Calibration of the geological time scale is achieved by independent radioisotopic and astronomical dating, but these techniques yield discrepancies of approximately 1.0% or more, limiting our ability to reconstruct Earth history. To overcome this fundamental setback, we compared astronomical and 40Ar/39Ar ages of tephras in marine deposits in Morocco to calibrate the age of Fish Canyon sanidine, the most widely used standard in 40Ar/39Ar geochronology. This calibration results in a more precise older age of 28.201 +/- 0.046 million years ago (Ma) and reduces the 40Ar/39Ar method's absolute uncertainty from approximately 2.5 to 0.25%. In addition, this calibration provides tight constraints for the astronomical tuning of pre-Neogene successions, resulting in a mutually consistent age of approximately 65.95 Ma for the Cretaceous/Tertiary boundary.

[1] South Pacific intraplate volcanoes have been active since the Early Cretaceous. Their HIMU-EMI-EMII mantle sources can be traced back into the West Pacific Seamount Province (WPSP) using plate tectonic reconstructions, implying that these distinctive components are enduring features within the Earth's mantle for, at least, the last 120 Myr. These correlations are eminent on the scale of the WPSP and the South Pacific Thermal and Isotopic Anomaly (SOPITA), but the evolution of single hot spots emerges notably more complicated. Hot spots in the WPSP and SOPITA mantle regions typically display intermittent volcanic activity, longevities shorter than 40 Myr, superposition of hot spot volcanism, and motion relative to other hot spots. In this review, we use 40 Ar/ 39 Ar seamount ages and Sr-Nd-Pb isotopic signatures to map out Cretaceous volcanism in the WPSP and to characterize its evolution with respect to the currently active hot spots in the SOPITA region. Our plate tectonic reconstructions indicate cessation of volcanism during the Cretaceous for the Typhoon and Japanese hot spots; whereas the currently active Samoan, Society, Pitcairn and Marquesas hot spots lack long-lived counterparts in the WPSP. These hot spots may have become active during the last 20 Myr only. The other WPSP seamount trails can be only ''indirectly'' reconciled with hot spots in the SOPITA region. Complex age distributions in the Magellan, Anewetak, Ralik and Ratak seamount trails would necessitate the superposition of multiple volcanic trails generated by the Macdonald, Rurutu and Rarotonga hot spots during the Cretaceous; whereas HIMU-type seamounts in the Southern Wake seamount trail would require 350-500 km of hot spot motion over the last 100 Myr following its origination along the Mangaia-Rurutu ''hotline'' in the Cook-Austral Islands. These observations, however, violate all assumptions of the classical Wilson-Morgan hot spot hypothesis, indicating that long-lived, deep and fixed mantle plumes cannot explain the intraplate volcanism of the South Pacific region. We argue that the observed short-lived and discontinuous intraplate volcanism has been produced by another type of hot spot-related volcanism, as opposed to the strong and continuous Hawaiian-type hot spots. Our results also indicate that other geological processes (plate tension, hotlines, faulting, wetspots, self-propagating volcanoes) may act in conjunction with hot spot volcanism in the South Pacific. In all these scenarios, intraplate volcanism has to be controlled by ''broad-scale'' events giving rise to multiple closely-spaced mantle plumelets, each with a distinct isotopic signature, but only briefly active and stable over geological time. It seems most likely that these plumelets originate and dissipate at very shallow mantle depths, where they may shoot off as thin plumes from the top of a ''superplume'' that is present in the South Pacific mantle. The absence of clear age progressions in most

