The Central Atlantic Magmatic Province (CAMP) in Morocco
The Central Atlantic Magmatic Province (CAMP) in Morocco
复制标题
摩洛哥中大西洋岩浆省 (CAMP)
作者：
A. Marzoli;H. Bertrand;N. Youbi;S. Callegaro;R. Merle;L. Reisberg;M. Chiaradia;Sarah I Brownlee;F. Jourdan;A. Zanetti;J. Davies;T. Cuppone;Abdelkader Mahmoudi;F. Medina;P. Renne;G. Bellieni;S. Crivellari;Hind El Hachimi;M. K. Bensalah;C. Meyzen;C. Tegner
中大西洋岩浆区（Central Atlantic Magmatic Province，CAMP）是一个由基性岩墙、岩床、层状侵入体和熔岩流组成的大型火成岩区，分布于大西洋周边的四大洲，形成于盘古大陆裂解之前。CAMP最古老、保存最完好、最完整的分省之一位于摩洛哥。根据以往研究中获得的地球化学、年代学、岩相学和磁性地层学资料，可识别出四个层化岩浆单元，即下、中、上和循环单元。在这项研究中，我们完成了一个详细的采样营地在摩洛哥，从南部的反阿特拉斯在北部的梅塞塔。我们提供了一个完整的矿物学，岩石学（全岩和矿物的主要和微量元素），地质年代学（40 Ar/39 Ar和U-Pb年龄）和地球化学数据集（包括Sr-Nd-Pb-Os同位素系统学）的玄武岩和玄武安山质熔岩流桩和它们的假定的馈线堤坝和岩床。结合野外观察，这些数据表明，超过95%的保存岩浆岩非常快速（<0.3Ma）侵位。特别是，新的和以前发表的数据，下到上单元样品产生了不可区分的40 Ar/39 Ar（平均年龄= 201·2 ± 0·8 Ma）和U-Pb年龄（201·57 ± 0·04 Ma），表明侵位与三叠纪末生物更替的主要阶段（约201·5至201·3 Ma）一致。火山爆发被认为是在五个主要的火山脉冲期间以超过10立方公里/年的速率脉冲，每个脉冲可能只持续几个世纪。如此高的喷发率加强了CAMP岩浆活动引发三叠纪末气候变化和大规模灭绝的可能性。只有经常性单位可能更年轻，但不超过1 Ma。全岩和矿物地球化学制约了CAMP玄武岩的成因。摩洛哥岩浆演化中地壳水库（7-20公里深）的大部分分化发生。然而，先前的结晶阶段可能发生在更深的地方。这四个单元不能通过封闭系统的分离结晶过程联系起来，但需要不同的母岩浆和/或不同的地壳同化过程。EC-AFC模型表明，有限的地壳同化（最大c.5-8%的同化，如Eburnean或泛非花岗岩）可以解释一些，但不是所有观察到的地球化学变化。中间单元岩浆显然是最受污染的，可能是来自类似于上部玄武岩的母岩浆（如这些单元的辉石分析中不可区分的微量元素含量所证明的）。中间单元中的中央高阿特拉斯和中阿特拉斯样品之间的化学差异可以用不同的地壳污染物来解释（前者是下地壳岩石或泛非花岗岩，后者是埃布尔尼亚花岗岩）。摩洛哥的CAMP单元可能来自富集橄榄岩源的5-10%熔融。四个单元的稀土元素比值的差异归因于源矿物学和熔融程度的变化。特别是，较低的玄武岩需要一个石榴石橄榄岩源，而上玄武岩可能形成于一个较浅的熔融区跨越石榴石尖晶石过渡。相反，循环玄武岩是主要由尖晶石橄榄岩产生的相对较浅的熔体。摩洛哥的CAMP单元的Sr-Nd-Pb-Os同位素比值与其他CAMP亚省的相似，表明俯冲地壳组分对幔源区的显著富集。富集的签名是由于参与约5-10%的回收地壳材料引入到周围的贫化或PREMA型地幔，而地幔柱成分的参与，如今天的中大西洋岛屿玄武岩（OIB，如佛得角和加那利群岛）的采样不支持所观察到的成分。只有循环玄武岩可能反映了类似于常见或FOZO组件的中大西洋羽状签名。
The Central Atlantic Magmatic Province (CAMP) is a large igneous province (LIP) composed of basic dykes, sills, layered intrusions and lava flows emplaced before Pangea break-up and currently distributed on the four continents surrounding the Atlantic Ocean. One of the oldest, best preserved and most complete sub-provinces of the CAMP is located in Morocco. Geochemical, geochronologic, petrographic and magnetostratigraphic data obtained in previous studies allowed identification of four strato-chemical magmatic units, i.e. the Lower, Intermediate, Upper and Recurrent units. For this study, we completed a detailed sampling of the CAMP in Morocco, from the Anti Atlas in the south to the Meseta in the north. We provide a complete mineralogical, petrologic (major and trace elements on whole-rocks and minerals), geochronologic (40Ar/39Ar and U–Pb ages) and geochemical set of data (including Sr–Nd–Pb–Os isotope systematics) for basaltic and basaltic–andesitic lava flow piles and for their presumed feeder dykes and sills. Combined with field observations, these data suggest a very rapid (<0·3 Ma) emplacement of over 95% of the preserved magmatic rocks. In particular, new and previously published data for the Lower to Upper unit samples yielded indistinguishable 40Ar/39Ar (mean age = 201·2 ± 0·8 Ma) and U–Pb ages (201·57 ± 0·04 Ma), suggesting