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Nutman A.P.,University of Wollongong | Bennett V.C.,Australian National University | Friend C.R.L.,Glendale | Yi K.,Korea Basic Science Institute | Lee S.R.,Korea Institute of Geoscience and Mineral Resources
Precambrian Research | Year: 2015

The Mesoarchaean Kapisilik and Eoarchaean Isukasia terranes in the Nuuk region of southern West Greenland were tectonically juxtaposed in the Archaean. The north of the Isukasia terrane is distal from the Kapisilik terrane and has only rare growth of ~2690Ma metamorphic zircon and no 2980-2950Ma metamorphic zircon. The southern part of the Isukasia terrane lies between two ~2690Ma shear zones, and has locally preserved high pressure granulite facies assemblages and widespread growth of 2980-2950Ma metamorphic zircon and also sporadic growth of ~2690Ma metamorphic zircon. Within this southern part of the Isukasia terrane there is a folded klippe of mylonitised Mesoarchaean detrital meta-sedimentary rocks (carrying >3600 and ~3070Ma detrital zircons), mafic and ultramafic rocks, with ~2970Ma metamorphic zircon overgrowths. South of the Isukasia terrane is the Kapisilik terrane, containing ~3070Ma arc-related volcanic rocks, gabbro-anorthosites and meta-tonalites, intruded by 2970-2960Ma granites. Zircons of an Ivisârtoq supracrustal belt ~3075Ma intermediate volcanic rock have initial e{open}Hf values of +2 to +5 thus are juvenile crustal additions. ~3070Ma tonalites along the northern edge of the Kapisilik terrane have whole rock positive initial e{open}Nd values and thus are also juvenile crustal additions. In contrast, igneous zircons in 2960Ma granites intruded into juvenile ~3075Ma supracrustal rocks of the Kapisilik terrane have initial e{open}Hf values of -5 to -10, and must have involved the partial melting of >3600Ma Isukasia terrane rocks.The integrated structural and zircon U-Th-Pb-Hf isotopic data show that at 2980-2950. Ma the Kapisilik terrane juvenile arc components collided with, and over-rid, the Isukasia terrane. The southern edge of the Isukasia terrane came to lie in the deep crust under the Ivisârtoq supracrustal belt and melted at 2970-2960. Ma to produce granites. These granites derived from ancient crust rose into the upper crust, where they intruded the overlying allochthonous juvenile ~3075. Ma Ivisârtoq supracrustal belt arc assemblages. The southern edge of the Isukasia terrane is interpreted as an interior nappe of Eoarchaean basement rocks interfolded with a klippe of Mesoarchaean metasedimentary and mafic/ultramafic rocks, both of which are affected by 2980-2950. Ma metamorphism. The mixed Eoarchaean-Mesoarchaean detrital provenance suggests that the klippe could be dismembered components of an accretionary prism or forearc crust. The northern part of the Isukasia terrane is interpreted as foreland, free of 2980-2950. Ma high-grade metamorphic overprint. This shows that the Isukasia terrane is not a coherent block, but contains ancient rocks that are parautochthonous or allochthonous to each other, with contrasting later metamorphic history.At ~2690. Ma the crustal architecture arisen from Mesoarchaean collision between an older continental block and an island arc was reworked along intra-crustal shear zones, coeval with amphibolite facies metamorphism. This reworking followed on from major terrane assembly at 2710-2700. Ma in the southern part of the Nuuk region, when the Eoarchaean Færingehavn terrane was juxtaposed with 2840-2825. Ma arc rocks. Thus the 2980-2950. Ma assembly of the Isukasia and Kapisilik terranes is distinct from the later 2710-2700. Ma terrane assembly further south in the Nuuk region. © 2015 Elsevier B.V.

Nutman A.P.,University of Wollongong | Bennett V.C.,Australian National University | Friend C.R.L.,Glendale | Hidaka H.,Hiroshima University | And 3 more authors.
American Journal of Science | Year: 2014

