Wolfgang Siebel

Provenance of lithogenic surface sediments and pathways of riverine suspended matter in the Eastern Mediterranean Sea: evidence from 143Nd/144Nd and 87Sr/86Sr ratios

In order to characterize the provenance of lithogenic surface sediments from the Eastern Mediterranean Sea (EMS), residual (leached) fraction of 34 surface samples have been analysed for their 143 Nd/ 144 Nd and 87 Sr/ 86 Sr isotope ratios. The sample locations bracket all important entrances of riverine suspended matter into the EMS as well as all sub-basins of the EMS. The combined analyses of these two isotope ratios provide a precise characterization of the lithogenic fraction of surface sediments and record their dilution towards the central sub-basins. We reconstruct provenance and possible pathways of riverine dispersal and current redistribution, assuming more or less homogenous isotopic signatures and flux rates of the eolian fraction over the EMS. Lithogenic sediments entering the Ionian Sea from the Calabrian Arc and the Adriatic Sea are characterized by high 87 Sr/ 86 Sr isotope ratios and low eNd(0) values (average 87 Sr/ 86 Sr=0.718005 and eNd(0)= � 11.06, n=5). Aegean Sea terrigenous sediments show an average ratio of 87 Sr/ 86 Sr=0.713089 (n=5) and values of eNd(0)= � 7.89 (n=5). The Aegean isotopic signature is traceable up to the southwest, south, and southeast of Crete. The sediment loads entering the EMS via the Aegean Sea are low and spread out mainly through the Strait of Casos (east of Crete). Surface sediments from the eastern Levantine Basin are marked by the highest eNd(0) values ( � 3.3, n=6) and lowest 87 Sr/ 86 Sr isotope ratios (average 0.709541, n=6), reflecting the predominant input of the Nile sediment. The influence of the Nile sediment is traceable up to the NE-trending, eastern flank of the Mediterranean Ridge. The characterization of the modern riverine dispersal and eolian flux, based on isotope data, may serve as a tool to reconstruct climate-coupled variations of lithogenic sediment input into the EMS. D 2002 Elsevier Science B.V. All rights reserved.

Provenance of the Beihuaiyang lower-grade metamorphic zone of the Dabie ultrahigh-pressure collisional orogen, China: evidence from zircon ages

The Beihuaiyang zone of the Dabie ultrahigh-pressure collisional belt, which was formed by the Early Mesozoic collision of the North and South China (Yangtze) Blocks, is diversely interpreted as an active or a passive sedimentary sequence. It comprises the Luzhenguan and Foziling complexes. Six granitoid rocks of the Luzhenguan complex are dated at 770 Ma to 720 Ma and one schist sample also contains detrital zircons of 760 Ma to 720 Ma. These data indicate that this complex was of the South China affinity and probably originated from the northern Yangtze Block. Two quartzite samples of the Foziling complex contain abundant detrital zircons of Archean to Paleozoic ages, clustering around 2.5 Ga, 1.9 ‐ 1.8 Ga, 1.0‐ 0.7 Ga, and 0.5 ‐ 0.4 Ga. This age spectrum demonstrates a mixed source of these two blocks. The youngest zircons suggest a Paleozoic deposition along an active continental margin south of the North China Block, while these Late Proterozoic zircons are characterized for the Yangtze Block. Subsequently, it is suggested that a terrain drifted from the northern Yangtze Block in Early Paleozoic must have been situated to the southern margin of the North China Block to provide material source prior to the final collision in Early Mesozoic. q 2003 Elsevier Ltd. All rights reserved.

Geochemistry and isotope systematics of small- to medium-volume Neogene–Quaternary ignimbrites in the southern central Andes: evidence for derivation from andesitic magma sources

The geochemical and isotopic compositions of small- to medium-volume (<10 km3, <50 km3) Neogene–Quaternary ignimbrite sheets of the southern central Andes (25°00′–26°45′S, 67°30′–69°30′W) have been analysed in order to assess the petrogenesis of this type of calc-alkaline magma. The ignimbrites are derived from the active volcanic zone around Salar de la Isla (SIS) in Chile and from behind the active arc in the area of the Salar de Antofalla (SAF), Argentina. The ignimbrites in both areas are characterized by 87Sr/86Sr(t) ratios (0.7066–0.7090) that are lower and eNd(t) values (−2.4 to −5.1) that are higher than in the large-volume, caldera-sourced ignimbrites of Cerro Galan, 100 km further east and those of ignimbrites from other megacalderas of the central Andes. This difference reflects smaller amounts of crustal material in the SIS and SAF ignimbrites rather than a change in basement composition as indicated by Pb provinciality. The isotope signature of the SIS and SAF ignimbrites is similar to that of late- to post-Miocene composite calc-alkalic andesite/dacite stratovolcanoes of the frontal arc in this region. This finding, combined with major and trace element modelling, lends support to a petrogenetic model for the SIS and SAF ignimbrites involving fractional crystallization from a LIL-depleted andesitic parental magma, which was beforehand modified by crustal contamination.

Detrital Zircon Ages and Hf‐Nd Isotopic Composition of Neoproterozoic Sedimentary Rocks in the Yangtze Block: Constraints on the Deposition Age and Provenance

The South China craton was formed by collision of the Yangtze and Cathaysia blocks during the Neoproterozoic Jiangnan orogeny (also termed the Jingnin or Sibao orogeny in Chinese literature). Basement rocks within the Yangtze block consist mainly of Proterozoic sediments of the Lengjiaxi and Banxi groups. U‐Pb ages of detrital zircons obtained by the laser ablation inductively coupled plasma mass spectrometry dating technique imply that the deposition of the Lengjiaxi Group continued until the Neoproterozoic. The youngest detrital zircons suggest a minimum deposition age of ∼830 Ma for the Lengjiaxi Group and an initial deposition age of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Geochronological and Petrological Constraints for Tectonic Evolution of the Central Greater Himalayan Sequence in the Kharta Area, Southern Tibet

785\pm 12

Geochronological evidence and tectonic significance of Carboniferous magmatism in the southwest Trabzon area, eastern Pontides, Turkey

\end{document} Ma for the Banxi Group, indicating a temporal hiatus of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Toward a comprehensive provenance analysis: A multi-method approach and its implications for the evolution of the Central Alps

48\pm 13