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The role of vegetation in setting strontium stable isotope ratios in the Critical Zone 植被在确定临界区锶稳定同位素比率中的作用
IF 2.9 3区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2021-10-01 DOI: 10.2475/08.2021.04
J. Bouchez, F. von Blanckenburg
At Earth's surface the stable isotope ratio of strontium (88Sr/86Sr) is predominantly set by biological uptake of Sr and its storage in plant litter. This conclusion was reached from a stable isotope mass balance that was independently validated by direct determination of elemental fluxes between the Critical Zone compartments (rock, soil, vegetation, and stream water) of three field sites located in the Swiss Alps, the US Sierra Nevada, and the tropical highlands of Sri Lanka. These sites cover a gradient in erosion rates, which is inversely related to the residence time of solids in the Critical Zone thereby constituting an “erodosequence”. For eroding landscapes, previous stable isotope models predicted that isotope ratios are set by the rate at which secondary solids form during the conversion of rock to regolith. Counter to this expectation we found that, after release from primary minerals, Sr is partitioned into one fraction taken up by plants and the remainder into dissolved Sr flux. The formation of secondary weathering products such as clays and oxides plays a subordinate role in determining the Sr budget. A Sr isotope fractionation factor for biological uptake was determined for each of the three ecosystems from the average Sr stable isotope composition in bulk plants and its dissolved counterpart in stream water. This fractionation factors range from ca. −0.3 ‰ for the Alps and Sierra Nevada to ∼0 ‰ for the tropical Sri Lanka site. That these isotope fingerprints caused by biologic uptake are preserved means that more Sr was physically removed in plant litter than recycled. Such Sr removal in plant litter appears to be strongest at the slowly-eroding site, whereas the dissolved Sr export by streams is highest at the site with the fastest erosion rate. There, all Sr taken up by plants is returned from litter back into solution. The site with short residence time of solids is the only one at which parent material and dissolved export differ in their Sr isotope composition. Our study shows that the behavior of Sr in the Critical Zone is in stark contrast to that of metals of which the isotope fractionation is not affected by biological uptake (for example lithium, mostly set by formation of secondary solids) or affected by both secondary solid formation and biological uptake (for example silicon). Strontium stable isotope signatures offer the new opportunity to quantify nutrient cycling in the Critical Zone as a function of environmental and ecological parameters.
在地球表面,锶的稳定同位素比率(88Sr/86Sr)主要由锶的生物吸收及其在植物垃圾中的储存决定。这一结论是根据稳定的同位素质量平衡得出的,该平衡通过直接测定瑞士阿尔卑斯山、美国内华达山脉和斯里兰卡热带高地三个现场的临界区隔间(岩石、土壤、植被和溪水)之间的元素通量而得到独立验证。这些地点的侵蚀率呈梯度,与固体在临界区的停留时间呈反比,从而构成“侵蚀序列”。对于侵蚀景观,以前的稳定同位素模型预测,同位素比率是由岩石转化为风化层期间次生固体形成的速率决定的。与这一预期相反,我们发现,在从原生矿物中释放后,Sr被分配为一部分,被植物吸收,其余部分被分解为溶解的Sr通量。次生风化产物(如粘土和氧化物)的形成在决定Sr预算方面起着次要作用。根据散装植物中Sr稳定同位素的平均组成及其在溪流中的溶解同位素,确定了三个生态系统中每一个生态系统的生物吸收Sr同位素分馏因子。这种分馏因子的范围从阿尔卑斯山和内华达山脉的约-0.3‰到热带斯里兰卡的约0‰。这些由生物吸收引起的同位素指纹被保存下来,这意味着植物垃圾中物理去除的Sr比回收的Sr更多。植物垃圾中的这种Sr去除似乎在缓慢侵蚀的地点最强,而溪流中溶解的Sr出口在侵蚀速度最快的地点最高。在那里,植物吸收的所有Sr都从垃圾中返回到溶液中。固体停留时间短的地点是母体物质和溶解出口Sr同位素组成不同的唯一地点。我们的研究表明,Sr在临界区的行为与同位素分馏不受生物吸收影响(例如锂,主要由次生固体的形成决定)或不受次生固体形成和生物吸收影响的金属(例如硅)形成鲜明对比。锶稳定同位素特征为量化作为环境和生态参数函数的临界区营养循环提供了新的机会。
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引用次数: 7
Rock weathering and nutrient cycling along an erodosequence 沿侵蚀层序的岩石风化和营养循环
IF 2.9 3区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2021-10-01 DOI: 10.2475/08.2021.01
F. von Blanckenburg, J. Schuessler, J. Bouchez, P. Frings, D. Uhlig, M. Oelze, D. Frick, T. Hewawasam, Jean L. Dixon, K. Norton
How flowing water and organisms can shape Earth's surface, the Critical Zone, depends on how fast this layer is turned over by erosion. To quantify the dependence of rock weathering and the cycling of elements through ecosystems on erosion we have used existing and new metrics that quantify the partitioning and cycling of elements between rock, saprolite, soil, plants, and river dissolved and solid loads. We demonstrate their utility at three sites along a global transect of mountain landscapes that differ in erosion rates – an “erodosequence”. These sites are the Swiss Central Alps, a rapidly-eroding, post-glacial mountain belt; the Southern Sierra Nevada, USA, eroding at moderate rates; and the slowly-eroding tropical Highlands of Sri Lanka. The backbone of this analysis is an extensive data set of rock, saprolite, soil, water, and plant geochemical and isotopic data. This set of material properties is converted into process rates by using regolith production and weathering rates from cosmogenic nuclides and river loads, and estimates of biomass growth. Combined, these metrics allow us to derive elemental fluxes through regolith and vegetation. The main findings are: 1) the rates of weathering are set locally in regolith, and not by the rate at which entire landscapes erode; 2) the degree of weathering is mainly controlled by regolith residence time. This results in supply-limited weathering in Sri Lanka where weathering runs to completion in the regolith, and kinetically-limited weathering in the Alps and Sierra Nevada where soluble primary minerals persist; 3) these weathering characteristics are reflected in the sites' ecosystem processes, namely in that nutritive elements are intensely recycled in the supply-limited setting, and directly taken up from soil and rock in the kinetically settings; 4) the weathering rates are not controlled by biomass growth; 5) at all sites we find a deficit in river solute export when compared to solute production in regolith, the extent of which differs between elements. Plant uptake followed by litter export might explain this deficit for biologically utilized elements of high solubility, and rare, high-discharge flushing events for colloidal-bound elements of low solubility. Our data and new metrics have begun to serve for calibrating metal isotope systems in the weathering zone, the isotope ratios of which depend on the flux partitioning between the compartments of the Critical Zone. We demonstrate this application in several isotope geochemical companion papers.