From the 3000 km2 Eoarchean Itsaq Gneiss Complex (IGC) of Greenland, zircon U-Pb dating of numerous meta-granitoid and orthogneiss samples is integrated with geologic observations, whole rock geochemistry and a strategic subset of zircon Hf and whole rock Nd isotopic measurements. This shows that there are multiple episodes of TTG suite formation from ∼3890 to 3660 Ma, characterized by zircon initial εHf≈0 and whole rock initial εNd of > +2. These rocks mostly have geochemical signatures of partial melting of eclogitized mafic sources, with a subset of high magnesian, low silica rocks indicating fusion by fluid fluxing of upper mantle sources. The TTG suites are accompanied by slightly older gabbros, basalts and andesites, which have geochemical signatures pointing to magmas originating from fluid fluxing of upper mantle sources. The data show the formation of juvenile crust domains in several discrete events from ∼3900 to 3660 Ma, probably at convergent plate boundaries in an environment analogous, but not identical to, modern island arcs. In the Isua area, a northern ∼3700 Ma terrane formed distal from a predominantly ∼3800 Ma terrane. These terranes were juxtaposed between 3680 and 3660 Ma - respectively the age of the youngest rocks unique to the northern terrane and the lithologically distinctive ultramafic-granitic Inaluk dykes common to both terranes. This shows the assembly of different domains of juvenile rocks to form a more expansive domain of "continental" crust. A rare occurrence of high-pressure granulite is dated at ∼3660 Ma, demonstrating that assembly involved tectonic crustal thickening. This continental crust was then reworked in the 3660 to 3600 Ma Isukasian orogeny. In the northern part of the Isua area, 3660 to 3600 Ma granites were emplaced into ∼3700 Ma tonalites. The earliest granites are nebulous, and sigmoidal schlieric inclusions within them demonstrate ductile extension. Younger granite sheets were emplaced into extensional ductile-brittle fractures. These granite-tonalite relationships are overprinted by widespread development of late Eoarchean (pre-3500 Ma Ameralik dyke) brittle-ductile extensional cataclastic textures, together demonstrating that extension was polybaric. The southern part of the Isua area largely escaped 3660 to 3600 Ma high temperature processes and has sparse granite sheets commonly focused into coeval shear zones. In the rest of the complex, deeper crustal levels during the Isukasian orogeny are widely preserved. These experienced upper amphibolite to granulite facies moderate-to low-pressure syn-kinematic metamorphism, forming complex migmatites rich in granitic-trondhjemitic neosome. The migmatites were intruded by composite ferrogabbro and granite bodies, in which syn-magmatic extensional features are locally preserved. Thus 3660 to 3600 Ma crustal recycling involved elevated crustal thermal gradients in an extensional regime. Crustal melts formed in the Isukasian orogeny have zircon initial εHf<0 and whole rock initial εNd of ≤0, showing incorporation of slightly older Eoarchean juvenile crust. A Phanerozoic example of collisional orogeny followed by crustal thinning is explored as an analog for the Isukasian orogeny.

Nutman A.P.,University of Wollongong | Nutman A.P.,Chinese Academy of Geological Sciences | Bennett V.C.,Australian National University | Chivas A.R.,University of Wollongong | And 3 more authors.
Precambrian Research | Year: 2015

This paper reports evidence for Earth's oldest-recognised low temperature alteration, at ~3800. Ma. Potassic felsic schists with a protolith age of 3806 ± 2. Ma form a ~30. km long unit in the amphibolite facies, deformed, Isua supracrustal belt (West Greenland). At a single locality, boudinaged layers (nodules) within the schists are low strain zones: they are fine-grained, weakly feldspar-phyric, contain quartz amygdules and have fiamme-like structures, all supporting a volcanic protolith.The nodules and surrounding schistose matrix contain abundant, 100-50μm, euhedral, oscillatory zoned 3806Ma zircons. The rare earth patterns of the zircons indicate crystallisation was magmatic. Some zircons contain axial lobate voids indicating that they grew at low pressure as the magma exsolved a fluid. Ti-in-zircon thermometry indicates crystallisation temperatures of 750-650°C. Taken together, these zircon features indicates growth at eutectic temperatures in a hypabyssal chamber as the magma was exsolving a fluid phase. The magmatic zircons have e{open}Hf initial values of ~0 and δ18OVSMOW of +5.0‰ (Hiess et al., 2009), showing that the source of the volcanic rocks was devoid of assimilated markedly older or weathered crustal material, and probably essentially juvenile. In contrast, the whole rock δ18OVSMOW values are elevated at +14.7 to +16.2‰, indicative of superimposed low-temperature alteration processes.The nodules and matrix schists have non-igneous bulk compositions, exemplified by strong enrichment in K2O and depletion in Na2O. They are depleted in Sr, have no negative Eu anomalies, but have high Rb/Sr, with an Rb-Sr age of 3760±140Ma (Jacobsen and Dymek, 1988). This indicates that the alteration involving strong degradation of plagioclase occurred in the Eoarchaean. Trace element compositions and establishment of alteration vectors suggest the protoliths were likely rhyolitic and dacitic in composition.The strongest-modified matrix schist compositions contain biotite±calcite±dolomite with increase in MgO relative to the nodules, which indicates early magnesian carbonate growth. The whole-rock chemistry, decoupling of the igneous zircon and whole-rock oxygen isotope signatures and the Rb-Sr dating indicate that after eruption, the 3806Ma felsic volcanic rocks underwent Eoarchaean low-temperature potassic alteration with weathering and groundwater circulation the most likely process. The geochemistry of the Isua felsic schists is compared with that of better-preserved volcanic rocks where the alteration conditions are known. This suggests a subaerial environment. The carbonatisation of the Isua felsic schists demonstrates drawdown of atmospheric CO2 into rocks made porous by the weathering. © 2015 Elsevier B.V.

