Regional zircon U-Pb geochronology for the Maniitsoq region, southwest Greenland

AbstractZircon U-Pb geochronology places high-temperature geological events into temporal context. Here, we present a comprehensive zircon U-Pb geochronology dataset for the Meso- to Neoarchean Maniitsoq region in southwest Greenland, which includes the Akia Terrane, Tuno Terrane, and the intervening Alanngua Complex. The magmatic and metamorphic processes recorded in these terranes straddle a key change-point in early Earth geodynamics. This dataset comprises zircon U-Pb ages for 121 samples, including 46 that are newly dated. A principal crystallization peak occurs across all three terranes at ca. 3000 Ma, with subordinate crystallization age peaks at 3200 Ma (Akia Terrane and Alanngua Complex only), 2720 Ma and 2540 Ma. Metamorphic age peaks occur at 2990 Ma, 2820–2700 Ma, 2670–2600 Ma and 2540 Ma. Except for one sample, all dated metamorphic zircon growth after the Neoarchean occurred in the Alanngua Complex or within 20 km of its boundaries. This U-Pb dataset provides an important resource for addressing Earth Science topics as diverse as crustal evolution, fluid–rock interaction and mineral deposit genesis.

Download Full-text

Early Earth Science

Nature ◽

10.1038/238417c0 ◽

1972 ◽

Vol 238 (5364) ◽

pp. 417-418

Author(s):

V. A. EYLES

Keyword(s):

Earth Science ◽

Early Earth

Download Full-text

High subcritical water-rock interaction for the formation of ferric minerals, in the absence of oxygen, UV light and microorganisms

E3S Web of Conferences ◽

10.1051/e3sconf/20199801002 ◽

2019 ◽

Vol 98 ◽

pp. 01002

Author(s):

Marie-Paule Bassez

Keyword(s):

Ferric Iron ◽

Subcritical Water ◽

Uv Light ◽

Early Earth ◽

Upper Crust ◽

Rock Interaction ◽

The Earth ◽

Acidic Conditions ◽

Ferric Oxides ◽

Water Rock Interaction

The formation of ferric minerals on the anoxic early Earth is usually explained with the action of microorganisms or UV light in acidic conditions. Results show that amorphous and crystalline ferric oxides and silicates can form in the absence of oxygen, microorganisms and UV light, when rocks, located in the upper crust of the Earth until ca 1 km depth, contain ferrous silicates which interact with water called high subcritical, at 300-350 °C and 10-25 MPa. This conclusion is established following the analyses of Eh-pH diagrams for the Fe-H2O system and solubility diagrams for quartz and amorphous silica. It is shown that water below the critical point and not above can lead to the formation of ferric iron in geological terrains on Earth and extraterrestrial objects where anoxic alkaline high subcritical water reacts with rocks containing ferrous silicates.

Download Full-text

About this title - Archean Granitoids of India: Windows into Early Earth Tectonics

Geological Society London Special Publications ◽

10.1144/sp489 ◽

2020 ◽

Vol 489 (1) ◽

pp. NP-NP

Author(s):

S. Dey ◽

J.-F. Moyen

Keyword(s):

Tectonic Setting ◽

Temporal Distribution ◽

Early Earth ◽

Crustal Evolution ◽

Reference Information ◽

Geodynamic Processes ◽

Emplacement Mechanism ◽

Available Information ◽

Metal Delivery ◽

Granite Petrology

Granitoids form the bulk of the Archean continental crust and preserve key information on early Earth evolution. India hosts five main Archean cratonic blocks (Aravalli, Bundelkhand, Singhbhum, Bastar and Dharwar). This book summarizes the available information on Archean granitoids of Indian cratons. The chapters cover a broad spectrum of themes related to granitoid typology, emplacement mechanism, petrogenesis, phase-equilibria modelling, temporal distribution, tectonic setting, and their roles in fluid evolution, metal delivery and mineralizations. The book presents a broader picture incorporating regional- to cratons-scale comparisons, implications for Archean geodynamic processes, and temporal changes thereof. This synthesis work, integrating modern concepts on granite petrology and crustal evolution, offers an irreplaceable body of reference information for any geologist interested in Archean Indian granitoids.

Download Full-text

Low-temperature fluid–rock interaction—an isotopic and mineralogical perspective of upper crustal evolution, eastern flank of the Juan de Fuca Ridge (JdFR), ODP Leg 168

Chemical Geology ◽

10.1016/s0009-2541(98)00138-7 ◽

1999 ◽

Vol 155 (1-2) ◽

pp. 3-28 ◽

Cited By ~ 27

Author(s):

A.G. Hunter ◽

P.D. Kempton ◽

P. Greenwood

Keyword(s):

Low Temperature ◽

Juan De Fuca Ridge ◽

Crustal Evolution ◽

Rock Interaction ◽

Fuca Ridge ◽

Eastern Flank ◽

Juan De Fuca

Download Full-text

Cometary impacts into ocean: Thermodynamical equilibrium calculations of high-temperature O2 generation on the early Earth

Journal of the Serbian Chemical Society ◽

10.2298/jsc0205353p ◽

2002 ◽

Vol 67 (5) ◽

pp. 353-365 ◽

Cited By ~ 2

Author(s):

Pavle Premovic ◽

Katja Panov

Keyword(s):

High Temperature ◽

Earth Science ◽

Theoretical Models ◽

Life Forms ◽

Early Earth ◽

Present Level ◽

Thermodynamical Equilibrium ◽

The Earth ◽

Primitive Atmosphere ◽

Equilibrium Calculations

The early Earth?s atmosphere apparently differed from the present atmosphere mainly in its lack of free O2, and this absence is believed to have been indispensable for the origin of early anaerobic life forms. One of the central problems in Earth science is to explain the apparent transition from the primitive atmosphere (free of O2) to the present atmosphere which contains 21% of the gas. Theoretical models suggest that the initial form of O2 in the Earth?s atmosphere may have been H2O, which was converted into atmospheric O2 mainly through photosynthesis. We have investigated an alternative (abiotic) method for the conversion of H2O to O2: a high-temperature shock generated during a cometary impact into an ocean (or on land). The calculations presented here show that 1% of the present level of O2 could have resulted from an icy 1.3x1016 kg comet entering the early (pre-oxygenic) Earth with a velocity of between about 11 and 30 km s-1.

Download Full-text