U-Pb geochronology and geochemistry of the Dashibao Basalts in the Songpan-Ganzi Terrane, SW China, with implications for the age of Emeishan volcanism
Permian marine basalts (the Dashibao Formation) in the Songpan-Ganzi Terrane to the west of the Yangtze Block, SW China, yield a SHRIMP zircon U-Pb weighted mean age of 263 ± 2 Ma. The Dashibao basalts are characterized by high TiO2 contents (1.73-4.65 wt. %) and Ti/Y ratios with a mean of 577, and...
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| Format: | Journal Article |
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American Journal of Science
2010
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| Online Access: | http://hdl.handle.net/20.500.11937/12486 |
| _version_ | 1848748089664339968 |
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| author | Zi, Jianwei Fan, W. Wang, Y. Cawood, P. Peng, T. Sun, L. Xu, Z. |
| author_facet | Zi, Jianwei Fan, W. Wang, Y. Cawood, P. Peng, T. Sun, L. Xu, Z. |
| author_sort | Zi, Jianwei |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | Permian marine basalts (the Dashibao Formation) in the Songpan-Ganzi Terrane to the west of the Yangtze Block, SW China, yield a SHRIMP zircon U-Pb weighted mean age of 263 ± 2 Ma. The Dashibao basalts are characterized by high TiO2 contents (1.73-4.65 wt. %) and Ti/Y ratios with a mean of 577, and OIB-like rare earth element (REE) and incompatible element patterns. Geochemical variation within the basalt succession allows division into two groups; Group 1 with an alkaline composition is distinguished by higher TiO2 and P2O5 contents, along with higher Ti/Y and Sm/Yb ratios than the underlying Group 2 that consists predominantly of tholeiitic lavas. Both groups possess weakly to moderately positive eNd(t) values (0.82 to 5.28), but the Group 2 tholeiitic basalts show relatively depleted signatures (most eNd(t) >2.5) when compared to their Group 1 counterparts (eNd(t) <2.5). REE modeling is consistent with variable degrees of melting of primitive mantle within the garnet stability field, and reveals that the Group 1 alkaline basalts could have been generated by lower degrees of melting (5-11%) than the Group 2 tholeiites (up to 19%). The initial Nd isotope discrepancy is interpreted in terms of depleted asthenospheric involvement in the early stage Group 2 tholeiitic magma. Combined geochronology, petrography and geochemistry for the Dashibao Formation confirms that it was temporally and genetically associated with the Emeishan basalts, and is therefore an integral part of the Emeishan large igneous province. The new zircon U-Pb dating supports the view that the Emeishan volcanism could be a boundary event occurring at or around the Middle-Late Permian (the Guadalupian-Lopingian) transition, and thereby confirms the validity of a causal connection with the end-Guadalupian mass extinction. |
| first_indexed | 2025-11-14T06:59:30Z |
| format | Journal Article |
| id | curtin-20.500.11937-12486 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T06:59:30Z |
| publishDate | 2010 |
| publisher | American Journal of Science |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-124862017-02-28T01:33:48Z U-Pb geochronology and geochemistry of the Dashibao Basalts in the Songpan-Ganzi Terrane, SW China, with implications for the age of Emeishan volcanism Zi, Jianwei Fan, W. Wang, Y. Cawood, P. Peng, T. Sun, L. Xu, Z. Permian marine basalts (the Dashibao Formation) in the Songpan-Ganzi Terrane to the west of the Yangtze Block, SW China, yield a SHRIMP zircon U-Pb weighted mean age of 263 ± 2 Ma. The Dashibao basalts are characterized by high TiO2 contents (1.73-4.65 wt. %) and Ti/Y ratios with a mean of 577, and OIB-like rare earth element (REE) and incompatible element patterns. Geochemical variation within the basalt succession allows division into two groups; Group 1 with an alkaline composition is distinguished by higher TiO2 and P2O5 contents, along with higher Ti/Y and Sm/Yb ratios than the underlying Group 2 that consists predominantly of tholeiitic lavas. Both groups possess weakly to moderately positive eNd(t) values (0.82 to 5.28), but the Group 2 tholeiitic basalts show relatively depleted signatures (most eNd(t) >2.5) when compared to their Group 1 counterparts (eNd(t) <2.5). REE modeling is consistent with variable degrees of melting of primitive mantle within the garnet stability field, and reveals that the Group 1 alkaline basalts could have been generated by lower degrees of melting (5-11%) than the Group 2 tholeiites (up to 19%). The initial Nd isotope discrepancy is interpreted in terms of depleted asthenospheric involvement in the early stage Group 2 tholeiitic magma. Combined geochronology, petrography and geochemistry for the Dashibao Formation confirms that it was temporally and genetically associated with the Emeishan basalts, and is therefore an integral part of the Emeishan large igneous province. The new zircon U-Pb dating supports the view that the Emeishan volcanism could be a boundary event occurring at or around the Middle-Late Permian (the Guadalupian-Lopingian) transition, and thereby confirms the validity of a causal connection with the end-Guadalupian mass extinction. 2010 Journal Article http://hdl.handle.net/20.500.11937/12486 American Journal of Science restricted |
| spellingShingle | Zi, Jianwei Fan, W. Wang, Y. Cawood, P. Peng, T. Sun, L. Xu, Z. U-Pb geochronology and geochemistry of the Dashibao Basalts in the Songpan-Ganzi Terrane, SW China, with implications for the age of Emeishan volcanism |
| title | U-Pb geochronology and geochemistry of the Dashibao Basalts in the Songpan-Ganzi Terrane, SW China, with implications for the age of Emeishan volcanism |
| title_full | U-Pb geochronology and geochemistry of the Dashibao Basalts in the Songpan-Ganzi Terrane, SW China, with implications for the age of Emeishan volcanism |
| title_fullStr | U-Pb geochronology and geochemistry of the Dashibao Basalts in the Songpan-Ganzi Terrane, SW China, with implications for the age of Emeishan volcanism |
| title_full_unstemmed | U-Pb geochronology and geochemistry of the Dashibao Basalts in the Songpan-Ganzi Terrane, SW China, with implications for the age of Emeishan volcanism |
| title_short | U-Pb geochronology and geochemistry of the Dashibao Basalts in the Songpan-Ganzi Terrane, SW China, with implications for the age of Emeishan volcanism |
| title_sort | u-pb geochronology and geochemistry of the dashibao basalts in the songpan-ganzi terrane, sw china, with implications for the age of emeishan volcanism |
| url | http://hdl.handle.net/20.500.11937/12486 |