Stephen R. Noble

Bio: Stephen R. Noble is an academic researcher from British Geological Survey. The author has contributed to research in topics: Zircon & Metamorphism. The author has an hindex of 34, co-authored 74 publications receiving 5206 citations. Previous affiliations of Stephen R. Noble include University of Nottingham & Natural Environment Research Council.

238U/235U Systematics in Terrestrial Uranium-Bearing Minerals

Abstract: The present-day 238U/235U ratio has fundamental implications for uranium-lead geochronology and cosmochronology. A value of 137.88 has previously been considered invariant and has been used without uncertainty to calculate terrestrial mineral ages. We report high-precision 238U/235U measurements for a suite of uranium-bearing minerals from 58 samples representing a diverse range of lithologies. This data set exhibits a range in 238U/235U values of >5 per mil, with no clear relation to any petrogenetic, secular, or regional trends. Variation between comagmatic minerals suggests that 238U/235U fractionation processes operate at magmatic temperatures. A mean 238U/235U value of 137.818 ± 0.045 (2σ) in zircon samples reflects the average uranium isotopic composition and variability of terrestrial zircon. This distribution is broadly representative of the average crustal and “bulk Earth” 238U/235U composition.

Hf-Nd Element and Isotope Perspective on the Nature and Provenance of Mantle and Subduction Components in Western Pacific Arc-Basin Systems

Abstract: This paper develops methods for using the integrated study of Hf-Nd element and isotope covariations to define the nature and provenance of the mantle and subduction inputs to subduction systems. In particular, it can be demonstrated that (1) Hf-Nd isotope space permits discrimination between mantle of Pacific and Indian provenance, (2) displacements from mantle arrays on Hf-Nd isotope and trace element projections can be related to the magnitude, source and composition of the subduction input, and (3) Hf-Nd isotope and trace element covariations can be used to interpret high field strength element (HFSE) anomalies [specifically, Hf anomalies on extended rare earth element (REE) patterns] in subduction-related magmas. These methods are tested using published volcanic arc data coupled with new data from the many components of the Izu-Bonin-Mariana (IBM) subduction system, namely the pre-subduction marginal basins, the Eocene to Recent volcanic arcs, and the crust, volcanogenic sediments and pelagic sediments of the subducting Pacific plate. The results of the IBM study show that the mantle that fed the IBM system was always of Indian provenance and that Pacific volcanogenic sediments make the most significant, though variable, contribution to the subduction component. Modelling demonstrates that the Nd/Hf ratio of the subduction component probably lay between 40 and infinity and thus was probably the main cause of the negative HFSE anomalies that characterize much of the Recent arc. This result may further indicate that the subducting sediment lost elements to the mantle wedge mostly by dehydration rather than fusion. In contrast, the data also show that the positive Hf anomalies that characterize much of the Protoarc cannot be attributed directly to subduction. One option consistent with Hf-Nd systematics is that the positive Hf anomalies in the Protoarc boninites were caused by fusion of mafic veins in their shallow mantle sources. Comparison with published data on other arcs shows significant inter-arc variations. For example, the subduction components in near-continent arcs (Banda, Lesser Antilles) appear to have lower Nd/Hf ratios more consistent with sediment fusion, and at least one arc (Tonga-Fiji) carries evidence of temporal variations in mantle provenance.

Common-Pb corrected in situ U–Pb accessory mineral geochronology by LA-MC-ICP-MS

Abstract: LA-MC-ICP-MS is shown to be a rapid, precise and accurate method for determination of U–Pb ages of accessory minerals. For the protocol described, total analysis time is <3 min with a main acquisition sequence of only 30 s. Using a raster ablation protocol, within-run inter-element fractionation can be effectively eliminated and an external ablation standard used to quantify an overall error for the analysis. Reproducibilities of 206Pb/238U = ca. 3% and 207Pb/206Pb = <1% (2 σ) are achieved, with the resulting age accurate to within 1% as determined using in-house samples previously characterised by TIMS. A key control on the Pb/Pb reproducibility is shown to be the size of the 207Pb peak and an error propagation curve is determined for the accurate representation of this data. Propagation of these errors allows each individual sample analysis to be considered a stand-alone result, removing the need for statistical averaging of multiple data points. Simultaneous collection of flat-topped peaks enables precise measurement and correction of isobaric interference from 204Hg and a procedure for the consistent correction of common-Pb using 204Pb is described. Determination and correction of the common-Pb component is shown to be critical to the reliable interpretation of the data for certain minerals including those phases where a correction is often deemed unnecessary. Combined with time-resolved analysis of the data, this allows the Pb-loss history and nature of discordance within individual crystal domains to be ascertained. Successful analyses of zircons using a non-matrix matched (monazite) standard are also demonstrated suggesting that particle size distribution, ionisation efficiency and plasma loading, are more important issues in controlling inter-element fractionation in the plasma than absolute matrix matching.

