Uplift and Mantle Plumes Ross Thompson

Causes of Uplift 3 Causes: Dynamic Uplift - Hot buoyant material Buoyancy of hot lithosphere - Heated by hot asthenosphere Magmatic Underplating - Change in isostacy (Ito, G., & Clift, P.D., 1998)

Uplift In The Geological Record E.g. North Sea (Tertiary) – Apatite fission track analysis and vitrinite reflectance. (Nadin 1997) Uplift ave Max. 900m Timing, distribution and magnitude are consistent with Icelandic plume, just off axis Further evidence from sediments (Mudge et al. 2004) Petrology of igneous rocks shows higher than ave. temperatures (Thompson 1974; Maclennan & Lovell 2002). No evidence of underplating from drilling

Uplift at Present Head of a mantle plume impinges on the lithosphere causing uplift Propagation of dykes vertically from the head of the plume. E.g. Giant radiating dyke swarms of NW North America Radial tectonic fracturing and formation of radial fractures by (Ernst, R.E., et al. 1995)

Problems with Plume Uplift A plume head m in diameter should produce 1000m- 2000m of uplift from seafloor. (Campbell & Griffiths 1990) No evidence of uplift in Columbia river basalts, Siberian Traps, or Ontong Java Plateau. Deccan Flood basalts does show evidence of uplift - post volcanic (Ollier & Pain 2001) - has over written pre-volcanic uplift

The Ontong Java Plateau Worlds largest IP Thought to be connected to the Louisville hotspot Isostacy calculations show 35km thick crust with original 7km oceanic crust (Farnetani & Richards, 1994)Farnetani & Richards, m above MSL Caused large amounts of sub-ariel volcanism

Iceland Uplift should be higher in west due to migration of plume eastward (Lawver, L.A., and Muller, R.D., 1994) Not seen in observations (Foulger G.R., Anderson D.L., & Natland J.H., 2003.)

Other Possible Causes of Uplift Changes in stress fields - i.e. crack proagation Geochemical changes – causing volume change Influx of magma body – creation of a Laccolith (Cruden, A.R. 1998)

Summary (1) Pre-Volcanic uplift did occur but decays and is then over printed by sub-sequent more recent uplift. (2) Uplift never did occur and the plume model is false. Uplift alternatives by themselves can not explain all uplift

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