流动的水和生物如何塑造地球表面,即关键地带,取决于这一层因侵蚀而翻转的速度。为了量化岩石风化和生态系统中元素循环对侵蚀的依赖,我们使用了现有的和新的指标来量化岩石、腐生岩、土壤、植物、河流溶解和固体负荷之间元素的分配和循环。我们在全球山脉景观样带的三个地点展示了它们的效用,这些地点的侵蚀速率不同-一个“侵蚀序列”。这些地点是瑞士中部阿尔卑斯山脉,一个快速侵蚀的后冰川山脉带;南内华达山脉,美国,以中等速度侵蚀;以及斯里兰卡缓慢侵蚀的热带高地。这种分析的主干是一个广泛的数据集,包括岩石、腐岩、土壤、水和植物的地球化学和同位素数据。这组材料特性通过使用宇宙核素和河流负荷产生的风化速率和风化速率,以及生物量增长的估计,转化为过程速率。这些指标结合起来,使我们能够推导出通过风化层和植被的元素通量。主要发现有:1)风化速率是由局部风化层决定的,而不是由整个景观的侵蚀速率决定的;2)风化程度主要受风化层停留时间控制。这导致了斯里兰卡的供应有限的风化作用,那里的风化作用在风化层中完成,而阿尔卑斯山和内华达山脉的动力有限的风化作用,那里的可溶性原生矿物持续存在;3)这些风化特征反映在遗址区生态系统过程中,即在供应受限的环境中,营养元素被强烈地循环利用,在动力环境中,营养元素直接从土壤和岩石中吸收;4)风化速率不受生物量增长的控制;5)在所有地点,我们都发现河流溶质输出与风化层溶质产生相比存在缺陷,其程度因元素而异。植物吸收之后的凋落物输出可能解释了高溶解度的生物利用元素的不足,以及低溶解度的胶体结合元素罕见的高流量冲洗事件。我们的数据和新指标已经开始用于校准风化带的金属同位素系统,其同位素比率取决于临界带各隔室之间的通量分配。我们在几篇同位素地球化学论文中论证了这一应用。
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引用次数: 10
Interpreting silicon isotopes in the Critical Zone 临界区硅同位素的解释
IF 2.9 3区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2021-10-01 DOI: 10.2475/08.2021.02
P. Frings, M. Oelze, Franziska Schubring, D. Frick, F. von Blanckenburg
Metal and metalloid stable isotope ratios have emerged as potentially powerful proxies for weathering, element cycling and export in the Critical Zone. The simplest possible interpretative framework for these isotope ratios has three parameters: (i) the isotope ratio of the parent minerals undergoing weathering, (ii) the partitioning of the element between solute and the new secondary phases, and (iii) the fractionation factors associated with the formation of new secondary phases. Using the example of silicon, we show how all three of these parameters vary along a gradient of erosion rate and regolith residence time defined by three sites located on granitoid bedrock. These sites run from the kinetically limited Rhone Valley in the Central Swiss Alps to the tectonically inactive and supply-limited Sri Lankan highlands, with the Sierra Nevada mountains as a site of intermediate weathering intensity. At each site, primary mineral specific 30Si/28Si ratios span >0.4‰. These minerals weather differentially, such that the isotope ratio of silicon solubilised from rock differs at the three sites and is not necessarily equal to bulk bedrock composition. The partitioning of silicon between secondary clay and solute is reflected in the clay mineralogy and chemical composition: more intense weathering produces Si-poor clays. The clay composition thus comprises a first-order mass-balance control on the extent to which any fractionation factor can be expressed. Finally, the Si isotope fractionation factor associated with clay formation varies systematically with clay mineralogy: the formation of Si-deplete clay minerals is associated with larger fractionation factors. The magnitude of the fractionation may be mechanistically linked to relative aluminium availability. These findings provide the framework needed to use Si isotope ratios as a quantitative proxy to explore Si cycling and reconstruct weathering in the present and past.
