Geochemical variations in igneous rocks of the Central Andean orocline (13°S to 18°S): Tracing crustal thickening and magma generation through time and space
Geochemical variations in igneous rocks of the Central Andean orocline (13°S to 18°S): Tracing crustal thickening and magma generation through time and space
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DOI：
10.1130/b26538.1
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发表时间：
2010
影响因子：
4.9
通讯作者：
M. Mamani;G. Wörner;T. Sempéré
中科院分区：
文献类型：
--
作者：
M. Mamani;G. Wörner;T. Sempéré
中安第斯俯冲相关火成岩组分的变化反映了该活动大陆边缘板块构造的时空演化。为了研究安第斯造山带上陆板块俯冲几何形态变化和地壳演化对岩浆活动的影响，本文对秘鲁南部和智利北部（安第斯中造山带）中、新生代（190 ~ 0 Ma）岩浆岩进行了1500多个主元素和微量元素数据点和650个Sr-、610个Nd-和570个pb -同位素分析，其中大部分来自新数据和文献。该数据集记录了侏罗纪以来的岩浆成分变化，其中以新近纪为重点，这一时期地壳主要增厚，对岩浆成分的影响最为明显。我们将观测到的Sr/Y、La/Yb、La/Sm、Sm/Yb、Dy/Yb比值以及Sr、Nd、pb同位素比值的变化与中安第斯造山斜的地壳结构和演化联系起来。特别是，Dy/Yb和Sm/Yb比值的演化，分别追踪了下地壳中高压矿物角闪洞和石榴石的存在，证明了地壳厚度随着时间的推移而增长。微量元素和同位素比值的空间变化进一步表明，不同组成和年龄的地壳域通过同化作用影响了岩浆的组成。通过简单的双组分混合，第四纪岩浆的地壳输入量在7% ~ 18%之间。将地球化学数据与隆升和地壳增厚的地质记录进行比较，发现岩浆岩的组成与安第斯造山运动的进展具有相关性。特别地，我们的结果支持了地壳在中渐新世（30 Ma）开始大规模增厚和隆升的解释，并且地壳厚度一直持续增加到今天。我们的数据不支持分层是安第斯山脉中部晚中新世主要隆起的一般原因，而是支持持续的地壳增厚。
Compositional variations of Central Andean subduction-related igneous rocks reflect the plate-tectonic evolution of this active continental margin through time and space. In order to address the effect on magmatism of changing subduction geometry and crustal evolution of the upper continental plate during the Andean orogeny, we compiled more than 1500 major- and trace-element data points, and 650 Sr-, 610 Nd-, and 570 Pb-isotopic analyses of Mesozoic-Cenozoic (190–0 Ma) magmatic rocks in southern Peru and northern Chile (Central Andean orocline), mostly from new data and the literature. This data set documents compositional variations of magmas since Jurassic time, with a focus on the Neogene period, when major crustal thickening developed and its influence on magma composition was most pronounced. We relate the observed variations in Sr/Y, La/Yb, La/Sm, Sm/Yb, and Dy/Yb ratios, as well as in Sr-, Nd-, and Pb-isotopic ratios, to the crustal structure and evolution of the Central Andean orocline. In particular, the evolution of Dy/Yb and Sm/Yb ratios, which track the presence of the higher-pressure minerals amphibole and garnet, respectively, in the lower crust, documents that crustal thickness has grown through time. Spatial variations in trace elements and isotopic ratios further suggest that crustal domains of distinct composition and age have influenced magma composition through some assimilation. The crustal input in Quaternary magmas is quantified to have been between 7% and 18% by simple two-components mixing. When comparing our geochemical data set to the geological record of uplift and crustal thickening, we observe a correlation between the composition of magmatic rocks and the progression of Andean orogeny. In particular, our results support the interpretation that major crustal thickening and uplift were initiated in the mid-Oligocene (30 Ma) and that crustal thickness has kept increasing until present day. Our data do not support delamination as a general cause for major late Miocene uplift in the Central Andes and instead favor continued crustal thickening.