Evidence for magma-evaporite interactions during the emplacement of the Central Atlantic Magmatic Province (CAMP) in Brazil
Evidence for magma-evaporite interactions during the emplacement of the Central Atlantic Magmatic Province (CAMP) in Brazil
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DOI：
10.1016/j.epsl.2018.11.018
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发表时间：
2019-01-15
影响因子：
5.3
通讯作者：
Planke, Sverre
中科院分区：
文献类型：
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作者：
Heimdal, Thea H.;Callegaro, Sara;Planke, Sverre
巴西中大西洋岩浆区（CAMP）的基性岩床与三叠纪末灭绝（埃特）有时间上的联系，后者是中生代最大的大规模灭绝之一。岩床位于巴西北方亚马逊盆地和索利莫伊斯盆地富含挥发物的沉积岩中。在这里，我们提出了一个新的地球化学研究的26个粗玄岩样品从6个深钻孔在巴西盆地，包括全岩主要和微量元素，全岩Sr-Nd同位素和详细的黑云母矿物化学。大部分的白云石的特点是单斜辉石和斜长石的斑晶在次蛇晶到粒间结构，铁钛氧化物，和罕见的橄榄石和斜方辉石。一个不同的矿物组合（微斑晶的碱长石，石英，黑云母和磷灰石）被发现在小的独立域，定位在框架内的粗斜长石和单斜辉石板条。这些细晶粒的演变域结晶在后期，演变熔体口袋中的间隙空间之间的早期结晶粗晶粒晶体。大多数研究的粗玄岩通常是演化的拉斑玄武岩和玄武安山岩，具有低TiO 2浓度（2.0重量%），在亚马逊盆地东部发现。低钛岩床和高钛岩床的全岩常量元素、微量元素和Sr-Nd同位素地球化学特征与已发表的两种岩浆类型的CAMP岩石相似。低Ti岩床显示出富集的同位素特征（Nd-143/Nd-144（201 Ma）0.51215 ~ 0.51244; Sr-87/Sr-86（201 Ma）0.70568 ~ 0.70756），并伴有不相容元素模式中的类地壳特征（如Nb和Ta亏损）。未蚀变的高钛样品显示出更亏损的同位素特征（Nd-143/Nd-144（201 Ma）0.51260至0.51262; Sr-87/Sr-86（201 Ma）0.70363至0.70398）。低钛白云石从亚马逊和Solimoes盆地含有黑云母极高的Cl浓度（高达4.7重量%）。我们发现，有一个很强的相关性之间的寄主岩石岩性和Cl浓度的黑云母的粗玄岩，并解释这反映了大规模的地壳污染的低Ti岩浆的富石盐的辉长岩。我们的研究结果支持了这一假设，即硅岩蒸发岩相互作用增加挥发性释放在侵位的CAMP。这加强了LIP在三叠纪末危机中的积极参与，并表明LIP的次火山部分在推动气候变化和大规模气候变化方面具有重要意义。(C)2018爱思唯尔B. V.保留所有权利。
Mafic sills of the Central Atlantic Magmatic Province (CAMP) in Brazil are temporally linked to the end-Triassic extinction (ETE), one of the largest mass extinctions of the Phanerozoic. The sills were emplaced into the volatile-rich sedimentary rocks of the Amazonas and Solimoes basins in northern Brazil. Here we present a new geochemical study of 26 dolerite samples from 6 deep boreholes in the Brazilian basins, including whole-rock major and trace elements, whole-rock Sr-Nd isotopes and detailed biotite mineral chemistry. The bulk of the dolerites are characterized by phenocrysts of clinopyroxene and plagioclase in subophitic to intergranular textures, Fe-Ti oxides, and rare olivine and orthopyroxene. A different mineralogical assemblage (microphenocrysts of alkali-feldspar, quartz, biotite and apatite) is found in small independent domains, localized within the framework of coarser plagioclase and clinopyroxene laths. These fine-grained evolved domains crystallized in late-stage, evolved melt pockets in the interstitial spaces between earlier crystallized coarser grained crystals. The majority of the studied dolerites are generally evolved tholeiitic basalts and basaltic andesites with low TiO2 concentrations (2.0 wt.%), and are found in the eastern part of the Amazonas Basin. Whole-rock major and trace element and Sr-Nd isotope geochemistry of both low and high-Ti sills is similar to that of previously published CAMP rocks from the two magma types. Low-Ti sills show enriched isotopic signatures (Nd-143/Nd-144(201Ma) 0.51215 to 0.51244; Sr-87/Sr-86(201Ma) 0.70568 to 0.70756), coupled with crustal-like characteristics in the incompatible element patters (e.g. depletion in Nb and Ta). Unaltered high-Ti samples show more depleted isotopic signatures (Nd-143/Nd-144(201Ma) 0.51260 to 0.51262; Sr-87/Sr-86(201Ma) 0.70363 to 0.70398). Low-Ti dolerites from both the Amazonas and Solimoes basins contain biotite with extremely high Cl concentrations (up to 4.7 wt.%). We show that there is a strong correlation between host-rock lithology and Cl concentrations in biotite from the dolerites, and interpret this to reflect large-scale crustal contamination of the low-Ti magmas by halite rich evaporites. Our findings support the hypothesis that sill-evaporite interactions increased volatile release during the emplacement of CAMP. This strengthens the case for active involvement of this LIP in the end-Triassic crisis, and suggests that the sub-volcanic part of a LIP can be of major importance in driving climate change and mass extinctions. (C) 2018 Elsevier B.V. All rights reserved.