金属和准金属稳定同位素比率已成为临界区风化、元素循环和输出的潜在有力指标。这些同位素比率的最简单的解释框架有三个参数:(i)经历风化的母体矿物的同位素比率,(ii)溶质和新次生相之间的元素分配,以及(iii)与新次生相形成相关的分馏因素。以硅为例,我们展示了这三个参数是如何沿着花岗岩类基岩上三个地点定义的侵蚀率和风化层停留时间的梯度变化的。这些地点从瑞士阿尔卑斯山脉中部动力学有限的罗纳河谷到构造不活跃且供应有限的斯里兰卡高地,内华达山脉是中等风化强度的地点。在每个地点,初级矿物比30Si/28Si的比值跨度>0.4‰。这些矿物的天气不同,因此从岩石中溶解的硅的同位素比值在三个地点不同,不一定等于整体基岩成分。硅在次生粘土和溶质之间的分配反映在粘土的矿物学和化学成分中:更强烈的风化产生贫硅粘土。因此,粘土组合物包括对任何分馏因子可以表达的程度的一阶质量平衡控制。最后,与粘土形成相关的硅同位素分馏因子随粘土矿物学系统地变化:硅贫化粘土矿物的形成与较大的分馏因子有关。分馏的程度可能与铝的相对可用性在机制上有关。这些发现提供了使用硅同位素比率作为定量指标来探索硅循环和重建现在和过去风化所需的框架。
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引用次数: 7
Quantifying biotic and abiotic Si fluxes in the Critical Zone with Ge/Si ratios along a gradient of erosion rates 利用Ge/Si比值沿侵蚀速率梯度量化临界带的生物和非生物硅通量
IF 2.9 3区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2021-10-01 DOI: 10.2475/08.2021.03
Patrick J. Frings,Franziska Schubring,Marcus Oelze,Friedhelm von Blanckenburg
Silicon (Si) is an important nutrient for many plant and algae species, and the ultimate source of Si is silicate mineral weathering reactions. These topics have inspired the application of Si isotope geochemistry to quantifying Si cycling in the Critical Zone, though the interpretations are often equivocal. Because germanium (Ge) geochemistry is similar to that of Si, the Ge/Si ratio is considered a tracer that provides additional constraints on Si cycling. Here, we provide Ge/Si ratios for three sites that span a gradient of erosion rates and thus time that material spends in the weathering zone before being removed. We present Ge/Si ratios in bulk rock, soil and saprolite, clay-size fractions, plant biomass, and river water from the Central Swiss Alps, the southern Californian Sierra Nevada, and the highlands of Sri Lanka. Our data perform two functions. First, they provide insight into the Ge/Si system. In particular, we document the presence of a substantial pool of Ge in plant biomass that is not associated with phytoliths, suggesting that overall plants do not discriminate against Ge relative to Si during uptake. We also quantify the preferential incorporation of Ge into clay minerals. We show that Ge/Si ratios in secondary clays may be a better proxy for weathering intensity (the fraction of denudation achieved chemically) than the Ge/Si ratio of river solutes. Ge/Si ratios in secondary clay minerals also perform as well as or even better than silicon isotopes as weathering intensity proxies. Second, the Ge/Si data are used in conjunction with silicon isotope data to develop a catchment Si mass-balance model. It suggests that the export of secondary, fractionated solids (largely clays and plant material) becomes increasingly important at shorter regolith residence times: 80−24+15% of total solubilized Si in the rapidly eroding Alps site, vs. 32−20+22% in the slowly eroding Sri Lanka site. The results also suggest that plant material is a surprisingly large contributor to Si export from these catchments, likely equivalent to 25 to110 % of dissolved Si export.
