Biography:

In the past M.T. McCulloch has collaborated on articles with G.W. Eberz and C. Class. One of their most recent publications is Research paperThe Nd- and Sr-isotopic composition of I-type microgranitoid enclaves and their host rocks from the Swifts Creek Pluton, southeast Australia. Which was published in journal Chemical Geology.

More information about M.T. McCulloch research including statistics on their citations can be found on their Copernicus Academic profile page.

M.T. McCulloch's Articles: (12)

Research paperThe Nd- and Sr-isotopic composition of I-type microgranitoid enclaves and their host rocks from the Swifts Creek Pluton, southeast Australia

AbstractInitial Nd- and Sr-isotopic compositions have been determined for microgranitoid enclaves and their host rocks from the Siluro-Devonian Swifts Creek Pluton within the Lachlan Fold Belt of southeastern Australia. Enclaves are of quartz dioritic to tonalitic composition and their textures support an igneous origin. Host rocks range from tonalite to granite.The isotopic data form an array in ϵNd87Sr86Sr space with enclaves systematically displaced towards higher ϵNd- and lower 87Sr86Sr values. Enclaves range in ϵNd (t=405 Ma) from −7.3 to −3.1 with a narrow range in 87Sr86Sr from 0.70613 to 0.70718 whereas host rocks range from −9.0 to −6.4 and 0.70761 to 0.70946 in ϵNd and 87Sr86Sr, respectively. The isotopic relations rule out simple crystal-liquid fractionation or restite unmixing alone as the major genetic link between enclaves and host rocks. The data are also incompatible with an origin of the enclaves by crystal accumulation or liquid immiscibility. Instead, mixing between a mafic, mantle-derived and a crustal-derived end-member to generate the host rock-enclave spectrum is compatible with the data.Because the initial isotopic ratios of enclaves and host rocks are well within the range of crustal rocks, we favour the alternative view that both enclave and host-rock magmas are of crustal origin. Consequently, we avoid extrapolations to hypothetical end-members. We suggest that the enclaves from the Swifts Creek Pluton are derived by partial melting of a mafic lower crust and mixed at or near the site of magma generation with a chemically less primitive and isotopically more evolved component to generate the enclave and host-rock spectrum. The isotopic heterogeneities within the enclave and host rocks survived the superimposed effects of crystal-liquid fractionation.Model ages (tDM) for enclaves and host rocks are almost identical averaging 1.7 and 1.6 Ga, respectively. These model ages indicate that both the enclave and host-rock protoliths were derived from a mantle reservoir during the Proterozoic.

Research paperGeochemistry of Pliocene to Quaternary alkali basalts from the Huri Hills, northern Kenya☆

AbstractPliocene to Quaternary basaltic lavas from the Huri Hills show a continuous change in eruptive style from earlier fissure-type eruptions producing extensive lava flows to later central-type activity, resulting in cinder cones and associated small lava flows. This change in eruptive style was accompanied by systematic variations in chemical composition and isotopic signature. With decreasing age, rock compositions change from alkali basalt to basanite (CIPW-normative nepheline increases from 3% to 22%). Whereas chondrite-normalised La abundances increase from ∼ 40 to 200, Yb stays almost constant at ∼ 10× chondritic. Concurrently, samples with Mg#>64 exhibit an increase in chondrite-normalised Tb/Yb and Zr/Y, as well as a decrease in Sc and Ti/Zr. Since no correlation between any of these parameters and the CaOAl2O3 ratio or Mg# is observed, the systematic temporal variations in trace-element ratios of slightly fractionated magmas can best be explained by an increasing amount of garnet in the residue of the melts. With decreasing age and increasing CIPW-normative nepheline, Huri Hills lavas show decreasing 87Sr86Sr ratios (0.7033-0.703) and increasing 143Nd144Nd (0.5129-0.51295) and 206Pb204Pb (18.7–19.3) ratios. Concurrently, ratios such as Ba/Th, K/La and Sr/Nd decrease. These covariations suggest binary mixing of two chemically and isotopically distinct end-member compositions. The first end-member, with high 206Pb204Pb ratios, is most probably derived from a plume source with HIMU affinities. The second end-member, showing low 206Pb204Pb, and high 87Sr86Sr, Ba/Nb and Sr/Nd ratios, is tentatively attributed to the lithospheric mantle but could also be a second plume component.

