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We present zircon and titanite U-Pb ages from granulite-facies transtensional shear zones and a greenschist facies strike-slip shear zone in the Karkkila-Vihti area, West Uusimaa. The zircon rim and titanite ages of c. 1815−1820 Ma from the transtensional shear zones constrain the evolution of the orogenic deformation from compression dominated to syn-compressional lateral-escape within this part of the Fennoscandian shield while the zircon rim and titanite ages of 1790−1800 Ma give the timing of the late- to post-orogenic low-grade reactivation of the large-scale Somero-Karkkila fault zone. The new age data further constrain the timing of the changes in the crustal deformation style during orogenesis from i) compression-dominated to combined transpression - lateral stretching and escape, to ii) the late- to post-orogenic transition into retrograde conditions.

We present zircon and titanite U-Pb ages from granulite-facies transtensional shear zones and a greenschist facies strike-slip shear zone in the Karkkila-Vihti area, West Uusimaa. The zircon rim and titanite ages of c. 1815-1820 Ma from the transtensional shear zones constrain the evolution of the orogenic deformation from compression-dominated to syn-compressional lateral-escape within this part of the Fennoscandian shield while the zircon rim and titanite ages of 1790-1800 Ma give the timing of the late- to post-orogenic low-grade reactivation of the large-scale Somero-Karkkila fault zone. The new age data further constrain the timing of the changes in the crustal deformation style during orogenesis from i) compression-dominated to combined transpression - lateral stretching and escape, to ii) the late- to post-orogenic transition into retrograde conditions. [ABSTRACT FROM AUTHOR]

The Holocene fluvial history of rivers draining the Romanian Carpathians has been assessed using a database resulting from the authors' own field research at more than 50 sites comprising natural exposures (riverbanks), anthropogenic exposures (gravel pits) and manual boreholes carried out in floodplains, as well as on the analysis of over 30 published sources. Thus, 196 dated fluvial units were obtained, of which, subsequent to filtering, 142 units were retained for application of Cumulative Probability Functions (CPFs). To this database we added 274 radiocarbon-dated lacustrine sedimentary units originating in small lakes and bogs linked to the fluvial network of the study area. The resulting data bases were classified, processed and analysed under the methodological framework of meta-analysis in order to reconstruct the phases of geomorphic activity of rivers during major flood events and periods of low hydroclimatic intensity throughout the Holocene, and to understand the river response in terms of dominant fluvial processes. Based on the analysis of probability frequency, 17 major flooding episodes were identified, of which 12 (mostly from the last 4500 years) coincide with wet phases determined for lacustrine sedimentary units from the study area. At regional scale, of the 17 centennial intervals with flood events recorded in fluvial archives from Romania in the last 10 ka, 15 intervals are synchronous with at least one area from Central or Eastern Europe, leading to the conclusion that the climatic factor manifested dominantly in SE Europe, as well. At local scale, the orographic barrier of the Carpathians interfering with the dominant circulation of western air masses has modified the magnitude and timing of flood events, resulting in increased rates of hydroclimatic and geomorphic processes in western rivers compared to rivers east of the Carpathian range. Other controls which have local influence on the evolution of hydroclimatic processes (i.e. vegetation changes and human impact) determined an increase in the susceptibility of areas located between 700 and 1000 m asl throughout Romania and contributed to the acceleration of fluvial systems dynamics post ca. 4500 cal BP. • Regional features, suballuvial morphology and sedimentary fill of Carpathian rivers. • Probability distributions of dated units in fluvial and lacustrine environments. • Evolution of Holocene fluvial activity indicators of rivers draining the Romanian Carpathians. • Correlations with other paleoenvironmental indicators in the study area. [ABSTRACT FROM AUTHOR]

We report new age determinations and compositions for rocks from 18 dredge hauls collected from eight submarine areas across Central Kerguelen Plateau (CKP). Sea knolls and volcanic fields with multiple small cones were targeted over a ∼125 000 km2region that includes Heard and McDonald Islands. Large early Miocene (22–16 Ma) sea knolls rise from the western margin of the CKP and are part of a NNW–SSE line of volcanic centres that lie between Îles Kerguelen and Heard and McDonald Islands. These are probably related to hotspot activity now underlying the Heard Island area. We see evidence of much younger activity (5 Ma to present) in volcanic fields to the north of, and up to 300 km NE of, Heard Island. Compositions include basanite, basalt and trachybasalt, which are broadly similar to plateau lava flows from nearby Ocean Drilling Program Site 1138, lower Miocene lavas at Îles Kerguelen, dredged rocks from the early Miocene sea knolls, and Big Ben lavas from Heard Island. Geochemical data indicate decreasing fractions of mantle source melting with time. We propose that a broad region of the CKP became volcanically active in Neogene time owing to incubation of plume material at the base of the relatively stationary overlying plateau. The presence of pre-existing crustal faults gave access for melts from the Heard mantle plume to rise to the surface. [ABSTRACT FROM PUBLISHER]

