闽西南宣和加里东期花岗岩锆石U-Pb年龄、地球化学特征及对华南造山的启示

龙岩宣和岩体是闽西南地区呈北东向弧形出露,最大的燕山期—加里东期复式岩体,但是有关该岩体的形成时代及成岩环境的认识仍存在分歧,进而制约了对闽西南地区构造环境的探讨.文章以出露于闽西南地区的宣和正长花岗岩为研究对象,在详细野外地质调查基础上,开展了岩石学、LA?ICP?MS锆石U?Pb地质年代学、岩石地球化学及Sr?Nd...     

Natural Titanite Reference Materials for In Situ U‐Pb and Sm‐Nd Isotopic Measurements by LA‐(MC)‐ICP‐MS

Titanite is a common accessory mineral that preferentially incorporates considerable amounts of U and light rare earth elements in its structure, making it a versatile mineral for in situ U‐Pb dating and Sm‐Nd isotopic measurement. Here, we present in situ U‐Pb ages and Sm‐Nd isotope measurement results for four well‐known titanite reference materials (Khan, BLR‐1, OLT1 and MKED1) and eight titanite crystals that could be considered potential reference material candidates (Ontario, YQ‐82, T3, T4, TLS‐36, NW‐IOA, Pakistan and C253), with ages ranging from ~ 20 Ma to ~ 1840 Ma. Results indicate that BLR‐1, OLT1, Ontario, MKED1 and T3 titanite have relatively homogeneous Sm‐Nd isotopes and low common Pb and thus can serve as primary reference materials for U‐Pb and Sm‐Nd microanalysis. YQ‐82 and T4 titanite can be used as secondary reference materials for in situ U‐Pb analysis because of their low common Pb. However, internal structures and mineral inclusions in YQ‐82 will require careful selection of suitable target domains. Pakistan titanite is almost concordant with an age of 21 Ma and can be used as a reference material when dating Cenozoic titanite samples.     

Rapid Determination of Trace Element Compositions in Peridotites by LA‐ICP‐MS Using an Albite Fusion Method

A rapid sample preparation procedure is described to determine trace element compositions of peridotites using LA‐ICP‐MS. Peridotite powders were fused with albite in a molybdenum–graphite assembly to obtain homogeneous glasses. Best conditions for the fusion procedure (heating at 1500–1550 °C for 10–15 min with a sample‐to‐flux ratio of 1:2) were constrained with melting experiments on two USGS reference materials, PCC‐1 and DTS‐2B. Mass fractions of first series transition elements, Ba and Pb, in quenched glasses of PCC‐1 and DTS‐2B are consistent with published data within 10% RSD. Three spinel peridotite xenoliths from eastern China were analysed following both our method and conventional solution ICP‐MS. Compared with solution ICP‐MS, the relative deviations of our method for most elements were within 10%, while for the REE, Ta, Pb, Th and U, the relative deviations were within 20%. In particular, volatile elements (e.g., Pb and Zn) are retained in the glass. Compared with conventional wet chemistry digestion, our method is faster. Additional advantages are complete sample fusion, especially useful for samples with acid‐resistant minerals (spinel and rutile), and long‐term conservation of glasses allowing unlimited repeated measurements with microbeam techniques. The same approach can be used for analyses of other mantle rocks, such as eclogites and pyroxenites.     

Assessment of Dissolution of Silicate Rock Reference Materials with Ammonium Bifluoride and Nitric Acid in a Microwave Oven

The complete dissolution of representative test portions of powdered rock samples for the determination of the mass fractions of trace elements by ICP‐MS relies either on aggressive and time‐consuming acid digestions or fusion/sintering with appropriate fluxes. Here, we evaluate a microwave oven dissolution method that employs a solution of NH₄HF₂ and HNO₃. The entire procedure occurs in a closed vessel system and takes up to 4 h. In hundreds of digestions, the precipitation of fluorides was never observed. Replicate decomposition of 100 mg of twenty‐one international reference materials (RMs) of igneous rocks, and also one of a shale presented mostly satisfactory recoveries of forty‐one trace elements. Important exceptions were Zr and Hf in G‐2 and GSP‐2 (mean recoveries of ca. 70%), although for four other felsic rock RMs, the digestion was complete. For ultramafic rock RMs, we present Cr results that indicate quantitative dissolution of Cr‐bearing phases. We discuss the findings and conclude that advances in sample preparation of geological materials for instrumental analysis would benefit from a better understanding of how specific characteristics, such as composition and crystallinity of certain minerals, may affect their reactivity.     

