A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence
<p>Numerous studies have revealed genetic similarities between Tethyan ophiolites and oceanic “proto-arc” sequences formed above nascent subduction zones. The Semail ophiolite (Oman–U.A.E.) in particular can be viewed as an analogue for this proto-arc crust. Though proto-arc magmatism and the...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2019-07-01
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| Series: | Solid Earth |
| Online Access: | https://www.solid-earth.net/10/1181/2019/se-10-1181-2019.pdf |
| _version_ | 1818966581348139008 |
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| author | T. M. Belgrano L. W. Diamond Y. Vogt A. R. Biedermann A. R. Biedermann S. A. Gilgen K. Al-Tobi |
| author_facet | T. M. Belgrano L. W. Diamond Y. Vogt A. R. Biedermann A. R. Biedermann S. A. Gilgen K. Al-Tobi |
| author_sort | T. M. Belgrano |
| collection | DOAJ |
| description | <p>Numerous studies have revealed genetic similarities between Tethyan
ophiolites and oceanic “proto-arc” sequences formed above nascent subduction
zones. The Semail ophiolite (Oman–U.A.E.) in particular can be viewed as an
analogue for this proto-arc crust. Though proto-arc magmatism and the
mechanisms of subduction initiation are of great interest, insight is
difficult to gain from drilling and limited surface outcrops in marine
settings. In contrast, the 3–5 km thick upper-crustal succession of the
Semail ophiolite, which is exposed in an oblique cross section, presents an
opportunity to assess the architecture and volumes of different volcanic
rocks that form during the proto-arc stage. To determine the distribution of
the volcanic rocks and to aid exploration for the volcanogenic massive
sulfide (VMS) deposits that they host, we have remapped the volcanic units
of the Semail ophiolite by integrating new field observations, geochemical
analyses, and geophysical interpretations with pre-existing geological maps.
By linking the major-element compositions of the volcanic units to rock
magnetic properties, we were able to use aeromagnetic data to infer the
extension of each outcropping unit below sedimentary cover, resulting in
a new map showing 2100 km<span class="inline-formula"><sup>2</sup></span> of upper-crustal bedrock.</p>
<p>Whereas earlier maps distinguished two main volcanostratigraphic units, we
have distinguished four, recording the progression from early spreading-axis
basalts (Geotimes), through axial to off-axial depleted basalts (Lasail), to
post-axial tholeiites (Tholeiitic Alley), and finally boninites (Boninitic
Alley). Geotimes (“Phase 1”) axial dykes and lavas make up <span class="inline-formula">∼55</span> vol % of the Semail upper crust, whereas post-axial (“Phase 2”) lavas
constitute the remaining <span class="inline-formula">∼45</span> vol % and ubiquitously cover
the underlying axial crust. Highly depleted boninitic members of the Lasail
unit locally occur within and directly atop the axial sequence, marking an
earlier onset of boninitic magmatism than previously known for the
ophiolite. The vast majority of the Semail boninites, however, belong to the
Boninitic Alley unit and occur as discontinuous accumulations up to 2 km
thick at the top of the ophiolite sequence and constitute <span class="inline-formula">∼15</span> vol % of the upper crust. The new map provides a basis for targeted
exploration of the gold-bearing VMS deposits hosted by these boninites. The
thickest boninite accumulations occur in the Fizh block, where magma ascent
occurred along crustal-scale faults that are connected to shear zones in the
underlying mantle rocks, which in turn are associated with economic
chromitite deposits. Locating major boninite feeder zones may thus be an
indirect means to explore for chromitites in the underlying mantle.</p> |
| first_indexed | 2024-12-20T13:35:11Z |
| format | Article |
| id | doaj.art-6d57128c12d248c59290efeb8c00c759 |
| institution | Directory Open Access Journal |
| issn | 1869-9510 1869-9529 |
| language | English |
| last_indexed | 2024-12-20T13:35:11Z |
| publishDate | 2019-07-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Solid Earth |
