The c.3·3 Ga Commondale komatiites located south of the Barberton greenstone belt in the Kaapvaal Craton are different from other komatiites, possessing compositional and textural features unique to this occurrence. Unlike almost all other known komatiite occurrences, they are not associated with komatiitic basalts or basalts. The komatiite flows are 0·5–25 m thick and are made up of a marginal zone of spinifex-textured and fine-grained aphyric rocks (low-Mg group) and an inner zone of olivine cumulates (high-Mg group), arranged in such a way to give highly symmetrical compositional profiles for many flows. Olivine is the dominant phase in all rocks, but orthopyroxene occurs as spinifex and elongate laths in the marginal zone. Clinopyroxene and plagioclase are entirely absent. The olivine cumulates formed from Mg-rich magma (36·1% MgO, 6·8% FeO) which caused inflation of the thicker flows. The maximum observed olivine composition in cores (Fo 96·6) is the highest recorded for any komatiite worldwide. The high-Mg magma would have erupted at a temperature close to 1670°C, the highest inferred temperature for an anhydrous terrestrial lava. The marginal zone is enriched in incompatible elements compared with the inner zone and formed by fractionation of the parental melt. However, all rock-types in the marginal zone are depleted in FeO (some as low as 3·5%) which could not have been derived by any primary magmatic process. The marginal zone rocks were modified by assimilation and/or alteration by seawater (or brine) components causing migration of iron and strong enrichment of sodium (up to 1·6 wt % Na₂O) and chlorine (up to 2400 ppm). Zirconium has an identical distribution to sodium, with both elements greatly enriched above what would result from fractional crystallization, and may result from speciation of these elements at high temperature followed by post-crystallization alteration. Rare earth elements, Y and Nb have contents commensurate with fractionation of the primitive parental magma. Dendritic-textured olivine-rich rocks with orthopyroxene spinifex spatially and compositionally transitional between the marginal zone and the olivine cumulates resulted from interaction of the high temperature parental magma in the centre of the flows with the fractionated melt at the flow margins. A further manifestation of this association is the development of highly regular fine-scale (5–15 cm) layering (up to 45 layers) of alternating olivine cumulate and spinifex near the base of thick flows. This is overlain by olivine cumulates in which the melt/crystal-mush became arranged into a 3-dimensional network controlled by re-distribution of the trapped melt manifest by a spectacular knobbly texture in outcrop. Over 200 flow units are recognized and detailed chemical and mineralogical studies were carried out on drill cores intersecting 375 m of stratigraphy. The parental magma was highly depleted (in ppm Nb 0·017, Zr 1·18, total REE 1·7 and Gd/Yb_N=0·3, La/Yb_N=0·038) and although generally regarded to fall into the rare category of Al-enriched komatiites (AEKs), it is considered that these lavas are a unique class of their own of ultra-depleted komatiites. Relative to other AEKs the Commondale komatiites are both enriched in Al as well as being markedly depleted in Ti (390 ppm), giving rise to the extremely high Al₂O₃/TiO₂ (81). The high temperature and low viscosity of the magma resulted in emplacement processes previously unrecognized in komatiites. The primary melt was derived by melting of mantle peridotite in equilibrium with olivine and orthopyroxene. The initial source was depleted in incompatible elements by small degrees of melting (3–4%) followed by high degrees of partial melting (70%) of the subsequent refractory source at 5 GPa (∼150 km).

中文翻译：

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上古时代的极度枯竭的Commondale Komatiites：地球上最热的熔岩和爆发的后果