Mass spectrometric isotope dilution analyses of tin in stony meteorites and standard rocks

AbstractThe abundance of tin in 21 stony meteorites and 12 standard rocks has been determined by the stable isotope dilution technique. The measurements of the C1 chondrite Orgueil gives a cosmic abundance for tin of 3.7 (with respect to Si= 106 atoms) and thus substantiates the peak in the cosmic abundance curve due to the closed proton shell forZ = 50. The low abundance of tin in ordinary chondrites allows tin to be reassigned to the strongly depleted group of elements in the context of the Larimer-Anders model. Our values for the standard rocks are in reasonable agreement with the presently accepted abundances of tin, except for the diabase W-1 and tonalite T-1 for which significantly lower values were obtained.

The isotopic composition and elemental abundance of lutetium in meteorites and terrestrial samples and the 176Lu cosmochronometer

AbstractThe isotopic composition of lutetium has been measured in a range of terrestrial and meteoritic materials using solid-source mass spectrometric techniques. The meteoritic and terrestrial isotopic abundances are identical within experimental errors. The absolute 175Lu/176Lu ratio as determined in this work is 37.36 ± 0.07 at the 95% confidence level. On the basis of this measurement the atomic weight of lutetium has been calculated to be 174.967 ± 0.002, which is in good agreement with the currently accepted figure of 174.97 ± 0.01.Using the stable isotope dilution technique the abundance of lutetium has been determined in 25 stone, 1 stony-iron and 8 iron meteorites, and in 12 standard rocks, with an accuracy of ±5% at the 95% confidence level. In general, there is good agreement between this work and other published data.The 176Lu-176Hf pair has been proposed as an s process nucleocosmochronometer, because of the long half-life of 176Lu and the unique fact that both are s process isobars. The isotopic and elemental abundances of lutetium as measured in this work have been used with published nuclear data to estimate the mean age of s process nucleosynthesis for this isobaric pair, using the Schramm-Wasserburg formalism. The mean age cannot be accurately determined at the present time because of the lack of 30 keV neutron capture cross-section data for s only process nuclides and an accurate measurement of the branching ratio of 175Lu + n. However, it is possible to place constraints on the nuclear parameters in this mass region using a reasonable s process chronology based on the decay of 176Lu.

Boninite petrogenesis: Chemical and Nd-Sr isotopic constraints

Major and trace element abundances and Nd and Sr isotopic compositions have been determined for boninites from the Bonin Islands, Cape Vogel (Papua New Guinea) and New Caledonia and for similar lavas from Cyprus and New Zealand. SiO2, CaO, incompatible element abundances and εNd values are shown to vary systematically with the degree of light rare earth element (LREE) enrichment. LaN/YbN varies from 5.4 to 0.3. The range of εNd values is from +8.0 to +1.9.These features are interpreted in terms of mixing of two components: a LREE-depleted magma, derived by partial melting of an already-depleted peridotite source, and a hydrous, LREE-enriched fluid. If La for the fluid is taken as 100 × chondrites, REE abundances observed in boninites can be reproduced by 1–15% addition of the LREE-enriched component. Using a LREE-depleted component inferred from the Cyprus samples (LaN/YbN=0.10), the LREE-enriched component for Tertiary boninites has been calculated to have a LaN/YbN∼20.Th9+-e LREE-depleted component contains most of the CaO, Sc, HREE and TiO2, and has an εNd of ⩾ +8. The enriched component contains H2O and most of the Zr, Nb and LREE, and has an εNd ranging from +6 to at least −5. Origins for the LREE-enriched fluid include derivation from mantle sources similar to those proposed for ocean islands or, more likely, from subducted oceanic or continental crust in island-arc settings.

