High-pressure metamorphic rocks in the Borborema Province, Northeast Brazil: Reworking of Archean oceanic crust during proterozoic orogenies  

作　　者：Alanielson da Câmara Dantas Ferreira Elton Luiz Dantas Ticiano JoséSaraiva dos Santos Reinhardt A.Fuck Mahyra Tedeschi 

机构地区：[1]Instituto de Geociências,Universidade de Brasília(UnB),70910-900,Brasília-DF,Brazil [2]Instituto de Geociências,Universidade Estadual de Campinas(UNICAMP),Departamento de Geologia e Recursos Naturais,13083-970,Campinas-SP,Brazil [3]Instituto de Geoci^encias,Universidade Federal de Minas Gerais(UFMG),31270-901,Belo Horizonte,MG,Brazil

出　　处：《Geoscience Frontiers》2020年第6期2221-2242,共22页地学前缘（英文版）

基　　金：the support of the INCT Estudos Tectônicos(CAPES/CNPq465613/2014-4 and FAPDF-193.001.263/2017)。

摘　　要：We present the first evidence of Archean oceanic crust submitted to Proterozoic high-pressure(HP)metamorphism in the South American Platform.Sm-Nd and Lu-Hf isotopic data combined with U-Pb geochronological data from the Campo Grande area,Rio Grande do Norte domain,in the Northern Borborema Province,reflect a complex Archean(2.9 Ga and 2.6 Ga)and Paleoproterozoic(2.0 Ga)evolution,culminating in the Neoproterozoic Brasiliano/Pan-African orogeny(ca.600 Ma).The preserved mafic rocks contain massive poikiloblastic garnet and granoblastic amphibole with variable proportions of plagioclase+diopside in symplectitic texture,typical of high-pressure rocks.These clinopyroxene-garnet amphibolites and the more common garnet amphibolites from the Campo Grande area are exposed as rare lenses within an Archean migmatite complex.The amphibolite lenses represent 2.65 Ga juvenile tholeiitic magmatism derived from depleted mantle sources(positive values of+3.81 to+30.66)later enriched by mantle metasomatism(negative εNd(t)values of-7.97).Chondrite and Primitive Mantle-normalized REE of analyzed samples and discriminant diagrams define two different oceanic affinities,with E-MORB and OIB signature.Negative Eu anomalies(Eu/Eu*=0.75-0.95)indicate depletion of plagioclase in the source.Inherited zircon cores of 3.0-2.9 Ga in analyzed samples indicate that the Neoarchean tholeiitic magmatism was emplaced into 2923±14 Ma old Mesoarchean crust(εNd(t)--2.58 and Nd TDM=3.2 Ga)of the Rio Grande do Norte domain.The age of retro-eclogite facies metamorphism is not yet completely understood.We suggest that two high-grade metamorphic events are recognized in the mafic rocks:the first at 2.0 Ga,recorded in some samples,and the second,at ca.600 Ma,stronger and more pervasive and recorded in several of the mafic rock samples.The Neoproterozoic zircon grains are found in symplectite texture as inclusions in the garnet grains and represent the age of HP conditions in the area.These zircon grains show a younger cluster of concordant analyses betwee

关 键 词：Archean oceanic crust Proterozoic orogens Borborema province 

分 类 号：P588.3[天文地球—岩石学] P534.3[天文地球—地质学]