硅(Si)是许多植物和藻类的重要营养物质,硅的最终来源是硅酸盐矿物的风化反应。这些问题启发了硅同位素地球化学在定量临界带硅循环中的应用,尽管解释往往模棱两可。由于锗(Ge)的地球化学与硅相似,Ge/Si比值被认为是一种示踪剂,为硅循环提供了额外的约束。在这里,我们提供了三个地点的Ge/Si比值,这些地点跨越了侵蚀速率梯度,因此材料在风化带中花费的时间在被移除之前。我们展示了来自瑞士中部阿尔卑斯山脉、南加州内华达山脉和斯里兰卡高地的大块岩石、土壤和腐岩、粘土大小的组分、植物生物量和河水中的Ge/Si比值。我们的数据执行两个功能。首先,它们提供了对Ge/Si系统的洞察。特别是,我们记录了植物生物量中存在大量与植物岩无关的Ge,这表明总体而言,植物在吸收过程中不会歧视Ge而不是Si。我们还量化了Ge在粘土矿物中的优先掺入。研究表明,次生粘土的Ge/Si比值可能比河流溶质的Ge/Si比值更能代表风化强度(化学剥蚀的比例)。次生粘土矿物的Ge/Si比值作为风化强度指标的表现也与硅同位素相当,甚至优于硅同位素。其次,将Ge/Si数据与硅同位素数据结合使用,建立流域Si质量平衡模型。这表明,在较短的风化层停留时间内,次级分选固体(主要是粘土和植物物质)的输出变得越来越重要:在快速侵蚀的阿尔卑斯遗址,总溶解Si的80−24+15%,而在缓慢侵蚀的斯里兰卡遗址,这一比例为32−20+22%。结果还表明,植物材料是这些流域硅出口的一个惊人的大贡献者,可能相当于溶解硅出口的25%至110%。
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引用次数: 0
Exploring multiple steady states in Earth's long-term carbon cycle 探索地球长期碳循环的多种稳定状态
IF 2.9 3区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2021-09-01 DOI: 10.2475/07.2021.01
Benjamin J. W. Mills, S. Tennenbaum, D. Schwartzman
The long-term carbon cycle regulates Earth's climate and atmospheric CO2 levels over multimillion-year timescales, but it is not clear that this system has a single steady state for a given input rate of CO2. In this paper we explore the possibility for multiple steady states in the long-term climate system. Using a simple carbon cycle box model, we show that the location of precipitation bands around the tropics and high mid-latitudes, coupled with the response of the terrestrial biosphere to local surface temperature, can result in system bi-stability. Here, maximum CO2 drawdown can occur when either the tropics or high mid-latitudes are at the photosynthetic optimum temperature of around 25°C, and a period of instability can exist between these states. We suggest that this dynamic has influenced climate variations over Phanerozoic time, and that higher steady state surface temperatures may be easier to reach than is commonly demonstrated in simple ‘GEOCARB style’ carbon cycle models.
长期的碳循环在数百万年的时间尺度上调节着地球的气候和大气中的二氧化碳水平,但对于给定的二氧化碳输入速率,这个系统是否有一个单一的稳定状态尚不清楚。本文探讨了长期气候系统中多种稳定状态的可能性。利用一个简单的碳循环箱模型,我们发现降水带在热带和中纬度高纬度附近的位置,加上陆地生物圈对当地地表温度的响应,可以导致系统双稳定性。在这里,当热带或高纬度地区处于25°C左右的光合作用最佳温度时,二氧化碳的最大减少可能发生,并且在这些状态之间可能存在一段不稳定时期。我们认为这种动态影响了显生宙时期的气候变化,并且更高的稳定表面温度可能比简单的“GEOCARB风格”碳循环模型中通常显示的更容易达到。
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引用次数: 5
A Laurentian cratonic reference from the distal Proterozoic basement of Western Newfoundland using tandem in situ and isotope dilution U-pb zircon and titanite geochronology 纽芬兰西部远元古代基底的劳伦克拉通参考,使用串联原位和同位素稀释U-pb锆石和钛矿地质年代学
IF 2.9 3区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2021-09-01 DOI: 10.2475/07.2021.02
E. Hodgin, F. Macdonald, J. Crowley, M. Schmitz
The Humber Margin of Newfoundland preserves the most distal exposures of Proterozoic basement in northeastern Laurentia. Age uncertainty has permitted a range of hypotheses for its origin and links to subsequent tectonic events. One hypothesis has proposed large-scale orogen-parallel displacement between basement blocks in western Newfoundland. The apparent absence of Grenville- (∼1250–950 Ma sensu lato) or Taconic-aged (∼480–450 Ma) magmatism or metamorphism on the Corner Brook Lake Block (CBLB), which are defining features of the Humber Margin, has been reconciled by restoring the CBLB to a pre-Taconic position in Labrador with >400 km of post-Taconic dextral motion along the Humber River Fault. To test this model and better define the basement and Paleozoic rifted margin of North America, we conducted a geochronological study of the CBLB and the basement of the adjacent Humber Margin at Indian Head Range using tandem in situ and isotope dilution U-Pb zircon and titanite geochronology. These basement blocks, separated by the Humber River Fault, consist of ∼1500 and ∼1250 Ma protoliths, 1140 to 1135 Ma magmatism, 1000 to 970 Ma metamorphism, and ∼607 Ma intraplate magmatism. These basement blocks are also overlain by similar late Ediacaran to Cambrian siliciclastic successions with similar detrital zircon age spectra. From this set of geological data, we conclude that the Humber River Fault did not accommodate significant orogen-parallel displacement. New basement ages and a revised compilation of detrital zircon ages from overlying rift-related deposits contribute to a geochronologic cratonic reference datum for western Newfoundland's crystalline basement, whose protolith has a restricted age range from circa 1500 to 950 Ma. New age constraints for metasedimentary rocks are also used to document a 1250 to 1135 Ma succession at Indian Head Range and a ∼1000 Ma succession on the CBLB associated with Grenvillian orogenesis. Protracted late Grenvillian tectono-thermal events are inferred from cores and metamorphic overgrowths of ∼990 to 920 Ma detrital titanite in late Ediacaran conglomerate overlying CBLB basement.