GHR1 Zircon – A New Eocene Natural Reference Material for Microbeam U‐Pb Geochronology and Hf Isotopic Analysis of Zircon

We present multitechnique U‐Pb geochronology and Hf isotopic data from zircon separated from rapakivi biotite granite within the Eocene Golden Horn batholith in Washington, USA. A weighted mean of twenty‐five Th‐corrected ²⁰⁶Pb/²³⁸U zircon dates produced at two independent laboratories using chemical abrasion‐isotope dilution‐thermal ionisation mass spectrometry (CA‐ID‐TIMS) is 48.106 ± 0.023 Ma (2s analytical including tracer uncertainties, MSWD = 1.53) and is our recommended date for GHR1 zircon. Microbeam ²⁰⁶Pb/²³⁸U dates from laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) and secondary ion mass spectrometry (SIMS) laboratories are reproducible and in agreement with the CA‐ID‐TIMS date to within < 1.5%. Solution multi‐collector ICP‐MS (MC‐ICP‐MS) measurements of Hf isotopes from chemically purified aliquots of GHR1 yield a mean ¹⁷⁶Hf/¹⁷⁷Hf of 0.283050 ± 17 (2s, n = 10), corresponding to a εHf₀ of +9.3. Hafnium isotopic measurements from two LA‐ICP‐MS laboratories are in agreement with the solution MC‐ICP‐MS value. The reproducibility of ²⁰⁶Pb/²³⁸U and ¹⁷⁶Hf/¹⁷⁷Hf ratios from GHR1 zircon across a variety of measurement techniques demonstrates their homogeneity in most grains. Additionally, the effectively limitless reserves of GHR1 material from an accessible exposure suggest that GHR1 can provide a useful reference material for U‐Pb geochronology of Cenozoic zircon and Hf isotopic measurements of zircon with radiogenic ¹⁷⁶Hf/¹⁷⁷Hf.     

Denudation history of the Kiso Range,central Japan,and its tectonic implications: Constraints from low‐temperature thermochronology

Fission‐track (FT) and (U–Th–Sm)/He (He) analyses are used to constrain the denudation pattern and history of the Kiso Range, a Japanese fault‐block mountain range which has been uplifted since ca 0.8 Ma. We obtained nine zircon FT ages ranging 59.3–42.1 Ma, 18 apatite FT ages ranging 81.9–2.3 Ma, and 13 apatite He ages ranging 36.7–2.2 Ma. The apatite FT and He ages are divided into an older group comparable to the zircon FT age range and a younger group of <18 Ma. The younger ages are interpreted as a reflection of uplift of the Kiso Range because they were obtained only to the east of the Seinaiji‐touge Fault, and the event age estimated from apatite FT data is consistent with the timing of the onset of the Kiso Range uplift. On the basis of the distribution of the younger ages, we propose westward tilting uplift of the Kiso Range between the boundary fault of the Inadani Fault Zone and Seinaiji‐touge Fault, which implies a model of bedrock uplift that is intermediate between two existing models: a pop‐up model in which the Kiso Range is squeezed upward between the two faults and a tilted uplift model which assumes that the Kiso Range is uplifted and tilted to the west by the Inadani Fault Zone. The original land surface before the onset of uplift/denudation of the Kiso Range is estimated to have been uplifted to an elevation of 2700–4900 m. We estimated denudation rates at 1.3–4.0 mm/y and maximum bedrock uplift rates at 3.4–6.1 mm/y since ca 0.8 Ma. The Seinaiji‐touge fault is interpreted as a back thrust of the west‐dipping Inadani Fault Zone. The older group of apatite FT and He ages is interpreted to reflect long‐term peneplanation with a probable denudation rate of <0.1 mm/y.     

Precise and Accurate Determination of Lu and Hf Contents,and Hf Isotopic Compositions in Chinese Rock Reference Materials by MC‐ICP‐MS

In this contribution, we report Hf isotopic data and Lu and Hf mass fractions for thirteen Chinese rock reference materials (GBW07 103–105, 109–113 and 121–125, that is GSR 1–3, 7–11 and 14–18, respectively) that span a broad compositional range. Powdered samples were spiked with a ¹⁷⁶Lu‐¹⁸⁰Hf enriched tracer and completely digested using conventional HF, HNO₃ and HClO₄ acid dissolution protocols. Fluoride salts were dissolved during a final H₃BO₃ digestion, and chemical purification was performed using a single Ln resin. All measurements were carried out on a MC‐ICP‐MS. This work provides the first comprehensive report of the Lu‐Hf isotopic composition of Chinese geochemical rock reference materials, and results indicate that they are of comparable quality to the well‐characterised and widely used USGS and GSJ rock reference materials.     

