Volumetric and compositional estimation of the Choiyoi Magmatic Province and its comparison with other Silicic Large Igneous Provinces
Volumetric and compositional estimation of the Choiyoi Magmatic Province and its comparison with other Silicic Large Igneous Provinces
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DOI：
10.1016/j.jsames.2020.102749
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发表时间：
2020-11-01
影响因子：
1.8
通讯作者：
Oliveros, Veronica
中科院分区：
文献类型：
--
作者：
Bastias-Mercado, Francisco;Gonzalez, Javiera;Oliveros, Veronica
Choiyoi岩浆区（Choiyoi Magmatic Province，ChMP）是南美洲南部的一个主要特征，包括早二叠世至早三叠世（286-247 Ma）的火山岩和深成岩，早于安第斯俯冲。其露头从智利北方（类似于南纬20度）下至阿根廷西南部的巴塔哥尼亚（类似于南纬44度），以及从安第斯地区至阿根廷东南部的前陆。这些岩石可细分为三个主要区域：安第斯山脉、拉潘帕二叠纪-三叠纪岩浆走廊（CMPT-LP）和北巴塔哥尼亚。尽管这三个地区具有相似的岩性组成和时间，CMPT-LP岩石的变形风格和地球化学特征表明，它们可能代表了不同于安第斯山脉地区的岩浆活动事件。另一方面，北巴塔哥尼亚和安第斯山脉地区的岩石被认为是同一大地构造背景的一部分，造山Choiyoi，即使北巴塔哥尼亚表现出更复杂的变形模式。对组成ChMP的所有单元的已发表年龄和岩性数据进行汇编，可以估计其面积范围（909，250 km（2）），火山产物的体积以及随时间的成分变化。Choiyoi岩浆区（ChMP-V）的火山产物由51%流纹岩、26%英安岩、22%安山岩和1%玄武岩组成，但火山作用的早期阶段以安山岩产物为主。深成岩占中国大陆板块总面积的25%，主要由花岗岩（约占65%）和花岗闪长岩（约占30%）组成，但代表中国大陆板块早期阶段的单元由花岗闪长岩、英云闪长岩和闪长岩组成，占60%。因此，很明显，Choiyoi岩浆活动，在其整个扩展，过渡到更多的流纹岩在其最后阶段占主导地位的中间。当考虑ChMP-V时，它们的估计体积（947，553 km（3））和时间跨度类似于硅质大火成岩省（SLIP）。然而，他们的岩性组成，特别是大量的中间岩石在第一阶段的ChMP-V不同于典型的SLIP，其中流纹岩和双峰（流纹岩玄武岩）成分占主导地位。迄今为止，西伯利亚的鄂霍次克-楚科奇火山带（OCVB）是最大的保存完好的火山区，但其成分模式与ChMP-V非常相似，早期阶段的岩浆活动主要是中间成分（类似于47%的露头），随后是体积更大且主要为流纹岩的阶段。事实上，OCVB和其他与会聚边缘有关的岩浆区，如Sikote-Alin带或Taupo火山带的演化与ChMP-V相似，这表明Choiyoi岩浆区可能部分产生于俯冲带环境。
The Choiyoi Magmatic Province (ChMP) is a major feature of southern South America comprising volcanic and plutonic rocks from the Early Permian to the Early Triassic (286-247 Ma), prior to the Andean subduction. Its outcrops are exposed from northern Chile (similar to 20 degrees S) down to southwestern Argentina in Patagonia (similar to 44 degrees S), and from the Andean region to the foreland in southeastern Argentina. These rocks can be subdivided in three main regions: Andes, La Pampa Permian-Triassic Magmatic Corridor (CMPT-LP) and North Patagonia. Despite the three regions have similar lithological composition and timing, the deformation style and geochemical features of the CMPT-LP rocks suggest that they may represent an event of magmatism distinct from the Andes region. On the other hand, the rocks from North Patagonia and the Andes regions are considered to be part of the same geotectonic setting, the Orogenic Choiyoi, even though North Patagonia exhibits a more complex deformation pattern. A compilation of published ages and lithological data for all the units that compose the ChMP, allowed an estimation of its areal extent (909,250 km(2)), the volume of its volcanic products, and the compositional variation through time. The volcanic products of Choiyoi Magmatic Province (ChMP-V) are composed of 51% rhyolite, 26% dacite, 22% andesite and 1% basalts, but the early stages of the volcanism were dominated by andesitic products. The plutonic rocks make up the 25% of the total area of the ChMP and they are dominated by granites (similar to 65%) and granodiorites (similar to 30%), although the units representing the early stages of the ChMP are composed up to 60% of granodiorites, tonalites and diorites. It is thus evident that the Choiyoi magmatism, in its whole extension, transitioned from dominantly intermediate to more rhyolitic at its final stages. When considering the ChMP-V, their estimated volume (947,553 km(3)) and time span are akin to a Silicic Large Igneous Province (SLIP). However, their lithological composition through time and especially the large amount of intermediate rocks in the first stage of the ChMP-V differ from typical SLIPs, in which rhyolitic and bimodal (rhyolite-basalt) compositions dominate. The largest preserved silicic province identified so far, the Okhotsk-Chukotka Volcanic Belt (OCVB) in Siberia, has nonetheless a compositional pattern very similar to the ChMP-V with an early stage in which the magmatism was dominantly intermediate in composition (similar to 47% of outcrops), followed by a more volumetric and mostly rhyolitic stage. The fact that the OCVB and other silicic provinces related to convergent margins, such as the Sikote-Alin Belt or the Taupo Volcanic Zone have a similar evolution than the ChMP-V, suggests that the Choiyoi Magmatic Province could have been partly generated in a subduction zone setting.