纽芬兰的亨伯边缘保留了劳伦斯东北部最远的元古代基底暴露。年龄的不确定性允许对其起源以及与随后的构造事件的联系进行一系列假设。一种假说提出了纽芬兰西部基底块体之间的大规模造山带平行位移。Corner Brook Lake地块(CBLB)上明显不存在Grenville-(~1250–950 Ma,广义)或Taconic时效(~480–450 Ma)岩浆作用或变质作用,这是Humber边缘的决定性特征,通过将CBLB恢复到拉布拉多的Taconic前位置,沿着Humber河断层进行>400 km的Taconic-后右旋运动,可以调和这一点。为了测试该模型并更好地确定北美洲的基底和古生代裂谷边缘,我们使用串联原位和同位素稀释U-Pb锆石和钛酸盐地质年代学对印度洋岬山脉的CBLB和邻近亨伯边缘的基底进行了地质年代学研究。这些基底块体由亨伯河断层分隔,由~1500和~1250 Ma的原岩、1140至1135 Ma的岩浆作用、1000至970 Ma的变质作用和~607 Ma的板内岩浆作用组成。这些基底块体也覆盖着类似的晚埃迪卡拉纪至寒武纪硅化碎屑序列,具有类似的碎屑锆石年龄谱。根据这组地质数据,我们得出结论,亨伯河断层没有容纳显著的造山带平行位移。新的基底年龄和上覆裂谷相关矿床碎屑锆石年龄的修订汇编为纽芬兰西部结晶基底的地质年代克拉通参考基准做出了贡献,其原岩的年龄范围约为1500至950 Ma。变质沉积岩的新年龄限制也被用于记录印度头山脉1250至1135 Ma的层序,以及与格伦维尔造山运动相关的CBLB上的~1000 Ma层序。从覆盖CBLB基底的晚埃迪卡拉纪砾岩中~990至920Ma碎屑钛酸岩的岩芯和变质过度生长推断出长期的晚格伦维尔期构造热事件。
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引用次数: 0
A comparative study of clay mineral authigenesis in terrestrial and martian lakes; an Australian example 陆地湖泊和火星湖泊中粘土矿物自生的比较研究;澳大利亚的一个例子
IF 2.9 3区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2021-09-01 DOI: 10.2475/07.2021.03
T. Bristow, A. Derkowski, D. Blake, G. Berlanga, P. Deckker
Clay mineral-bearing mudstones are a prominent component of ancient fluvial-lacustrine deposits, 100s of meters thick, documented by the Mars Science Laboratory (MSL) rover, in Gale crater, Mars. Most of the clay minerals documented by MSL are hypothesized to have formed in situ, at or close to the time of deposition ∼3.5 Ga ago, by aqueous alteration of basaltic detritus. Here we study the mechanisms, controls, and timescales of clay mineral authigenesis in a series of lakes with a wide range of water chemistries from the Western Volcanic District, Victoria, SE Australia, as an analog to the Gale crater mudstones. X-ray diffraction (XRD) analysis reveals that the sediments of most of the Western Volcanic District lakes studied contain mixtures of kaolinite, illite, mixed-layer illite-smectite (I-S), and dioctahedral smectite clay minerals. Comparisons of this mineral assemblage with regional soils and creek bedload material confirm previous assertions of significant inputs of detrital clay minerals into the lakes. A trioctahedral clay mineral phase is also detected, making up to 39 wt.% of bulk sediments. The abundance of trioctahedral clay minerals correlates with contemporary lake hydrology and proxies for past lake water Mg concentration. This indicates in situ formation of trioctahedral clay minerals by the uptake of Mg and Si from lake waters and pore fluids at rates determined by local physico-chemical conditions. Examination of crater lake sediments, where detrital clay mineral input is minimized, demonstrate that neoformed trioctahedral clay minerals are poorly crystalline trioctahedral smectites. Neoformation of trioctahedral smectites also occurs in lakes where detrital clay minerals are more abundant. However, an additional authigenic transformation process is indicated by the proportions of Mg and Si added to detrital clay minerals as well as evidence for the uptake of K from lake waters. The transformation process probably involved the incorporation of Mg into the octahedral sheets of detrital clay minerals, leading to irreversible uptake of K into interlayer sites (illitization). The distribution of trioctahedral smectites and radiocarbon ages from sediment cores show that clay mineral authigenesis occurred before sediment consolidation, on timescales of years to 100s of years. These results support