Nutman A.P.,University of Wollongong | Bennett V.C.,Australian National University | Friend C.R.L.,Glendale
American Journal of Science | Year: 2015

A synthesis of the geological record of Earth's ten remaining oldest surviving gneiss complexes, each containing >3.6 Ga rocks, reveals a common history. We propose that the simplest scenario compatible with all observations is that of formation of an ancient continental mass, here named Itsaqia, by 3.66 Ga from amalgamation of earlier quartzofeldspathic crust, followed by initiation of continental break-up at 3.53 Ga by rifting. Evidence for this is reconstructed from the remaining oldest rock record (only ca. 10,000 km2 globally). Dominating the surviving fragments of the proposed Itsaqia continent are 3.9 to 3.66 Ga tonalites that represent juvenile crustal additions with whole-rock initial εNd >+1 and zircon initial εHf ≈ 0. Their trace element chemistry shows that they were derived by ca. 30 percent partial melting of garnetiferous, mostly eclogitized basic rocks, leaving behind a subcrustal garnet-rich restite. The tonalites contain inclusions of mafic rocks with chemical signatures diagnostic of mantle wedge fluxing, such as enrichment in the light rare earths and depletion of Nb and Ti. We interpret that this juvenile crust formed repeatedly in arc-like constructs at convergent plate boundaries. The Acasta Gneiss of Canada is the only undisputed surviving rock record of the proposed Itsaqia continent where crust formation extends back to the Hadean. Before ca. 3.66 Ga, individual gneiss complexes show distinct chronologies of crust formation, yet despite their present-day isolation, they underwent identical 3.66 to 3.6 Ga high temperature orogenic events (Isukasian orogeny) - which we contend indicates that from 3.66 Ga these complexes had amalgamated into a single continental mass. Rare surviving 3.66 Ga high-pressure granulite rocks that underwent rapid decompression indicate tectonic crustal thickening then collapse during amalgamation. This was followed by almost 50 million years of high heat flow and lower pressure metamorphism, most probably in an extensional setting. Starting from ca. 3.53 Ga, we propose that komatiite and basalt eruption and dike emplacement marked the start of Itsaqia's dismemberment by rifting. We further speculate that the deep mantle upwelling responsible for this plume-related magmatism was triggered by either the cascade of pre-3.66 Ga sub-Itsaqia high density garnet-rich restitic subduction graveyards into the lower mantle or the thermal insulation effect of Itsaqia. This resembles the mechanisms of supercontinent breakup throughout Earth's history. Hence we propose that Wilson Cycles of continent amalgamation and breakup were already initiated by the Eoarchean, near the start of the rock record. Australia's East Pilbara region was over the top of the plume, where the thermal impact destroyed Itsaqia by melting to give rise to felsic igneous rocks coeval with komatiites. Greenland's Itsaq Gneiss Complex was peripheral to the plume, and hence was heavily diked at ca. 3.5 Ga, but was not melted.

Nutman A.P.,University of Wollongong | Nutman A.P.,University of New South Wales | Bennett V.C.,Australian National University | Friend C.R.L.,Glendale | And 2 more authors.
Nature | Year: 2016

Biological activity is a major factor in Earth's chemical cycles, including facilitating CO2 sequestration and providing climate feedbacks. Thus a key question in Earth's evolution is when did life arise and impact hydrosphere-atmosphere-lithosphere chemical cycles? Until now, evidence for the oldest life on Earth focused on debated stable isotopic signatures of 3,800-3,700 million year (Myr)-old metamorphosed sedimentary rocks and minerals from the Isua supracrustal belt (ISB), southwest Greenland. Here we report evidence for ancient life from a newly exposed outcrop of 3,700-Myr-old metacarbonate rocks in the ISB that contain 1-4-cm-high stromatolites - macroscopically layered structures produced by microbial communities. The ISB stromatolites grew in a shallow marine environment, as indicated by seawater-like rare-earth element plus yttrium trace element signatures of the metacarbonates, and by interlayered detrital sedimentary rocks with cross-lamination and storm-wave generated breccias. The ISB stromatolites predate by 220 Myr the previous most convincing and generally accepted multidisciplinary evidence for oldest life remains in the 3,480-Myr-old Dresser Formation of the Pilbara Craton, Australia. The presence of the ISB stromatolites demonstrates the establishment of shallow marine carbonate production with biotic CO2 sequestration by 3,700 million years ago (Ma), near the start of Earth's sedimentary record. A sophistication of life by 3,700 Ma is in accord with genetic molecular clock studies placing life's origin in the Hadean eon (>4,000 Ma). © 2016 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.

