Calc-Alkaline Magmatism at the Archean^Proterozoic Transition: the Caico¤ Complex Basement (NE Brazil)
Calc-Alkaline Magmatism at the Archean^Proterozoic Transition: the Caico¤ Complex Basement (NE Brazil)
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DOI：
10.1093/petrology/egm055
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发表时间：
2007-11
影响因子：
3.9
通讯作者：
Z. Souza;H. Martin;J. Peucat;E. F. J. D. Sá;M. Macedo
中科院分区：
文献类型：
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作者：
Z. Souza;H. Martin;J. Peucat;E. F. J. D. Sá;M. Macedo
巴西东北部Serido地区凯科复杂基底的古元古代变质岩石为研究控制地壳生长的岩石成因过程提供了重要而关键的见解，并可能成为了解太古代→元古代过渡的潜在代表。这些岩石由高钾钙碱性闪长岩至花岗岩组成，其Rb^Sr、U^Pb、Pb^Pb和Sm^Nd年龄为c。225^215 Ga.它们具有较高的YbN、K_2O/Na_2O和Rb/Sr比值，较低的ISr比值，是富大离子亲石元素（LILE）的准晶质矿物。岩石学和地球化学数据表明，它们属于分异系列，由低压分馏作用演化，从而产生花岗闪长质液体。我们提出了一个模式，其中凯科 * 复式正片麻岩的岩石成因开始于部分熔融的交代富集的尖晶石-石榴石的二辉橄榄岩（以高硅埃达克岩熔体作为交代剂），产生基性岩浆，随后通过橄榄石的分离结晶作用，在深部演化，随后是低压壳内分离作用。俯冲带设置提出了这种岩浆作用，占两个负异常高场强元素（HFSE）和大离子亲石富集。在萨奥弗朗西斯科、西非古陆和法属圭亚那也发现了相同年龄的幔源幼年岩浆活动，因此太古宙至元古代的转变标志着一个非常重要的大陆增生事件。它也代表了从板状为主（在太古代）到楔状为主的后太古代岩浆活动的过渡。
The Paleoproterozoic metaplutonic rocks of the Caico* Complex Basement (Serido* region, NE Brazil) provide important and crucial insights into the petrogenetic processes governing crustal growth and may potentially be a proxy for understanding the Archean^ Proterozoic transition. These rocks consist of high-K calc-alkaline diorite to granite, with Rb^Sr, U^Pb, Pb^Pb and Sm^Nd ages of c. 225^215 Ga. They are metaluminous, with high YbN, K2O/Na2Oand Rb/Sr, low ISr ratios, and are large ion lithophile elements (LILE) enriched. Petrographic and geochemical data demonstrate that they belong to differentiated series that evolved by low-pressure fractionation, thus resulting in granodioritic liquids.We propose a model in which the petrogenesis of the Caico* Complex orthogneisses begins with partial melting of a metasomatically enriched spinel- to garnet-bearing lherzolite (with high-silica adakite melt as the metasomatic agent), generating a basic magma that subsequently evolved at depth through fractional crystallization of olivine, followed by low-pressure intracrustal fractionation. A subduction zone setting is proposed for this magmatism, to account for both negative anomalies in high field strength elements (HFSE) and LILE enrichment. Mantle-derived juvenile magmatism with the same age is also known in the SaÐ o Francisco andWest Africa cratons, as well as in French Guyana, and thus the Archean^Proterozoic transition marks a very important continental accretion event. It also represents a transition from slab-dominated (in the Archean) to wedge-dominated post-Archean magmatism.