syndepositional interpretations of analogous Mg-rich clay minerals documented by MSL, and their use as proxies for chemical conditions in ancient Gale lakes. In comparison with the Western Volcanic District lakes, clay mineral-bearing lacustrine mudstones from Gale crater exhibit only modest chemical weathering of basaltic detrital materials and rarely contain carbonate minerals in quantities detectable by XRD. These observations highlight significant differences in weathering regimes and regolith mineralogy on ancient Mars that could be linked to lake catchment geomorphology, climate, atmospheric CO2 content, and the absence of biotic
火星科学实验室(MSL)火星车在火星盖尔陨石坑记录到,含有粘土矿物的泥岩是100米厚的古代河流-湖泊沉积物的重要组成部分。MSL记录的大多数粘土矿物被假设是在沉积时间~3.5 Ga之前或接近沉积时间通过玄武岩碎屑的水性蚀变原位形成的。在这里,我们研究了澳大利亚东南部维多利亚州西部火山区一系列具有广泛水化学成分的湖泊中粘土矿物自生的机制、控制和时间尺度,类似于盖尔火山口泥岩。X射线衍射(XRD)分析表明,所研究的大多数西部火山区湖泊的沉积物含有高岭石、伊利石、混合层伊利石-蒙脱石(I-S)和二八面体蒙脱石粘土矿物的混合物。将这种矿物组合与区域土壤和河流推移质物质进行比较,证实了之前关于碎屑粘土矿物向湖泊中大量输入的断言。还检测到三面体粘土矿物相,占散装沉积物的39重量%。三面体粘土矿物的丰度与当代湖泊水文和过去湖水镁浓度的指标相关。这表明通过以当地物理化学条件确定的速率从湖水和孔隙流体中吸收Mg和Si,原位形成了三面体粘土矿物。对火山口湖沉积物的检查表明,新形成的三八面体粘土矿物是结晶性较差的三八面体蒙脱石。三面体蒙脱石的新形成也发生在碎屑粘土矿物更丰富的湖泊中。然而,添加到碎屑粘土矿物中的Mg和Si的比例以及从湖水中吸收K的证据表明了额外的自生转化过程。转化过程可能涉及将Mg掺入碎屑粘土矿物的八面体片中,导致K不可逆地吸收到层间位置(矿化)。沉积物岩芯中八面体蒙脱石的分布和放射性碳年龄表明,粘土矿物自生发生在沉积物固结之前,时间尺度为年至100年。这些结果支持MSL记录的类似富镁粘土矿物的同沉积解释,以及它们作为古代盖尔湖化学条件的替代物的用途。与西部火山区湖泊相比,盖尔火山口的含粘土矿物的湖泊泥岩仅表现出玄武岩碎屑物质的适度化学风化,并且很少含有可通过XRD检测到的碳酸盐矿物。这些观测结果突出了古代火星上风化状态和风化层矿物学的显著差异,这可能与湖泊集水区地貌、气候、大气二氧化碳含量以及火星上没有生物过程有关。
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引用次数: 2
A Highly dynamic hot hydrothermal system in the subduction environment: Geochemistry and geochronology of jadeitite and associated rocks of the Sierra del Convento mélange (eastern Cuba) 俯冲环境中的高动态热液系统:Sierra del Convento mélange(古巴东部)翡翠和伴生岩石的地球化学和地质年代
IF 2.9 3区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2021-06-01 DOI: 10.2475/06.2021.06
J. Cárdenas-Párraga, A. Garcia‐Casco, I. Blanco-Quintero, Y. Rojas‐Agramonte, K. N. Cambra, G. Harlow
A U-Pb zircon date of ∼113 Ma revealed that a variety of jadeitites and related omphacitite, chloritite and albite-rich rocks from the subduction-related Sierra del Convento block-in-serpentinite-matrix mélange (eastern Cuba) formed nearly synchronously with MORB metabasite-derived anatectic trondhjemitic liquids at high-temperature and pressure in a hot subduction environment. Field, petrologic and geochemical data indicate hydrothermal/metasomatic processes triggered by juvenile fluids likely evolved from the crystallizing hydrous trondhjemitic melts. These fluids, variably mixed with sediment-derived fluids and channelized along fractures in the supra-slab mantle, precipitated relatively pure jadeitite with geochemical patterns depleted in REE and HFSE and epidote-rich jadeitite with LILE- (notably Ba) enriched compositions with respect to N-MORB. The crystallization of jadeitite veins was accompanied by formation of chloritite blackwalls at the vein-ultramafic rock contact and omphacititic patches at the outer parts of the veins, denoting wall rock-fluid interactions. Further pervasive flow of external fluid within the rock bodies triggered modal and cryptic (geochemical) metasomatic transformation of earlier jadeitite, producing mica-rich jadeitite and albite-epidote (-chlorite) rocks. Altogether these rocks document a discrete episode of massive flow of fluid in the supra-slab mantle roughly coeval with hydrous melting of subducted MORB metabasite.
