Petrochemistry and petrology of I-type granitoids in an arc setting: the composite Torul pluton, Eastern Pontides, NE Turkey

The Upper Cretaceous Torul pluton, located in the Eastern Pontides, is of sub-alkaline affinity and displays features typical of volcanic arc granitoids. It is a composite pluton consisting of granodiorite, biotite hornblende monzogranite, quartz monzodiorite, quartz monzonite and hornblende biotite monzogranite. The oldest syenogranite (77.9 ± 0.3 Ma) and the youngest quartz diorite form small stocks within the pluton. Samples from the granodiorites, biotite hornblende monzogranites, quartz monzodiorites, quartz monzonites and hornblende biotite monzogranites have SiO₂ between 57 and 68 wt% and display high-K calc-alkaline, metaluminous to peraluminous characteristics. Chondrite-normalized REE patterns are fractionated (La_cn/Lu_cn = 6.0?14.2) with pronounced negative Eu anomalies (Eu/Eu* = 0.59–0.84). Initial ?_Nd(i) values vary between ?3.1 and ?4.1, initial ⁸⁷Sr/⁸⁶Sr values between 0.7058 and 0.7072, and δ¹⁸O values between +4.4 and +7.3‰. The quartz diorites are characterized by relatively high Mg-number of 36–38, low contents of Na₂O (2.3–2.5 wt%) and SiO₂ (52–55 wt%) and medium-K calc-alkaline, metaluminous composition. Chondrite-normalized REE patterns are relatively flat [(La/Yb)_cn =  2.8–3.3; (Tb/Yb)_cn =  1.2] and show small negative Eu anomalies (Eu/Eu* = 0.74–0.76). Compared to the other rock types, radiogenic isotope signatures of the quartz diorites show higher ⁸⁷Sr/⁸⁶Sr (0.7075–0.7079) and lower ?_Nd(i) (–4.5 to –5.3). The syenogranites have high SiO₂ (70–74 wt%) and display high-K calc-alkaline, peraluminous characteristics. Their REE patterns are characterized by higher La_cn/Lu_cn (12.9) and Eu/Eu* (0.76–0.77) values compared to the quartz diorites. Isotopic signatures of these rocks [?_Nd(i) =  ?4.0 to ?3.3; ⁸⁷Sr/⁸⁶Sr_(i) =  0.7034?0.7060; δ¹⁸ O =  + 4.9 to + 8.2] are largely similar to the other rock types but differ from that of the quartz diorites. Fractionation of plagioclase, hornblende, pyroxene and Fe–Ti oxides played an important role in the evolution of Torul granitoids. The crystallization temperatures of the melts ranged from 800 to 900°C as determined from zircon and apatite saturation thermometry. All these characteristics, combined with low K₂O/Na₂O, low Al₂O₃/(FeO_T + MgO + TiO₂), and low (Na₂O + K₂O)/(FeO_T + MgO + TiO₂) ratios suggest an origin through dehydration melting of mafic lower crustal source rocks.     

Erosion rates on subalpine paleosurfaces in the western Mediterranean by in-situ <Superscript>10</Superscript>Be concentrations in granites: implications for surface processes and long-term landscape evolution in Corsica (France)

A study of erosion rates by in-situ ¹⁰Be concentrations in granites of Miocene high-elevation paleosurfaces in Corsica indicates maximum erosion rates between 8 and 24 mm/kyear. The regional distribution of measured erosion rates indicates that the local climatic conditions, namely precipitation, the petrographic composition of granites, and the degree of brittle deformation govern erosion rates. Chemical erosion dominates even at elevations around 2,000 m in presently subalpine climate conditions. Field evidence indicates that erosion operates by continuous dissolution and/or disintegration to grains (grusification). The erosion rates are relatively high with respect to the preservation of inferred Early Miocene landscapes. We infer temporal burial in the Middle Miocene and significantly lower erosion rates in the Neogene until ∼3 Ma to explain the preservation of paleosurfaces, in line with fission track data. Valley incision rates that are a magnitude higher than erosion rates on summit surfaces result in relief enhancement and long-term isostatic surface uplift. On the other hand, widening and deepening of valleys by cyclic glaciation progressively destroys the summit surface relics.

