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Featured researches published by Thomas F. Kokfelt.


Nature | 2012

Hafnium isotope evidence for a transition in the dynamics of continental growth 3.2 Gyr ago.

Tomas Næraa; Anders Scherstén; Minik T. Rosing; Ais Kemp; J. E. Hoffmann; Thomas F. Kokfelt; Martin J. Whitehouse

Earth’s lithosphere probably experienced an evolution towards the modern plate tectonic regime, owing to secular changes in mantle temperature. Radiogenic isotope variations are interpreted as evidence for the declining rates of continental crustal growth over time, with some estimates suggesting that over 70% of the present continental crustal reservoir was extracted by the end of the Archaean eon. Patterns of crustal growth and reworking in rocks younger than three billion years (Gyr) are thought to reflect the assembly and break-up of supercontinents by Wilson cycle processes and mark an important change in lithosphere dynamics. In southern West Greenland numerous studies have, however, argued for subduction settings and crust growth by arc accretion back to 3.8 Gyr ago, suggesting that modern-day tectonic regimes operated during the formation of the earliest crustal rock record. Here we report in situ uranium–lead, hafnium and oxygen isotope data from zircons of basement rocks in southern West Greenland across the critical time period during which modern-like tectonic regimes could have initiated. Our data show pronounced differences in the hafnium isotope–time patterns across this interval, requiring changes in the characteristics of the magmatic protolith. The observations suggest that 3.9–3.5-Gyr-old rocks differentiated from a >3.9-Gyr-old source reservoir with a chondritic to slightly depleted hafnium isotope composition. In contrast, rocks formed after 3.2 Gyr ago register the first additions of juvenile depleted material (that is, new mantle-derived crust) since 3.9 Gyr ago, and are characterized by striking shifts in hafnium isotope ratios similar to those shown by Phanerozoic subduction-related orogens. These data suggest a transitional period 3.5–3.2 Gyr ago from an ancient (3.9–3.5 Gyr old) crustal evolutionary regime unlike that of modern plate tectonics to a geodynamic setting after 3.2 Gyr ago that involved juvenile crust generation by plate tectonic processes.


Earth and Planetary Science Letters | 2011

On- and off-axis chemical heterogeneities along the South Atlantic Mid-Ocean-Ridge (5–11°S): Shallow or deep recycling of ocean crust and/or intraplate volcanism?

Kaj Hoernle; Folkmar Hauff; Thomas F. Kokfelt; Karsten M. Haase; Dieter Garbe-Schönberg; Reinhard Werner


Gondwana Research | 2013

Remnants of arc-related Mesoarchaean oceanic crust in the Tartoq Group of SW Greenland

Kristoffer Szilas; Vincent J. van Hinsberg; Alexander F.M. Kisters; J. Elis Hoffmann; Brian F. Windley; Thomas F. Kokfelt; Anders Scherstén; Robert Frei; Minik T. Rosing; Carsten Münker


Precambrian Research | 2012

Complex calc-alkaline volcanism recorded in Mesoarchaean supracrustal belts north of Frederikshåb Isblink, southern West Greenland: Implications for subduction zone processes in the early Earth

Kristoffer Szilas; J. Elis Hoffmann; Anders Scherstén; Minik T. Rosing; Brian F. Windley; Thomas F. Kokfelt; Nynke Keulen; Vincent J. van Hinsberg; Tomas Næraa; Robert Frei; Carsten Münker


Precambrian Research | 2013

Archaean andesite petrogenesis : insights from the Grædefjord Supracrustal Belt, southern West Greenland

Kristoffer Szilas; J. Elis Hoffmann; Anders Scherstén; Thomas F. Kokfelt; Carsten Münker


Precambrian Research | 2014

Metamorphic record of accretionary processes during the Neoarchaean: The Nuuk region, southern West Greenland

Annika Dziggel; Johann F.A. Diener; Jochen Kolb; Thomas F. Kokfelt


Lithos | 2012

Origin of Mesoarchaean arc-related rocks with boninite/komatiite affinities from southern West Greenland

Kristoffer Szilas; Tomas Næraa; Anders Scherstén; Henrik Stendal; Robert Frei; Vincent J. van Hinsberg; Thomas F. Kokfelt; Minik T. Rosing


Precambrian Research | 2012

Geodynamic setting and deformation history of an Archaean terrane at mid-crustal level: The Tasiusarsuaq terrane of southern West Greenland

Jochen Kolb; Thomas F. Kokfelt; Annika Dziggel


Lithos | 2015

The Majorqaq Belt: A record of Neoarchaean orogenesis during final assembly of the North Atlantic Craton, southern West Greenland

Brendan Dyck; Barry L. Reno; Thomas F. Kokfelt


Marine and Petroleum Geology | 2014

Provenance signal variations caused by facies and tectonics: Zircon age and heavy mineral evidence from Miocene sand in the north-eastern North Sea Basin

Mette Olivarius; Erik S. Rasmussen; Volkert Siersma; Christian Knudsen; Thomas F. Kokfelt; Nynke Keulen

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Karsten M. Haase

University of Erlangen-Nuremberg

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Tomas Næraa

Geological Survey of Denmark and Greenland

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Nynke Keulen

Geological Survey of Denmark and Greenland

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Jochen Kolb

Geological Survey of Denmark and Greenland

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Kaj Hoernle

University of California

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