Mantle reservoir geochemistry from statistical analysis of ICP-MS trace element data of equatorial mid-Atlantic MORB glasses
Mantle reservoir geochemistry from statistical analysis of ICP-MS trace element data of equatorial mid-Atlantic MORB glasses
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DOI：
10.1016/s0009-2541(00)00335-1
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发表时间：
2001-06
期刊：
影响因子：
3.9
通讯作者：
R. Hannigan;A. Basu;F. Teichmann
中科院分区：
文献类型：
--
作者：
R. Hannigan;A. Basu;F. Teichmann
本文报道了沿赤道中大西洋海脊(MAR；5°N至5°S)一段1500公里长的58个站采集的51个玄武岩玻璃中21种元素的电感耦合等离子体质谱(ICPMS)痕量元素浓度数据。这些玻璃的同位素系统学揭示了两个同位素截然不同的玻璃之间的混合(Schling，J.-G.，Hanan，B.B.，McCully，B.，Kingsley，R.H.，1994)。塞拉利昂地幔热柱对赤道MAR的影响：Nd锶铅同位素研究。J.地球物理。回复：99,12005-12028。)HIMU和DM地幔来源。这里提供的微量元素数据描述了三个不同的地幔储集层。基于我们新的微量元素数据，我们确定了赤道MAR之下的三个，可能是四个端元地幔储集层。赤道北部MAR(5°N~0°)的玻璃以HIMU型特征为主，La/BA、La/Th和稀土元素(REE)值与P型大洋中脊玄武岩相似(MORB分别为0.1、9.11、(La/Yb)N=5.5)。南部地区(0°~5°S)玄武岩玻璃属轻度放射性铅成因，轻稀土亏损，La/BA、La/Th和REE分别为0.8、40.0、(La/Yb)N<；0.6的N型MORB微量元素。我们利用微量元素浓度数据估计了沿1500公里断面喷发的玻璃中的地幔岩浆来源特征，并确定了地幔端元组分的相对贡献。具体地说，我们认识到在罗曼奇和链状断裂带之间存在着一个统计和地球化学上截然不同的亏损Th和Ba的地幔储集层，相对于平均亏损的MORb。为了充分发挥这一数据集的潜力，我们使用改进的Q型因子分析对地幔储集层的组成进行了模拟。这些数据的多变量分类和归约清楚地区分了微量元素组，每个元素组反映了MAR这个地区存在的地幔来源不均一性。对这些新的痕量元素的统计分析和对相同样品的可用的Ndsr-Pb同位素数据确定了四个具有统计意义的不同端元地幔成分。以往根据HIMU和N-MORB两个地幔储层混合的地球化学数据建立的二元混合模型不能充分解释这些痕量元素数据的差异。不相容元素浓度和比值最好地描述了模拟的端元油藏，它们是HIMU(HPM)、过渡N-MORB(TNM)、贫化N-MORB(DNM)和第四不相容元素富集组分(EPM)。统计确定的端元解释了种群中100%的地球化学变化，但它们的模拟成分可能与过程控制变化有关。我们阐明了统计储集层和地球化学储集层之间的关系，并得出结论：显然有必要建立一个包括三个已识别储集层的多地幔组分模型来描述赤道中大西洋MORBs的微量元素特征。我们的统计方法为这些模拟的地幔组分中的每一个产生了表格的微量元素浓度数据，并通过允许估计这些端元组分在51个玄武岩玻璃样品中的相对贡献，提供了对MAR系统的洞察，这是任何其他技术都无法获得的。
We report Inductively Coupled Plasma Mass Spectrometer (ICP-MS) trace element concentration data for 21 elements in 51 basaltic glasses recovered from 58 stations along a 1500-km segment of the equatorial mid-Atlantic Ridge (MAR; 5°N to 5°S). Isotope systematics of these glasses revealed mixing between two isotopically distinct (Schilling, J.-G., Hanan, B.B., McCully, B., Kingsley, R.H., 1994. Influence of the Sierra Leone mantle plume on the equatorial MAR: a Nd–Sr–Pb isotopic study. J. Geophys. Res., 99, 12005–12028.) HIMU and DM mantle sources. Trace element data presented here describe three distinct mantle reservoirs. Based on our new trace element data, we identified three, and possibly four, end-member mantle reservoirs beneath the equatorial MAR. HIMU-type signatures dominate the glasses from the northern equatorial MAR (5°N to 0°) with La/Ba, La/Th and rare earth element (REE) values similar to P-type mid-Ocean Ridge Basalts (MORB; 0.1, 9.11, (La/Yb)N=5.5, respectively). The basaltic glasses from the southern region (0° to 5°S) are mildly radiogenic in Pb and light REE depleted with N-type MORB trace element values for La/Ba, La/Th and REE (0.8, 40.0, (La/Yb)N<0.6, respectively). We estimate the mantle magma-source characteristics and identify the relative contributions of the mantle end-member components in the glasses erupted along the 1500-km transect using the trace element concentration data. Specifically, we recognize the presence of a statistically and geochemically distinct mantle reservoir depleted in Th and Ba relative to average depleted MORB between the Romanche and the Chain fracture zones. To reach the full potential of this data set, we model mantle reservoir compositions using a modification of Q-MODE factor analysis. Multivariate classification and reduction of these data clearly distinguish trace element groups each reflective of mantle source heterogeneities present in this region of the MAR. Statistical analysis of these new trace element and available Nd–Sr–Pb isotope data for the same samples defines four statistically significant distinct end-member mantle components. The binary mixing model developed previously from geochemical data that invoked the mixing of two mantle reservoirs, HIMU and N-MORB, cannot adequately explain the variance in these trace element data. Incompatible element concentrations and ratios best describe the modeled end-members reservoirs, which are HIMU (HPM), transitional N-MORB (TNM), depleted N-MORB (DNM) and an fourth incompatible element-enriched component (EPM). The statistically determined end-members explain 100% of the geochemical variance in the population but their modeled compositions may be related to process controlled variation. We clarify the relationship between statistical and geochemical reservoirs and conclude that a multiple mantle component model involving three of the identified reservoirs is clearly necessary to describe, specifically, the trace element characteristics of the equatorial mid-Atlantic MORBs. Our statistical methods yield tabulated trace element concentration data for each of these the modeled mantle components and provide insights into the MAR system, unavailable by any other technique, by allowing an estimation of the relative contributions of these end-member components in each of the 51 basaltic glass samples.