~ 113 Ma的U-Pb锆石表明,在俯冲相关的Sierra del Convento地块蛇纹岩基msamulange(古巴东部),在高温高压的热俯冲环境下,与MORB变质岩衍生的闪辉质流体几乎同时形成了多种硬玉岩及其相关辉长岩、绿泥岩和富含钠长岩的岩石。野外、岩石学和地球化学资料表明,幼流体引发的热液/交代过程可能是由含水岩浆熔体结晶演化而来的。这些流体与沉积流体的混合程度不同,并沿着上板块地幔的裂缝形成通道,沉淀出相对纯净的翡翠岩和富含绿帘石的翡翠岩,这些翡翠岩的地球化学模式缺乏REE和HFSE,而相对于N-MORB,富含LILE-(特别是Ba)成分。翡翠脉的结晶过程伴随着脉与超镁铁质岩石接触处绿泥岩黑壁的形成和脉外侧红辉质斑块的形成,表明了围岩与流体的相互作用。岩体内部外部流体的进一步普遍流动触发了早期翡翠岩的模态和隐式(地球化学)交代转化,生成了富云母的翡翠岩和钠长绿帘石(-绿泥石)岩石。总的来说,这些岩石记录了上板块地幔中大量流体流动的离散事件,大致与俯冲的MORB变质岩的含水熔融同时发生。
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引用次数: 4
Multiphase ophiolite formation in the Northern Altyn Tagh Orogen, southeastern Tarim 塔里木东南部阿尔金北塔格造山带多期蛇绿岩形成
IF 2.9 3区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2021-06-01 DOI: 10.2475/06.2021.05
Qian Liu, T. Tsunogae, Guochun Zhao, Jianhua Li, Jinlong Yao, Yigui Han, Peng Wang
Early Paleozoic ophiolitic mélanges in the Altyn Tagh Orogen, southeastern Tarim, yield a large range of formation ages and geochemical affinities. This study focused on the Hongliugou ophiolitic mélange in the North Altyn Tagh subduction-accretion belt and involved mineral chemical, zircon geochronological, and whole-rock elemental and isotopic investigations of the ultramafic and mafic rocks. In the studied lherzolite samples, Cr-spinel, olivine, and pyroxene show mineral chemistry akin to that of abyssal peridotite. Subhedral-anhedral Cr-spinel grains with high Cr# values (100*Cr/[Cr+Al] of 30–40) and negative oxygen fugacity (fO2) values represent original spinel formed during mid-ocean ridge basalt (MORB) melt extraction. Other subhedral-anhedral and euhedral Cr-spinel with low Cr# values of < 30 to 20 display a wide range of negative to positive fO2 values, indicating interaction of peridotite with MORB magma. New zircon U-Pb dating results record ages of ca. 490 Ma for gabbro and ca. 486 Ma for diabase in the Hongliugou ophiolitic mélange. Whole-rock geochemical compositions suggest that the gabbro and diabase samples are tholeiitic and show MORB affinities or transitional affinities between MORB and island arc tholeiite. These mafic rocks might have been derived from a depleted MORB-source mantle that was variably metasomatized by subduction-induced fluids based on their variable Th/Yb, high La/Nb, low Th/Nb, and depleted isotopes (initial 87Sr/86Sr ratios of 0.703073 to 0.703385 and εNd(t) values of +6.2 to +6.3). New results, when integrated with previous work, clarify that ca. 520 to 510 Ma ophiolites formed in the initial subduction setting and ca. 490 to 480 Ma ophiolites in a back-arc setting. Minor ca. 450 Ma ophiolite probably represents a late phase of ophiolite formation due to the presence of a very minor remnant ocean.
塔东南阿尔金-塔格造山带早古生代蛇绿混杂岩具有较大的形成时代和地球化学亲和性。本研究以北阿尔金-塔吉克俯冲吸积带红柳沟蛇绿混杂岩为研究对象,对超镁铁质和镁铁质岩石进行了矿物化学、锆石地质年代学、全岩元素和同位素研究。在所研究的二辉橄榄岩样品中,铬尖晶石、橄榄石和辉石显示出类似于深海橄榄岩的矿物化学性质。具有高Cr#值(100*Cr/[Cr+Al]为30–40)和负氧逸度(fO2)值的亚面体二面体Cr尖晶石颗粒代表大洋中脊玄武岩(MORB)熔体提取过程中形成的原始尖晶石。其他具有低Cr#值的半自形和自形Cr尖晶石 < 30至20显示出大范围的负至正fO2值,表明橄榄岩与MORB岩浆的相互作用。新的锆石U-Pb测年结果记录了红柳沟蛇绿混杂岩中辉长岩的年龄约为490 Ma,辉绿岩的年龄约486 Ma。全岩地球化学成分表明,辉长岩和辉绿岩样品为拉斑玄武岩,并显示出MORB亲和力或MORB与岛弧拉斑玄武岩之间的过渡亲和力。这些镁铁质岩石可能来源于一个贫化的MORB源地幔,该地幔根据其可变的Th/Yb、高La/Nb、低Th/Nb和贫化同位素(初始87Sr/86Sr比值为0.703073至0.703385,εNd(t)值为+6.2至+6.3)被俯冲诱导流体可变交代,阐明约520至510 Ma蛇绿岩形成于初始俯冲环境,约490至480 Ma蛇绿岩在弧后环境。小约450 Ma蛇绿岩可能代表了蛇绿岩形成的晚期,因为存在非常小的残留海洋。
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引用次数: 2
Foreword 前言
IF 2.9 3区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2021-06-01 DOI: 10.2475/06.2021.11
Tsung-Pin Chen, Chih-Lung Lin, Kuo-Chin Fan, Wanzun Lin