Harrat Hutaymah is an alkali basalt volcanic field in north-central Saudi Arabia, at the eastern margin of a large Neogene continental, intraplate magmatic province. Lava flow, tephra and spatter cone compositions in the field include alkali olivine basalts and basanites. These compositions contrast with the predominantly tholeiitic, fissure-fed basalts found along the eastern margin of the Red Sea. The Hutaymah lava flows were erupted through Proterozoic arc-associated plutonic and meta-sedimentary rocks of the Arabian shield, and commonly contain a range of sub-continental lithospheric xenoliths, although the lavas themselves show little indication of crustal contamination. Previous radiometric dating of this volcanic field (a single published K–Ar age; 1.8 Ma) is suspiciously old given the field measurement of normal magnetic polarity only (i.e. Brunhes interval, ≤ 780 Ka). We report new age determinations on 14 lava flows by the 40 Ar– 39 Ar laser step heating method, all younger than ~ 850 Ka, to better constrain the time frame of volcanism, and major, trace and rare earth element compositions to describe the chemical variation of volcanic activity at Harrat Hutaymah. Crystal fractionation was dominated by olivine ± clinopyroxene at a range of upper mantle and crustal pressures. Rapid ascent and eruption of magma is indicated by the array of lower crustal and lithospheric xenoliths observed in lava flows and tephra. Modeling suggests 1–7% melting of an enriched asthenospheric mantle source occurred beneath Harrat Hutaymah under a relatively thick lithospheric cap (60–80 km). [ABSTRACT FROM AUTHOR]

We report40Ar–39Ar laser step-heating age determinations on 15 stratigraphically controlled lava flows and intrusive rocks from Heard Island, Central Kerguelen Plateau (Indian Ocean). The island history began with uplift of pelagic limestone intruded by 22 Ma gabbro sills. Subaerial and wave erosion levelled the early island, producing an unconformity onto which pillow lavas, tuffaceous sediments and shallow-water, fossiliferous marine siltstone (Drygalski Formation) were deposited, beginning in late Miocene time. Two volcanic systems then formed in the late Quaternary. Big Ben dominates the larger southeast part of the island, while Mount Dixon occupies the northwest Laurens Peninsula. Feeder dykes and the early lava flows in both systems are 400–200 ka. Lava flows with evolved compositions (trachytes, trachyandesites) erupted 100–20 ka. Well-preserved parasitic cones exposed at low elevations are 15–10 ka and younger. Mawson Peak, near the summit of Big Ben, has erupted lava flows as recently as 2007. Heard Island, and nearby active McDonald Island, are subaerial features of a larger Neogene volcanic region of Central Kerguelen Plateau that includes several large sea knolls and recently identified submarine fields of small cones. This broadly distributed volcanic activity is linked to incubation of plume material at the base of the nearly stationary overlying Central Kerguelen Plateau. [ABSTRACT FROM PUBLISHER]

Abstract: The importance of brachiopod shells as archives of past environmental changes, via chemical proxies (isotopes and trace elements), will increase significantly if the age of specimens can be determined accurately. Here, we evaluate the interpretation of spiral shell deviations throughout the ontogeny of the modern brachiopod species Laqueus rubellus collected from Sagami Bay (Japan), in combination with high-resolution biogeochemistry. The determination of spiral maxima and minima indicates that there is a different growth rate for ventral and dorsal valves, as well as for juvenile and adult specimens, and that the anterior shell regions provide a more accurate record of shell growth. The combination of trace element proxies (P/Ca and Mg/Ca) with shell spiral deviations indicates that the maxima represent prominent periods of shell growth that occurs during the beginning of the autumn. By counting the maxima on dorsal valves of fully mature specimens, these specimens can record shell growth up to 6–7years, which is confirmed by independent morphological and isotopic studies in the same brachiopod species. The integration of statistical measurements of shell morphologies with chemical measurements represents an innovative methodology for specimen-age determinations in brachiopods, and provides a better understanding of trace element proxies. Overall, the application of this approach to fossil brachiopods may open a new avenue for paleoseasonality and paleoceanography studies. [Copyright &y& Elsevier]

Abstract: We present a revised lithostratigraphy for the Voltaian Supergroup of Ghana, based on a review of existing literature, interpretations of remotely sensed data and reconnaissance field survey of the Volta Basin. These strata thicken eastwards, to a maximum of between 5 and 6km adjacent to the Pan-African Dahomeyide orogen. They began to accumulate some time after about 1000Ma, along the margin of an epicontinental sea. Initial sedimentation, comprising the age-equivalent Kwahu and Bombouaka Groups, shows a cyclical mode of deposition controlled by eustatic changes in sea-level that produced a range of nearshore marine, littoral and terrestrial environments. A major erosional interval was followed by deposition of the 3–4km thick Oti-Pendjari Group. Basal tillites and associated sandy diamictons are correlated with the Marinoan (end-Cryogenian) glaciation, indicating a maximum depositional age of about 635Ma. The overlying cap carbonates and tuffs were deposited within a shallow epeiric sea bordered by a volcanically active rift system. The main part of the group records the transition from a rifted passive margin to a fully developed foreland basin receiving marine flysch in the form of argillaceous strata interbedded with highly immature wacke-type sandstones and conglomerates. Maximum accommodation space was developed within a foredeep adjacent to the Dahomeyide belt. Towards the end of the orogenic phase, the foredeep succession became partially inverted and then was buried under coarse terrestrial, red-bed molasse of the Obosum Group. [ABSTRACT FROM AUTHOR]

We report U-Pb and 39Ar-40Ar measurements on plutonic rocks recovered from the Ocean Drilling Program (ODP) Legs 173 and 210. Drilling revealed continental crust (Sites 1067 and 1069) and exhumed mantle (Sites 1070 and 1068) along the Iberia margin and exhumed mantle (Site 1277) on the conjugate Newfoundland margin. Our data record a complex igneous and thermal history related to the transition from rifting to seafloor spreading. The results show that the rift-to-drift transition is marked by a stuttering start of MORB-type magmatic activity. Subsequent to initial alkaline magmatism, localized mid-oceanic ridge basalts (MORB) magmatism was again replaced by basin-wide alkaline events, caused by a low degree of decompression melting due to tectonic delocalization of deformation. Such "off-axis" magmatism might be a common process in (ultra-) slow oceanic spreading systems, where "magmatic" and "tectonic" spreading varies in both space and time. [ABSTRACT FROM AUTHOR]