Search results for " ROC"

A layered basic intrusion, deformed and metamorphosed in granulite faciès of the Sri Lanka basement

1991

A layered basic intrusion has been found in the Central Granulite Belt of the Sri Lanka continental basement. It intruded parallel to bedding, before all or early during deformation of neighbouring metasediments. Deformation, affecting metasediments and the intrusion alike, includes flattening to c. 1/20 of the original thickness and NNW-stretching to c. 20 times the original length. The intrusion is now 170–300 m thick. Most of the deformation was acquired under granulite facies metamorphism. The intrusion was then folded, still at high T, by a large F4-synform with an axis parallel to str1 and a steep axial plane. A steep axial plane cleavage and minor folds are related to this big fold. …

Mineralogical variability of Callovo-Oxfordian clays from the Paris Basin and the Subalpine Basin.

2006

High-resolution clay mineralogical data at the Middle/Upper Jurassic boundary from the French Subalpine Basin, the Jura Mountains and the Paris Basin (ANDRA boreholes) from Callovo-Oxfordian clayey deposits allow spatial and temporal terrigenous flux evolution to be considered over a period of 6 to 7 Myr. Recorded diachronisms of major mineralogical changes and complex clays distribution at the Paris Basin scale result to combined palaeogeographic/eustatic variations and climate input. In the French Subalpine Basin, mineralogical homogeneity confirms the burial diagenesis influence, but other terrigenous supplies must be involved in contrast to the Paris Basin domains. Volcanogenic clays (b…

Storage and release of fossil organic carbon related to weathering of sedimentary rocks

2007

International audience; The biogeochemical carbon cycle, which plays an undeniable role in global climate change, is defined both by the size of carbon reservoirs (such as the atmosphere, biomass, soil and bedrock) and the exchange between them of various mineral and organic carbon forms. Among these carbon forms, fossil organic carbon (FOC) (i.e., the ancient organic matter stored in sedimentary rocks) is widely observed in modern environments but is not included in the supergene carbon budget. Using a digitized map of the world and an existing model of CO2 consumption associated with rock weathering, we establish the global distribution of FOC stored in the first meter of sedimentary rock…

Climate variation during the Holocene influenced the skeletal properties of Chamelea gallina shells in the North Adriatic Sea (Italy)

2021

Understanding how marine taxa will respond to near-future climate changes is one of the main challenges for management of coastal ecosystem services. Ecological studies that investigate relationships between the environment and shell properties of commercially important marine species are commonly restricted to latitudinal gradients or small-scale laboratory experiments. This paper aimed to explore the variations in shell features and growth of the edible bivalve Chamelea gallina from the Holocene sedimentary succession to present-day thanatocoenosis of the Po Plain-Adriatic Sea system (Italy). Comparing the Holocene sub-fossil record to modern thanatocoenoses allowed obtaining an insight o…

A multiproxy record of palaeoenvironmental conditions at the Middle Palaeolithic site of Abric del Pastor (Eastern Iberia)

2019

This paper presents a multiproxy palaeoenvironmental study from Abric del Pastor (Alcoy, Spain), a rock shelter which has yielded evidence for Middle Palaeolithic human occupation. The sedimentary sequence has been analysed for lipid biomarker n-alkane abundances (ACL, CPI), compound specific leaf wax δH and δC, and bulk organic geochemistry (TOC, %N, %S), providing a record of past climate and local vegetation dynamics. Site formation processes have been reconstructed through the application of soil micromorphology. Analyses of anthracological, microvertebrate and macrofaunal assemblages from selected subunits are also presented here. Our data indicates that a variable climate marked by pr…

Emergence of blueschists on Earth linked to secular changes in oceanic crust composition

2015

The oldest blueschists—metamorphic rocks formed during subduction—are of Neoproterozoic age1, and 0.7–0.8 billion years old. Yet, subduction of oceanic crust to mantle depths is thought to have occurred since the Hadean, over 4 billion years ago2. Blueschists typically form under cold geothermal gradients of less than 400 °C GPa−1, so their absence in the ancient rock record is typically attributed to hotter pre-Neoproterozoic mantle prohibiting such low-temperature metamorphism; however, modern analogues of Archaean subduction suggest that blueschist-facies metamorphic conditions are attainable at the slab surface3. Here we show that the absence of blueschists in the ancient geological rec…

Early exhumation of high-pressure rocks in extrusion wedges: Cycladic blueschist unit in the eastern Aegean, Greece, and Turkey

2007

Structural, metamorphic, and geochronologic work shows that the Ampelos/Dilek nappe of the Cycladic blueschist unit in the eastern Aegean constitutes a wedge of high-pressure rocks extruded during early stages of orogeny. The extrusion wedge formed during the incipient collision of the Anatolian microcontinent with Eurasia when subduction and deep underthrusting ceased and the Ampelos/Dilek nappe was thrust southward over the greenschist-facies Menderes nappes along its lower tectonic contact, the Cycladic-Menderes thrust, effectively cutting out a ∼30- to 40-km-thick section of crust. The upper contact of the Ampelos/Dilek extrusion wedge is the top-to-the-NE Selcuk normal shear zone, alon…

METAMORPHIC EVOLUTION OF SPESSARTINE QUARTZITES (COTICULES) IN THE HIGH-PRESSURE, LOW-TEMPERATURE COMPLEX AT BAHIA MANSA, COASTAL CORDILLERA OF SOUTH…

2001

Lenses of spessartine quartzites (coticules) are associated with greenschist intercalations in coastal exposures at Bahia Mansa within the mainly metapsammopelitic Western Series, which forms most of the basement in the Coastal Cordillera of central to southern Chile. The chemical compositions of the coticules can be explained by protoliths formed from ferriferous and manganiferous hydrothermal precipitates mixed with aluminous alteration-derived material on top of oceanic crust. The peak conditions of metamorphism were calculated with multivariant reactions: 270–370 °C, 6–8 kbar. A retrograde P–T evolution was marked by decompression to 2 kbar during cooling below 300°C, influx of an exter…

Omphacite textures in eclogites of the Tauern Window: Implications for the exhumation of the Eclogite Zone, Eastern Alps

2008

Abstract We discuss the relationship of omphacite lattice preferred orientation (LPO) patterns in eclogite and kinematic indicators in the matrix surrounding the eclogite during the very rapid exhumation of the deeply buried Eclogite Zone in the Tauern Window of the Eastern Alps. LPO patterns are presented from profiles parallel to the eclogite stretching lineation across the Eclogite Zone. The omphacite textures show symmetric patterns across the entire Eclogite Zone; only in few cases slight asymmetries are observed. The patterns are characterized by an alignment of {110} with the foliation and a maximum of 〈001〉 close to the lineation and are indicative of deformation by intracrystalline…

2001

The roles of volume loss, coaxial versus noncoaxial flow, and blueschist exhumation in subduction-related accretionary wedges are still poorly understood. In our study at Leech Lake Mountain in the Eastern belt of the Franciscan subduction complex, we focus on these subjects. In the specific example of the Franciscan, the tectonic significance of the boundary between the Eastern and Central belts remains controversial. The Leech Lake Mountain area in northern California is situated immediately above this boundary and, therefore, appears to be of crucial importance for understanding aspects of the tectonic evolution of the Franciscan. The structural development at Leech Lake Mountain is char…