Oceanic Core Complex Development in Modern and Ancient Oceanic Lithosphere: Gabbro‐Localized versus Peridotite‐Localized Detachment Models

Abstract

A B S T R A C TDrilling and submersible studies of the Atlantis Bank (Southwest Indian Ridge) and the Atlantis Massif (Mid-Atlantic Ridge) oceanic core complexes reveal "gabbro-localized" and "peridotite-localized" end-member models of strain localization and deformation during core complex development, in which the gabbroic fault rocks exhibit extensive and rare high-temperature ductile-deformation fabrics, respectively. Both models emphasize a footwall cored by gabbroic intrusions, therefore precluding an amagmatic origin of core complex formation. We test these models by using relict oceanic core complexes preserved in the western Mirdita Ophiolite in Albania. The Puka and Krabbi massifs display traits of the peridotite-localized detachment model, whereby amagmatic tectonic extension is not required for the formation of this category of core complexes.

A Jurassic oceanic core complex in the high-pressure Monviso ophiolite (western Alps, NW Italy)

“…The texture and composition of the talc-andchlorite schist within the Baracun shear zone are quite similar to those observed in hydrothermally metasomatized oceanic rocks along the detachment fault zone in the Atlantis Massif core complex at the Mid-Atlantic Ridge (Mével, 2003;Boschi et al, 2006;Miranda and Dilek, 2010). Amphibole and chlorite in these rocks were produced from a gabbroic source, whereas talc was produced from serpentinite.…”

“…Basaltic lavas and the Upper Jurassic clastic rocks in the hanging wall represent a synextensional (i.e., synrift) sequence resting on the peridotites and gabbros. These processes are reminiscent of those that produce oceanic core complexes, in which deformed older rocks are tectonically overlain along detachment faults by relatively unde- formed, younger syntectonic sediments and basaltic lava flows (e.g., for ancient orogenic belts- Miranda and Dilek, 2010;Manatschal et al, 2011;e.g., for present-day oceanic settings-Cann et al, 1997;Tucholke et al, 1998;Cannat et al, 2006;Smith et al, 2014).…”

Multiple episodes of melting, depletion, and enrichment of the Tethyan mantle: Petrogenesis of the peridotites and chromitites in the Jurassic Skenderbeu massif, Mirdita ophiolite, Albania

“…The peridotites contain lherzolite-harzburgite, plagioclase lherzolite, plagioclase dunite, and rare amphibole peridotites (olivine hornblendite). Plutonic rocks, which are locally intrusive into and overlying the peridotites, consist of troctolite, olivine gabbro, ferrogabbro, gabbro, and rare amphibole gabbro, and generally display an olivine-plagioclase-orthopyroxene (ol-pl-opx) order of crystallization (Beccaluva et al, 1994(Beccaluva et al, , 2005Saccani and Photiades, 2004;Miranda and Dilek, 2010;Shenjatari and Beqiraj, 2010). Extrusive rocks, composed mainly of massive to pillow lavas and hyaloclastites, form a nearly 600-m-thick sequence that directly overlies serpentinized peridotites and gabbroic rocks along primary contacts (Dilek et al, 2005).…”

An Overview of the Albanian Ophiolite and Related Ore Minerals

“…These lateral and vertical changes from MORB to SSZ geochemical affinities for the upper mantle peridotites and crustal units in the west-east section of the Middle Jurassic ophiolite of Albania are related to the oceanic suprasubduction (Beccaluva et al, 1994;Gjata et al, 1996;Dilek et al, 2001;Dilek et al, 2005;Dilek et al, 2008;Morishita et al, 2011). Eastern-type of the Albanian opiolite include all subunits of a typical Penrose-type ophiolite having thickness 10-12 km (Shallo & Dilek, 2003), whereas the western Albanian opiolite type is similar to the architecture of modern slow-spread lithosphere with a reduced and discontinuous oceanic crust (Miranda & Dilek, 2010). Evidence for the occurrence of detachement faults linked to the formation of the Oceanic Core complexes in the Mirdita ophiolite are documented in the Krrabi and Puka massifs (Miranda & Dilek, 2010;Tremblay et al, 2009).…”

“…Eastern-type of the Albanian opiolite include all subunits of a typical Penrose-type ophiolite having thickness 10-12 km (Shallo & Dilek, 2003), whereas the western Albanian opiolite type is similar to the architecture of modern slow-spread lithosphere with a reduced and discontinuous oceanic crust (Miranda & Dilek, 2010). Evidence for the occurrence of detachement faults linked to the formation of the Oceanic Core complexes in the Mirdita ophiolite are documented in the Krrabi and Puka massifs (Miranda & Dilek, 2010;Tremblay et al, 2009). The eastern ophiolites are constituted by thick harzburgitic tectonites, followed by dunitic and pyroxenitic cumulates, gabbros and plagiogranites, a well-developed, but not classical, sheeted dyke complex and volcanic sequence that consists of low-Ti basalts and andesites, dacite and rhyodacites.…”