Mantle sources and magma evolution in Europe's largest rare earth element belt (Gardar Province, SW Greenland): New insights from sulfur isotopes
Mantle sources and magma evolution in Europe's largest rare earth element belt (Gardar Province, SW Greenland): New insights from sulfur isotopes
复制标题
欧洲最大稀土元素带（格陵兰岛西南部加尔达尔省）的地幔来源和岩浆演化：来自硫同位素的新见解
DOI：
10.1016/j.epsl.2021.117034
复制
发表时间：
2021
影响因子：
5.3
通讯作者：
Hutchison W
中科院分区：
文献类型：
--
作者：
Hutchison W
碱性火成岩复合体通常富含稀土元素 (REE) 和现代技术必需的其他金属。尽管各种岩浆和热液过程可以解释单个矿床的出现，但几乎所有研究都发现了一个共同特征，那就是来自岩石圈地幔的富含稀土元素的母体熔体。关于地幔源在富稀土岩浆成因中的起源和重要性仍然存在基本问题。特别是，通常不清楚碱性省内的局部富集是否反映了地幔源岩性的异质性（由先前的俯冲或羽流活动引起）或很大程度上均质源的部分熔融和分异程度的变化。硫同位素提供了一种检验这些假设的方法，因为它们不受高温部分熔化过程的影响，并且可以识别不同的地幔来源。尽管我们必须小心地排除岩浆上升、脱气和地壳相互作用过程中随后发生的同位素分馏。在这里，我们展示了中元古代加尔达省一系列碱性岩浆单元和地壳岩性的新硫浓度和同位素 (δ 34 S) 测量结果，以及主量元素和微量元素数据的汇编。样本涵盖了 Gardar 岩浆作用 (1330–1140 Ma) 的所有阶段，包括区域岩脉、裂谷熔岩以及碱性复合体 Motzfeldt 和 Ilímaussaq，它们代表了欧洲最大的两个稀土矿床。我们表明，115 个样品中的绝大多数的 S 含量> 100 ppm，δ 34 S 为− 1 至 5 ‰。只有 8 个样本（硫含量低，< 100 ppm）显示出地壳相互作用的证据，这意味着绝大多数加达熔体保留了其岩浆源的硫同位素特征。重要的是，来自整个加尔达省的样本的 δ 34 S 高于标准地幔范围 (≤− 1.4‰)，因此需要在其地幔源中回收表面 S。升高的 δ 34 S 值可以通过一段安第斯式俯冲和地幔交代作用来解释，该时期发生在裂谷开始前约 500 Ma，并且也得到与现代俯冲带相匹配的微量元素特征（例如 Ba/La）的支持。比较各代Gardar岩浆，我们发现δ 34 S值、大离子亲石元素（K、Ba、P）和选择性不相容元素（Nb和轻稀土元素）在晚期Gardar岩脉、碱性杂岩和空间上与碱性杂岩伴生的二氧化硅不饱和岩脉簇中特别富集。这些数据表明，与俯冲相关的加达地幔交代作用在空间上是不均匀的，并且碱性复合物源自富含 34 S、REE、碱金属和挥发物（特别是 F）的局部地幔域。由于碱金属和挥发物在推动碱性熔体和流体的极端分异中发挥着重要作用，因此我们认为这些物质加上高浓度的不相容金属在岩石圈地幔中的共存是世界级碱性稀土矿床形成的关键的第一步。 S 同位素是识别富集地幔域和矿化碱性火成体来源的有力工具。
Alkaline igneous complexes are often rich in rare earth elements (REE) and other metals essential for modern technologies. Although a variety of magmatic and hydrothermal processes explain the occurrence of individual deposits, one common feature identified in almost all studies, is a REE-enriched parental melt sourced from the lithospheric mantle. Fundamental questions remain about the origin and importance of the mantle source in the genesis of REE-rich magmas. In particular, it is often unclear whether localized enrichments within an alkaline province reflect heterogeneity in the mantle source lithology (caused by prior subduction or plume activity) or variations in the degree of partial melting and differentiation of a largely homogeneous source. Sulfur isotopes offer a means of testing these hypotheses because they are unaffected by high temperature partial melting processes and can fingerprint different mantle sources. Although one must be careful to rule out subsequent isotope fractionation during magma ascent, degassing and crustal interactions. Here, we present new S concentration and isotope (δ 34 S) measurements, as well as a compilation of major and trace element data, for a suite of alkaline magmatic units and crustal lithologies from the Mesoproterozoic Gardar Province. Samples span all phases of Gardar magmatism (1330–1140 Ma) and include regional dykes, rift lavas and the alkaline complexes Motzfeldt and Ilímaussaq, which represent two of Europe's largest REE deposits. We show that the vast majority of our 115 samples have S contents> 100 ppm and δ 34 S of− 1 to 5‰. Only 8 samples (with low S contents,< 100 ppm) show evidence for crustal interactions, implying that the vast majority of Gardar melts preserve the S isotopic signature of their magma source. Importantly, samples from across the Gardar Province have δ 34 S above the canonical mantle range (≤− 1.4‰) and therefore require recycled surface S in their mantle source. Elevated δ 34 S values are explained by a period of Andean-style subduction and mantle metasomatism which took place∼ 500 Ma before rift onset and are also supported by trace elements signatures (eg Ba/La) which match modern subduction zones. Comparing the various generations of Gardar magmas, we find that δ 34 S values, large ion lithophile elements (K, Ba, P) and selective incompatible elements (Nb and light REE) are particularly enriched in the Late Gardar dykes, alkaline complexes and clusters of silica-undersaturated dykes spatially associated with the alkaline complexes. These data indicate that subduction-related metasomatism of the Gardar mantle was spatially heterogeneous, and that alkaline complexes are sourced from localized mantle domains highly enriched in 34 S, REE, alkalis and volatiles (particularly, F). Since alkalis and volatiles play an essential role in driving extreme differentiation of alkaline melts and fluids, we suggest the co-location of these species plus incompatible metals at high concentrations in the lithospheric mantle is a critical first-step in the genesis of a world-class alkaline REE deposit. S isotopes are powerful tools for identifying enriched mantle domains and the sources of mineralized alkaline igneous bodies.
登录
查看更多内容
格陵兰岛南部加尔达尔省元古代埃里克斯峡湾玄武岩的地球化学和 Sr-Nd-O 同位素研究：重建地壳污染的裂谷相关玄武岩中的 OIB 特征
影响因子：
2.7
作者：
R. Halama;T. Wenzel;B. Upton;W. Siebel;G. Markl
通讯作者：
G. Markl
格陵兰岛南部过碱性 Ilı́maussaq 侵入体复杂、封闭系统流体演化的 Nd、O 和 H 同位素证据
影响因子：
5
作者：
M. Marks;T. Vennemann;W. Siebel;G. Markl
通讯作者：
G. Markl
影响因子：
3.9
作者：
Fiege, Adrian;Holtz, Francois;Goettlicher, Joerg
通讯作者：
Goettlicher, Joerg
部分熔融过程中可忽略不计的硫同位素分馏：来自加勒特变换断层玄武岩的证据，对晚单板和玄武岩的影响
影响因子：
5.3
作者：
Jabrane Labidi;P. Cartigny
通讯作者：
P. Cartigny
影响因子：
3.9
作者：
B. Scaillet;R. Macdonald
通讯作者：
B. Scaillet;R. Macdonald