The origin of spheroidal patterns of weathering in the Pados-Tundra mafic-ultramafic complex, Kola Peninsula, Russia
We document a new and unusual occurrence of patterns of protruding spheroidal weathering developed in a dunitic rock of the Pados-Tundra mafic-ultramafic complex of Early Proterozoic age, Kola Peninsula, Russia. It provides an example similar to that reported recently from a mineralized harzburgite...
Published in: | Bulletin of the Geological Society of Finland |
---|---|
Main Authors: | , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
Geological Society of Finland
2016
|
Subjects: | |
Online Access: | https://doi.org/10.17741/bgsf/88.2.004 https://doaj.org/article/216a1d3fb73a40f98abb74649aa3b387 |
id |
ftdoajarticles:oai:doaj.org/article:216a1d3fb73a40f98abb74649aa3b387 |
---|---|
record_format |
openpolar |
spelling |
ftdoajarticles:oai:doaj.org/article:216a1d3fb73a40f98abb74649aa3b387 2023-05-15T16:13:09+02:00 The origin of spheroidal patterns of weathering in the Pados-Tundra mafic-ultramafic complex, Kola Peninsula, Russia A.Y. Barkov A.A. Nikiforov T.A.A. Halkoaho J.P. Konnunaho 2016-12-01T00:00:00Z https://doi.org/10.17741/bgsf/88.2.004 https://doaj.org/article/216a1d3fb73a40f98abb74649aa3b387 EN eng Geological Society of Finland http://www.geologinenseura.fi/bulletin/Volume88/Bulletin_vol88_2_2016_Barkov.pdf https://doaj.org/toc/0367-5211 https://doaj.org/toc/1799-4632 doi:10.17741/bgsf/88.2.004 0367-5211 1799-4632 https://doaj.org/article/216a1d3fb73a40f98abb74649aa3b387 Bulletin of the Geological Society of Finland, Vol 88, Iss 2, Pp 105-113 (2016) spheroidal weathering chemical weathering mafic-ultramafic rocks Pados-Tundra complex Kola Peninsula Fennoscandian Shield Russia Geology QE1-996.5 article 2016 ftdoajarticles https://doi.org/10.17741/bgsf/88.2.004 2022-12-31T02:31:19Z We document a new and unusual occurrence of patterns of protruding spheroidal weathering developed in a dunitic rock of the Pados-Tundra mafic-ultramafic complex of Early Proterozoic age, Kola Peninsula, Russia. It provides an example similar to that reported recently from a mineralized harzburgite in the Monchepluton layered complex in the same region. These patterns are genetically different from common results of “normal spheroidal weathering” sensu stricto. The spheroidally weathered dunite at Pados-Tundra consists of a high-Fo olivine, Ol (Fo 87. 5), which is, in fact, not altered. Accessory grains of aluminous chromite are present. Relief spheroids (1.5 to 4 cm in diameter; up to ~5 vol. %) are distributed sparsely and heterogeneously. They are hosted by the olivine matrix and composed of talc, Tlc, and tremolite, Tr, (Mg# = 95-96) formed presumably at the expense of orthopyroxene, Opx, (i.e., pre-existing oikocrysts) during a deuteric (autometasomatic) alteration. In contrast, oikocrystic Opx (En 86.0) is quite fresh in related spheroids at Monchepluton, in which only minor deuteric alteration (Tlc + Tr) are observed. We infer that (1) the ball-shaped morphology of the weathered surface is a reflection of the presence of oikocrysts of Opx, which crystallized after Ol at the magmatic stage; they were entirely replaced by the deuterically induced Tlc + Tr at Pados-Tundra. (2) Differential rates of weathering are implied for rock-forming minerals in these ultramafic rocks, with a higher resistance of Opx vs. Fo-rich Ol, and Tlc + Tr vs. Fo-rich Ol. (3) The ball-like shape of the large spheroids, produced by magmatic processes, may likely represent an additional factor of their higher stability to weathering in the superficial environment. Similar patterns can be expected in other mafic-ultramafic complexes, especially in layered intrusions. Article in Journal/Newspaper Fennoscandian kola peninsula Tundra Directory of Open Access Journals: DOAJ Articles Kola Peninsula Pados ENVELOPE(29.800,29.800,68.101,68.101) Bulletin of the Geological Society of Finland 88 2 105 113 |
institution |
Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
spheroidal weathering chemical weathering mafic-ultramafic rocks Pados-Tundra complex Kola Peninsula Fennoscandian Shield Russia Geology QE1-996.5 |
spellingShingle |
