Improved Inter-calibration of Faraday Cup and Ion Counting forIn SituPb Isotope Measurements Using LA-MC-ICP-MS: Application to the Study of the Origin of the Fangshan Pluton, North China

摘要: A laser ablation multi-collector inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) method was developed to obtain precise and accurate Pb isotopic ratio measurements in low-Pb materials (< 10 μg g−1) using a combination of Faraday cups ion counters (FC–IC). The low abundance 204Pb (~ 1.4%) collected an IC. NBS 981 standard solution used cross-calculate the FC–IC gain investigate signal response characteristics significant, continuous linear decrease observed within 1 hr, but this drift could be corrected calibrator-sample-calibrator bracketing method. In addition, non-linear IC study by correction algorithm, which established measuring series gravimetrically prepared solutions (NIST SRM 981). Compared with conventional arrangement, use newly designed X skimmer cone Jet sample improved intensities from isotopes factor 1.9. only cups, array found enhance measurement repeatability (RSD) 20xPb/204Pb approximately one order magnitude when intensity < 8 mV. Eight natural glasses NIST 612 reference material glass (as calibration material) were measured evaluate new protocol for isotope determination. analytical results agreement values 2s uncertainties. For MPI-DING ATHO-G (5.67 μg g−1 total Pb), KL2-G (2.07 μg g−1 Pb) ML3B-G (1.38 μg g−1 typical accuracies 0.09% preferred precisions < 0.33% (2RSD). ratios feldspars granodiorite mafic microgranular enclaves (MMEs) Fangshan pluton, North China, present compositions whole host show that are radiogenic margin zone gradually become less radiogenic. MMEs, highly variable overlap those granodiorite. single-grain feldspar, strong rim-core-rim variations trace elements interpreted have been generated via magma mixing. These suggest pluton underwent mixing mantle-derived magmas felsic magmas, proportion influx decreased over time. Une methode par couplee un spectrometre de masse source plasma et multi-collection ete developpe pour obtenir des rapports isotopiques du precis exacts dans les materiaux faible teneur en (<10 μg g−1) utilisant une combinaison cages compteurs d'ions. L'isotope abondance (~ 1,4%) recueilli compteur Une utilisee le calcul croise cage Faraday/compteur d'ions (FC-IC) etudier la reponse caracteristique diminution significative, continue lineaire FC-IC observee moins d'une heure, mais cette derive peut etre corrigee l'encadrement l’echantillon standards. En outre, non-lineaire utilise etude algorithme non-lineaire, qui etablie mesurant serie etalons preparee gravimetrie Par rapport disposition classique, l'utilisation nouvelle configuration avec cone « skimmer X » « Jet sample » ameliore intensites signaux provenant facteur 1,9. Comparativement seule, il est montre que repetabilite mesure d'environ ordre grandeur lorsque l'intensite < 8 mV. Huit verres naturels ainsi verre (comme materiau d’etalonnage) ont mesures evaluer nouveau protocole determination isotopique Pb. Les resultats analytiques sont accord valeurs tenant compte incertitudes (2s). Pour (5,67 μg g−1 total), (2,07 μg g−1 total) (1,38 μg g−1 exactitudes typiques etaient 0,09% preferees 0,33% feldspaths au sein mafiques microgranulaires Fangshan, Chine Nord, presentee ici. plomb hote montrent qu'ils radiogeniques bordure progressivement ils deviennent radiogeniques. tres variables se recoupent celles hote. seul grain feldspath, fortes bordure-cœur-bordure traces interpretees comme resultant d'un melange magmas. Ces suggerent subi processus entre derives manteau felsiques, diminue fil temps.