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This study explores the significance of the mantle lithosphere in preserving early Archaean 'arcs'. Analysis of isotopes and mass balancing in CC recycling sheds light on the mechanisms and processes related to the formation and survival of continental crust. Examination reveals insights into the nature of mantle depletion, the operation of subduction, and alternative mechanisms for the creation of continental crust. The research indicates the challenges and processes involved in the conservation of the continental geological record.
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The importance of the mantle lithosphere for preservation of early Archaean ‘arcs’ Balz Kamber Department of Earth Sciences
147Sm-143Nd ‘age’ of CC 2.0-2.2 Ga
CC vs. MORB Pb isotopes 207Pb/206Pb imposes a limit on CC recycling
U and Pb mass balance? For mass of CC = 2 .1 x 10e25g
Nb/Th systematics of basalts 18 14 Nb/Th 10 6 Age (Ma)
Conclusion 1 Continental crust with high survival potential is and was difficult to make Possibility of high infant mortality cannot be excluded Armstrong model of constant continental mass violates combined Nd&Pb isotope systematics
Conclusion 2 Subduction operated at 3.7 Ga but was ineffective as evidenced by slow increase in preserved continental mass Continental geological record heavily biases towards subduction
Conclusion 3 Throughout Archaean both continental and oceanic lithosphere represented minor proportion of plates The major plates (oceanic plateaus?) did not form a deep lithospheric mantle keel and were ultimately recycled
Conclusion 4 Alternative mechanisms for creation of continental crust did exist. Geochemistry requires that crustal dense reside was recycled into the mantle