The Role of the Core in Mantle Plumes Graham Smith University of Durham Dept. of Earth Sciences.

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The Role of the Core in Mantle Plumes Graham Smith University of Durham Dept. of Earth Sciences

description

Why a CMB Origin? Size of some large igneous provinces requires an origin in the lower mantle or the CMB Mechanism of heat removal from the CMB area Large Igneous ProvincesEarth’s Heat BudgetEarth’s Geodynamo Modified from Condie (2003) CRETACEOUS SUPERCHRON 50-75% increase in rate of crustal production “Superplume” events correlate well with patterns of magnetic reversal

Transcript of The Role of the Core in Mantle Plumes Graham Smith University of Durham Dept. of Earth Sciences.

Page 1: The Role of the Core in Mantle Plumes Graham Smith University of Durham Dept. of Earth Sciences.

The Role of the Core in Mantle Plumes

Graham Smith University of Durham

Dept. of Earth Sciences

Page 2: The Role of the Core in Mantle Plumes Graham Smith University of Durham Dept. of Earth Sciences.

How is the Core Involved?

Source of HEAT

Origin of plumes at the Core-

Mantle Boundary (CMB)?

from Ritsema et al. 1999.

Page 3: The Role of the Core in Mantle Plumes Graham Smith University of Durham Dept. of Earth Sciences.

Why a CMB Origin?

Size of some large igneous provinces requires an origin in the lower mantle or the CMBMechanism of heat removal from the CMB area

Large Igneous ProvincesEarth’s Heat BudgetEarth’s Geodynamo

Modified from Condie (2003)

CRETACEOUS SUPERCHRON

50-75% increase in rate of crustal production

“Superplume” events correlate well with patterns of magnetic reversal

www.creaso.com

Page 4: The Role of the Core in Mantle Plumes Graham Smith University of Durham Dept. of Earth Sciences.

Outer core enriched in Os by 300x mantle values

High 187Os/188Os and 186Os/188Os

OSMIUM“Plume-related” basalts carry this signal

Addition of ≤1wt.% outer core material

BUT, High Os ratios can also be generated in the crust

Page 5: The Role of the Core in Mantle Plumes Graham Smith University of Durham Dept. of Earth Sciences.

Why Not the Upper Mantle?

PUM = Primitive Upper MantleFrom Brandon et al. 1999.

Page 6: The Role of the Core in Mantle Plumes Graham Smith University of Durham Dept. of Earth Sciences.

OSMIUMCRUSTAL CONTAMINATION

e.g. Koolau lavas, Hawaii

High 187Os/188Os

Low 186Os/188Os

High d18O

High Sr Low Nd

Page 7: The Role of the Core in Mantle Plumes Graham Smith University of Durham Dept. of Earth Sciences.

HELIUMCore enriched in primordial He during accretion High 3He/4He ratios

MORB = 8±1 RaModified from van Keken et al. (2002)

Page 8: The Role of the Core in Mantle Plumes Graham Smith University of Durham Dept. of Earth Sciences.

FOZO: A common theme

Geochemical signatures all point to a common component

OIBs comprise a variety of different isotopic endmembers

Material rising from the CMB incorporates deep mantle material

But, FOZO is poor in Os

FOZO

Page 9: The Role of the Core in Mantle Plumes Graham Smith University of Durham Dept. of Earth Sciences.

Ultra-Low Velocity Zones

Page 10: The Role of the Core in Mantle Plumes Graham Smith University of Durham Dept. of Earth Sciences.

ImplicationsOsmium systematics suggest incorporation of outer core material at CMBPresence of recycled ancient crust suggests that slabs sink to CMB

Less degassed lower mantle separated from degassed upper mantle points to a double-layer mantle system.

Primordial 3He points strongly to a CMB origin for plumes

Courtesy of University of Hawaii, Institute for Astronomy

Page 11: The Role of the Core in Mantle Plumes Graham Smith University of Durham Dept. of Earth Sciences.

ReferencesBrandon et al. (1998). Nature 280 1570-73.

Brandon et al. (1999). Earth & Planetary Science Letters 174 25-42.

Campbell & Griffiths(1992). J.Geol. 92 497-523.

Condie. (2003) Plate Tectonics and Crustal Evolution, 4th ed.. Butterworth-Heinemann.

Dubrovinsky et al. (2001). Nature 412 527-29.

Gurnis et al. (1998). The Core-Mantle Boundary Region. AGU Geodynamics Series 28.

Jacobs (1993). Deep Interior of the Earth. Chapman & Hall.

Jephcoat (1998). Nature 393 355-58.

Knittle & Jeanloz (1991). Science 251 1438-43.

Larson (1991). Geology 19 547-50.

Li & Agee (1996). Nature 381 686-89.

Macpherson et al. (2000). Earth & Planetary Science Letters 176 171-83.

Marty et al. (1996). Earth & Planetary Science Letters 144 223-37.

McElhinny (1979). The Earth: Its Origin, Structure & Evolution.

Peltier (1989). Fluid Mechanics of Astrophysics & Geophysics 4.

Rost & Revenaugh (2001). Science 294 1911-14.

Schubert et al. (2001). Mantle Convection in the Earth & Planets.

Tschauner et al. (1999). Nature 398 604-7.

Van Keken et al. (2002). Annu. Rev. Earth Planet. Sci. 30 493-525

Walker et al. (1995). Science 269 819-22.

Widom & Shirey (1996). Earth & Planetary Science Letters 142 451-65.


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