Re-Os Isotope and HSE Abundance Systematics of the 2.9 Ga Komatiites and Basalts from the Sumozero-Kenozero Greenstone Belt, SE Fennoscandian Shield: Implications for the Mixing Rates of the Mantle

IF 1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
Igor S. Puchtel
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引用次数: 2

Abstract

Rhenium-Os isotope and highly siderophile element (HSE, including Re, Os, Ir, Ru, Pt, and Pd) abundance systematics of Archean komatiites can be used to estimate the stirring rates of the mantle for the HSE and the timing of homogenization of late accreted materials within the mantle. In this study, we report Re-Os isotope and HSE abundance data for ~2.9 Ga komatiites and basalts from the Sumozero-Kenozero greenstone belt in the SE Fennoscandian Shield. The lavas are characterized by excellent preservation of the primary textural, chemical, and Re-Os isotope characteristics. The Re-Os isotopic data for spinifex-textured and cumulate komatiite and massive basalt samples from the lowermost sequences define a precise 10-point isochron (MSWD = 2.6) with an age of 2904 ± 18 Ma and an initial 187Os/188Os = 0.10758 ± 18 (γ187Os(2904) = +0.45 ± 0.17). This is the first direct age determination for the Sumozero-Kenozero lower komatiite-basalt sequences. Our modeling indicates that the mantle source of the komatiites and basalts evolved with a time-integrated 187Re/188Os = 0.418 ± 6. This ratio is well within the uncertainty of the bulk chondritic average 187Re/188Os = 0.410 ± 51 (2SD), also consistent with the chondritic evolution of the majority of komatiite mantle sources observed globally. The mantle source of the Sumozero-Kenozero komatiites has been calculated to contain the total HSE abundances of 58 ± 7% of those in the estimates for modern Bulk Silicate Earth (BSE). This estimate is in the middle of the range for other late Archean and Proterozoic komatiite systems. Using the estimated HSE abundances in the sources of komatiite systems as a function of their ages and ISOPLOT regression analysis, we calculated the average time in the past by which late accreted materials have been completely homogenized within the mantle to be 2.48 ± 0.23 Ga. These data require that the residence times of the late accreted planetesimals within the mantle, before complete homogenization, were on average 1.92 ± 0.23 Ga. This estimate represents a constraint on the average mixing rates of the mantle in terms of the HSE abundances in the Hadean and the Archean.

Abstract Image

Fennoscandian Shield东南sumo0 - kenozero绿岩带2.9 Ga科马提岩和玄武岩Re-Os同位素和HSE丰度系统:地幔混合速率的意义
太古宙科马长岩的铼-Os同位素和高亲铁元素(HSE,包括Re、Os、Ir、Ru、Pt和Pd)丰度系统可用于估算地幔对HSE的搅拌速率和地幔内晚期吸积物质的均匀化时间。本文报道了芬诺斯坎德地盾东南部sumo0 - kenozero绿岩带~2.9 Ga花岗岩和玄武岩的Re-Os同位素和HSE丰度数据。火山岩的主要特征是原始结构、化学和Re-Os同位素特征保存完好。从最下层的层序中得到的尖晶石纹理和堆积的科马铁矿和块状玄武岩样品的Re-Os同位素数据定义了一个精确的10点等时线(MSWD = 2.6),年龄为2904±18 Ma,初始187Os/188Os = 0.10758±18 (γ187Os(2904) = +0.45±0.17)。这是首次对sumo0 - kenozero下科马铁矿-玄武岩层序进行直接年龄测定。模拟结果表明,科马长岩和玄武岩的地幔源演化时间积分为187Re/188Os = 0.418±6。该比值完全符合总体球粒陨石平均值187Re/188Os = 0.410±51 (2SD)的不确定度,也与全球观测到的大多数科马地岩地幔源球粒陨石演化一致。经计算,sumo0 - kenozero科马岩源幔源中HSE总丰度为现代块状硅酸盐土(BSE)估算值的58±7%。对其他晚太古宙和元古宙的科马岩系的估算值处于中等范围。利用估算的科马地岩源中HSE丰度与年龄的函数关系和ISOPLOT回归分析,我们计算出过去晚期吸积物质在地幔内完全均匀化的平均时间为2.48±0.23 Ga。这些数据表明,在完全均匀化之前,晚期吸积星子在地幔内的停留时间平均为1.92±0.23 Ga。根据冥古宙和太古宙的HSE丰度,这一估计代表了对地幔平均混合率的限制。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Petrology
Petrology 地学-地球科学综合
CiteScore
2.40
自引率
20.00%
发文量
27
审稿时长
>12 weeks
期刊介绍: Petrology is a journal of magmatic, metamorphic, and experimental petrology, mineralogy, and geochemistry. The journal offers comprehensive information on all multidisciplinary aspects of theoretical, experimental, and applied petrology. By giving special consideration to studies on the petrography of different regions of the former Soviet Union, Petrology provides readers with a unique opportunity to refine their understanding of the geology of the vast territory of the Eurasian continent. The journal welcomes manuscripts from all countries in the English or Russian language.
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