Institut für Geowissenschaften

Abstract Investigation by Raman spectroscopy of samples from different geological settings shows that the occurrence of TiO 2 polymorphs other than rutile can hardly be predicted, and furthermore, the occurrence of anatase is more widespread than previously thought.

Abstract: The abundances of 24 trace elements in clinopyroxene, amphibole and garnet from 4 garnet pyroxenites from Kakanui, New Zealand, were obtained by laser ablation microprobe (LAM). Since equilibrium conditions can be proven, the data are evaluated for their use of calculating reliable and consistent partition coefficients between minerals and melt.

Abstract Metamorphic textures in low-to medium-grade (∼ 500-550◦ C) metasedimentary rocks from the Erzgebirge give evidence for prograde rutile growth from ilmenite. Newly formed grains occur as rutile-rich polycrystalline aggregates that mimic the shape of the ilmenites. In-situ trace element data (EMP and SIMS) show that rutiles from the lowest grade samples (∼ 480◦ C) mirror the Nb/Ti ratio of ilmenite. Under these conditions, rutile did not equilibrate chemically with the remaining ilmenites.

Abstract (english) This study focuses on the trace element behaviour in high pressure metamorphic rocks. The eclogite locality Tescolmen in the Adula Nappe was found to be an ideal natural laboratory that preserves a wealth of information about former conditions under high pressure.

Climate variability in the North Atlantic has been linked in part to the North Atlantic Oscillation (NAO). The NAO influences marine ecosystems in the northwestern Atlantic and transport variability of the cold Labrador Current. Understanding historic patterns of NAO variability requires long-term and high-resolution climate records that are not available from instrumental data.

In order to compare thermometry results from both mineral types, a total of 62 sand samples from local creeks (small catchment areas< 10km3) were collected in the eastern Erzbgebirge. The exposed rocks range up to more than 2.9 GPa and 850 C in formation conditions, as found by conventional thermobarometry.

In a recent study we demonstrated that the Zr content in rutile is strongly temperature dependent if it is buffered by quartz and zircon.(ZACK et al., 2004). We analysed rutilequartz-zircon assemblages of 31 metamorphic rocks spanning a temperature range from 430 to 1100 C. Electron microprobe measurements of Zr concentrations in rutile vary from 30 to 8400 ppm, being highly dependent on metamorphic grade. No pressure dependence is observed.

Results Phases were analysed with the Laser Ablation-ICPMS at Memorial University. In the investigated samples, it was found that zoisite has the highest affinity for Th (1.0 to 2.5 ppm), U (0.5 to 1.0 ppm), Pb (150 to 350 ppm), Sr (2900 to 5400 ppm) and the LREE (eg Ce 60 to 130 ppm). In contrast, phengite shows only moderate (Pb, Sr) to insignificant (Th, U, REE) concentrations for these elements but has the highest affinity for Ba (1300 to 3200 ppm), Rb (300 to 520 ppm) and Cs (6 to 12 ppm).

Page 1. The geochemistry of rutile in modern sediments from the Erzgebirge, Germany S. Triebold (1), H. von Eynatten (1), T. Zack (2), GL Luvizotto (2) (1) Geowissenschaftliches Zentrum der Universität Göttingen, Germany (2) Mineralogisches Institut, Universität Heidelberg, Germany corresponding author: Silke Triebold striebo@gwdg.de EGU General Assembly - Vienna, April 2006 Introduction Fig. 1: Plot of Nb vs. Cr contents of rutile from different metamorphic environments.

Serpentinized subarc mantle peridotites act as an important sink for Li and B. These mobile light elements are carried by H2O-rich fluids released from the downgoing Pacific slab during subduction. We studied variably serpentinized harzburgite clasts recovered after drilling in the forearc region of the Mariana arc-basin system (ODP Leg 195, Site 1200). Our goal was to determine the course of serpentinization by studying various textural features and their B and Li signatures.

Electron microprobe and stable isotope studies were undertaken on Recent rhodolith specimens (coralline red algae) in order to accurately determine their growth rates and palaeotemperature signal. Results show a cyclic variation of the Mg/Ca ratio and an amplitude of the oxygen isotope curve that accurately reflects the sea-surface temperature.

Arctic Ocean freshening can exert a controlling influence on global climate, triggering strong feedbacks on ocean-atmospheric processes and affecting the global cycling of the world's oceans. Glacier-fed ocean currents such as the Alaska Coastal Current are important sources of freshwater for the Bering Sea shelf, and may also influence the Arctic Ocean freshwater budget. Instrumental data indicate a multiyear freshening episode of the Alaska Coastal Current in the early 21st century.

