Precise measurements of U and Th concentrations and Sr, Th and O isotopes in a suite of samples f... more Precise measurements of U and Th concentrations and Sr, Th and O isotopes in a suite of samples from the 1783-84 Lakagigar eruption, reveal an extreme homogeneity in the 15 km3 lave flow. However, geochemical constraints suggest that the quartz-tholeiite magma results from the assimilation of approximately 20% of the lower crust by a mantle derived olivine-tholeiite magma. The constant
Oxygen isotope ratios in phenocrysts from recent Theistareykir lavas (Iceland) are consistently 1... more Oxygen isotope ratios in phenocrysts from recent Theistareykir lavas (Iceland) are consistently 18O-depleted relative to common terrestrial basalts (e.g. δ18O olivine=4.7–4.1‰) and correlate with geochemical indices of ‘enrichment’ (e.g. K2O/TiO2; La/Sm) and major element indices of differentiation (e.g. Mg#; CaO/Na2O). The sense of these correlations is that decreasing δ18O is accompanied by increasing ‘enriched’ geochemical signatures and an increasing extent
Olivine and clinopyroxene phenocrysts contained in late Tertiary basalts from Selardalur, northwe... more Olivine and clinopyroxene phenocrysts contained in late Tertiary basalts from Selardalur, northwest Iceland, carry volatiles with the highest helium isotope ratio yet reported for any mantle plume. 3He/4He ratios measured on three different samples and extracted by stepped crushing in vacuo fall consistently ˜37 RA (RA = air 3He/4He) — significantly higher than previously reported values for Iceland or Loihi
Tephra abundance data and geochemistry in Late-glacial and Holocene sediments on the East Greenla... more Tephra abundance data and geochemistry in Late-glacial and Holocene sediments on the East Greenland shelf are presented. Two well-known tephras were identified from electron microprobe analysis of tephra shards picked from ash peaks in the cores. These are the Vedde Ash and Saksunarvatn Ash, which probably were deposited on the shelf after transport on drifting ice. The radiocarbon dates (marine
A suite of 70 basaltic samples from the Herdubreid region of the Northern Volcanic Zone (NVZ) in ... more A suite of 70 basaltic samples from the Herdubreid region of the Northern Volcanic Zone (NVZ) in central Iceland has been analysed for major and trace element compositions. The average light rare earth element concentration of these basalts is more than a factor of 2 higher than that of basalts from the Theistareykir volcanic system near the northern end of
... best fitting material. The compositions of cumulates from the Oman ophiolite are the average ... more ... best fitting material. The compositions of cumulates from the Oman ophiolite are the average cumulate gabbro [24] and a representative wehrlite composition (Ken Koga, personal communication, 1999). The trapped-melt gabbro ...
Four previously known ash layers (Ash Zones I and II, Saksunarvatn and the Settlement layer) all ... more Four previously known ash layers (Ash Zones I and II, Saksunarvatn and the Settlement layer) all originating in Iceland, have been identified in the Central Greenland ice core GRIP. This correlation of the ash between the different environments is achieved by comparison ...
Precise measurements of U and Th concentrations and Sr, Th and O isotopes in a suite of samples f... more Precise measurements of U and Th concentrations and Sr, Th and O isotopes in a suite of samples from the 1783-84 Lakagigar eruption, reveal an extreme homogeneity in the 15 km3 lave flow. However, geochemical constraints suggest that the quartz-tholeiite magma results from the assimilation of approximately 20% of the lower crust by a mantle derived olivine-tholeiite magma. The constant
Oxygen isotope ratios in phenocrysts from recent Theistareykir lavas (Iceland) are consistently 1... more Oxygen isotope ratios in phenocrysts from recent Theistareykir lavas (Iceland) are consistently 18O-depleted relative to common terrestrial basalts (e.g. δ18O olivine=4.7–4.1‰) and correlate with geochemical indices of ‘enrichment’ (e.g. K2O/TiO2; La/Sm) and major element indices of differentiation (e.g. Mg#; CaO/Na2O). The sense of these correlations is that decreasing δ18O is accompanied by increasing ‘enriched’ geochemical signatures and an increasing extent
Olivine and clinopyroxene phenocrysts contained in late Tertiary basalts from Selardalur, northwe... more Olivine and clinopyroxene phenocrysts contained in late Tertiary basalts from Selardalur, northwest Iceland, carry volatiles with the highest helium isotope ratio yet reported for any mantle plume. 3He/4He ratios measured on three different samples and extracted by stepped crushing in vacuo fall consistently ˜37 RA (RA = air 3He/4He) — significantly higher than previously reported values for Iceland or Loihi
Tephra abundance data and geochemistry in Late-glacial and Holocene sediments on the East Greenla... more Tephra abundance data and geochemistry in Late-glacial and Holocene sediments on the East Greenland shelf are presented. Two well-known tephras were identified from electron microprobe analysis of tephra shards picked from ash peaks in the cores. These are the Vedde Ash and Saksunarvatn Ash, which probably were deposited on the shelf after transport on drifting ice. The radiocarbon dates (marine
A suite of 70 basaltic samples from the Herdubreid region of the Northern Volcanic Zone (NVZ) in ... more A suite of 70 basaltic samples from the Herdubreid region of the Northern Volcanic Zone (NVZ) in central Iceland has been analysed for major and trace element compositions. The average light rare earth element concentration of these basalts is more than a factor of 2 higher than that of basalts from the Theistareykir volcanic system near the northern end of
... best fitting material. The compositions of cumulates from the Oman ophiolite are the average ... more ... best fitting material. The compositions of cumulates from the Oman ophiolite are the average cumulate gabbro [24] and a representative wehrlite composition (Ken Koga, personal communication, 1999). The trapped-melt gabbro ...
Four previously known ash layers (Ash Zones I and II, Saksunarvatn and the Settlement layer) all ... more Four previously known ash layers (Ash Zones I and II, Saksunarvatn and the Settlement layer) all originating in Iceland, have been identified in the Central Greenland ice core GRIP. This correlation of the ash between the different environments is achieved by comparison ...
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