emplacement coincident with the main phase of the end-Triassic biotic turnover (c.201·5 to 201·3 Ma). Eruptions are suggested to have been pulsed with rates in excess of 10 km3/year during five main volcanic pulses, each pulse possibly lasting only a few centuries. Such high eruption rates reinforce the likelihood that CAMP magmatism triggered the end-Triassic climate change and mass extinction. Only the Recurrent unit may have been younger but by no more than 1 Ma. Whole-rock and mineral geochemistry constrain the petrogenesis of the CAMP basalts. The Moroccan magmas evolved in mid-crustal reservoirs (7–20 km deep) where most of the differentiation occurred. However, a previous stage of crystallization probably occurred at even greater depths. The four units cannot be linked by closed-system fractional crystallization processes, but require distinct parental magmas and/or distinct crustal assimilation processes. EC-AFC modeling shows that limited crustal assimilation (maximum c.5–8% assimilation of e.g. Eburnean or Pan-African granites) could explain some, but not all the observed geochemical variations. Intermediate unit magmas are apparently the most contaminated and may have been derived from parental magmas similar to the Upper basalts (as attested by indistinguishable trace element contents in the augites analysed for these units). Chemical differences between Central High Atlas and Middle Atlas samples in the Intermediate unit could be explained by distinct crustal contaminants (lower crustal rocks or Pan-African granites for the former and Eburnean granites for the latter). The CAMP units in Morocco are likely derived from 5–10% melting of enriched peridotite sources. The differences observed in REE ratios for the four units are attributed to variations in both source mineralogy and melting degree. In particular, the Lower basalts require a garnet peridotite source, while the Upper basalts were probably formed from a shallower melting region straddling the garnet–spinel transition. Recurrent basalts instead are relatively shallow-level melts generated mainly from spinel peridotites. Sr–Nd–Pb–Os isotopic ratios in the CAMP units from Morocco are similar to those of other CAMP sub-provinces and suggest a significant enrichment of the mantle-source regions by subducted crustal components. The enriched signature is attributed to involvement of about 5–10% recycled crustal materials introduced into an ambient depleted or PREMA-type mantle, while involvement of mantle-plume components like those sampled by present-day Central Atlantic Ocean Island Basalts (OIB, e.g. Cape Verde and Canary Islands) is not supported by the observed compositions. Only Recurrent basalts may possibly reflect a Central Atlantic plume-like signature similar to the Common or FOZO components.
影响因子：
5.3
作者：
M. Ruhl;S. Hesselbo;S. Hesselbo;L. Hinnov;H. Jenkyns;Weimu Xu;J. Riding;M. Storm;D. Minisini-
通讯作者：
M. Ruhl;S. Hesselbo;S. Hesselbo;L. Hinnov;H. Jenkyns;Weimu Xu;J. Riding;M. Storm;D. Minisini-