In situ cosmogenic 10Be and 21Ne in sanidine and in situ cosmogenic 3He in Fe–Ti-oxide minerals
In situ cosmogenic 10Be and 21Ne in sanidine and in situ cosmogenic 3He in Fe–Ti-oxide minerals
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原位宇宙成因 10Be 和 21Ne 在铁钛氧化物矿物中原位宇宙成因 3He
DOI：
10.1016/j.epsl.2005.05.020
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发表时间：
2005
影响因子：
5.3
通讯作者：
P. Kubik
中科院分区：
文献类型：
--
作者：
F. Kober;S. Ivy‐Ochs;I. Leya;H. Baur;T. Magna;R. Wieler;P. Kubik
我们报告的浓度在现场宇宙成因的10 Be和21 Ne从共存的石英和透长石分离和宇宙成因的3 He共存的Fe-Ti-氧化物矿物从熔结凝灰岩继承的北方智利（Oxaya和Lauca熔结凝灰岩）。新的矿物-同位素对，如透长石和铁-钛-氧化物矿物，有助于定量地貌学的地质环境中的岩性缺乏常用的矿物石英，辉石或橄榄石。透长石和铁钛氧化物矿物的生产率是通过将核素浓度归一化到石英中的既定生产率来确定的。实验确定的生产率进行比较，模型生产率计算与新的横截面为3 He，21 Ne，和10 Be生产的个别目标元素。五个透长石样品的平均实验21 Ne产生率为30.4±3.7 atoms g− 1 yr −1（30.4±5.4 atoms g− 1 yr − 1，包括石英中21 Ne产生率的不确定性，P21 Neqtz）。这与28.3原子g− 1 yr −1的模型值非常一致，估计不确定性为20%。透长石中21 Ne的产生率比石英中高50%左右。透长石中的宇宙成因氖在低温步骤（400-600 °C）中完全释放，并且没有观察到干扰核成因氖组分的迹象。这与石英形成鲜明对比，使透长石成为陆地宇宙成因氖研究的一种有吸引力的矿物。初步结果还表明透长石非常适合于10 Be的研究。两个透长石样品的平均实验10 Be产生率为4.45±0.38原子g− 1 yr −1（4.45±0.42原子g− 1 yr − 1，包括P10 Beqtz的不确定性），非常接近模型值4.55原子g− 1 yr −1，估计不确定性为20%。我们强调透长石中~（10）Be和~（21）Ne的产生是成分依赖性的。因此，应进行主要元素分析，并逐个样本计算生产率。铁钛氧化物矿物对~ 3 He有定量的保留。实验得出的生产率与物理模型得出的新值非常一致。五个铁钛氧化物矿物样品的平均实验3 He产生率为120±11原子g− 1 yr −1（120±12原子g− 1 yr − 1，包括P21 Neqtz的不确定性），而平均模型值为124原子g− 1 yr −1，估计不确定性为20%。Fe-Ti-氧化物矿物固溶体线的化学和结构组成的变化对总的3 He产率几乎没有影响。宇宙成因的21 Ne在铁钛氧化物矿物中没有大量产生，因为没有合适的目标元素。
We report concentrations of in situ cosmogenic10Be and21Ne from coexisting quartz and sanidine separates and of cosmogenic3He in coexisting Fe–Ti-oxide minerals from ignimbritic successions of northern Chile (Oxaya and Lauca ignimbrites). New mineral-isotope pairs such as sanidine and Fe–Ti-oxide minerals are helpful in quantitative geomorphology for geological settings where the lithology lacks the commonly used minerals quartz, pyroxene or olivine. Production rates in sanidine and Fe–Ti-oxide minerals were determined by normalizing nuclide concentrations to established production rates in quartz. The experimentally determined production rates are compared to model production rates calculated with new cross-sections for3He,21Ne, and10Be production from the individual target elements. The mean experimental21Ne production rate for five sanidine samples is 30.4±3.7 atoms g−1yr−1(30.4±5.4 atoms g−1yr−1including the uncertainty of the21Ne production rate in quartz, P21Neqtz). This is in excellent agreement with the modelled value of 28.3 atoms g−1yr−1, which has an estimated uncertainty of 20%. The21Ne production rate in sanidine is thus about 50% higher than that in quartz. The cosmogenic neon in sanidine is entirely released in low temperature steps (400–600 °C) and no signs of an interfering nucleogenic neon component were observed. This is in stark contrast to quartz and makes sanidine an attractive mineral for terrestrial cosmogenic neon studies.3He diffuses out of the sanidine structure. Preliminary results also indicate that sanidine is well suited for10Be studies. The mean experimental10Be production rate from two sanidine samples is 4.45±0.38 atoms g−1yr−1(4.45±0.42 atoms g−1yr−1including uncertainty of P10Beqtz), very close to the modelled value of 4.55 atoms g−1yr−1, which has an estimated uncertainty of 20%. We emphasize that10Be and21Ne production in sanidine is composition dependent. Therefore, major element analyses should be carried out and production rates calculated on a sample by sample basis. Fe–Ti-oxide minerals retain3He quantitatively. Experimentally derived production rates are in excellent agreement with new values derived from physical modelling. The mean experimental3He production rate for five Fe–Ti-oxide minerals samples is 120±11 atoms g−1yr−1(120±12 atoms g−1yr−1including the uncertainties of P21Neqtz), compared to a mean modelled value of 124 atoms g−1yr−1, which has an estimated uncertainty of 20%. The variable chemical and structural composition of the solid solution lines of Fe–Ti-oxide minerals has little effect on the total3He production rate. Cosmogenic21Ne is not produced in significant quantities in Fe–Ti-oxide minerals due to the absence of suitable target elements.