We summarize the available geological information on the Sierra Maestra Mountains in southeastern Cuba and report new zircon fission track and biotite Ar-Ar ages for this region. Two different and genetically unrelated volcanic arc sequences occur in the Sierra Maestra, one Cretaceous in age (pre-Maastrichtian) and restricted to a few outcrops on the southern coast, and the other Palaeogene in age, forming the main expression of the mountain range. These two sequences are overlain by middle to late Eocene siliciclastic, carbonatic and terrigenous rocks as well as by late Miocene to Quaternary deposits exposed on the southern flank of the mountain range. These rocks are britle deformed and contain extension gashes filled with calcite and karst material. The Palaeogene volcanic arc successions were intruded by calc-alkaline, low-to medium-K tonalites and trondhjemites during the final stages of subduction and subsequent collision of the Caribbean oceanic plate with the North American continental plate. U-Pb SHRIMP single zircon dating of five granitoid plutons yielded 206 Pb/ 238 U emplacement ages between 60.5 ± 2.2 and 48.3 ± 0.5 Ma. These granitoids were emplaced at pressures ranging from 1.8 to 3.0 kbar, corresponding to depths of ca. 4.5-8 km. 40 Ar/ 39 Ar dating of two biotite concentrates yielded ages of 50 ± 2 and 54 ± 4 Ma, indicating cooling through ca. 300 ºC. Zircon and apatite fission track ages range from 32 ± 3 to 46 ± 4 Ma and 31 ± 10 to 44 ± 13 Ma, respectively, and date cooling through 250 ± 50 ºC and 110 ± 20 ºC. The granitoids are the result of subduction-related magmatism and have geochemical characteristics similar to those of magmas from intra-oceanic island-arcs such as the Izu Bonin-Mariana arc and the New Britain island arc. Major and trace element patterns suggest evolution of these rocks from a single

Partial melting of subducted oceanic crust has been identified in the Sierra del Convento me¤ lange (Cuba). This serpentinite-matrix me¤ lange contains blocks of mid-ocean ridge basalt (MORB)-derived plagioclase-lacking epidote AE garnet amphibolite intimately associated with peraluminous trondhjemitic^tonalitic rocks. Field relations, major element bulk-rock compositions, mineral assemblages, peak metamorphic conditions (c. 7508C, 14^16 kbar), experimental evidence, and theoretical phase relations support formation of the trondhjemitic^tonalitic rocks by wet melting of subducted amphibolites. Phase relations and mass-balance calculations indicate eutectic-and peritectic-like melting reactions characterized by large stoichiometric coefficients of reactant plagioclase and suggest that this phase was completely consumed upon melting. The magmatic assemblages of the trondhjemitic^tonalitic melts, consisting of plagioclase, quartz, epidote, AE paragonite, AE pargasite, and AE kyanite, crystallized at depth (14^15 kbar).The peraluminous composition of the melts is consistent with experimental evidence, explains the presence of magmatic paragonite and (relict) kyanite, and places important constraints on the interpretation of slab-derived magmatic rocks. Calculated P^T conditions indicate counterclockwise P^T paths during exhumation, when retrograde blueschist-facies overprints, composed of combinations of omphacite, glaucophane, actinolite, tremolite, paragonite, lawsonite, albite, (clino)zoisite, chlorite, pumpellyite and phengite, were formed in the amphibolites and trondhjemites. Partial melting of subducted oceanic crust in eastern Cuba is unique in the Caribbean realm and has important consequences for the plate-tectonic interpretation of the region, as it supports a scenario of onset of subduction of a young oceanic lithosphere during the early Cretaceous (c. 120 Ma). The counterclockwise P^T paths were caused by ensuing exhumation during continued subduction.

In this study, we address the late Miocene to Recent tectonic evolution of the North Caribbean (Oriente) Transform Wrench Corridor in the southern Sierra Maestra mountain range, SE Cuba. The region has been affected by historical earthquakes and shows many features of brittle deformation in late Miocene to Pleistocene reef and other shallow water deposits as well as in pre-Neogene, late Cretaceous to Eocene basement rocks. These late Miocene to Quaternary rocks are faulted, fractured, and contain calcite-and karst-filled extension gashes. Type and orientation of the principal normal palaeostress vary along strike in accordance with observations of large-scale submarine structures at the south-eastern Cuban margin. Initial N-S extension is correlated with a transtensional regime associated with the fault, later reactivated by sinistral and/or dextral shear, mainly along E-W-oriented strike-slip faults. Sinistral shear predominated and recorded similar kinematics as historical earthquakes in the Santiago region. We correlate palaeostress changes with the kinematic evolution along the boundary between the North American and Caribbean plates. Three different tectonic regimes were distinguished for the Oriente transform wrench corridor (OTWC): compression from late Eocene-Oligocene, transtension from late Oligocene to Miocene (?) (D 1 ), and transpression from Pliocene to Present (D 2 -D 4 ), when this fault became a transform system. Furthermore, present-day structures vary along strike of the Oriente transform wrench corridor (OTWC) on the south-eastern Cuban coast, with dominantly transpressional/ compressional and strike-slip structures in the east and transtension in the west. The focal mechanisms of historical earthquakes are in agreement with the dominant ENE-WSW transpressional structures found on land. D