Geochemical and geodynamical constraints on subduction zone magmatism

AbstractThe geochemical and geodynamical parameters that may influence the composition of island-arc basalts (IAB's) are evaluated. Systematic correlations amongst high-field strength (HFS) elemental ratios (Zr/Nb, Sm/Nb and TiO2/Zr) relative to Nb abundances, indicate that HFS element systematics are not controlled by the presence of residual Nb-bearing phases in the slab. This provides confirmation of models whereby high-field strength (HFS) and HREE elements remain immobile during slab-fluxing processes and are thus derived from the mantle wedge without additional enrichments from the slab. In contrast enrichment of large-ion-lithophile elements (LIL) such as Rb, Cs, Ba, Sr, Pb, U and LREE (i.e., La, Ce) in IAB's is consistent with slab involvement, with their relative enrichment, being due to a combination of both their high rock-melt incompatibility and slab-“fluid” mobility. As a consequence, the low abundances of HFS elements such as Nb, Ti, Zr, and Hf in IAB's reflect a depleted (relative to MORB source) mantle wedge overlying the subduction slab. Depletion of the arc mantle wedge in HFS elements is attributed to previous melting events in the mantle wedge, and to geodynamic conditions associated with the formation and evolution of coupled island arcs and back-arc basins. These processes ensure a budgetary deficit in the HFS elements relative to those elements derived from the subducted slab (predominantly LILE and LREE). Thus, although in MORB's and OIB's, Nb has a similar incompatibility to U, in subduction zones the main factor controlling its abundance is its highly immobile character, particularly relative to elements like U which are mobile during prograde dehydration reactions in the slab. Based on these observations, a quantitative model has been developed for IAB petrogenesis with the transfer of trace elements from the slab to the mantle wedge being modelled with empirical slab-“fluid” partition coefficients whilst the mantle-wedge to arc-crust transfer is constrained by melt-solid partitioning. The empirically derived slab-“fluid” partition coefficients indicate that the enrichment factors characteristic of slab fluxing processes have a distinctive pattern particularly for the elements Nb, U, Th, and Sr.

Sm-Nd and U-Pb zircon isotopic constraints on the provenance of sediments from the Amadeus Basin, central Australia: Evidence for REE fractionation☆

AbstractThe Amadeus Basin of central Australia is a Late Proterozoic to Late Palaeozoic ensialic depositional basin located between two Proterozoic basement blocks of different Nd crustal formation ages, the older Arunta Block (TDMNd = 2.0 to 2.2 Ga, U-Pb zircon ages = 1.5–1.9 Ga) to the north and the younger Musgrave Block (TDMNd = 1.7 to 1.9 Ga, U-Pb zircon ages = 1.0–1.7 Ga) to the south. Initial Nd isotopic compositions of the Amadeus Basin sediments generally fall into the region defined by the evolutionary trajectories of these two basement blocks, indicating that the sediments are dominated by essentially two source components: the older Arunta Block [147Sm/144Nd ≈ 0.114 and ϵNd(0) ≈ −20.4] and younger Musgrave Block [147Sm/144Nd ≈ 0.118 and ϵNd(0) ≈ −14.7] and/or their equivalents. Stratigraphically higher sediments plot more closely to the evolutionary trajectory of the Musgrave Block. This result, together with the average provenance ages, indicates the proportion of material from the Musgrave Block increases as the sediments become younger. The Sm-Nd isotopic data preclude a substantial involvement of Archaean sources.U-Pb zircon ion probe analyses of the Late Proterozoic Heavitree Quartzite and the late Cambrian Goyder Formation are consistent with the Sm-Nd isotopic constraints. Most of the zircons from the basal Heavitree Quartzite give concordant U-Pb zircon ages of 1500 to 1900 Ma, consistent with derivation from an Arunta-type source, whilst zircons from the younger Goyder sandstone give six discrete U-Pb zircon age groups of 511 ±20, 615 ± 15, 960 ± 109, 1190 ± 54, 1633 ±24 and 1878 ±48 Ma, indicative of a dominantly Musgrave-type source with a minor contribution from the Arunta Block or reworked preexisting Amadeus Basin sediments. The two youngest U-Pb zircon ages probably indicate some contribution from Late Proterozoic-Cambrian volcanics in central Australia or a previously unrecognised younger local source in the basement blocks. The 511 ±20 Ma constrains the maximum depositional age of the sediment.The Amadeus Basin sediments have a surprisingly wide range of 147Sm/144Nd ratios (0.077–0.136), irrespective of grain size and rock types. In addition, the calculated TDMNd values for samples from the same stratigraphic unit are well correlated with 147Sm/144Nd ratios, with samples of different stratigraphic units forming sub-parallel arrays. These phenomena are interpreted in terms of REE fractionation and preferential sorting of preexisting REE-rich phases during sedimentary recycling and deposition. This process can lead to either an increase or a decrease in 147Sm/144Nd ratio of a sediment relative to its source and therefore an erroneous estimate of its TDMNd provenance age. A theoretical model is developed which accounts for the observed correlation between TDMNd and 147Sm/144Nd ratios for suites of Stratigraphically related sediments and allows a reliable estimate to be made of the provenance age of individual stratigraphic units, assuming the average 147Sm/144Nd ratio of the source is known or can be estimated. The provenance age for each stratigraphic unit of the Amadeus Basin has been calculated using this method.The Sm-Nd isotopic systematics in the Amadeus Basin sediments suggest that 1.(1) REE fractionation during sedimentary recycling can in some cases be an important factor and needs to be considered;2.(2) the provenance of the Amadeus Basin sediments was controlled by local source regions and cannot be used to infer large-scale continental averages. Hence, some caution must be evoked in using Sm-Nd isotopic constraints from restricted sampling for more generalised models of crustal evolution.

