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Geoinformatic approach to global nepheline syenite and carbonatite distribution: Testing a Wilson cycle model

¹ Department of Geosciences, University of Houston, Houston, Texas 77204-5007, USA

View larger version (25K): [in this window] [in a new window]   Figure 1. Cartoons illustrating two current hypotheses about the origin of alkaline rocks and carbonatites (ARCS). A: In the plume model, ARCs are derived from mantle plumes (here defined simply as magma sources of distinctive chemical composition within the convecting mantle). B: In the deformed alkaline rocks and carbonatites (DARC) model, ARCs are derived from melting that involves deformed alkaline rock and carbonatite material that was carried into the lithospheric mantle during an ancient subduction episode.

View larger version (61K): [in this window] [in a new window]   Figure 2. A: Cartoon illustrating how alkaline rocks and carbonatites (ARCs) are erupted into intracontinental rifts. B: Cartoon illustrating how those ARCs may come to lie on a rifted continental margin as an ocean develops on the site of the rift. C: Cartoon illustrating how the ARCs from the rifted continental margin may become involved in a continental collision to become deformed alkaline rocks and carbonatites (DARCs). Some of those DARCs are subducted and become part of the continental lithosphere; others remain in the crust. D: An interval of hundreds of millions of years may pass without activity. E: Renewed rifting localized on the ancient suture zone may lead to the eruption of new alkaline igneous rocks and carbonatites by partial melting that involves the DARC sources in the underlying mantle lithosphere.

View larger version (60K): [in this window] [in a new window]   Figure 3. Deformed alkaline rocks and carbonatites (DARCs) lie on Proterozoic suture zones near the edges of and within (dashed line) African cratons. Younger alkaline igneous rocks and carbonatites, e.g., in Malawi (13°S, 35°E), have erupted in rifts on top of African suture zones (simplified from Burke et al., 2003). If South America is rotated back to its former position adjacent to Africa, the suture zone on the southern border of the West African craton becomes continuous. The only recognized DARC in South America lies on that suture (Woolley, 1987).

View larger version (110K): [in this window] [in a new window]   Figure 4. Map of India showing the distribution of nearly 50 deformed alkaline rocks and carbonatites (DARCs) within the S-shaped Great Indian Proterozoic fold belt. These DARCs formed from alkaline igneous rock and carbonatites (ARCs) erupted ca. 2.0 Ga into rifts. They became involved in arc and continental collisions between ca. 1.8 and ca. 0.55 Ga (Leelanandam et al., 2005).

View larger version (115K): [in this window] [in a new window]   Figure 5. This map shows how Sengör and Natalin (2001) mapped 700 intracontinental rifts. We use these results and those of world suture maps (Burke et al., 1977) as databases, which we plan to refine in our geoinformatics study of alkaline igneous rock and carbonatite (ARC) and deformed alkaline rock and carbonatite (DARC) distribution. Rectangles labeled Figs. 4 and 5 on this map refer to additional maps in Sengör and Natalin (2001).

View larger version (61K): [in this window] [in a new window]   Figure 6. A: Database architecture for alkaline igneous rock and carbonatite (ARC) and deformed alkaline rock and carbonatite (DARC) distribution. The database system will be integrated with ArcIMS (ARC Internet Map Server) via ArcSDE. ArcSDE is a geographic information system (GIS) gateway that facilitates management of spatial data in relational database management systems, whereas ArcIMS is currently widely utilized in the integration of local GIS data sources with Internet data sources for display, query, and analysis using a Web browser. Visualization will be made available through ArcIMS to GEOWALL. B: Flow chart explaining process of making customized maps via Web browser.

View larger version (111K): [in this window] [in a new window]   Figure 7. Landsat image (bands 7-4-3) of a part of the Kola Peninsula of Russia and (above) maps from Volume 2 of the Woolley catalog of alkaline rocks and carbonatites (Kogarko et al., 1995). In this paper, we report on a pilot study of the area of this image. Kurginskii and Soustova (#15 and #18 on the map) are deformed alkaline rocks and carbonatites (DARCs) of Early Proterozoic age. Lovozero and Khibina (#16 and #17 on the map) are alkaline igneous rocks and carbonatites (ARCs) of Devonian age. Yellow dashed lines are gneissic foliation concordant with that of Soustova. The eruption sites of Lovozero and Khibina are bracketed by the locations of Kurginskii and Soustova. This is consistent with the idea that ARCs may be derived from partial melting involving underlying DARCs.

View larger version (50K): [in this window] [in a new window]   Figure 8. Sketch map based on the work of Daly et al. (2001) and Figure 7, showing how the Early Proterozoic Lapland-Kola orogenic belt (LKO; gray) and its sutured boundary (black line) lie between two distinct blocks of Archean rock (green). The deformed alkaline rocks and carbonatites (DARCs) of Kurginskii and Soustova lie within the area in which rift facies rocks related to the opening of an ocean on the site of the LKO have been recognized. The alkaline igneous rocks and carbonatites (ARCs) of Khibina and Lovozero lie within the poorly defined Devonian "Kola aulacogen" (Kogarko et al., 1995), which extends south-southeastward roughly along the trend of the Early Proterozoic suture zone.