Elsevier

Journal of Structural Geology

Volume 17, Issue 7, July 1995, Pages 1071-1073, 1075
Journal of Structural Geology

Small-scale convection at the interface between stratified layers of mafic and silicic magma, Campbell Ridges, NW Palmer Land, Antarctic Peninsula: Syn-magmatic way-up criteria

https://doi.org/10.1016/0191-8141(95)00010-BGet rights and content

Abstract

Experimental data suggest that some igneous mafic inclusions are formed at the interface between underlying mafic magma and more silicic magma in a reservoir by a process of gas exsolution and vesiculation. We report cm-scale plume-like structures exposed over several m2 at a candidate interface in a large composite pluton from NW Palmer Land, Antarctic Peninsula and suggest that, as well as representing ‘frozen’ mafic inclusion formation, plume-like structures of this type can be used as way-up criteria and may be of particular value in the interpretation of palaeomagnetic data.

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  • A review of mesoscopic magmatic structures and their potential for evaluating the hypersolidus evolution of intrusive complexes

    2019, Journal of Structural Geology
    Citation Excerpt :

    Besides cross-cutting intrusive boundaries (Fig. 2a), mesoscale magmatic structures available to provide local growth directions include: (1) local cross-cutting boundaries in compositionally defined structures (Fig. 2d, f, q, 5a); (2) mineral grading (Fig. 2b, f, 5a); (3) magmatic load cast and flame structures (Fig. 5e; Puziewicz and Wojewoda, 1984); (4) asymmetric contact characteristics (Figs. 2b and 5b), such as the chilled versus hybrid margins of Wiebe and Collins (1998); and (5) enclave channels (Figs. 2c and 5d) with mineral molding at base (Wiebe and Collins, 1998). Proposed 'way-up' or 'paleo-vertical' indicators include: (1) load casts, flame structures (Puziewicz and Wojewoda, 1984; Vaughan et al., 1995); (2) block sinking patterns in non-convecting magma (Fig. 5f; Paterson et al., 1998; Emeleus and Troll, 2014); (3) axes of undeformed pipes and tubes (Fig. 2d, p, 5c; Wiebe and Collins, 1998; Paterson, 2009), and (4) 'dish and pillar' structures during which rising melts deflect layering upwards (Fig. 2i). Kinematics caused by deviatoric strain during movement of magma, can be established from: (1) crystal orientation patterns defining S–C structures, shear bands, and hyperbolic patterns in dikes (Fig. 5i, m, n, o; Komar, 1972; Shelley, 1985; Vernon, 1987; Miller and Paterson, 1994; Correa-Gomes et al., 2001; Geoffroy et al., 2002); (2) imbricate phenocrysts (Fig. 5h; Blumenfeld and Bouchez, 1988); (3) broken, sheared and rotated phenocrysts (Fig. 5g, q) (Vernon, 1987; Blumenfeld and Bouchez, 1988); (4) granophyre wisps (Fig. 5i; Philpotts and Asher, 1994); (5) asymmetric folds (Fig. 5s); (6) segregations attached to phenocrysts (Fig. 5g); (7) Riedel shears (Fig. 5r); and (8) ramp structures (Fig. 5n; Philpotts and Asher, 1994).

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