Geochemical and tectonic evolution of Late Cretaceous to early Paleocene magmatism along the Southern Central Andes (35-36°S)
Geochemical and tectonic evolution of Late Cretaceous to early Paleocene magmatism along the Southern Central Andes (35-36°S)
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安第斯山脉中南部（35-36°S）晚白垩世至早古新世岩浆作用的地球化学和构造演化
DOI：
10.1016/j.jsames.2017.12.008
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发表时间：
2018
影响因子：
1.8
通讯作者：
A. Folguera
中科院分区：
文献类型：
--
作者：
S. Iannelli;L. Fennell;V. Litvak;L. Fernández Paz;A. Encinas;A. Folguera
安第斯山脉中南部晚白垩世-早古新世岩浆活动以不完整和保存不好的露头为代表。在门多萨省南部（35°30′S）的安第斯山脉火山-沉积序列中，最近的U-Pb年龄确定了晚中生代-早新生代岩浆活动，这是以前没有记录的。我们专注于该序列的岩石学和地球化学特征，非正式地命名为Los Ángeles单元（67 Ma）。这一岩浆组合包括玄武岩和安山质熔岩流与火山角砾岩和岩屑砂岩互层;所有这些熔岩流都被近垂直的玄武岩岩墙侵入。从地球化学角度来看，火山岩主要是拉斑玄武岩，具有弧形特征，相对于HFSE含量，LILE较高。一般富集不相容的元素被认为是对上层和年轻的熔岩流，与更年轻的碱性字符。通过对Los Ángeles单元与安第斯山脉中南部（35°-41 ° S）其他晚白垩世-古新世弧岩浆岩系的区域对比，发现与同时代的南部单元相比，该弧岩浆岩系的弧特征较弱，板状流体影响较小。这种对比鲜明的地球化学行为被认为是在1.70 Ma时Farallon-Bark扩张脊俯冲到所研究的纬度（35°30′S）以下的结果。因此，沿着火山序列观察到的富集现象，以及在洛杉矶单元较年轻的火山层中观察到的类碱性特征，可能与无水洋壳的俯冲有关，并可能与板片窗的初期发育有关。在南部始新世皮尔卡尼约带（北方）露头（南纬40°; 44 Ma）的岩浆表现中也看到了类似的地球化学特征，因为它们显示出有限的弧形特征和板内成分。Farallon-Bark扩张脊的分段几何形状及其由北向南的渐进迁移被认为是形成时间和空间上对比鲜明的岩浆组合的主要原因。
Late Cretaceous-early Paleocene magmatism at Southern Central Andes is represented by incomplete and not well-preserved outcrops. A recent U-Pb age from a volcano-sedimentary sequence in the southern Andes of Mendoza province (35°30′S) led to identify Late Mesozoic-Early Cenozoic magmatism, which was not previously registered. We focus on the petrological and geochemical characterization of this sequence, informally named as Los Ángeles Unit (67 Ma). This magmatic association comprises basaltic and andesitic lava flows interbedded with volcanic breccias and lithic sandstones; all of them intruded by subvertical basaltic dykes. Geochemically, the volcanic rocks are mainly tholeiitic with an arc-like signature and high LILE relative to HFSE content. A general enrichment in incompatible elements is seen towards the upper and younger lava flows, associated with a more alkaline character in the youngest ones. A regional comparison among Los Ángeles Unit and other Late Cretaceous-Paleocene arc magmatic series along the Southern Central Andes (35°-41°S) shows that the studied sequence has a weaker arc-like signature and less slab-fluid influence than in coeval southern units. This contrasting geochemical behavior is proposed to be a consequence of the subduction of the Farallon-Aluk spreading ridge beneath the studied latitudes (35°30′S) at ∼70 Ma. Thus, the enrichment seen along the volcanic sequence together with the alkaline-like signature seen in the younger volcanic levels of Los Ángeles Unit would be related to the subduction of anhydrous oceanic crust and potentially the incipient development of a slab window. Similar geochemical features are seen to the south in the magmatic expressions of the northern Eocene Pilcaniyeu Belt outcrops (∼40°S; 44 Ma), as they show a limited arc-like signature and an intraplate-like composition. The segmented geometry of the Farallon-Aluk spreading ridge and its progressive migration from north to south is considered to be the main cause of the development of contrasting magmatic associations during time and space.