Research paperThe geochemistry and petrogenesis of basalts from the Taupo Volcanic Zone and Kermadec Island Arc, S.W. Pacific

AbstractBasalts from the Taupo Volcanic Zone (TVZ), New Zealand, the Kermadec Island Arc (KA) and its back-arc basin, the Havre Trough show systematic variations in trace-element and isotope geochemistry which are attributed to differences in tectonic setting and source heterogeneity along a more or less continuous plate boundary.Basalts from the Kermadec Arc are characterised by low abundances of high field strength elements (HFSE) such as Ti, Zr, Nb, Ta and Hf and have high ratios of Ti/Zr and low ratios of Ti/Sc and Ti/V relative to typical MORB. Basalts from TVZ also show low abundances of the HFS elements relative to MORB but show lower Ti/Zr, higher Ti/V and Ti/Sc ratios and generally higher Zr abundances than KA most basalts. The Havre Trough basalt is mildly alkaline (< 1% normative nepheline) like many back-arc basin basalts from the Pacific rim, contrasting with the hypersthene normative TVZ and KA rocks. It has higher Zr than most TVZ basalts and all KA basalts. Ratios such as Ti/V, Ti/Sc and Ti/Zr are within the range of TVZ and MORB basalts but distinct from KA basalts.The depleted (relative to MORB) HFSE characteristics of the KA and TVZ basalts are complemented by high abundances of large ion lithophile elements (LIL), such as Ba, Rb and K, when compared to MORB, yielding the distinctive LIL-enriched pattern of subduction related rocks on a normalised multi-element plot. In contrast, the Havre Trough basalt is MORB-like. Chondrite-normalised Rare Earth Element (REE) patterns for the TVZ basalts show a field overlapping with that defined by the southern KA (Rumble Sea Mounts), with light REE enriched patterns (Ce/Ybn = ∼ 1.8−3) and flat heavy REE (Tb-Lu). Basalts from the northern KA are typically light REE depleted (Ce/Ybn = 0.5) or slightly enriched (Ce/Ybn = 1.5). The REE pattern of the Havre Trough basalt is distinctive from both the KA and TVZ fields, being richer in the heavy REE, yet similar to many basalts from back-arc basins.Sr and Nd isotopes show considerable variation from a depleted MORB-like ratio in the Havre Trough basalt (TVZ-19, 87Sr/86Sr = 0.702556, ϵNd = +9.3) to radiogenic ratios in the Tarawera basalt (TVZ-4, 87Sr/86Sr = 0.7052, ϵNd = +2.2) from TVZ suggestive of crustal contamination. Between these extreme values the data from the KA and TVZ define distinctive arrays trending towards the evolved andesites, rhyolites and supracrustal basement rocks of central New Zealand. This curvilinear Nd-Sr array of the TVZ data is best explained as a result of crustal contamination. At the unradiogenic-Sr end of the array, the Sr and Nd isotopic ratios of primitive TVZ basalts overlap with those from southern KA suggesting that primitive TVZ basalts were derived from sources that are isotopically similar to those from which the southern KA basalts derived. Basalts from northern KA (Herald, Raoul and Macauley Islands) are appreciably less radiogenic than those from the central part (Curtis and L'Esperance) and the southern (Rumble Seamounts) part of the arc.Using non-slab-derived HFSE ratios and abundances as a guide to relative source depletion, it is inferred that the KA source varies from strongly depleted in the north to less depleted in the TVZ in the south. The KA source has generally experienced more extensive extraction of mafic magmas and hence is impoverished in incompatible HFSE. This leads to high Ti/Zr and low (absolute) Zr, Hf, Ta and Nb abundances. The Havre Trough source is relatively fertile with regard

Dating of chemical weathering processes by in situ measurement of U-series disequilibria in supergene Fe-oxy/hydroxides using LA-MC-ICPMS