Linear birefringence and X-Ray diffraction studies of the structural phase transition in titanite,CaTiSiO5

The antiferroelectric phase transition in titanite characterised by a collinear displacement of Ti-atoms from their central octahedral position is investigated using linear optical birefringence and X-ray diffraction techniques. Both methods indicate a continuous transition near 496 K and extra contributions to δΔn and X-ray intensity signals at higher temperatures. The critical exponent of the macroscopic order parameter is found to be β = 0.14 ± 0.02 and the transformation is interpreted in terms of a two-dimensional quasi-spin model. Topological features of the structure agree well with the spatial distribution of the diffuse scattering of the superstructure reflection 40 \(\bar 3\) .     

Acceleration of cometary plasma tails

Cometary plasma tails are accelerated by the solar wind to half its velocity, corresponding to some 10² times the solar-wind momentum density. We corroborate Alfvén's (1957) wind-sock mechanism according to which the momentum transfer is brought about by magnetic rigidity.     

Late stage differential exhumation of crustal blocks in the central Eastern Alps: evidence from fission track and (U–Th)/He thermochronology

Thermal history modelling based on zircon‐ and apatite fission track and apatite (U–Th)/He data constrain and refine the near‐surface exhumation of the south‐eastern Tauern Window (Penninic units) and neighbouring Austroalpine basement units in the Eastern Alps. Fast exhumation on both sides of the Penninic/Austroalpine boundary coincides with a period of lateral extrusion and tectonic denudation of the Penninic units in Miocene time (22–12 Ma). The jump to older ages occurs within the Austroalpine unit along the Polinik fault, which therefore defines the boundary between the tectonically denuded units and the hangingwall at that time. According to the different (U–Th)/He ages between the Penninic Hochalm‐ and Sonnblick Domes we demonstrate a differential cooling history of these two domes in the latest Miocene and early Pliocene.     

Hemipelagic cephalopods from the Maastrichtian (late Cretaceous) Parras Basin at La Parra,Coahuila, Mexico,and their implications for the correlation of the lower Difunta Group

Few biostratigraphic data exist from the Parras and La Popa basins, mainly due to the absence of index fossils. This paper describes 19 ammonoid species from 15 genera and 1 nautilid from La Parra, southeastern Coahuila, Mexico. The assemblage consists of Tethyan [(Baculites ovatus, Brahmaites (Anabrahmaites) vishnu, Fresvillia constricta, Hauericeras rembda, Pachydiscus (P.) ex gr. neubergicus, Solenoceras reesidei, Tetragonites cf. superstes], cosmopolitan (Anagaudryceras politissimum, Desmophyllites diphylloides, Diplomoceras cylindraceum, Gaudryceras kayei, Phyllopachyceras forbesianum, Pseudophyllites indra), and cold water taxa [Fresvillia teres, Hypophylloceras (Neophylloceras) surya, H. (N.) hetonaiense, Pachydiscus (P.) cf. egertoni]. Eutrephoceras sp. and Menuites juv. sp. were not determined to species level. A similar assemblage was recently described from the coeval Méndez Formation at Cerralvo, Nuevo León. Species endemic to North America, particularly the Western Interior Seaway, are absent at La Parra. The ammonoid assemblage and associated planktonic foraminifers allow for precise biostratigraphic assignation to the early Maastrichtian planktonic foraminiferal zone CF 5, and thus provide an important marker level for correlation of the lower Difunta Group. The new biostratigraphic data presented herein allow for the first time precise dating of the Cañon del Tule Formation of the Difunta Group. Their combination with existing sequence- and magnetostratigraphic data improve the correlation of the lower Difunta Group with time-equivalent lithostratigraphic units such as the Cárdenas Formation in Mexico. They also provide new insight into ammonoid migration patterns induced by sea-level changes. Baculites ovatus migrated into the La Popa Basin as a result of the sea-level highstand documented at La Parra.