| Titre | Late Tonian (ca. 785 Ma) subduction-related mafic-ultramafic cumulates in the West Cathaysia terrane, South China |
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| Auteur | Wang, L; Zhang, K; Lin, S; Bédard, J H; Santos, G; He, W; Yin, C; Xiao, W |
| Source | Precambrian Research vol. 387, 106980, 2023 p. 1-17, https://doi.org/10.1016/j.precamres.2023.106980 |
| Image |  |
| Année | 2023 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20220555 |
| Éditeur | Elsevier |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.1016/j.precamres.2023.106980 |
| Media | papier; numérique; en ligne |
| Formats | pdf |
| Région | South China; Shenshan; Jiangxi Province |
| Lat/Long OENS | 110.0000 115.0000 30.0000 25.0000 |
| Sujets | roches mafiques; roches ultramafiques; Cathaysie; géochimie; Précambrien; Protérozoïque |
| Illustrations | cartes de localisation; photographies; photomicrographies; diagrammes |
| Diffusé | 2023 02 14 |
| Résumé | (disponible en anglais seulement)
The Neoproterozoic tectonic setting of the West Cathaysia terrane and its relationship with the Yangtze Block are critical to understanding the formation and
tectonic evolution of South China. A detailed study of late Tonian mafic-ultramafic cumulate slivers embedded in the Shenshan tectonic mélange along the northwest margin of West Cathaysia is presented here with the aim of elucidating its
Neoproterozoic tectonic history. These partly-altered mafic-ultramafic rocks include olivine-bearing cumulates (olivine pyroxene hornblendite or olivine hornblende pyroxenite), pyroxene hornblendite, and gabbroic cumulates. The early crystallization
of clinopyroxene and the abundance of hornblende indicate that they formed from hydrous magmas. The rocks have similar geochemical distribution patterns, but show variable initial 87Sr/86Sr ratios (0.702679 to 0.709742) and eNd(t) values (+2.10 to
+4.52). The mineral compositions of the clinopyroxene and hornblende and their whole-rock extended normalized trace element patterns show features (e.g. negative Nb anomalies, LILE enrichment) typical of rocks with an arc affinity. The high
calculated Mg# values (58-77, average 71) of the equilibrium magmas are close to those of primary mantle-derived basalts. We conclude that these mafic and ultramafic cumulates were derived from a subduction-related, hydrous, magnesian basalt in a
subduction setting. The estimated crystallization temperature and pressure, based on the composition of the amphiboles, suggest that the minerals accumulated in magma chambers at middle to lower crustal depths. LA-ICP-MS U-Pb dating of zircon from
the gabbroic cumulate indicates crystallization at ca. 785 Ma. These mafic-ultramafic cumulates display similarities with coeval Neoproterozoic Alaskan-type mafic-ultramafic intrusions from the Arabian-Nubian Shield that are interpreted to be related
to subduction of the oceanic lithosphere of the Mozambique Ocean prior to assembly of the Gondwana supercontinent. A previous interpretation for West Cathaysia at this time involved a post-collisional rift basin (the Nanhua basin) that overlapped the
southeastern margin of the Yangtze Block and the northwestern margin of West Cathaysia. In contrast, our results suggest that West Cathaysia was an arc at ca. 785 Ma, which supports the interpretation that the amalgamation between Yangtze and West
Cathaysia did not occur in the Tonian, but more likely in the early Paleozoic. |
| Sommaire | (Résumé en langage clair et simple, non publié)
Une étude détaillée de roches plutoniques du fin- Tonian a été fait sur le mélange Shenshan, qui suit la marge nord du terrane West Cathaysia.
Les roches incluent des cumulats à olivine gabbroiques. Les températures et pressions de cristallization estimées suggèrent des chambres magmatiques à la base de la croûte. Les valeurs élevées de Mg/Fe calculées à partire des minéraux suggèrent des
basaltes primitifs. L'abondance de hornblende indiquent la formation à partir de magmas hydratés. Les rohes ont des valeurs élevées et variables en isotopes radiogéniques (Sr -Nd). Les compositions minéraes et analyses de traces roche totale
indiquent peut-être une affinité d'arcy. Les datations U-Pb sur zircon indiquent la cristallization à 785 Ma. Ces roches cumulatives ressemblent à des roches de type Alaskan-type synchrones su bouclier Arabo-Nubien, qui sont interprétés commeétant
reliés à la subduction de la lithospère océanique de l'Océan Mozambique Ocean avant l'assemblage du continent Gondwana. Ces données supportent l'interprétation que l'amalgame entre les terranes de Yangtze et West Cathaysia n'a pas eu lieu au Tonian,
mais au début du Paléozoique. |
| GEOSCAN ID | 331413 |
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