40Ar/39Ar ages and Sr–Nd–Pb–Os geochemistry of CAMP tholeiites from Western Maranhão basin (NE Brazil)
40Ar/39Ar ages and Sr–Nd–Pb–Os geochemistry of CAMP tholeiites from Western Maranhão basin (NE Brazil)
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西马拉尼昂盆地（巴西东北部）CAMP 拉斑玄武岩的 40Ar/39Ar 年龄和 Sr-Nd-Pb-Os 地球化学
DOI：
10.1016/j.lithos.2010.12.010
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发表时间：
2011
期刊：
影响因子：
3.5
通讯作者：
M. Ernesto
中科院分区：
文献类型：
--
作者：
R. Merle;A. Marzoli;H. Bertrand;L. Reisberg;C. Vérati;C. Zimmermann;M. Chiaradia;G. Bellieni;M. Ernesto
中大西洋岩浆省（CAMP）位于三叠系—侏罗系（T-J）边界（~200Ma），是地球上最大的火成岩省之一。巴西东北部的maranh<e:1>盆地位于内陆约700公里处，距离最早的盘古大陆断裂地点约2000公里。CAMP拉斑岩仅分布在盆地西部，被描述为低钛和高钛。本文记录了马兰赫<e:1>奥盆地西部高钛拉斑岩体中两个亚群的赋存情况。主微量元素和Sr-Nd-Pb同位素比值确定了低ti （TiO2<1.3wt）对应的三个化学基团。%)、高ti （TiO2~2.0wt.%）和演化的高ti （TiO2>3wt.%）西马兰赫<s:1>盆地拉斑岩（WMBT）。从斜长石分离得到的高ti（199.7±2.4Ma）和进化的高ti WMBT（197.2±0.5Ma和198.2±0.6Ma）的新40ar /39Ar平台年龄与先前分析的低ti WMBT（198.5±0.8Ma）和CAMP的平均40ar /39Ar年龄（199±2.4Ma）没有区别。我们还首次获得了CAMP玄武岩的Re-Os同位素数据。低ti和高ti样品表现出地幔样初始（187Os/188Os），范围为0.1267 ~ 0.1299，而演化的高ti样品更具有放射性成因（187Os/188Os），最高可达0.184。我们认为，高ti WMBT来源于亚岩石圈软流圈，在上升过程中与次大陆岩石圈地幔（SCLM）相互作用而受到污染。演化出的高ti WMBT同样来源于软流圈，但经历了地壳污染。低钛组的化学特征可以解释为在古俯冲过程中交代的最肥沃部分的部分熔融。或者，低ti WMBT可能来源于岩石圈下软流圈，但由此产生的熔体可能受到了SCLM的污染。高钛玄武岩的出现显然并不局限于最初的大陆分裂区域，这可能会使人们对以前的解释产生疑问，例如那些将高钛CAMP岩浆活动与大西洋脊扩张的开始或深地幔柱的表达联系起来的解释。我们认为，马兰- h<s:1> o盆地的CAMP岩浆活动可能是由于盘古超大陆边缘驱动对流和大规模地幔变暖共同作用下的局部热地幔条件所致。不能排除具有软流层样同位素特征的地幔柱作为WMBT的主要来源成分之一或作为热源的可能性。
The Central Atlantic Magmatic Province (CAMP), emplaced at the Triassic–Jurassic (T–J) boundary (~200Ma), is among the largest igneous provinces on Earth. The Maranhão basin in NE Brazil is located around 700km inland and 2000km from the site of the earliest Pangea disruption. The CAMP tholeiites occur only in the western part of the basin and have been described as low and high-Ti. Here we document the occurrence of two sub-groups among the high-Ti tholeiites in the Western Maranhão basin. The major and trace elements and the Sr–Nd–Pb isotopic ratios define three chemical groups corresponding to the low-Ti (TiO2<1.3wt.%), high-Ti (TiO2~2.0wt.%) and evolved high-Ti (TiO2>3wt.%) western Maranhão basin tholeiites (WMBT). The new40Ar/39Ar plateau ages obtained on plagioclase separates for high-Ti (199.7±2.4Ma) and evolved high-Ti WMBT (197.2±0.5Ma and 198.2±0.6Ma) are indistinguishable and identical to those of previously analyzed low-Ti WMBT (198.5±0.8Ma) and to the mean40Ar/39Ar age of the CAMP (199±2.4Ma). We also present the first Re–Os isotopic data for CAMP basalts. The low and high-Ti samples display mantle-like initial (187Os/188Os)iranging from 0.1267 to 0.1299, while the evolved high-Ti samples are more radiogenic ((187Os/188Os)iup to 0.184) We propose that the high-Ti WMBT were derived from the sub-lithospheric asthenosphere, and contaminated during ascent by interaction with the subcontinental lithospheric mantle (SCLM). The evolved high-Ti WMBT were derived from the same asthenospheric source but experienced crustal contamination. The chemical characteristics of the low-Ti group can be explained by partial melting of the most fertile portions of the SCLM metasomatized during paleo-subduction. Alternatively, the low-Ti WMBT could be derived from the sub-lithospheric asthenosphere but the resulting melts may have undergone contamination by the SCLM. The occurrences of high-Ti basalts are apparently not restricted to the area of initial continental disruption which may bring into question previous interpretations such as those relating high-Ti CAMP magmatism to the initiation of Atlantic ridge spreading or as the expression of a deep mantle plume. We propose that the CAMP magmatism in the Maranhão basin may be attributed to local hotter mantle conditions due to the combined effects of edge-driven convection and large-scale mantle warming under the Pangea supercontinent. The involvement of a mantle-plume with asthenosphere-like isotopic characteristics cannot be ruled out either as one of the main source components of the WMBT or as a heat supplier.
二叠纪峨眉山陆相玄武岩的Os、Pb、Nd同位素地球化学：对大型火成岩省源头的洞察
DOI：
--
发表时间：
2005
期刊：
IFREE REPORT for 2003-2004 (In press)
影响因子：
--
作者：
Xu;J.-F.;Suzuki;K.;Xu;Y.-G.;Mei;H;-J.;Li;J.
通讯作者：
J.