The Greenland Ice Core Chronology 2005, 15–42 ka. Part 2: comparison to other records

A new Greenland Ice Core Chronology (GICC05) based on multi-parameter counting of annual layers has been obtained for the last 42 ka. Here we compare the glacial part of the new time scale, which is based entirely on records from the NorthGRIP ice core, to existing time scales and reference horizons covering the same period. These include the GRIP and NorthGRIP modelled time scales, the Meese-Sowers GISP2 counted time scale, the Shackleton–Fairbanks GRIP time scale (SFCP04) based on ¹⁴C calibration of a marine core, the Hulu Cave record, three volcanic reference horizons, and the Laschamp geomagnetic excursion event occurring around Greenland Interstadial 10. GICC05 is generally in good long-term agreement with the existing Greenland ice core chronologies and with the Hulu Cave record, but on shorter time scales there are significant discrepancies. Around the Last Glacial Maximum there is a more than 1 ka age difference between GICC05 and SFCP04 and a more than 0.5 ka discrepancy in the same direction between GICC05 and the age of a recently identified tephra layer in the NorthGRIP ice core. Both SFCP04 and the tephra age are based on ¹⁴C-dated marine cores and fixed marine reservoir ages. For the Laschamp event, GICC05 agrees with a recent independent dating within the uncertainties.     

Geochronology of the Tananao Schist complex, Taiwan, and its regional tectonic significance

Isotopic analyses (Rb-Sr, U-Pb, Sm-Nd, K-Ar) on rocks and minerals of the Tananao Schist complex (the Tailuko—Tienhsiang and the Nanao areas of eastern Taiwan) have yielded significant new age data corresponding to several important geologic events in the crustal evolution of Taiwan. The ages and corresponding events are summarized as follows: Crustal history 0–10 Ma: Arc-continent collision; regional metamorphism III (Penglai Orogeny). 35–40 Ma: Continental rifting and opening of the South China Sea; regional metamorphism II. 80–90 Ma: Granitic intrusions in Taiwan; regional metamorphism I (Nanao Orogeny). Overlapped with the most important world-wide, particularly circum-Pacific, thermal events of 90–110 Ma (Jahn, 1974; Jahn et al., 1976). 200–240 Ma: Deposition of carbonates and clastic sediments, probably in a geosynclinal environment. Beginning of the crustal history of Taiwan. Pre-crustal history 500–650 Ma (or older): Separation of protoliths for the granitoids of Taiwan from a chondritic (or depleted mantle) reservoir. 1000–1700 Ma: Crystallization of zircons, of which some grains have survived and been finally incorporated in the young (ca. 90 Ma) granitic magmas.     

Geochemical and isotopic characteristics of blueschist facies rocks from the Île de Groix, Armorican Massif (northwest France)

Nine samples of blueschist facies metabasic rocks and four samples of associated metasedimentary lithologies were analysed for REE contents and Nd isotopic composition. Sampling includes the main rock types exposed on Groix, concentrating on those metabasic rocks with least dispersed Rb---Sr systems. The REE abundance patterns appear not to have suffered significant alteration since emplacement of the protolith magma despite subsequent blueschist facies metamorphism. The data, when integrated into a wider geochemical data-base, allow the identification and characterization of both tholeiitic and alkaline magma-types in the original igneous suite which was differentiated from depleted mantle sources. The basalts probably originated in an oceanic context. Some sediments are predominantly volcaniclastic, in which a continental crustal component may be recognized. Other sediments are closer in composition to continental crust with variable additions of tholeiitic or alkali-basalt debris. The volcanic-sedimentary assemblage on Groix is suggestive of ocean-island magmatic activity associated with a sedimentary sequence derived from a nearby continent.