Search results for "Geochemistry"
showing 10 items of 2967 documents
Complex-forming properties of peat humic acids from a raised bog profiles
2013
Abstract Humic substances (HS) belong to the most powerful complex-forming agents, significantly affecting major and trace element speciation in natural environment. Several authors have focused on humic–metal interactions, using differing methods and comparing humic substances on different sources. However, the intrinsic differences among the HS of different origin and the impact of humification degree on the complex formation between humic substances and metals have not received the necessary attention until now. The aim of this study is to determine the Cu(II) complexing capacity and stability constants of Cu(II) complexes of humic acids (HA) isolated from two well-characterized raised b…
The Wadi Onib Mafic-Ultramafic Complex: A Neoproterozoic Supra-Subduction Zone Ophiolite in the Northern Red Sea Hills of the Sudan
2004
Publisher Summary The Wadi Onib mafic–ultramafic complex represents the best preserved, though tectonically dismembered, Neoproterozoic (Pan-African) ophiolite in the northern Red Sea Hills of the Sudan. Arabian–Nubian shield (ANS) is the northern continuation of the Mozambique belt and, together, they have been referred to as the East African Orogen (EAO). The Wadi Onib mafic—ultramafic complex constitutes one of the best preserved, though tectonically fragmented, ophiolitic sequence within the ANS and makes up the major part of the prominent, southwest to northeast oriented Onib–Sol Hamed suture. An improved understanding of the composition and history of this complex has important region…
Quantifying the P-T-t conditions of north-south Lhasa terrane accretion: new insight into the pre-Himalayan architecture of the Tibetan plateau
2014
An integrated field, petrological and geochronological study of the Basong Tso region of south-eastern Tibet has constrained the timing and P–T conditions of north–south Lhasa terrane accretion and provides new insight into the tectonothermal evolution of the Tibetan plateau. Two distinct high-grade metamorphic belts are recognized in the region: a southern belt (the Basong Tso complex) that consists of sheared schist and orthogneiss; and a northern belt (the Zhala complex) that comprises paragneiss and granite. Combined pseudosection modelling and U–Pb geochronology of monazite and zircon indicates that the Basong Tso complex records peak metamorphic conditions of 9 ± 0.5 kbar and 690 ± 25…
Development of topography in 3-D continental-collision models
2015
Understanding the formation and evolution of high mountain belts, such as the Himalayas and the adjacent Tibetan Plateau, has been the focus of many tectonic and numerical models. Here we employ 3-D numerical simulations to investigate the role that subduction, collision, and indentation play on lithosphere dynamics at convergent margins, and to analyze the conditions under which large topographic plateaus can form in an integrated lithospheric and upper mantle-scale model. Distinct dynamics are obtained for the oceanic subduction side (trench retreat, slab rollback) and the continental-collision side (trench advance, slab detachment, topographic uplift, lateral extrusion). We show that sla…
Subduction of the Nazca Ridge and the Inca Plateau: Insights into the formation of ore deposits in Peru
2005
A large number of ore deposits that formed in the Peruvian Andes during the Miocene (15-5 Ma) are related to the subduction of the Nazea plate beneath the South American plate. Here we show that the spatial and temporal distribution of these deposits correspond with the arrival of relatively buoyant topographic anomalies, namely the Nazca Ridge in central Peru and the now-consumed Inca Plateau in northern Peru, at the subduction zone. Plate reconstruction shows a rapid metallogenic response to the arrival of the topographic anomalies at the subduction trench. This is indicated by clusters of ore deposits situated within the proximity of the laterally migrating zones of ridge subduction. It …
Late Quaternary slip rates for the southern Elsinore fault in the Coyote Mountains, southern California from analysis of alluvial fan landforms and c…
2019
Abstract Offset alluvial fans along the Elsinore fault in the south-central Coyote Mountains were studied to resolve an average late Quaternary slip rate for this major western strand of the San Andreas fault system in southern California. Alluvial fans and their offsets were mapped using high-resolution DEMs combined with field observations of fan-surface morphology and the character of the soils developed in each fan remnant. Clast assemblage data was used to determine the source of each alluvial fan upstream of the fault, and U-series dating of pedogenic carbonate was used to estimate minimum ages of the alluvial fan surfaces. Forty U-Th dates on pedogenic carbonate confirm the utility o…
Characterization, provenance, and tectonic setting of Fig Tree greywackes from the Archaean Barberton Greenstone Belt, South Africa
1999
Abstract In this study, mineralogical and geochemical data, as well as Sr and Nd isotopic compositions of early Archaean greywackes from the Fig Tree Group are presented to provide further information about the evolution of the Barberton Greenstone Belt (BGB) of the Kaapvaal Craton, South Africa. The chemical data on the collected greywackes from the BGB suggest limited chemical modification of the source rocks. The Eu/Eu * anomaly is negative with an average value of 0.76 which is slightly higher than that of Eu-depleted crustal rocks (0.65). High Cr and Ni concentrations and a Cr/Ni ratio of about 1.6 indicate derivation from ultramafic sources without fractionation. Although rounded zirc…
Archean and Proterozoic ancestry in late Precambrian to early Paleozoic crustal elements of southern Turkey as revealed by single-zircon dating
1990
Detrital zircon ages and paleontology limit the age of the oldest known metasedimentary rocks in the Menderes-Taurus block of southwestern Turkey to between 657 {plus minus}5 Ma and Middle Cambrian (ca. 533 Ma). A mylonitic granite, also part of the basement, yielded a date of intrusion of 543 {plus minus}7 Ma. The scatter of both detrital and xenocryst zircon ages between 612 {plus minus}6 and 3,140 {plus minus}2 Ma virtually precludes northeastern Africa and Arabia as their provenance, but is compatible with a source in the Angara craton of Siberia. These results suggest that the Pan-African evolution in the Middle East may have ended by Angara's collision with Gondwana in the Early Cambr…
Mineral chemical and geochronological constraints on the age and provenance of the eastern Circum-Rhodope Belt low-grade metasedimentary rocks, NE Gr…
2010
Abstract In north-eastern Greece the mid-greenschist facies Makri Unit and the anchizonal Melia Formation belong to the eastern Circum-Rhodope Belt that forms the uppermost tectonostratigraphic unit of the Rhodope metamorphic nappe pile. The two metasedimentary successions had different source areas, although they now lie in close proximity in the Rhodope Massif. The U–Pb isotopic ages of detrital zircons from a metasandstone of the Makri Unit analysed using LA–SF–ICP–MS and SHRIMP-II gave age clusters at ca. 310–290 Ma and at ca. 240 Ma for magmatic zircons, which may have been derived from Carboniferous–Permian basement rocks of the Thracia Terrane (Lower Tectonic Unit of the Rhodope Mass…
Modelling of piping collapses and gully headcut landforms: Evaluating topographic variables from different types of DEM
2021
Abstract The geomorphic studies are extremely dependent on the quality and spatial resolution of digital elevation model (DEM) data. The unique terrain characteristics of a particular landscape are derived from DEM, which are responsible for initiation and development of ephemeral gullies. As the topographic features of an area significantly influences on the erosive power of the water flow, it is an important task the extraction of terrain features from DEM to properly research gully erosion. Alongside, topography is highly correlated with other geo-environmental factors i.e. geology, climate, soil types, vegetation density and floristic composition, runoff generation, which ultimately inf…