Fabric development in a weathering profile at a basement–cover interface, the sub-Cambrian peneplain, Israel: Implications for decollement tectonics

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• 作者：T. Angerer^a ; ¹ ; ^{t.angerer@web.de"" rel=""nofollow} ; R.O. Greiling^a ; D. Avigad^b
• 关键词：Anisotropy of magnetic susceptibility ; Basement-cover interface ; Decollement ; Palaeoweathering ; Roded granite
• 刊名：Journal of Structural Geology
• 出版年：2011
• 出版时间：May 2011
• 年：2011
• 卷：33
• 期：5
• 页码：819-832
• 全文大小：2743 K

文摘

The present study examines a fossil saprock–saprolite–laterite-profile beneath the sub-Cambrian peneplain in the Pan-African Roded Granite, Israel, with regard to structure and magnetic fabrics (anisotropy of magnetic susceptibility, AMS), and image analysis of compaction. The deformed granite shows two pre-weathering foliations, S_1m (magmatic) and S_2g (gneissic). Pre-Early Cambrian weathering comprised weathering-brecciation in saprock and saprolite, and chemical weathering with clay-formation in saprolite and laterite. During subsequent Phanerozoic burial the laterite was vertically compacted to 73 % of its original thickness. In the laterite, compaction produced an unconformity-parallel cleavage (S_3d) with increasing intensity towards the unconformity. Bulk susceptibility (κ_bulk) and anisotropy (P′) decrease from the unweathered granite into the saprolite, as a result of progressive magnetite breakdown, martitization and weathering-brecciation. In the laterite, an enrichment of haematite and relic Fe–Mg–mica lead to increased κ_bulk. Here, magnetic fabrics trace the compaction fabrics. The subhorizontal, compactional clay–/mica-fabric S_3d defines a structurally weak and impermeable layer. The mechanical weakness of a clay-enriched weathering horizon with an unconformity-parallel, planar shape-preferred orientation, combined with the potentially overpressured state due to the sealing character of such a zone provides a viable explanation for the abundant localization of decollement horizons at or beneath basement-cover interfaces.