火山中心的形成和热液蚀变:兰塞斯海脊(北冰洋加克尔海脊)的熔体汇集和质量转移

IF 2.6 3区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Marine Geology Pub Date : 2024-07-06 DOI:10.1016/j.margeo.2024.107347
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引用次数: 0

摘要

火山中心是超低展布洋中脊的特征,也是全球海脊系统中开发最少的部分。火山中心可以让人们了解这些海脊的深层岩浆和变质过程。在此,我们展示了位于东经 60-62° 的加克尔海脊上最大的火山中心 Langseth 海脊的数据。Langseth 海脊宽 10 千米,由三座海峰组成,海拔 585 米,高出周围海底约 3-4 千米。它垂直于 Gakkel 的扩张方向,可追溯 40 千米,这意味着它的年龄为 8 百万年。海底成像显示了大量的(枕状)玄武岩,同时也显示了贯穿朗塞斯海脊的裂缝和地质断层。我们的样本是正常至贫化的中洋脊玄武岩成分,由于岩浆过程、巨晶体堆积和热液蚀变作用,主要元素和痕量元素含量范围很广。放射性同位素比率,尤其是 143Nd/144Nd 和 208Pb/206Pb 比率,随着与裂谷距离的增加,呈从典型裂谷成分到同位素富集值的趋势。这种趋势可能意味着来自不同来源的熔体汇集,可能代表了从裂谷下的浅层熔化到富集源的深层熔化以及兰塞斯下的更高程度熔化的转变。矿物成分和斜长石筛网纹理意味着岩浆在喷发前在深部长期贮存。热液蚀变发生在一系列条件下。来自山顶的玄武岩在温度≪100 °C时发生了微弱的蚀变,这很可能是在山顶的原位发生的。辉绿岩样本经历了绿化和白化,并显示出在 >300 °C 温度下形成的表土和石英脉。这些组合和温度是低地壳层的典型特征,意味着样本隆升了 1 千米。我们的研究结果表明,所研究的火山中心起源于火山和构造作用的结合,这可能意味着此类复合体一般可能是由于岩浆作用和构造作用的相互作用而形成的。对火山中心的研究有可能进一步加深我们对超低展布海脊深层和浅层地壳过程的理解,从而进一步了解这些中心作为岩石圈和水圈之间的纽带以及它们所维持的(深层)生物圈的作用。
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Formation and hydrothermal alteration of a volcanic center: Melt pooling and mass transfers at Langseth Ridge (Gakkel Ridge, Arctic Ocean)

Volcanic centers are characteristic features of ultraslow-spreading mid-ocean ridges, the least-explored parts of the global ridge system. Volcanic centers can provide insights into deep magmatic and metamorphic processes at these ridges. Here, we present data from the largest volcanic center on the Gakkel Ridge, the Langseth Ridge, situated at 60–62°E. Langseth is ∼10 km wide, consisting of three peaks that rise to 585 m water depth, some 3–4 km above the surrounding seafloor. It strikes perpendicular to Gakkel's spreading direction and can be traced for ∼40 km, which translates to an age of ∼8 Myr. Seafloor imaging revealed abundant (pillow) basalt but also fissures and geologic faults across the Langseth Ridge. Basaltic rocks were sampled at all summits and diabase at the slope of the northern summit that dips into the rift valley.

Our samples are of normal to depleted mid-ocean ridge basalt composition and exhibit a wide range of major and trace element contents, due to magmatic processes, accumulation of macrocrysts, and hydrothermal alteration. Radiogenic isotope ratios, most notably 143Nd/144Nd and 208Pb/206Pb, trend from typical rift valley compositions to isotopically enriched values with increasing distance to the rift valley. This trend may imply melt pooling from different sources, potentially representing a shift from shallow melting beneath the rift valley to deeper melting of enriched sources and higher degrees of melting underneath Langseth. Mineral compositions and plagioclase sieve textures imply prolonged storage of magma at depth prior to eruption. Hydrothermal alteration occurred over a range of conditions. Basalt from the summits is weakly altered at temperatures ≪100 °C, which likely occurred in situ at the summit sites. Diabase samples experienced chloritization and albitization and display epidote and quartz veins, which formed at >300 °C. These assemblages and temperatures are typical for lower crustal levels and imply uplift of the samples of >1 km. Diabase samples from the Afanasenkov Seamount, another volcanic center on the Gakkel Ridge that we investigated for comparison, were altered under comparable conditions.

Our findings suggest a combined volcanic–tectonic origin of the studied volcanic centers, potentially implying that such complexes may generally form due to the interplay of magmatism and tectonics. Researching volcanic centers has the potential to further our understanding of both deep and shallow crustal processes at ultraslow-spreading ridges, providing further insights into the role of these centers as linkages between lithosphere and hydrosphere and the (deep) biosphere they sustain.

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来源期刊
Marine Geology
Marine Geology 地学-地球科学综合
CiteScore
6.10
自引率
6.90%
发文量
175
审稿时长
21.9 weeks
期刊介绍: Marine Geology is the premier international journal on marine geological processes in the broadest sense. We seek papers that are comprehensive, interdisciplinary and synthetic that will be lasting contributions to the field. Although most papers are based on regional studies, they must demonstrate new findings of international significance. We accept papers on subjects as diverse as seafloor hydrothermal systems, beach dynamics, early diagenesis, microbiological studies in sediments, palaeoclimate studies and geophysical studies of the seabed. We encourage papers that address emerging new fields, for example the influence of anthropogenic processes on coastal/marine geology and coastal/marine geoarchaeology. We insist that the papers are concerned with the marine realm and that they deal with geology: with rocks, sediments, and physical and chemical processes affecting them. Papers should address scientific hypotheses: highly descriptive data compilations or papers that deal only with marine management and risk assessment should be submitted to other journals. Papers on laboratory or modelling studies must demonstrate direct relevance to marine processes or deposits. The primary criteria for acceptance of papers is that the science is of high quality, novel, significant, and of broad international interest.
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