Tectonic evolution of the Mogok metamorphic belt, Burma (Myanmar) constrained by U-Th-Pb dating of metamorphic and magmatic rocks

Abstract: [1] The Mogok metamorphic belt (MMB) extends for over 1500 km along the western margin of the Shan-Thai block, from the Andaman Sea north to the eastern Himalayan syntaxis. Previous geochronology has suggested that a long-lasting Jurassic–early Cretaceous subduction-related event resulted in emplacement of granodiorites and orthogneisses (171–120 Ma) and a poorly constrained Tertiary metamorphic event. On the basis of new U-Pb isotope dilution thermal ionization mass spectrometry and U-Th-Pb laser ablation–multicollector–inductively coupled plasma mass spectrometer geochronology presented here, we propose two Tertiary metamorphic events affected the MMB in Burma. The first was a Paleocene event that ended with intrusion of crosscutting postkinematic biotite granite dikes at ∼59 Ma. A second metamorphic event spanned late Eocene to Oligocene (at least from 37, possibly 47, to 29 Ma). This resulted in the growth of metamorphic monazite at sillimanite grade, growth of zircon rims at 47–43 Ma, sillimanite + muscovite replacing older andalusite, and synmetamorphic melting producing garnet and tourmaline bearing leucogranites at 45.5 ± 0.6 Ma and 24.5 ± 0.7 Ma. These data imply high-temperature sillimanite + muscovite metamorphism peaking at 680°C and 4.9 kbar between 45 and 33 Ma, to around 606–656°C and 4.4–4.8 kbar at 29.3 ± 0.5 Ma. The later metamorphic event is older than 24.5 ± 0.3 Ma, the age of leucogranites that crosscut all earlier fabrics. Our structural and geochronological data suggest that the MMB links north to the unexposed middle or lower crust rocks of the Lhasa terrane, south Tibet, and east to high-grade metamorphic core complexes in northwest Thailand.

Three natural zircon standards for u‐th‐pb, lu‐hf, trace element and ree analyses

Abstract: We report here the results of a study to develop natural zircon geochemical standards for calibrating the U-(Th)-Pb geochronometer and Hf isotopic analyses. Additional data were also collected for the major, minor and trace element contents of the three selected sample sets. A total of five large zircon grains (masses between 0.5 and 238 g) were selected for this study, representing three different suites of zircons with ages of 1065 Ma, 2.5 Ma and 0.9 Ma. Geochemical laboratories can obtain these materials by contacting Geostandards Newsletter.

Geologic Evolution of the Himalayan-Tibetan Orogen

Abstract: A review of the geologic history of the Himalayan-Tibetan orogen suggests that at least 1400 km of north-south shortening has been absorbed by the orogen since the onset of the Indo-Asian collision at about 70 Ma. Significant crustal shortening, which leads to eventual construction of the Cenozoic Tibetan plateau, began more or less synchronously in the Eocene (50–40 Ma) in the Tethyan Himalaya in the south, and in the Kunlun Shan and the Qilian Shan some 1000–1400 km in the north. The Paleozoic and Mesozoic tectonic histories in the Himalayan-Tibetan orogen exerted a strong control over the Cenozoic strain history and strain distribution. The presence of widespread Triassic flysch complex in the Songpan-Ganzi-Hoh Xil and the Qiangtang terranes can be spatially correlated with Cenozoic volcanism and thrusting in central Tibet. The marked difference in seismic properties of the crust and the upper mantle between southern and central Tibet is a manifestation of both Mesozoic and Cenozoic tectonics. The form...