From unweathered core to regolith in a single weathering andesitic clast: Rates and trends of in situ chemical weathering on a tropical volcanic island (Basse Terre Island, French Guadeloupe)
From unweathered core to regolith in a single weathering andesitic clast: Rates and trends of in situ chemical weathering on a tropical volcanic island (Basse Terre Island, French Guadeloupe)
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从未风化的核心到单一风化安山岩碎屑中的风化层：热带火山岛（法属瓜德罗普岛巴斯特尔岛）原位化学风化的速率和趋势
DOI：
10.1016/j.chemgeo.2018.08.015
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发表时间：
2018
期刊：
影响因子：
3.9
通讯作者：
Daniel, Christopher
中科院分区：
文献类型：
--
作者：
Sak, Peter B.;Murphy, Mariah;Ma, Lin;Gaillardet, Jerome;Herndon, Elizabeth M.;Brantley, Susan L.;Daniel, Christopher
我们进行X射线微探针，化学和U-系列同位素分析定向风化碎屑从风化第四纪火山碎屑流的风化层收集在法国瓜德罗普。样品由未风化的玄武安山岩核心包围的风化外壳，和一个硬结外壳，从覆盖的土壤基质分离外壳。U/Th不平衡测年结果表明，壳层年龄从核-壳边界逐渐增大，最大值为66 ka。这意味着果皮前进速率约为0.2 mm kyr-1，与巴斯特尔岛其他地方计算的果皮前进速率大致一致。上覆硬化地壳是72 ka，表明可能的最小持续时间的外皮形成。元素的变化受到限制的散装化学分析沿着垂直断面从核心覆盖的土壤基质和平行的电子探针分析。核-壳界面上元素损失的等级顺序为Ca > Na> Mg > K > Mn > Si > Al > Ti = 0 > P > Fe，与斜长石-玻璃-辉石>磷灰石>钛铁矿碎屑中相的相对损失一致。在核-壳边界处的Ca、Na和孔隙度反应前沿的宽度小于900 μm，其突变长度约等于未风化岩心中观察到的斜长石斑晶的长度。在树皮-土壤界面处，反应前沿宽度小于1000 μm，以Fe、Mn富集的硬化层为标志，并向土壤基质中Mn、Ba、Al、Mg和K的富集过渡。与以前研究的碎屑，保留的外皮-土壤界面允许表征的风化反应和风化核心，外皮，和周围的土壤基质之间的物质交换，脱落的见解之间的通信包封风化外皮和主机风化层。缺乏一个富集信号的锰风化壳内表明，风化过程中活跃的碎屑是不同的周围土壤形成过程。
We conduct X-ray microprobe, chemical and U-series isotope analyses on an oriented weathering clast collected from the regolith of a weathered Quaternary volcanoclastic debris flow on Basse Terre Island, French Guadeloupe. The sample consists of an unweathered basaltic andesite core surrounded by a weathering rind, and an indurated crust that separates the rind from the overlying soil matrix. U/Th disequilibria dating indicates that rind age increases away from the core-rind boundary to a maximum of 66 ka. This translates to a rind-advance rate of ~0.2 mm kyr−1, broadly consistent with rind advance rates calculated elsewhere on Basse Terre Island. The overlying indurated crust is 72 ka, indicating a possible minimum duration of the rind formation. Elemental variations are constrained by a bulk chemical analysis along a vertical transects from the core to the overlying soil matrix and parallel electron microprobe analyses. The hierarchy of elemental loss across the core-rind boundary varies in the order Ca > Na ≈ Mg > K > Mn > Si > Al > Ti = 0 > P > Fe, consistent with the relative loss of phases in the clast from plagioclase ≈ glass ≈ pyroxene > apatite > ilmenite. The abrupt, <900 μm wide, Ca, Na and porosity reaction fronts at the core-rind boundary approximately equal the length of the long dimension of plagioclase phenocrysts observed in the unweathered core. The <1000 μm wide reaction front at the rind-soil interface is marked by an indurated horizon with Fe and Mn enrichment that spans into enrichment of Mn, Ba, Al, Mg and K in the soil matrix. Unlike previously studied clasts, the preservation of the rind-soil interface permits characterization of weathering reactions and material exchanges between the weathering core, the rind, and the surrounding soil matrix, shedding insights into communication between the enveloping weathering rind and host regolith. The lack of an enrichment signal of Mn within the weathered rind suggests that weathering processes active within clasts are distinct from surrounding soil formation processes.
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DOI：
10.1080/00040851.1981.12004224
发表时间：
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期刊：
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影响因子：
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