This is the second of three issues of American Journal of Science in which the papers have been submitted by friends and colleagues as a mark of respect to Alfred Kroner, who passed away just a few months before his 80 birthday in 2019. Alfred has left an indelible mark on the geoscience community, with his boundless energy and dedication, and especially his application of detailed fieldwork and microanalysis to solve the bigger issues. As the subtitle ‘From Cratons to Orogens’ indicates, Alfred was always cognizant of how his work related to global events, and this is reflected by the nine papers that constitute this volume. The first paper by Allen Nutman and co-workers presents an overview of the 3.8 Ga Outer Arc of the Isua Greenstone Belt in West Greenland. This forms an integral part of the oldest and best-preserved volcano-sedimentary sequence on Earth. Utilizing rare low-strain zones, accompanied by new and published geochronology, the authors endeavor to unravel the stratigraphy of the arc. The lowermost mafic unit contains pillow lavas, indicating a subaqueous depositional environment. The overlying formation commences with a unit of fuchsitic quartzite, overlain by various carbonate and silicate units; some with relict sedimentary structures. There is an upward transition to chemical sediments and then into units showing a greater influx of felsic volcanic components. The uppermost unit is felsic, with both lavas and pyroclastic rocks, interpreted as forming in an arc. The authors therefore support a plate tectonic scenario and not a stagnant lid environment for the early Eoarchean of Greenland. Xiao Wang and co-workers investigate Archean/Paleoproterozoic rocks in the Khondalite Belt, which marks the Paleoproterozoic collision zone between the Yinshan and Ordos blocks, and is located in the western block of the North China Craton. The authors describe TTG rocks of I-type affinity in the Daqingshan Complex, whose ages straddle the Archean/Proterozoic boundary and define oceanic subduction beneath the southern margin of the Yinshan Block. Docking of the Ordos Block led to closure of the ocean with the TTG rocks undergoing high-grade metamorphism between 1.95-1.85 Ga. In a companion paper, Xiao Wang and co-workers analyze and date high-grade metamorphic rocks of the Daqingshan Complex, interpreted as bimodal volcanics that formed in a back arc setting prior to the collision of the Yinshan and Ordos block, as detailed above. The volcanic rocks formed between 2.47-2.40 Ga and were metamorphosed at high grade between 1.95-1.85 Ga, similar to the TTG rocks in the complex. This latter event is one of the global collisions marking assembly of Colombia/Nuna. In another paper on the North China Craton where Alfred worked extensively, Yue-Lan Kang and co-workers investigate the late Mesozoic granitoids to the east and west of the Tan-Lu Fault, one of the most significant late Phanerozoic structures in China. In the Taihang Mountains to the west,
这是朋友和同事提交的三期《美国科学杂志》中的第二期,以纪念阿尔弗雷德·克罗纳,他在2019年80岁生日前几个月去世。阿尔弗雷德以其无穷的精力和奉献精神,尤其是他应用详细的实地调查和微观分析来解决更大的问题,在地球科学界留下了不可磨灭的印记。正如副标题“从陨石坑到奥罗根斯”所表明的那样,阿尔弗雷德一直意识到他的作品与全球事件的关系,这一点在本卷的九篇论文中得到了反映。Allen Nutman及其同事的第一篇论文概述了西格陵兰岛Isua Greenstone带3.8 Ga外弧。这是地球上最古老、保存最完好的火山沉积序列的组成部分。作者利用罕见的低应变带,结合新的和已发表的地质年代学,努力揭示弧的地层学。最下面的镁铁质单元包含枕状熔岩,表明存在水下沉积环境。上覆地层以紫红色石英岩单元开始,上覆各种碳酸盐和硅酸盐单元;一些带有残余沉积结构。向上过渡到化学沉积物,然后进入长英质火山成分大量涌入的单元。最上面的单元是长英质,包括熔岩和火山碎屑岩,被解释为形成弧形。因此,作者支持格陵兰早太古代的板块构造场景,而不是停滞的盖层环境。小王及其同事研究了孔达岩带中的太古宙/古元古代岩石,孔达岩地带标志着阴山地块和鄂尔多斯地块之间的古元古代碰撞带,位于华北克拉通西部地块。作者描述了大青山杂岩中I型亲和TTG岩石,其年龄跨越太古宙/元古代边界,并确定了阴山地块南缘下的海洋俯冲。鄂尔多斯地块的对接导致了海洋的闭合,TTG岩石在1.95-1.85 Ga之间经历了高级变质作用。在一篇配套论文中,小王及其同事分析并确定了大青山杂岩的高级变质岩的年代,这些岩石被解释为阴山和鄂尔多斯地块碰撞前在弧后环境中形成的双峰火山岩,如上所述。火山岩形成于2.47-2.40 Ga之间,在1.95-1.85 Ga之间发生高品位变质,类似于杂岩中的TTG岩石。后一项活动是哥伦比亚/努纳全球碰撞标志大会之一。在另一篇关于Alfred广泛工作的华北克拉通的论文中,Yue Lan Kang及其同事研究了中国最重要的晚显生宙构造之一——郯庐断裂东部和西部的中生代晚期花岗岩。在西部太行山区,花岗岩类岩浆被认为是由玄武岩底板和下地壳熔体的混合物形成的。在云梦山断层以东,岩浆的变化更大,被解释为与古太平洋俯冲和华北克拉通东部下方岩石圈分层的开始有关。作者进一步认为郯庐断裂带是地幔岩浆和流体运移的控制因素。最后一篇关于中国地质学的论文将我们带到塔里木克拉通东南部的北阿尔金-塔格造山带。在这里,钱柳及其同事利用全岩和矿物地球化学,以及锆石U/Pb地质年代学,研究了一系列早古生代蛇绿岩之一。红柳沟蛇绿混杂岩包含490 Ma辉长岩和480 Ma辉绿岩,来源于贫化的MORB源地幔,被俯冲相关流体进行了各种交代。当与该地区其他蛇绿岩的结果相结合时,他们认为520-510 Ma的蛇绿岩代表初始俯冲,490-480 Ma的
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