Post-collisional ultrapotassic volcanic rocks and ultramafic xenoliths in the Eslamieh Peninsula, NW Iran: petrological and geochemical constraints on mantle source and metasomatism
The Eslamieh Peninsula in NW Iran exposes Miocene potassic to ultrapotassic volcanic rocks that are often associated with a variety of ultramafic xenoliths. Based on geochemical features, the rocks investigated in this study can be subdivided into two main groups: 1) MgO-rich (8.0–13.9 wt%) basic (S...
| Main Authors: | , , , , , |
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| Format: | Journal article |
| Language: | English |
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Elsevier
2023
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| _version_ | 1811141265468686336 |
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| author | Sepidbar, F Homam, SM Shu, Q Palin, RM Besharati, P Lustrino, M |
| author_facet | Sepidbar, F Homam, SM Shu, Q Palin, RM Besharati, P Lustrino, M |
| author_sort | Sepidbar, F |
| collection | OXFORD |
| description | The Eslamieh Peninsula in NW Iran exposes Miocene potassic to ultrapotassic volcanic rocks that are often associated with a variety of ultramafic xenoliths. Based on geochemical features, the rocks investigated in this study can be subdivided into two main groups: 1) MgO-rich (8.0–13.9 wt%) basic (SiO2 = 46.1–50.9 wt%) rocks, which comprise mafic lamprophyres and pyroxenite xenoliths, and 2) MgO-poor (1.5–6.4 wt%) basic to intermediate (SiO2 = 48.2–61.2 wt%) rocks, mainly consisting of trachytes, felsic lamprophyres, and analcime-bearing tephriphonolites and phonotephrites. Rocks in both groups have variable but generally low Ni (10–115 ppm; mostly <60 ppm) and Cr (6–628 ppm; mostly <200 ppm), and display enrichment in LREE over HREE (e.g., La/Yb = 17–55), with a large overlap between the MgO-rich and MgO-poor types. These features are coupled with enriched LILE/HFSE ratios (e.g., Ba/Nb mostly 16–116), negative Nb-Ta-Ti anomalies and positive Pb peaks in primitive mantle-normalised diagrams (e.g., Nb/Nb* mostly <0.7). Both high-and poor-MgO samples have strongly radiogenic (87Sr/86Sr)i ratios (0.7078–0.7086), (143Nd/144Nd)i below the Chondritic Uniform Reservoir (CHUR) = 0.51235–0.51244, and ɛHfi ranging from −3.1 to −11.1‰, suggesting involvement of a lower continental crust component in their genesis. The major oxide and trace element contents the high-MgO and high-CaO rocks indicate derivation from a subcontinental lithospheric mantle source, variably metasomatised by fluids and melts released by a subducted slab in a mantle wedge. Primitive melts evolved via mafic mineral fractionation and possible assimilation of lower crust, generating the SiO2 higher and CaO-MgO-poorer group. We suggest that small degree partial melting of the enriched mantle sources could have been triggered by Neo-Tethys slab roll-back during the Arabian-Iranian collision. |
| first_indexed | 2024-09-25T04:35:08Z |
| format | Journal article |
| id | oxford-uuid:7a860138-ffab-4e11-9435-cc24a57b1935 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-09-25T04:35:08Z |
| publishDate | 2023 |
| publisher | Elsevier |
| record_format | dspace |
| spelling | oxford-uuid:7a860138-ffab-4e11-9435-cc24a57b19352024-09-16T11:26:31ZPost-collisional ultrapotassic volcanic rocks and ultramafic xenoliths in the Eslamieh Peninsula, NW Iran: petrological and geochemical constraints on mantle source and metasomatismJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:7a860138-ffab-4e11-9435-cc24a57b1935EnglishSymplectic ElementsElsevier2023Sepidbar, FHomam, SMShu, QPalin, RMBesharati, PLustrino, MThe Eslamieh Peninsula in NW Iran exposes Miocene potassic to ultrapotassic volcanic rocks that are often associated with a variety of ultramafic xenoliths. Based on geochemical features, the rocks investigated in this study can be subdivided into two main groups: 1) MgO-rich (8.0–13.9 wt%) basic (SiO2 = 46.1–50.9 wt%) rocks, which comprise mafic lamprophyres and pyroxenite xenoliths, and 2) MgO-poor (1.5–6.4 wt%) basic to intermediate (SiO2 = 48.2–61.2 wt%) rocks, mainly consisting of trachytes, felsic lamprophyres, and analcime-bearing tephriphonolites and phonotephrites. Rocks in both groups have variable but generally low Ni (10–115 ppm; mostly <60 ppm) and Cr (6–628 ppm; mostly <200 ppm), and display enrichment in LREE over HREE (e.g., La/Yb = 17–55), with a large overlap between the MgO-rich and MgO-poor types. These features are coupled with enriched LILE/HFSE ratios (e.g., Ba/Nb mostly 16–116), negative Nb-Ta-Ti anomalies and positive Pb peaks in primitive mantle-normalised diagrams (e.g., Nb/Nb* mostly <0.7). Both high-and poor-MgO samples have strongly radiogenic (87Sr/86Sr)i ratios (0.7078–0.7086), (143Nd/144Nd)i below the Chondritic Uniform Reservoir (CHUR) = 0.51235–0.51244, and ɛHfi ranging from −3.1 to −11.1‰, suggesting involvement of a lower continental crust component in their genesis. The major oxide and trace element contents the high-MgO and high-CaO rocks indicate derivation from a subcontinental lithospheric mantle source, variably metasomatised by fluids and melts released by a subducted slab in a mantle wedge. Primitive melts evolved via mafic mineral fractionation and possible assimilation of lower crust, generating the SiO2 higher and CaO-MgO-poorer group. We suggest that small degree partial melting of the enriched mantle sources could have been triggered by Neo-Tethys slab roll-back during the Arabian-Iranian collision. |
| spellingShingle | Sepidbar, F Homam, SM Shu, Q Palin, RM Besharati, P Lustrino, M Post-collisional ultrapotassic volcanic rocks and ultramafic xenoliths in the Eslamieh Peninsula, NW Iran: petrological and geochemical constraints on mantle source and metasomatism |
| title | Post-collisional ultrapotassic volcanic rocks and ultramafic xenoliths in the Eslamieh Peninsula, NW Iran: petrological and geochemical constraints on mantle source and metasomatism |
| title_full | Post-collisional ultrapotassic volcanic rocks and ultramafic xenoliths in the Eslamieh Peninsula, NW Iran: petrological and geochemical constraints on mantle source and metasomatism |
| title_fullStr | Post-collisional ultrapotassic volcanic rocks and ultramafic xenoliths in the Eslamieh Peninsula, NW Iran: petrological and geochemical constraints on mantle source and metasomatism |
| title_full_unstemmed | Post-collisional ultrapotassic volcanic rocks and ultramafic xenoliths in the Eslamieh Peninsula, NW Iran: petrological and geochemical constraints on mantle source and metasomatism |
| title_short | Post-collisional ultrapotassic volcanic rocks and ultramafic xenoliths in the Eslamieh Peninsula, NW Iran: petrological and geochemical constraints on mantle source and metasomatism |
| title_sort | post collisional ultrapotassic volcanic rocks and ultramafic xenoliths in the eslamieh peninsula nw iran petrological and geochemical constraints on mantle source and metasomatism |
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