Structural analyses along selected transects across the Menderes Massif and incorporation of existing data have resulted in a synthetic cross section across southwestern Turkey. The tectonic interpretation has been combined with 40 Ar/ 39 Ar laser-probe experiments on two syn-kinematic white mica populations, which, respectively, predate and overprint documented Early Miocene deformational fabrics. Our results indicate that the regional extension had initiated by Eocene±Oligocene times. A 362 Ma 40 Ar/ 39 Ar age derived from white mica which formed during a regionally observed, northward-directed tectonic transport suggests that the extension was contemporaneous with the tectonic emplacement of mid-crustal continental basement. Alternatively, the age may relate to the regional cooling of the basement sequence, and thus postdates the tectonic emplacement. In the latter scenario, the analysis fails to solve the present ambiguity on the Pan-African or Alpine affinity of the northward-directed transport. Further exhumation of basement rocks is characterized by a dominant displacement along the north-dipping Gediz Detachment at the northern margin of the massif, which developed under ductile conditions in the Early Miocene by partial exploitation of older zones of weakness, which originated from an earlier phase of basement emplacement. Youngest (semi)ductile activity along the Gediz Detachment has been recorded as having a 71 Ma 40 Ar/ 39 Ar age derived from syn-kinematic white mica in the top of the detachment. Following the initiation of the ductile Gediz Detachment, an antithetic, semibrittle, and south-dipping Büyük Menderes Detachment had developed in the center of the massif, which, together with the Gediz Detachment, accommodated further doming of the central part of the Menderes Massif and controlled the architecture of the surrounding supradetachment basins.

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The manufacture of geometric engravings is generally interpreted as indicative of modern cognition and behaviour. Key questions in the debate on the origin of such behaviour are whether this innovation is restricted to Homo sapiens, and whether it has a uniquely African origin. Here we report on a fossil freshwater shell assemblage from the Hauptknochenschicht ('main bone layer') of Trinil (Java, Indonesia), the type locality of Homo erectus discovered by Eugène Dubois in 1891 (refs 2 and 3). In the Dubois collection (in the Naturalis museum, Leiden, The Netherlands) we found evidence for freshwater shellfish consumption by hominins, one unambiguous shell tool, and a shell with a geometric engraving. We dated sediment contained in the shells with (40)Ar/(39)Ar and luminescence dating methods, obtaining a maximum age of 0.54 ± 0.10 million years and a minimum age of 0.43 ± 0.05 million years. This implies that the Trinil Hauptknochenschicht is younger than previously estimated. Together, our data indicate that the engraving was made by Homo erectus, and that it is considerably older than the oldest geometric engravings described so far. Although it is at present not possible to assess the function or meaning of the engraved shell, this discovery suggests that engraving abstract patterns was in the realm of Asian Homo erectus cognition and neuromotor control.

U'Ar/"Ar age spectrum analysis of phengite separates from Naxos, part of the Attic Cycladic Metamorphic Belt in Greece, indicates that cooling following high-pressure, low-to medium-temperature metamorphism, M I , occurred about 50 Ma ago. Phengite has *"AT* gradients that suggest that part of the scatter observed in conventional K-Ar ages was caused by diffusion of radiogenic argon from the minerals during a younger metamorphism, M2. In central Naxos, this metamorphism ( M 2 ) has overprinted the original mineral assemblages completely, and is associated with development of a thermal dome. Excellent "'Ar/'yAr plateaus at 15.0 2 0.1 Ma, 11.8 -C 0.1 Ma, and 11.4 2 0.1 Ma, obtained on hornblende, muscovite and biotite, respectively, from the migmatite zone, indicate that relatively rapid cooling followed the M2 event, and that no significant thermal overprinting occurred subsequent to Mz. Toward lower M I metamorphic grade, Q'Ar/"9Ar plateau ages of hornblendes increase to 19.8 2 0.1 Ma; concomitantly the proportion of excess '"Ar in the spectra increases as well. We propose that the peak of M 2 metamorphism occurred beween 15.0 and 19.8 Ma ago. K-Ar ages of biotites from a granodiorite on the west coast are indistinguishable from those found in the metamorphic complex, and hornblende K-Ar ages from the same samples are in the range 12.1-13.6 Ma. As the latter ages are somewhat younger than most ages obtained from the metamorphic complex, intrusion of the granodiorite most likely followed the peak of the M 2 metamorphism.The metamorphic evolution of Naxos is consistent with rapid crustal thickening during the Cretaceous or early Tertiary, causing conditions at which supracrustal rocks experienced pressures in the range 900-1500 MPa. Transition to normal crustal thicknesses ended the 'Current address: Z. W.O. Laboratorium voor Isotopen Geologie, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands.M , metamorphism about 50 Ma ago. The M 2 metamorphism and granodiorite intrusion occurred during a period of heat input into the crust, possibly related to the migration of the Hellenic volcanic arc in a southerly direction through the area.

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