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Ophiolite Complex (ophiolite + complex)

Distribution by Scientific Domains

Earth and Environmental Science	83%

Selected Abstracts

The Cansiwang Melange of Southeast Bohol (Central Philippines): Origin and tectonic implications

ISLAND ARC, Issue 4 2000
Joel V. De Jesus
Abstract The Cansiwang Melange underlies the Southeast Bohol Ophiolite Complex (SEBOC) and is composed mainly of sheared ophiolite-derived blocks such as harzburgites, microgabbros, basalts and cherts in a pervasive serpentinite matrix. Available field, as well as geophysical evidence show that this melange unit is not diapiric, nor does it have a sedimentary origin considering that it lacks slump and flow structures. A tectonic origin for the Cansiwang Melange is favored in view of the numerous thrust faults, which cut across the exposures, as well as the tectonic contacts that the melange has with the overlying and underlying formations. The presence of the Cansiwang Melange in between the SEBOC and the Alicia Schist provides evidence that the amphibolite of the Alicia Schist do not correspond to the metamorphic sole of SEBOC. Similar to what is recognized in the Josephine Ophiolite, this suggests a ,cold' emplacement of the ophiolite over the Alicia Schist. The Cansiwang Melange represents an accretionary prism product which marks the location of an ancient subduction zone in what is now Central Philippines. [source]

Gravity variations along the Southeast Bohol Ophiolite Complex (SEBOC), Central Philippines: Implications on Ophiolite Emplacement

ISLAND ARC, Issue 4 2000
Jenny Anne L. Barretto
Abstract The basement complex of Bohol Island consists of the Southeast Bohol Ophiolite Complex (SEBOC), Cansiwang Melange and Alicia Schist. The SEBOC is a complete, but dismembered ophiolite with outcrops generally trending northeast, southwest and dipping north-west. The harzburgite units of the SEBOC are almost always observed to be thrusted onto the Cansiwang Melange, which in turn is thrusted onto the Alicia Schist. Bouguer gravity values on Bohol range from about +60 mGal in the west to +120 mGal in the east, in the region to the north-east of the SEBOC outcrops. Based on the present distribution of the SEBOC units and their thrust fault relationship with the Cansiwang Melange and Alicia Schist, it is proposed that the SEBOC was emplaced by onramping towards the south-eastward direction. However, the orientation of the Bouguer highs suggests that the thrusting direction of the ophiolite units is towards the south-west and not towards the south-east. [source]

SHAFT-HOLE AXES FROM SLOVENIA AND NORTH-WESTERN CROATIA: A FIRST ARCHAEOMETRIC STUDY ON ARTEFACTS MANUFACTURED FROM META-DOLERITES*

ARCHAEOMETRY, Issue 6 2009
F. BERNARDINI
A group of Copper Age shaft-hole axes from Caput Adriae (northeastern Italy, western Slovenia and northwestern Croatia) manufactured using meta-dolerite have been analysed for major and trace elements. All the samples show magmatic textures and well recognizable relicts of primary mineralogical phases. Petrographic observations suggest an ophiolitic provenance of the protolithic source(s) while geochemical data indicate that the original magmas originated in a fore arc or pre arc tectonic setting. Strong similarity has been found with several lithotypes from the Banija Ophiolite Complex (Croatia), here indicated as the most probable source area. Considering the available archaeometric data about shaft-hole axes found in northern Italy and Caput Adriae in comparison to those of axe blades discovered in the same area, it emerges that there is a utilization of different rock types, the source of which appears to be quite close to the discovery sites. In the investigated area the shaft-hole axes are largely made from ophiolitic-related rocks which are associated with copper deposits. Consequently there may have been a relation between the localization of the geological sources of shaft-hole axes and the development of metallurgical activities. [source]

Tectonic control of bioalteration in modern and ancient oceanic crust as evidenced by carbon isotopes

ISLAND ARC, Issue 1 2006
Harald Furnes
Abstract We review the carbon-isotope data for finely disseminated carbonates from bioaltered, glassy pillow rims of basaltic lava flows from in situ slow- and intermediate-spreading oceanic crust of the central Atlantic Ocean (CAO) and the Costa Rica Rift (CRR). The ,13C values of the bioaltered glassy samples from the CAO show a large range, between ,17 and +3, (Vienna Peedee belemnite standard), whereas those from the CRR define a much narrower range, between ,17, and ,7,. This variation can be interpreted as the product of different microbial metabolisms during microbial alteration of the glass. In the present study, the generally low ,13C values (less than ,7,) are attributed to carbonate precipitated from microbially produced CO2 during oxidation of organic matter. Positive ,13C values >0, likely result from lithotrophic utilization of CO2 by methanogenic Archaea that produce CH4 from H2 and CO2. High production of H2 at the slow-spreading CAO crust may be a consequence of fault-bounded, high-level serpentinized peridotites near or on the sea floor, in contrast to the CRR crust, which exhibits a layer-cake pseudostratigraphy with much less faulting and supposedly less H2 production. A comparison of the ,13C data from glassy pillow margins in two ophiolites interpreted to have formed at different spreading rates supports this interpretation. The Jurassic Mirdita ophiolite complex in Albania shows a structural architecture similar to that of the slow-spreading CAO crust, with a similar range in ,13C values of biogenic carbonates. The Late Ordvician Solund,Stavfjord ophiolite complex in western Norway exhibits structural and geochemical evidence for evolution at an intermediate-spreading mid-ocean ridge and displays ,13C signatures in biogenic carbonates similar to those of the CRR. Based on the results of this comparative study, it is tentatively concluded that the spreading rate-dependent tectonic evolution of oceanic lithosphere has a significant control on the evolution of microbial life and hence on the ,13C biosignatures preserved in disseminated biogenic carbonates in glassy, bioaltered lavas. [source]

Serpentinites of the Zermatt-Saas ophiolite complex and their texture evolution

JOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2004
X.-P. Li
Abstract The Zermatt-Saas serpentinite complex is an integral member of the Penninic ophiolites of the Central Alps and represents the mantle part of the oceanic lithosphere of the Tethys. Metamorphic textures of the serpentinite preserve the complex mineralogical evolution from primary abyssal peridotite through ocean-floor hydration, subduction-related high-pressure overprint, meso-Alpine greenschist facies metamorphism, and late-stage hydrothermal alteration. The early ocean floor hydration of the spinel harzburgites is still visible in relic pseudomorphic bastite and locally preserved mesh textures. The primary serpentine minerals were completely replaced by antigorite. The stable assemblage in subduction-related mylonitic serpentinites is antigorite,olivine,magnetite ± diopside. The mid-Tertiary greenschist facies overprint is characterized by minor antigorite recrystallization. Textural and mineral composition data of this study prove that the hydrated mineral assemblages remained stable during high-pressure metamorphism of up to 2.5 GPa and 650 °C. The Zermatt-Saas serpentinites thus provide a well documented example for the lack of dehydration of a mantle fragment during subduction to 75 km depth. [source]