widespread main foliation, dominated by flattening, that subsequently localized to a network of anastomosing shear bands that evolved to planar shear zones. Qz-fsp gneisses and neighbouring mafic granulites were exhumed at > 3 mm yr −1 , and the exhumation path involved a cooling of ∼ 20 • C/100 MPa, These figures are comparable to currently active subduction zones, although exhumation P-T trajectory and ascent rates are at the hotter and slower end in comparison with currently active similar settings, suggesting an extremely ductile deformation environment during the exhumation of qz-fsp gneisses within a coherent Cabo Ortegal nappe.

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Section: Tectonic Evolution Of the High-grade Cabo Ortegal Nappementioning

confidence: 95%

Section: Tectonic Evolution Of the High-grade Cabo Ortegal Nappementioning

confidence: 99%

Section: Migmatitic Gneissesmentioning

confidence: 99%

Section: Metamorphic Evolution In the Gneissesmentioning

confidence: 99%

Section: Characteristics Of the Exhumation Of Cabo Ortegal Nappe Rocksmentioning

confidence: 99%

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Insights on high-grade deformation in quartzo-feldspathic gneisses during the early Variscan exhumation of the Cabo Ortegal nappe, NW Iberia

et al. 2016

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Petrology and Geochemistry of Metamorphosed Basic Intrusives from Chilka Lake Granulites, Eastern Ghats Belt, India: Implications for Rodinia Breakup

Bose

Das²,

Chakraborty

et al. 2011

Dyke Swarms:Keys for Geodynamic Interpretation

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U-Pb evidence for a polyorogenic evolution of the HP-HT units of the NW Iberian Massif

Fernández‐Suárez

Corfú²,

Arenas

et al. 2002

Contributions to Mineralogy and Petrology

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A isotope dilution thermal ionisation mass spectrometry U Pb geochronological study was carried out on the high-pressure and high-temperature units (HP HT units) overlying the oceanic suture in the Allo chthonous Complexes of the NW Iberian Variscan Belt. The rocks investigated are seven granulite-to eclogite facies paragneisses and one leucosome within mafi c high pressure granulites in the Ordenes and Cabo Ortegal Complexes of NW Spain. U Pb dating of zircon, monazite, titanite and rutile reveal the presence of a pervasive Early Ordovician metamorphic event at ca. 500 480 Ma and a later Early Devonian event at ca. 400 380 Ma. The U Pb ages, in conjunction with petrological and structural data, indicate that the high-pressure event recorded by these rocks is Early Ordovician in age. Monazite ages in the paragneisses suggest that peak metamorphic conditions were reached at ca. 500 485 Ma. Subsequently, the rock ensemble underwent exhumation accompanied by partial melting and zircon growth at ca. 485 470 Ma. Melting of mafi c granulites was coeval with this latter episode as indicated by zircon crystallisation age in the leucosomes dated at ca. 486 Ma. Based on these data and on the general features of magmatism and metamorphic evolution, it is proposed that this process took place at a convergent plate boundary within a peri Gondwanan oceanic domain. Monazite, titanite and rutile data in some of the samples studied show evidence of a second metamorphic episode that took place between ca. 400 and 380 Ma (with a peak at ca. 390 385 Ma). This Early Devonian event, at variance with the previous one, was not pervasive, but, rather, was localised in areas of intense Variscan tectonothennal reworking. It is claimed that this later metamorphic event was recorded by the U Pb system in areas where monazite and titanite growth was enhanced by fluid circulation in highly strained rocks (Variscan shear zones). According to previous structural studies and Ar Ar dating of fabrics, this Early Devonian episode took place as the HP HT units were deformed and thrusted upon the ophiolitic units in the early stages of the Variscan collision.

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The metamorphic evolution of the high pressure mafic granulites of the Bacariza Formation (Cabo Ortegal Complex, Hercynian belt, NW Spain)

Cited by 30 publications

References 61 publications

Insights on high-grade deformation in quartzo-feldspathic gneisses during the early Variscan exhumation of the Cabo Ortegal nappe, NW Iberia

Insights on high-grade deformation in quartzo-feldspathic gneisses during the early Variscan exhumation of the Cabo Ortegal nappe, NW Iberia

Petrology and Geochemistry of Metamorphosed Basic Intrusives from Chilka Lake Granulites, Eastern Ghats Belt, India: Implications for Rodinia Breakup

U-Pb evidence for a polyorogenic evolution of the HP-HT units of the NW Iberian Massif

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