PubMed | Australian National University, Glendale, University of Wollongong and University of New South Wales
Type: Journal Article | Journal: Nature | Year: 2016

Biological activity is a major factor in Earths chemical cycles, including facilitating CO

Radley J.D.,University of Birmingham | Akers P.,Binley Road | Ellis B.,Claverdon Road | Fenwick I.,Swift Close | Friend C.R.L.,Glendale
Proceedings of the Geologists' Association | Year: 2013

Wood Farm Pit, Bubbenhall, Warwickshire, central England, was one of a complex of sand and gravel quarries within unconsolidated Middle Pleistocene fluvial and glaciogenic sediments of the Baginton and Wolston formations. These strata document the development of the pre-Anglian Bytham River and its eventual destruction during the Anglian glaciation. They have yielded a freshwater and terrestrial fossil biota and Lower Palaeolithic handaxes, and demonstrate well-preserved sedimentary structures. These features underline the value of the local Middle Pleistocene sites as scientific and educational resources. The Warwickshire Geological Conservation Group introduced an experimental soft-sediment conservation scheme at Wood Farm Pit during 2005-2007. This involved designing, installing and monitoring a screen to protect a representative geological exposure. The structure proved highly effective in terms of low cost, ease of installation, protection of the face and allowing rapid re-exposure. The experiment was halted by flooding within the quarry, following high rainfall. © 2012 The Geologists' Association.

Jenner F.E.,Carnegie Institution of Washington | Jenner F.E.,Australian National University | Bennett V.C.,Australian National University | Yaxley G.,Australian National University | And 2 more authors.
Geology | Year: 2013

The majority of >3 Ga metabasalts have chemical features, such as high field strength element (HFSE) depletions, that are characteristic of modern island-arc basalts. These compositions have been interpreted as evidence for subduction of oceanic crust early in Earth's history. Alternatively, the apparent absence of Archean mafic rocks with mid-oceanic ridge basalt (MORB) and ocean island basalt (OIB) compositions and the ubiquitous occurrence of metabasalts with HFSE anomalies suggest that these chemical features may instead be a widespread characteristic of the Archean mantle related to early chemical differentiation and unrelated to modern-style recycling of crust. Here we present major- and trace-element data for a suite of metabasalts from Innersuartuut Island, southwest Greenland, which have a minimum age constraint of 3.75 Ga and are likely as old as ≥3.85 Ga. Samples from Innersuartuut show no evidence for crustal contamination or subduction-related magmatism, and have a petrogenesis comparable to modern OIB. The new data demonstrate that a compositional range for volcanic rocks comparable to that seen in the Phanerozoic existed in the Eoarchean. Therefore, rather than a global anomaly, subduction-related processes are the likely origin for the compositions of the most commonly preserved Archean mafic rocks with island-arc basalt characteristics. © 2013 Geological Society of America.

Weinreb R.N.,University of California at San Diego | Ong T.,Bausch & Lomb | Sforzolini B.S.,Bausch & Lomb | Vittitow J.L.,Bausch & Lomb | And 24 more authors.
British Journal of Ophthalmology | Year: 2015

Aim To assess the efficacy and safety of latanoprostene bunod (LBN) compared with latanoprost 0.005%, and to determine the optimum drug concentration(s) of LBN in reducing intraocular pressure (IOP) in subjects with open angle glaucoma or ocular hypertension. Methods Randomised, investigator-masked, parallelgroup, dose-ranging study. Subjects instilled one drop of study medication in the study eye once daily each evening for 28 days and completed five study visits. The primary efficacy endpoint was the reduction in mean diurnal IOP at Day 28. Results Of the 413 subjects randomised (LBN 0.006%, n=82; LBN 0.012%, n=85; LBN 0.024%, n=83; LBN 0.040%, n=81; latanoprost, n=82), 396 subjects completed the study. Efficacy for LBN was dosedependent reaching a plateau at 0.024%-0.040%. LBN 0.024% led to significantly greater reductions in diurnal IOP compared with latanoprost at the primary endpoint, Day 28 (p=0.005), as well as Days 7 (p=0.033) and 14 (p=0.015). The incidence of adverse events, mostly mild and transient, was numerically higher in the LBN treatment groups compared with the latanoprost group. Hyperaemia was similar across treatments. Conclusions LBN 0.024% dosed once daily was the lower of the two most effective concentrations evaluated, with significantly greater IOP lowering and comparable side effects relative to latanoprost 0.005%. LBN dosed once daily for 28 days was well tolerated.

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