spheroidal weathering chemical weathering mafic-ultramafic rocks Pados-Tundra complex Kola Peninsula Fennoscandian Shield Russia Geology QE1-996.5 A.Y. Barkov A.A. Nikiforov T.A.A. Halkoaho J.P. Konnunaho The origin of spheroidal patterns of weathering in the Pados-Tundra mafic-ultramafic complex, Kola Peninsula, Russia |
topic_facet |
spheroidal weathering chemical weathering mafic-ultramafic rocks Pados-Tundra complex Kola Peninsula Fennoscandian Shield Russia Geology QE1-996.5 |
description |
We document a new and unusual occurrence of patterns of protruding spheroidal weathering developed in a dunitic rock of the Pados-Tundra mafic-ultramafic complex of Early Proterozoic age, Kola Peninsula, Russia. It provides an example similar to that reported recently from a mineralized harzburgite in the Monchepluton layered complex in the same region. These patterns are genetically different from common results of “normal spheroidal weathering” sensu stricto. The spheroidally weathered dunite at Pados-Tundra consists of a high-Fo olivine, Ol (Fo 87. 5), which is, in fact, not altered. Accessory grains of aluminous chromite are present. Relief spheroids (1.5 to 4 cm in diameter; up to ~5 vol. %) are distributed sparsely and heterogeneously. They are hosted by the olivine matrix and composed of talc, Tlc, and tremolite, Tr, (Mg# = 95-96) formed presumably at the expense of orthopyroxene, Opx, (i.e., pre-existing oikocrysts) during a deuteric (autometasomatic) alteration. In contrast, oikocrystic Opx (En 86.0) is quite fresh in related spheroids at Monchepluton, in which only minor deuteric alteration (Tlc + Tr) are observed. We infer that (1) the ball-shaped morphology of the weathered surface is a reflection of the presence of oikocrysts of Opx, which crystallized after Ol at the magmatic stage; they were entirely replaced by the deuterically induced Tlc + Tr at Pados-Tundra. (2) Differential rates of weathering are implied for rock-forming minerals in these ultramafic rocks, with a higher resistance of Opx vs. Fo-rich Ol, and Tlc + Tr vs. Fo-rich Ol. (3) The ball-like shape of the large spheroids, produced by magmatic processes, may likely represent an additional factor of their higher stability to weathering in the superficial environment. Similar patterns can be expected in other mafic-ultramafic complexes, especially in layered intrusions. |
format |
Article in Journal/Newspaper |
author |
A.Y. Barkov A.A. Nikiforov T.A.A. Halkoaho J.P. Konnunaho |
author_facet |
A.Y. Barkov A.A. Nikiforov T.A.A. Halkoaho J.P. Konnunaho |
author_sort |
A.Y. Barkov |
title |
The origin of spheroidal patterns of weathering in the Pados-Tundra mafic-ultramafic complex, Kola Peninsula, Russia |
title_short |
The origin of spheroidal patterns of weathering in the Pados-Tundra mafic-ultramafic complex, Kola Peninsula, Russia |
title_full |
The origin of spheroidal patterns of weathering in the Pados-Tundra mafic-ultramafic complex, Kola Peninsula, Russia |
title_fullStr |
The origin of spheroidal patterns of weathering in the Pados-Tundra mafic-ultramafic complex, Kola Peninsula, Russia |
title_full_unstemmed |
The origin of spheroidal patterns of weathering in the Pados-Tundra mafic-ultramafic complex, Kola Peninsula, Russia |
title_sort |
origin of spheroidal patterns of weathering in the pados-tundra mafic-ultramafic complex, kola peninsula, russia |
publisher |
Geological Society of Finland |
publishDate |
2016 |
url |
https://doi.org/10.17741/bgsf/88.2.004 https://doaj.org/article/216a1d3fb73a40f98abb74649aa3b387 |
long_lat |
ENVELOPE(29.800,29.800,68.101,68.101) |
geographic |
Kola Peninsula Pados |
geographic_facet |
Kola Peninsula Pados |
genre |
Fennoscandian kola peninsula Tundra |
genre_facet |
Fennoscandian kola peninsula Tundra |
op_source |
Bulletin of the Geological Society of Finland, Vol 88, Iss 2, Pp 105-113 (2016) |
op_relation |
http://www.geologinenseura.fi/bulletin/Volume88/Bulletin_vol88_2_2016_Barkov.pdf https://doaj.org/toc/0367-5211 https://doaj.org/toc/1799-4632 doi:10.17741/bgsf/88.2.004 0367-5211 1799-4632 https://doaj.org/article/216a1d3fb73a40f98abb74649aa3b387 |
op_doi |
https://doi.org/10.17741/bgsf/88.2.004 |
container_title |
Bulletin of the Geological Society of Finland |
container_volume |
88 |
container_issue |
2 |
container_start_page |
105 |
op_container_end_page |
113 |
_version_ |
1765998752064077824 |