Geothermobarometry of basaltic glasses from the Tamu Massif, Shatsky Rise oceanic plateau
Geothermobarometry of basaltic glasses from the Tamu Massif, Shatsky Rise oceanic plateau
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DOI：
10.1002/ggge.20231
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发表时间：
2013-10
期刊：
影响因子：
3.7
通讯作者：
Anika Husen;R. Almeev;F. Holtz;J. Koepke;T. Sano;K. Mengel
中科院分区：
文献类型：
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作者：
Anika Husen;R. Almeev;F. Holtz;J. Koepke;T. Sano;K. Mengel
我们介绍了对塔穆地块（地点U1347）岩芯样本进行岩石学研究的结果，这些岩芯样本是在沙茨基海隆综合大洋钻探计划（IODP）第324次探险期间采集的。来自U1347站点的玄武岩玻璃是演化的拉斑玄武岩，含有5.2- 6.8wt%的MgO，并且主要位于洋中脊玄武岩（MORB）的成分范围内，但它们具有系统性较高的FeO，较低的Al 2 O3，SiO2和Na 2 O浓度，并且CaO/Al 2 O3比值是MORB已知的最高值之一。从这个意义上说，来自U1347站点的玻璃更接近于来自Ontong Java Plateau（OJP）的玄武岩浆，尽管它们仍然具有较低的SiO2浓度。与MORB相反，与OJP相似，我们的分馏校正值的Na 2 O和CaO/Al 2 O 3表明，超过20%的部分熔融的地幔在塔穆地块的母岩浆的产生。通过中红外傅里叶变换红外（FTIR）光谱测定的玻璃中的水含量是MORB-样的，并且在0.18和0.6重量% H2O之间变化。计算的压力（P）-温度（T）条件下，天然玻璃代表钴橄榄石-斜长石-单斜辉石组成范围为0.1至240 MPa和1100至1150°C，反映了岩浆储存在浅深度。玻璃成分的变化和模拟的P-T条件与相对年龄的相关性表明，至少有两个不同的岩浆旋回，其特征在于喷发风格（块状流或枕状熔岩），化学成分，挥发分含量和喷发前的P-T条件的变化。每一岩浆旋回都代表了一批较原始岩浆注入后，在多压结晶过程中的渐进分异。岩浆结晶和喷发事件之后，岩浆活动不活跃，反映在核心序列的沉积层。我们的数据表明，塔穆地块，类似于翁东爪哇海洋高原，结晶下Shatsky隆起发生在不同的地壳水平。
We present the results of a petrological study of core samples from Tamu Massif (Site U1347), recovered during the Shatsky Rise Integrated Ocean Drilling Program (IODP) Expedition 324. The basaltic glasses from Site U1347 are evolved tholeiitic basalts containing 5.2–6.8 wt% MgO, and are principally located within the compositional field of mid‐ocean ridge basalts (MORBs) but they have systematically higher FeO, lower Al2O3, SiO2, and Na2O concentrations, and the CaO/Al2O3 ratios are among the highest known for MORBs. In this sense, glasses from Site U1347 more closely resemble basaltic magmas from the Ontong Java Plateau (OJP), although they still have lower SiO2 concentrations. In contrast to MORB and similar to OJP, our fractionation corrected values of Na2O and CaO/Al2O3 indicate more than 20% of partial melting of the mantle during the generation of the parental magmas of Tamu Massif. The water contents in the glasses, determined by midinfrared Fourier transform infrared (FTIR) spectroscopy, are MORB‐like, and vary between 0.18 and 0.6 wt% H2O. The calculated pressure (P)‐temperature (T) conditions at which the natural glasses represent cotectic olivine‐plagioclase‐clinopyroxene compositions range from 0.1 to 240 MPa and 1100 to 1150°C reflecting magma storage at shallow depth. The variation of the glass compositions and the modeled P‐T conditions in correlation with the relative ages indicate that there were at least two different magmatic cycles characterized by variations in eruptive styles (massive flows or pillow lavas), chemical compositions, volatile contents, and preeruptive P‐T conditions. Each magmatic cycle represents the progressive differentiation in course of polybaric crystallization after the injection of a more primitive magma batch. Magma crystallization and eruption episodes are followed by magmatic inactivity reflected in the core sequence by a sedimentary layer. Our data for Tamu Massif demonstrate that, similar to Ontong Java ocean Plateau, the crystallization beneath Shatsky Rise occurs at different crustal levels.