Happy Jack Uraninite: A New Reference Material for High Spatial Resolution Analysis of U‐Rich Matrices

There is currently a lack of well‐characterised matrix‐matched reference materials (RMs) for forensic analysis of U‐rich materials at high spatial resolution. This study reports a detailed characterisation of uraninite (nominally UO_2+x) from the Happy Jack Mine (UT, USA). The Happy Jack uraninite can be used as a RM for the determination of rare earth element (REE) mass fractions in nuclear materials, which provide critical information for source attribution purposes. This investigation includes powder X‐ray diffraction (pXRD) data, as well as major, minor and trace element abundances determined using a variety of micro‐analytical techniques. The chemical signature of the uraninite was investigated at the macro (cm)‐scale with micro‐X‐ray fluorescence (µXRF) mapping and at high spatial resolution (tens of micrometre scale) using electron probe microanalysis (EPMA) and laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) analyses. Based on EPMA results, the uraninite is characterised by homogeneous UO₂ and CaO contents of 91.57 ± 1.49% m/m (2s uncertainty) and 2.70 ± 0.38% m/m (2s), respectively. Therefore, CaO abundances were used as the internal standard when conducting LA‐ICP‐MS analyses. Overall, the major element and REE compositions are homogeneous at both the centimetre and micrometre scales, allowing this material to be used as a RM for high spatial resolution analysis of U‐rich samples.     

Ageing of Dissolved Halogenated Humic Substances and the Microbiological Influence on this Process

The distribution of halogens in various fractions of humic substances (HS), separated by their molecular weight, was found to be different for the different halogens. This was demonstrated for chlorine, bromine, and iodine in sewage and brown water samples by applying inductively coupled plasma mass spectrometry coupled with size‐exclusion chromatography. Quantification of the different fractions of iodinated humic substances was obtained by quadrupole mass spectrometry in connection with the isotope dilution technique using an ¹²⁹I‐enriched spike solution. Quantitative analysis was not possible for the corresponding chlorine and bromine species because of spectrometric interferences in the quadrupole instrument. The ageing of HS/halogen species was followed with respect to possible transformations of these species in a ground and sewage water sample up to eight weeks. Even if a distinct structural variation of the humic substance was observed with time by measuring the UV absorption, chlorine remained in the same molecular weight fraction and only a small change was found for the HS/bromine species after eight weeks. In contrast to these findings a substantial transformation of HS/iodine compounds took place, which demonstrated that the transfer probability of halogens from one to another HS fraction is increased with decreasing strength of the halogen bond to carbon. By comparing the results of an original sewage water sample with a filtered one and with another one which was enriched by microorganisms cultivated from the same original sample, a strong microbiological influence on the transformation of HS/iodine species was found. A quantitative balance of the corresponding HS/iodine fractions was calculated for an ageing period of eight weeks showing that iodine was preferably transferred to newly formed UV active HS substances of high molecular weight. In total, no iodine was released from the humic substances.     

Determination of Sm‐Nd Isotopic Compositions in Fifteen Geological Materials Using Laser Ablation MC‐ICP‐MS and Application to Monazite Geochronology of Metasedimentary Rock in the North China Craton

In this study, we report both ¹⁴³Nd/¹⁴⁴Nd and ¹⁴⁷Sm/¹⁴⁴Nd values in twelve minerals (apatite, titanite, monazite and eudialyte) based on analyses over 4 years using LA‐MC‐ICP‐MS. The positive correlation between the measured β_Sm and β_Nd (r² = 0.9981) over this time in our laboratory demonstrates the excellent long‐term stability of the method. Compared with the normal method, Sm and Nd signal intensities were improved by a factor of 2.9 with the use of X skimmer and Jet sample cones in combination with the addition of nitrogen at 3–6 ml min^?1 to the central gas flow. The enhancement of signal intensity benefits the accurate in situ determination of the Sm‐Nd isotopes of samples poor in these elements. ¹⁴³Nd/¹⁴⁴Nd values were also determined in two manganese nodules and GSMC Co‐rich crust with low mass fractions of Nd (94–293 μg g^?1). Generally, most of the obtained Sm‐Nd isotopic compositions in these geological materials are consistent with published values. ‘External reproducibility’ (2s) of ¹⁴³Nd/¹⁴⁴Nd and ¹⁴⁷Sm/¹⁴⁴Nd was typically better than 0.06‰ and 2.5‰, respectively, demonstrating that the Durango, Otter Lake, NW‐1 and MAD apatites, the Khan, and OLT‐1 titanites, MGMH#117531 monazite and LV01 eudialyte are promising candidate reference materials for in situ Sm‐Nd isotopic determinations. The Trebilcock, Mae Klang and 44069 monazites are only suitable for in situ Nd isotopic determinations because of their heterogeneous Sm/Nd compositions. The heterogeneous Sm‐Nd composition of titanite BLR‐1 demonstrates that it is not a suitable reference material for in situ Sm‐Nd isotopic determinations. Deep‐sea samples (NOD‐A‐1 and NOD‐P‐1 manganese nodule, GSMC Co‐rich crust) with low mass fractions of Nd also show homogenous Nd isotopic compositions. Sm‐Nd isotopic ratios of a monazite (MQG‐22) from the North China Craton were measured as a case study and gave a ¹⁴⁷Sm‐¹⁴³Nd isochron age of 1792 ± 35 Ma (MSWD = 3.2) consistent with the published metamorphic age of the host metasedimentary rocks. The results for both candidate reference materials and geological samples demonstrate that the in situ LA‐MC‐ICP‐MS analytical protocol described is feasible and robust for research in geological evolution.