The oldest rocks on Earth: Time constraints and geological controversies
Ages in the range 3.6-4.0 Ga (billion years) have been reported for the oldest, continental, granitoid orthogneisses, whose magmatic precursors were probably formed by partial melting or differentiation from a mafic, mantle-derived source. The geological interpretation of some of the oldest ages in...
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ftunivqespace:oai:espace.library.uq.edu.au:UQ:1112271 2023-05-15T16:30:11+02:00 The oldest rocks on Earth: Time constraints and geological controversies Kamber, B. S. Moorbath, S. Whitehouse, M. J. 2001-12-17 https://espace.library.uq.edu.au/view/UQ:1112271 eng eng doi:10.1144/GSL.SP.2001.190.01.13 issn:0305-8719 1907 Geology 2212 Ocean Engineering 2312 Water Science and Technology Journal Article 2001 ftunivqespace https://doi.org/10.1144/GSL.SP.2001.190.01.13 2020-08-06T08:56:58Z Ages in the range 3.6-4.0 Ga (billion years) have been reported for the oldest, continental, granitoid orthogneisses, whose magmatic precursors were probably formed by partial melting or differentiation from a mafic, mantle-derived source. The geological interpretation of some of the oldest ages in this range is still strongly disputed. The oldest known supracrustal (i.e. volcanic and sedimentary) rocks, with an age of 3.7-3.8 Ga, occur in West Greenland. They were deposited in water, and several of the sediments contain C-depleted graphite microparticles, which have been claimed to be biogenic. Ancient sediments (c. 3 Ga) in western Australia contain much older detrital zircons with dates ranging up to 4.4 Ga. The nature and origin of their source is highly debatable. Some ancient (magmatic) orthogneisses (c. 3.65-3.75 Ga) contain inherited zircons with dates up to c. 4.0 Ga. To clarify whether zircons in orthogneisses are inherited from an older source region or cogenetic with their host rock, it is desirable to combine imaging studies and U-Pb dating of single zircon grains with indepedent dating of the host rock by other methods, including Sm-Nd, Lu-Hf and Pb/Pb. Initial Nd, Hf and Pb isotopic ratios of ancient orthogneisses are essential parameters for investigating the degree of heterogeneity of early Archaean mantle. The simplest interpretation of existing isotopic data is for a slightly depleted, close-to-chondritic, essentially homogeneous early Archaean mantle; this does not favour the existence of a sizeable, permanent continental crust in the early Archaean. By anlogy with the moon, massive bolide impacts probably terminated on Earth by c. 3.8-3.9 Ga, although no evidence for them has yet been found. By c. 3.65 Ga production of continental crust was well underway, and global tectonic and petrogenetic regimes increasingly resembled those of later epochs. Article in Journal/Newspaper Greenland The University of Queensland: UQ eSpace Greenland Geological Society, London, Special Publications 190 1 177 203 |
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Open Polar |
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The University of Queensland: UQ eSpace |
op_collection_id |
ftunivqespace |
language |
English |
topic |
1907 Geology 2212 Ocean Engineering 2312 Water Science and Technology |
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1907 Geology 2212 Ocean Engineering 2312 Water Science and Technology Kamber, B. S. Moorbath, S. Whitehouse, M. J. The oldest rocks on Earth: Time constraints and geological controversies |
topic_facet |
1907 Geology 2212 Ocean Engineering 2312 Water Science and Technology |
description |
Ages in the range 3.6-4.0 Ga (billion years) have been reported for the oldest, continental, granitoid orthogneisses, whose magmatic precursors were probably formed by partial melting or differentiation from a mafic, mantle-derived source. The geological interpretation of some of the oldest ages in this range is still strongly disputed. The oldest known supracrustal (i.e. volcanic and sedimentary) rocks, with an age of 3.7-3.8 Ga, occur in West Greenland. They were deposited in water, and several of the sediments contain C-depleted graphite microparticles, which have been claimed to be biogenic. Ancient sediments (c. 3 Ga) in western Australia contain much older detrital zircons with dates ranging up to 4.4 Ga. The nature and origin of their source is highly debatable. Some ancient (magmatic) orthogneisses (c. 3.65-3.75 Ga) contain inherited zircons with dates up to c. 4.0 Ga. To clarify whether zircons in orthogneisses are inherited from an older source region or cogenetic with their host rock, it is desirable to combine imaging studies and U-Pb dating of single zircon grains with indepedent dating of the host rock by other methods, including Sm-Nd, Lu-Hf and Pb/Pb. Initial Nd, Hf and Pb isotopic ratios of ancient orthogneisses are essential parameters for investigating the degree of heterogeneity of early Archaean mantle. The simplest interpretation of existing isotopic data is for a slightly depleted, close-to-chondritic, essentially homogeneous early Archaean mantle; this does not favour the existence of a sizeable, permanent continental crust in the early Archaean. By anlogy with the moon, massive bolide impacts probably terminated on Earth by c. 3.8-3.9 Ga, although no evidence for them has yet been found. By c. 3.65 Ga production of continental crust was well underway, and global tectonic and petrogenetic regimes increasingly resembled those of later epochs. |
format |
Article in Journal/Newspaper |
author |
Kamber, B. S. Moorbath, S. Whitehouse, M. J. |
author_facet |
Kamber, B. S. Moorbath, S. Whitehouse, M. J. |
author_sort |
Kamber, B. S. |
title |
The oldest rocks on Earth: Time constraints and geological controversies |
title_short |
The oldest rocks on Earth: Time constraints and geological controversies |
title_full |
The oldest rocks on Earth: Time constraints and geological controversies |
title_fullStr |
The oldest rocks on Earth: Time constraints and geological controversies |
title_full_unstemmed |
The oldest rocks on Earth: Time constraints and geological controversies |
title_sort |
oldest rocks on earth: time constraints and geological controversies |
publishDate |
2001 |
url |
https://espace.library.uq.edu.au/view/UQ:1112271 |
geographic |
Greenland |
geographic_facet |
Greenland |
genre |
Greenland |
genre_facet |
Greenland |
op_relation |
doi:10.1144/GSL.SP.2001.190.01.13 issn:0305-8719 |
op_doi |
https://doi.org/10.1144/GSL.SP.2001.190.01.13 |
container_title |
Geological Society, London, Special Publications |
container_volume |
190 |
container_issue |
1 |
container_start_page |
177 |
op_container_end_page |
203 |
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1766019896068538368 |