Apatites for destruction: Reference apatites from Morocco and Brazil for U-Pb petrochronology and Nd and Sr isotope geochemistry
Apatites for destruction: Reference apatites from Morocco and Brazil for U-Pb petrochronology and Nd and Sr isotope geochemistry
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DOI：
10.1016/j.chemgeo.2021.120689
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发表时间：
2022-02-20
期刊：
影响因子：
3.9
通讯作者：
Seward, Gareth G. E.
中科院分区：
文献类型：
--
作者：
Apen, Francisco E.;Wall, Corey J.;Seward, Gareth G. E.
原位磷灰石U-Pb岩石年代学和Sr-Nd同位素地球化学需要良好表征和基质匹配的参考材料（RM），但目前只有少数合适的磷灰石RM可用。为了改善这一问题，我们确定了U-Pb，Sm-Nd，Sr同位素和元素组成的一套前瞻性磷灰石RM使用同位素稀释（ID）TIMS和激光消融（LA）ICP-MS。这两个RM，从摩洛哥（MRC-1）和巴西（BRZ-1），厘米大小，可在显着的数量。MRC-1等时线年龄为153.3 ± 0.2 Ma。这一年龄与激光消融分流ICP-MS（LASS）分析结果一致，该分析得出的等时线年龄为152.7 +/- 0.6 Ma。Nd-143/Nd-144分析的ID-TIMS分析的加权平均值为0.512677 +/- 3，Sm-147/Nd-144为0.10923 +/- 9，Sr-87/Sr-86为0.707691 +/- 2。TIMS Sm-Nd同位素数据的范围和平均值是可重复的LA-ICP-MS，但激光烧蚀Sr数据始终偏移向更多的放射性值。对于BRZ-1磷灰石，ID-TIMS U-Pb分析是分散的，但数据的一个子集产生了一致的年龄截距为2078 +/- 13 Ma。绝大多数LASS点断面横跨磷灰石产生的等时线，定义一个年轻的年龄为2038 +/- 14马。我们将其解释为BRZ-1中隐藏的、较年轻的改变结构域的掺入。不一致的U-Pb斑点分析与化学上不同的裂缝有关，可能是流体渗透的结果。BRZ-1的ID-TIMS分析的加权平均值产生Nd-143/Nd-144 = 0.510989 +/- 5、Sm-147/Nd-144 = 0.10152 +/- 8和Sr-87/Sr-86 = 0.709188 +/- 3。用LA-MC-ICP-MS方法测定的Nd同位素组成分布与TIMS分析结果基本一致。相比之下，Sr-87/Sr-86测量LA-ICP-MS是不准确的，并表现出很大的不确定性，但这个RM可以是有用的经验校正原位Sr-87/Sr-86测量。结果表明，MRC-1型磷灰石可能是U-Pb、Sm-Nd和SrRM，而BRZ-1型磷灰石最有可能是Sm-Nd RM。这些潜在的RM为原位磷灰石化学分析和实验室间校准提供了新的基准。
In situ apatite U-Pb petrochronology and Sr-Nd isotope geochemistry requires well-characterized and matrix-matched references materials (RMs), yet only a few suitable apatite RMs are currently available. To ameliorate this issue, we determined the U-Pb, Sm-Nd, and Sr isotopic and elemental compositions of a suite of prospective apatite RMs using isotope dilution (ID) TIMS and laser ablation (LA) ICP-MS. The two RMs, from Morocco (MRC-1) and Brazil (BRZ-1), are cm-sized and available in significant quantities. The U-Pb ID-TIMS data yield an isochron age of 153.3 +/- 0.2 Ma for MRC-1. This age is consistent with laser ablation split stream ICP-MS (LASS) analyses that produce an isochron age of 152.7 +/- 0.6 Ma. The weighted mean of ID-TIMS analyses for Nd-143/Nd-144 analyses is 0.512677 +/- 3, for Sm-147/Nd-144 is 0.10923 +/- 9, and for Sr-87/Sr-86 is 0.707691 +/- 2. The range and mean of TIMS Sm-Nd isotopic data are reproducible by LA-ICP-MS, but laser ablation Sr data are consistently offset towards more radiogenic values. For BRZ-1 apatite, ID-TIMS U-Pb analyses are dispersed, but a subset of the data yields a coherent age intercept of 2078 +/- 13 Ma. The vast majority of LASS spot transects across the apatite produce an isochron that define a younger age of 2038 +/- 14 Ma. We interpret this as incorporation of cryptic, younger altered domains within BRZ-1. Discordant U-Pb spot analyses are associated with chemically distinct cracks, likely a result of fluid infiltration. The weighted means of ID-TIMS analyses of BRZ-1 yield Nd-143/Nd-144 = 0.510989 +/- 5, Sm-147/Nd-144 = 0.10152 +/- 8, and Sr-87/Sr-86 = 0.709188 +/- 3. The distribution of Nd isotopic compositions of this RM measured by LA-MC-ICP-MS analyses are comparable to TIMS analyses. By contrast, Sr-87/Sr-86 measurements by LA-ICP-MS are inaccurate and exhibit large uncertainties, but this RM can be useful for empirically correcting in situ Sr-87/Sr-86 measurements. The data indicate that MRC-1 apatite may serve well as a U-Pb, Sm-Nd, and Sr RM, whereas BRZ-1 apatite has the most potential as a Sm-Nd RM. These potential RMs provide new benchmarks for in situ apatite chemical analyses and inter-laboratory calibrations.