AbstractConstraints on the timing of weathering processes in the northern Australian regolith have been obtained by in situ measurement of U-series disequilibria in U-rich supergene Fe-oxy/hydroxides using a laser ablation-MC-ICPMS technique. This approach has permitted the measurement of 234U/238U and 230Th/238U activity ratios in finely crystalline Fe-oxy/hydroxides from the Ranger uranium deposit with sufficient precision and spatial resolution to constrain the age of formation of these phases and to develop a geochronological framework for weathering processes.230Th/238U systematics in the finely crystalline Fe-oxy/hydroxides yield 230Th-ages ranging from 60 to 350 ka. The most reliable 230Th-ages cluster between 122 and 216 ka, suggesting Fe-oxy/hydroxides formation and associated weathering, peaked during the previous 2 interglacial periods. This is supported by the 230Th-ages and isotope composition of pisolith (Fe-oxy/hydroxide pedogenic nodules) cores which are demonstrated to behave as closed systems. The U isotopic composition of the Fe-oxy/hydroxides is consistent with an origin from groundwater in equilibrium with dissolved uraninite. Secondary overprinting is evident in some samples as a large range in 234U/238U. Our results suggest that weathering intensity varies with global climate cycles and that, together with weathering events dated by 40Ar/39Ar of Mn-oxides elsewhere in northern Australia ([Feng, Y.X. and Vasconcelos, P., 2001. Quaternary continental weathering qeochronology by laser-heating 40Ar/39Ar analysis of supergene cryptomelane. Geology, 29(7): 635–638.]), weathering rates in this region are orbitally forced.

Coupling of in-situ Sm–Nd systematics and U–Pb dating of monazite and allanite with applications to crustal evolution studies

AbstractHere we demonstrate the capabilities of LA-MC-ICPMS Sm–Nd-isotope measurements applied to two of the most common LREE-enriched minerals in the Earth's crust: monazite and allanite. We show that high precision measurements of 143Nd/144Nd comparable to solution-based MC-ICPMS measurements (< 0.5 epsilon units) can be achieved for laser spot sizes ranging from 16 to 50 μm. At this scale, sub-grain domains previously dated using in-situ U–Th–Pb geochronology (e.g., ion-microprobe) can be characterized with in-situ Nd-isotopic and Sm/Nd elemental measurement to determine robust initial 143Nd/144Nd ratios and investigate grain-scale isotopic heterogeneities. In addition, the LREE-enriched pattern and Eu⁎ anomaly can be simultaneously determined from in-situ Ce, Nd Sm, Eu, and Gd concentration measurements. This approach is applied here to granulite-facies metamorphic rocks previously dated in-situ using an ion-microprobe. It is shown that precise initial 143Nd/144Nd ratios and LREE concentrations measured in monazite and allanite grains by LA-MC-ICPMS on grain mounts and in-situ in polished thin sections can provide constraints on isotopic inheritance, and an understanding of the origin of compositional domains (e.g., core-overgrowth features) within a textural context. Differences between monazite U–Pb and garnet-whole-rock Sm–Nd isochron ages can also be used to estimate crustal cooling rates, thereby elucidating the timescales of crustal residence of high-grade terrains.

Reduced calcification in Western Australian corals during anomalously high summer water temperatures

Highlights•In situ coral calcification rates in Western Australia•Corals monitored for two years during the anomalously high summer temperatures•Summer calcification either similar to or reduced compared to winter•Reduced growth in temperature-sensitive branching species compared to massives•Corals under temperature stress during the warm summers of 2012 and 2013

Geomorphic evidence of major sea-level fluctuations during marine isotope substage-5e, Cape Cuvier, Western Australia

AbstractA detailed geomorphologic and morphostratigraphic investigation of raised marine terraces at Cape Cuvier, Western Australia, reveals two morphologically distinct units. A lower, well-developed accretional reef terrace between 3 and 5.5 m above MLWS (mean low-water springs; hereafter denoted as “+”) represents an extended interval of stable sea level. An upper erosional terrace and incipient coralgal rim between + 8.5 to 10.5 m represents a brief sea-level stillstand at this higher elevation. These features suggest the lower and upper terraces developed during discrete sea-level events. In an attempt to better define the timing of emplacement of each marine unit, 20 coral samples collected along vertical and lateral reef growth axis from both terraces were analysed with U-series dating. Unfortunately, all coral samples exhibited elevated δ234Uinitial values, suggesting that pervasive uptake of 234U-enriched uranium and 230Th thorium had occurred. Despite the shortcomings of absolute dating, a succession of events can be resolved though morphostratigraphic relationships. Comparison of the facies relationships, coral growth, and morphostratigraphic features between the lower and upper terraces indicates that an early to mid MIS 5e stillstand at + 3 to 5 m was followed by a late rise to + 8.5 to 10.5 m. This agrees with an emerging global view of MIS 5e sea-level history derived from stable carbonate platforms, rejecting the hypothesis that these higher sea-level benchmarks are an artefact of localized tectonic processes.

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