| spelling | doaj.art-6d57128c12d248c59290efeb8c00c7592022-12-21T19:38:59ZengCopernicus PublicationsSolid Earth1869-95101869-95292019-07-01101181121710.5194/se-10-1181-2019A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequenceT. M. Belgrano0L. W. Diamond1Y. Vogt2A. R. Biedermann3A. R. Biedermann4S. A. Gilgen5K. Al-Tobi6Institute of Geological Sciences, University of Bern, Baltzerstrasse 3, 3012 Bern, SwitzerlandInstitute of Geological Sciences, University of Bern, Baltzerstrasse 3, 3012 Bern, SwitzerlandInstitute of Geological Sciences, University of Bern, Baltzerstrasse 3, 3012 Bern, SwitzerlandInstitute of Geological Sciences, University of Bern, Baltzerstrasse 3, 3012 Bern, SwitzerlandInstitute for Rock Magnetism, University of Minnesota, 100 Union St SE, 55455 Minneapolis, USAInstitute of Geological Sciences, University of Bern, Baltzerstrasse 3, 3012 Bern, SwitzerlandNational Earth Secrets Co., P.O. Box 1242, PC 130 Athaibah, Muscat, Sultanate of Oman<p>Numerous studies have revealed genetic similarities between Tethyan ophiolites and oceanic “proto-arc” sequences formed above nascent subduction zones. The Semail ophiolite (Oman–U.A.E.) in particular can be viewed as an analogue for this proto-arc crust. Though proto-arc magmatism and the mechanisms of subduction initiation are of great interest, insight is difficult to gain from drilling and limited surface outcrops in marine settings. In contrast, the 3–5 km thick upper-crustal succession of the Semail ophiolite, which is exposed in an oblique cross section, presents an opportunity to assess the architecture and volumes of different volcanic rocks that form during the proto-arc stage. To determine the distribution of the volcanic rocks and to aid exploration for the volcanogenic massive sulfide (VMS) deposits that they host, we have remapped the volcanic units of the Semail ophiolite by integrating new field observations, geochemical analyses, and geophysical interpretations with pre-existing geological maps. By linking the major-element compositions of the volcanic units to rock magnetic properties, we were able to use aeromagnetic data to infer the extension of each outcropping unit below sedimentary cover, resulting in a new map showing 2100 km<span class="inline-formula"><sup>2</sup></span> of upper-crustal bedrock.</p> <p>Whereas earlier maps distinguished two main volcanostratigraphic units, we have distinguished four, recording the progression from early spreading-axis basalts (Geotimes), through axial to off-axial depleted basalts (Lasail), to post-axial tholeiites (Tholeiitic Alley), and finally boninites (Boninitic Alley). Geotimes (“Phase 1”) axial dykes and lavas make up <span class="inline-formula">∼55</span> vol % of the Semail upper crust, whereas post-axial (“Phase 2”) lavas constitute the remaining <span class="inline-formula">∼45</span> vol % and ubiquitously cover the underlying axial crust. Highly depleted boninitic members of the Lasail unit locally occur within and directly atop the axial sequence, marking an earlier onset of boninitic magmatism than previously known for the ophiolite. The vast majority of the Semail boninites, however, belong to the Boninitic Alley unit and occur as discontinuous accumulations up to 2 km thick at the top of the ophiolite sequence and constitute <span class="inline-formula">∼15</span> vol % of the upper crust. The new map provides a basis for targeted exploration of the gold-bearing VMS deposits hosted by these boninites. The thickest boninite accumulations occur in the Fizh block, where magma ascent occurred along crustal-scale faults that are connected to shear zones in the underlying mantle rocks, which in turn are associated with economic chromitite deposits. Locating major boninite feeder zones may thus be an indirect means to explore for chromitites in the underlying mantle.</p>https://www.solid-earth.net/10/1181/2019/se-10-1181-2019.pdf |
| spellingShingle | T. M. Belgrano L. W. Diamond Y. Vogt A. R. Biedermann A. R. Biedermann S. A. Gilgen K. Al-Tobi A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence Solid Earth |
| title | A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence |
| title_full | A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence |
| title_fullStr | A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence |
| title_full_unstemmed | A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence |
| title_short | A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence |
| title_sort | revised map of volcanic units in the oman ophiolite insights into the architecture of an oceanic proto arc volcanic sequence |
| url | https://www.solid-earth.net/10/1181/2019/se-10-1181-2019.pdf |
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