Journal and Proceedings of
The Royal Society of New South Wales
Volume 132 Parts 3 and 4 [Issued December, 1999]
CONTENTS
AUTHORS & TITLES
PAGES
Baker, Anthony T. The Contribution of Dwyer and Lions to the Design of Sexadentate
65-82
Ligands
Arculus R.J. Origins of the Continental Crust
[Clarke Memorial Lecture for 1999]
Theses Abstracts
[Not available on this page, but reproduced here]
Cooper, Ian Geology And Geochemistry of The Wallendbeen Area, N.S.W.
Corbyn John Andrew Air Movement in the Human Sleeping Environment and Sudden
Infant Death
Low, Chun Yu Danny Prediction of the Dimensional Accuracy of Small Extra-coronal
Titanium Castings
Murphy-Poulton, Susam F. A Study of Some Ternary Tetradentate Complexes As
Phenanthrene-based Chiral Metallointercalators
Orr, Rhonda Effect of Exercise on Diffusing Capacity in Patients with Cystic Fibrosis
83-110
111-112
113-114
115
116
117
v. 132 pts 3-4, pp. 65-82
The Contribution of Dwyer and Lions to the Design of Sexadentate Ligands
Anthony T. Baker
ABSTRACT The series of papers published by Dwyer, Lions and their collaborators on metal
complexes of sexadentate ligands represented one of the first attempts to design ligands which
would yield metal complexes with particular structures. These papers are reviewed and their
impact on contemporary and subsequent workers in coordination chemistry is assessed. Also
included as Appendices are a supplement to complete the list of Dwyer’s publications and some
biographical notes on Dwyer and Lions. The collaboration of an organic chemist and a chemist
from an analytical / inorganic background yielded important results for the field of coordination
chemistry in the 1950s, a time when that field was developing rapidly. Dwyer and Lions have left
a lasting impression on Australian coordination chemistry through their students and others
adopting their approach of designing ligands to achieve particular structures for metal
complexes.
Keywords: sexadentate ligands, ligand design, metal complexes, optical isomers.
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v. 132 pts 3-4, pp. 83-110
Origins of the Continental Crust
R. J. Arculus
[Clarke Memorial Lecture for 1999]
Abstract The genesis of the continental crust is a first-order geological and geochemical
problem. The marked enrichment of a number of elements such as Cs and Rb (by ~100 fold) in
the continental crust compared with estimates of primitive mantle abundances, is matched by
complementary depletions in the global mantle source regions tapped by mid-ocean ridge basalts.
The “depleted mantle” source of the most abundant crustal rock type (oceanic) represents a
residue from continental crust extraction. At least 60% of the mantle has been involved in
formation of the continental crust, and maybe all has been affected to some degree by mixing
either with residues from crustal formation or with deeply recycled continent-derived sediments.
There is a strong geochemical argument that any depleted (“refractory”) mantle component of
the continental lithosphere can only represent a small fraction of the total mantle involved in
continental crust formation. There can be no enduring retention of residual mantle in any
vertical, continental crust-mantle differentiation process; vertical juxtaposition may likely
represent a fortuitous linkage of buoyant crust and mantle.
The dioritic-to-tonalitic major element composition of the continental crust can only be formed
via a 2-stage process from the upper mantle: a first stage of basalt (or high-Mg andesite)
formation; and a second stage (or more) of differentiation of this protolith. The second stage
typically involves H2O as a critical component through: 1. fractional crystallisation of basalt; 2.
direct melting of subducted/underplated mafic lithosphere; 3. fractionation of high-Mg andesites
generated by wet melting of peridotite. A major constraint on all models of continental crustal
genesis is the necessity of residue (1st stage depleted mantle; 2nd stage cumulates or restite)
disposal. Mass balance indicates the MORB source represents the former, but the location of the
latter for Late Proterozoic to Phanerozoic crust is problematic. In detail, it is clear that much of
the crust, while produced initially in the Archean and early Proterozoic, has been subjected to
considerable intra-crustal recycling. Island arc magmas alone of the common terrestrial magma
types are characterised by elevated (and strongly fractionated) Pb/Ce and U/Nb that are also
distinctive of the continental crust.
Reasonably well-constrained estimates of the magmatic flux in present-day intra-oceanic arcs are
80 to 200 km3km-1 arc strike length m.y.-1, equivalent to a global crustal production rate of ~3 to
7 km3a-1. These fluxes can be compared with an incremental linear survival rate for continental
crust over 4 billion years of ~1.6 km3a-1, and a present-day subducted sediment flux of 1 km3a-1.
If arc magmas are not involved in continental crustal genesis, then a considerably larger
subducted sediment flux is needed to dispose of the surplus crust produced in supra-subduction
zone environments. Detailed consideration of the best-studied intra-oceanic arc crustal structure
(Izu Bonin) suggests a considerable tonalite fraction and a bulk composition equivalent to mafic
andesite. Accumulation sub-Moho of olivine-clinopyroxene-rich cumulates and their
incorporation into the advecting mantle wedge and recycling deep into the mantle is advocated.
In essence this hypothesis constitutes a revival of S.R. Taylor’s (1967) “andesite model” for the
origin of the continental crust.
Temporal changes in continental crust genesis through Earth history have nevertheless been
important. Partial melts of subducted and hydrated mafic lithosphere were significant juvenile
crustal constituents in the Archean. Mantle wedge melting triggered by slab-derived (through
dehydration) fluids has been significant from at least the Proterozoic onwards. Post-Proterozoic
constraints on continental crustal growth are: 1. without deep recycling of H2O, neither melting
of a subducted slab nor overlying mantle wedge occurs. Furthermore, the order of crystalline
phase appearance in cooling basalt magmas containing a few % H2O is: olivine, pyroxene,
plagioclase – the delay in plagioclase appearance in the “wet basalt case” enhances concentration
of Si, Al, Na, and K in residual magmas (key elements present in abundance in granites). The
presence of hydrated minerals (amphibole/biotite) in crystallisation products of wet magmas is
also important in generation of granitic magmas during ultra-metamorphism of continental crust.
2. a key requirement for fractional crystallisation is for the system to “be left alone” (i.e., allowed
to cool and crystallise) with minimal accompanying magma chamber tapping or replenishment.
Neglect is a function of local magma flux, and in arcs, this is ~0.1 to 0.3 of the mid-ocean ridge
flux. 3. disposal of ultramafic/mafic crystalline cumulates from basalt fractionation processes is
crucial for production of granodioritic crust. Cumulates may be underplated (sub-Moho) as part
of the continental lithosphere or dynamically removed. Melts escaping from a supra-subduction
zone system are not coupled to crystal cumulates and residual mantle; the latter are advectively
dragged by the subducted lithosphere and recycled deep into the mantle. A summary of this
Phanerozoic style of growth would emphasise “damp, neglect, and waste disposal” as crucial
factors.
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