February 21, 2012

Persistent paleo-Pacific?

Filed under: Letters from Ionia — Tags: , , — zankaon @ 6:38 pm

Might any regional mantle upwelling be consistent with continental blocks never migrating into south Pracific? Might such upwelling have persisted since ancient times? Might the impact of planetesimal with proto-earth ~4.5 byrs ago, set in motion mantle upwelling and downwellings on a planetary wide basis? Not just a heat engine, since downwelling? What force could subsequently alter such momentum, once established? No eddies, even over a long period? Thus might such massIve momentum continue indefinitely? Always a paleo-Pacific, with no continental block intrusions? Thus are all massive mantle upwellings and downwellings of a permanent location; likewise for Hawaiian hot spots, and plume? Since ‘wellings’ are more massive, probably most likely of the three to persist in situ? Might any Australian plate diversion, from a track leading into Pacific, be consistent with such Pacific upwelling effect?

Might perhaps any apparent positional permanence of Pacific plate be due to differences in inertia of upper and/or lower mantle? For example, an asthenospheric counterflow to lithospheric motion? (3) Or perhaps any differences in mass distribution and composition; for example, upthrust over New Guinea region? (3) The latter is still part of continental crustal shelf, and hence still on Australian plate.

Also might there be statistical differences in prevalence of plumes/sinks in mantle? Might any differences in inertia, or plumes/sinks, for such plate, result in more central stasis? That is, might there be an analogy to the Sagasso sea in Atlantic, with it’s central stasis and surrounding currents? Analogously for Pacific plate, then might one have greater inertia and stasis centrally, with rheological change more common in periphery of such plate?

Might differences in shear velocity near upper mantle and lower mantle boundary (1), resulting perhaps in resistance to flow, be associated with any Australian continent slower advance into Pacific? However might such shear stress differences be evident else where, but without continental impedance? Might other upper mantle dynamics be involved, such as mantle rheology and continental roots (2); hence slowing migration of Australia into Pacific? Might there be eddies in upper mantle, resulting in retardation? However is the plate moving alright, but not the continent?

Perhaps is mass density of Australia sufficiently less than Indian subcontinent so that one has relative ‘backsliding’ of Australian continent (with shallow roots, or none?), in comparison to lower aspect of crust, wherein earthquakes no longer occur? That is, does the flow (i.e. rheology) increase for such lower level of crust; higher than asthenosphere of upper mantle? Does the root structure differ for continent and subcontinent? Is this related to difference in average mass density? If plate motion is indeed at such depth, wherein viscosity decreases, and rheology ensues (that is lower level of crust), then why would not the continent move with such plate motion? Can Australian plate move, but without it’s shallow rooted continent; that is, the appearance of comparative stasis? If plate rheology has a relatively shallow depth, is it associated with a physical phase change, in mineral composition and rheological properties – simulated in diamond anvil experiments?

Does Australia have an archean shield? Might zircon inclusions have been transported via glaciers from other regions of South polar complex before break up? Might iron ore deposits in northern Minnesota near Canadian shield serve as a model for iron ore deposits of western Australia? That is, wherein for the former, terraines may have carried banded iron formation sediments towards the shield, wherein they accumulated as iron ore deposits. If this were so for western Australia, would it seem like such sediment iron deposits accumulated at the edge of an ancient continental platform? Might repeated ice age stages over billions of years have lead to eroding away of a continental platform?

1. Gu J.Y., Dziewonski A.M., Ekstrom G., SU W.-J., J. 2001 Geophys. Res., 106,11169-99.

2. Shun-ichiro Karato, Tectonophysics 481 (2010) 82–98,
Rheology of the deep upper mantle and its implications for preservation of continental roots: A review

3. Turcotte D, Schubert G, Geodynamics 2nd edition, 2002, Cambridge University Press.

p.s. ontong java oceanic plateau: oceanic crust upthrust (under sediments) – just an igneous province; or in part surfacing of any differentiated left over siliceous continental material? A hint of ancient past continent building process? See Ontong Java blog. TMM


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