位于Kaapvaal Craton的Barberton绿岩带以南的c.3·3 Ga Commondale科马提岩不同于其他科马提石，具有这种现象独特的成分和质地特征。与几乎所有其他已知的高锰铁矿不同，它们与科迈特玄武岩或玄武岩无关。科马蒂岩流的厚度为0·5–25 m，由尖晶石质和细粒状灰生岩的边缘区（低镁组）和橄榄石堆积的内部区（高镁组）组成。以这种方式为许多流动提供高度对称的成分分布。橄榄石是所有岩石中的主要相，而邻苯二甲醚则以尖晶石和细长板条出现在边缘区。完全不存在斜发rox和斜长石。富含镁的岩浆（36·1％MgO，6·8％FeO）导致较粗的流膨胀。观察到的岩心中最大的橄榄石成分（Fo 96·6）是全世界任何科马提岩中记录的最高值。高镁岩浆将在接近1670°C的温度爆发，这是无水陆地熔岩的最高推断温度。与内部区域相比，边缘区域富含不相容元素，并通过母体熔体的分馏形成。但是，边缘带的所有岩石类型都被FeO耗尽（某些低至3·5％），而FeO不可能通过任何一次岩浆作用过程获得。边缘带岩石经过海水（或盐水）的同化和/或蚀变而被改性，从而引起铁的迁移和钠的强富集（Na含量高达1·6 wt％观察到的岩心中最大的橄榄石成分（Fo 96·6）是全世界任何科马提岩中记录的最高值。高镁岩浆将在接近1670°C的温度下喷发，这是无水陆地熔岩的最高推断温度。与内部区域相比，边缘区域富含不相容元素，并通过母体熔体的分馏形成。但是，边缘带的所有岩石类型都被FeO耗尽（某些低至3·5％），而FeO不可能通过任何一次岩浆作用过程获得。边缘带岩石经过海水（或盐水）的同化和/或蚀变而被改性，从而引起铁的迁移和钠的强富集（Na含量高达1·6 wt％观察到的岩心中最大的橄榄石成分（Fo 96·6）是全世界任何科马提岩中记录的最高值。高镁岩浆将在接近1670°C的温度爆发，这是无水陆地熔岩的最高推断温度。与内部区域相比，边缘区域富含不相容元素，并通过母体熔体的分馏形成。但是，边缘带的所有岩石类型都被FeO耗尽（某些低至3·5％），而FeO不可能通过任何一次岩浆作用过程获得。边缘带岩石经过海水（或盐水）成分的同化和/或蚀变而被改性，从而引起铁的迁移和钠的强富集（至多1·6 wt％的钠）高镁岩浆将在接近1670°C的温度爆发，这是无水陆地熔岩的最高推断温度。与内部区域相比，边缘区域富含不相容元素，并通过母体熔体的分馏形成。但是，边缘带的所有岩石类型都被FeO耗尽（某些低至3·5％），而FeO不可能通过任何一次岩浆作用过程获得。边缘带岩石经过海水（或盐水）的同化和/或蚀变而被改性，从而引起铁的迁移和钠的强富集（Na含量高达1·6 wt％高镁岩浆将在接近1670°C的温度爆发，这是无水陆地熔岩的最高推断温度。与内部区域相比，边缘区域富含不相容元素，并通过母体熔体的分馏形成。然而，边缘带的所有岩石类型都被FeO耗尽（某些低至3·5％），而FeO不可能通过任何一次岩浆作用过程获得。边缘带岩石经过海水（或盐水）的同化和/或蚀变而被改性，从而引起铁的迁移和钠的强烈富集（Na含量高达1·6 wt％边缘带的所有岩石类型都贫化了FeO（有些低至3·5％），这是任何一次岩浆作用都无法产生的。边缘带岩石经过海水（或盐水）的同化和/或蚀变而被改性，从而引起铁的迁移和钠的强富集（Na含量高达1·6 wt％边缘带的所有岩石类型都贫化了FeO（有些低至3·5％），这是任何一次岩浆作用都无法产生的。边缘带岩石经过海水（或盐水）成分的同化和/或蚀变而被改性，从而引起铁的迁移和钠的强富集（至多1·6 wt％的钠）₂O）和氯气（最高2400 ppm）。锆与钠具有相同的分布，两种元素的含量都大大高于分步结晶所产生的含量，并且可能是由于这些元素在高温下形成晶态后结晶后发生了变化。稀土元素Y和Nb的含量与原始母岩浆的分级相当。边缘区与橄榄石堆积之间具有邻位邻位四方尖晶石的树突状富集橄榄石的岩石在空间上和组成上的过渡是由于流动中心的高温母岩浆与流动边缘的分馏熔体相互作用所致。这种联系的进一步体现是在厚流的底部附近出现了高度规则的精细尺度（5-15厘米）分层（最多45层），交替出现橄榄石堆积物和尖顶。这被橄榄石堆积物覆盖，其中熔体/晶体糊状物被排列成3维网络，该网络由被捕获的熔体清单的重新分布控制，而露头的壮观的knob节质地又使之得以重新分布。公认的200多个流量单位，并在与375 m地层相交的钻芯上进行了详细的化学和矿物学研究。母岩浆高度耗尽（Nb 0·017，Zr 1·18，总REE 1·7和Gd / Yb）这被橄榄石堆积物覆盖，其中熔体/晶体糊状物被排列成3维网络，该网络由被捕获的熔体清单的重新分布控制，而露头的壮观的knob节质地又使之得以重新分布。公认的200多个流量单位，并在与375 m地层相交的钻芯上进行了详细的化学和矿物学研究。母岩浆高度耗尽（Nb 0·017，Zr 1·18，总REE 1·7和Gd / Yb）这被橄榄石堆积物覆盖，其中熔体/晶体糊状物被排列成3维网络，该网络由被捕获的熔体清单的重新分布控制，而露头的壮观的knob节质地又使之得以重新分布。公认的200多个流动单位，并在相交375 m地层的钻芯上进行了详细的化学和矿物学研究。母岩浆高度耗尽（Nb 0·017，Zr 1·18，总REE 1·7和Gd / Yb）_N = 0·3，La / Yb _N = 0·038），尽管通常被认为是富含Al的科马铁矿（AEK）的稀有类别，但据认为这些熔岩是它们自身的独特类别。耗尽的科马蒂岩。相对于其他AEK，Commondale科马蒂岩不仅富含Al，而且还显着地贫化了Ti（390 ppm），从而产生了极高的Al ₂ O ₃ / TiO ₂（81）。岩浆的高温和低粘度导致了高马铁矿中以前无法识别的沉积过程。初始熔体是通过熔融橄榄岩和橄榄石与邻二甲苯而形成的地幔橄榄岩而形成的。最初的来源因不相容元素的消耗而变小，其熔化程度较小（3-4％），随后在5 GPa（〜150 km）的情况下，随后的耐火材料部分熔化程度较高（70％）。