Geochemistry of Paleoproterozoic (1770 Ma) mafic dikes from the Trans-North China Orogen and tectonic implications
- 作者：Yuejun Wang ; Guochun Zhao ; Peter A. Cawood ; Weiming Fan ; Touping Peng ; Linhua Sun
- 关键词：Geochemistry ; Mafic dikes ; Subduction-related lithospheric mantle ; Paleoproterozoic ; Trans-North China Orogen
- 刊名：Journal of Asian Earth Sciences
- 出版年：2008
- 期刊代码：40_13679120
- 类别：ear
- 出版时间：20 June 2008
- 卷：33
- 期：1-2
- 页码：61-77
- 文件大小：4610 K
摘要
Paleoproterozoic (
1770 Ma) mafic dikes occur throughout the Trans-North China Orogen. These dikes can be divided into three geochemically distinct groups. Group 1 with FeOt of 12.73–18.06%, (Nb/La)N 0.18–0.39, (Th/La)N of, 0.60–1.24, εNd(t) of −5.1 to −2.4, and an enrichment in LILE’s and a depletion in HFSE’s. Group 2 has flat REEs and incompatible elements patterns, and possesses (Nb/La)N = 0.64–0.87, (Th/La)N = 0.61–1.20 and εNd(t) = −1.7 to 1.1. Group 3 has low FeOt contents (8.19–11.57%) and (Th/La)N ratios (0.29–0.72), but similar (Nb/La)N ratios and εNd(t) values to those of Group 1. Petrological and geochemical data suggest that these dikes may have originated from different sources. Group 1 could be derived from a “re-fertilized” lithospheric source incorporating a continental basaltic component trapped from a earlier phase of subduction. Group 2 was likely a product of a subduction-modified lithospheric mantle hybridized by recycled gabbroic lower crust. By contrast, Group 3 originated from a mixture of subduction-modified lithospheric mantle with a MORB component. In combination with the available data, we propose that the sources of the mafic dikes were initially modified by the 1.85 Ga subduction/collision event that assembled the North China Craton, and partially melted under subsequent rifting in response to the upwelling convective mantle.
1770 Ma) mafic dikes occur throughout the Trans-North China Orogen. These dikes can be divided into three geochemically distinct groups. Group 1 with FeOt of 12.73–18.06%, (Nb/La)N 0.18–0.39, (Th/La)N of, 0.60–1.24, εNd(t) of −5.1 to −2.4, and an enrichment in LILE’s and a depletion in HFSE’s. Group 2 has flat REEs and incompatible elements patterns, and possesses (Nb/La)N = 0.64–0.87, (Th/La)N = 0.61–1.20 and εNd(t) = −1.7 to 1.1. Group 3 has low FeOt contents (8.19–11.57%) and (Th/La)N ratios (0.29–0.72), but similar (Nb/La)N ratios and εNd(t) values to those of Group 1. Petrological and geochemical data suggest that these dikes may have originated from different sources. Group 1 could be derived from a “re-fertilized” lithospheric source incorporating a continental basaltic component trapped from a earlier phase of subduction. Group 2 was likely a product of a subduction-modified lithospheric mantle hybridized by recycled gabbroic lower crust. By contrast, Group 3 originated from a mixture of subduction-modified lithospheric mantle with a MORB component. In combination with the available data, we propose that the sources of the mafic dikes were initially modified by the 1.85 Ga subduction/collision event that assembled the North China Craton, and partially melted under subsequent rifting in response to the upwelling convective mantle.