The komatiite testimony to ancient mantle heterogeneity
The komatiite testimony to ancient mantle heterogeneity
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科马提岩对古代地幔异质性的证明
DOI：
10.1016/j.chemgeo.2022.120776
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发表时间：
2022
期刊：
影响因子：
3.9
通讯作者：
Walker, Richard J.
中科院分区：
文献类型：
--
作者：
Puchtel, Igor S.;Blichert-Toft, Janne;Horan, Mary F.;Touboul, Mathieu;Walker, Richard J.
科马提岩是高温、高 MgO 熔岩的结晶样本，在太古代很常见，但在元古代和显生宙变得越来越罕见。尽管科马提岩的起源仍然是一个争论的话题，但本次综述中包括的所有科马提岩，年龄范围为 3.6 至 2.0 Ga，都被解释为很可能源自地幔柱的无水熔融。据估计，这些羽流起源于地幔的不同深度，因此，提供了有关早期地球化学演化的重要信息。这些科马提岩的 142、143Nd、176Hf、182W、187Os 和 186Os 系统学以及痕量和高亲铁元素 (HSE) 丰度为地球历史上半段地幔中同位素和化学异质性的存在提供了有力的证据。这些异质性可能反映了以下因素的综合影响：（1）不同的岩浆后海洋硅酸盐区域共存，其特征是亲石元素和亲铁元素丰度变化； (2) 存在不同的储层，其中包括晚期吸积、分化的星子的地幔和核心； (3)跨核幔边界的同位素交换。这些数据凸显了科马提岩地幔来源的复杂性，其中没有一个在成分上与现代块状硅酸盐地球（BSE）的估计相似。此外，没有单一的岩石成因模型可以解释科马提岩显着不同的化学和同位素组成。镁铁质-超镁铁质岩石记录中可解析的正负 142Nd 异常以及解耦的 143Nd-176Hf 同位素特征消失约 2.5 Ga，这表明，到太古代末期，最早的硅酸盐储层是通过原始岩浆海洋形成的由于剧烈的地幔对流混合，结晶已被很大程度上破坏。这意味着，在冥宙和太古宙期间，地幔需要大约1.5 Ga才能通过大规模地幔对流混合掉早期形成的142Nd异质性。与 142Nd 系统学类似，似乎已经从 2.5 Ga 之前的科马提岩地幔源区中大部分正 182W 异常转变为 2.5 Ga 后科马提岩地幔源区中没有 182W 偏移。再加上相对于现代 BSE 而言，预计科马提岩地幔源中的 HSE 消耗在 ~2.5 Ga 时消失，这种转变可能表明，到太古代末期，晚期吸积的星子在地幔内已基本均质化，并且核-地幔相互作用成为产生 182W 同位素异常的主要驱动力，可能与现代板块构造开始的时间一致。地球。
Komatiites are crystallized samples of high-temperature, high-MgO lavas that were common during the Archean, but became increasingly rarer in the Proterozoic and Phanerozoic. Although the origin of komatiites remains a subject of debate, all komatiites included in this review, ranging in age from 3.6 to 2.0 Ga, are interpreted to have most likely been derived from anhydrous melting in mantle plumes. These plumes are estimated to have been initiated at different depths in the mantle, thus, providing important information about the chemical evolution of the early Earth.The142,143Nd,176Hf,182W,187Os, and186Os systematics and trace- and highly siderophile element (HSE) abundances of these komatiites provide strong evidence for the presence of isotopic and chemical heterogeneities in the mantle during the first half of Earth history. These heterogeneities likely reflect the combined effects of (1) the co-existence of diverse post-magma ocean silicate domains that were characterized by variably-fractionated lithophile and siderophile element abundances; (2) the presence of distinct reservoirs that included mantles and cores of late accreted, differentiated planetesimals; and (3) isotopic exchange across the core-mantle boundary. These data highlight the complexity of komatiite mantle sources, none of which were similar in composition to estimates for the modern bulk silicate Earth (BSE). Moreover, no single petrogenetic model can account for the remarkably diverse chemical and isotopic compositions of komatiites.The disappearance of resolvable positive and negative142Nd anomalies, as well as decoupled143Nd-176Hf isotopic signatures, in the mafic-ultramafic rock record by ~2.5 Ga indicate that, by the end of the Archean, the earliest silicate reservoirs, formed through primordial magma ocean crystallization, had been largely destroyed as a result of vigorous convective mantle mixing. This implies that, during the Hadean and Archean, it took the mantle ~1.5 Ga to mix away the early formed142Nd heterogeneitiesviawholesale mantle convection. Similar to142Nd systematics, there appears to have been a shift from mostly positive182W anomalies in pre-2.5 Ga komatiite mantle sources to no182W offsets in post-2.5 Ga komatiite mantle sources. Coupled with the disapperance of projected HSE depletions in komatiite mantle sources at ~2.5 Ga, relative to the modern BSE, this shift may indicate that, by the end of the Archean, late accreted planetesimals had become largely homogenized within the mantle, and core-mantle interaction took over as the main driving force of creating182W isotope anomalies, possibly coincident with the timing of the onset of modern-style plate tectonics on Earth.
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影响因子：
5.3
作者：
Schneider;Hoffmann;Münker;Kröner
通讯作者：
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DOI：
--
发表时间：
1977
期刊：
影响因子：
--
作者：
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通讯作者：
N. Arndt
影响因子：
3.9
作者：
Mundl-Petermeier, A.;Walker, R. J.;Halldorsson, S. A.
通讯作者：
Halldorsson, S. A.
高压和高温下锇在硅酸盐中的溶解度较低
DOI：
--
发表时间：
2009
期刊：
影响因子：
--
作者：
T. Yokoyama;T. Yokoyama;D. Walker;R. Walker
通讯作者：
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影响因子：
2.2
作者：
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