U–Pb and Sm–Nd evidence for 1.76–1.77 Ga magmatism in the Moriru region, Mato Grosso, Brazil: implications for province boundaries in the SW Amazon Craton
- 作者：Pinho ; Marcia A.S.B. ; Chemale Jr ; Farid ; Van Schmus ; W. Randall ; Pinho ; Francisco E.C.
- 关键词：Amazon Craton ; Geochronology ; Paleoproterozoic ; Post-tectonic ; Brazil
- 刊名：Precambrian Research
- 出版年：2003
- 期刊代码：75_03019268
- 类别：ear
- 出版时间：September 15, 2003
- 卷：126
- 期：1-2
- 页码：1-25
- 文件大小：815 K
摘要
The Moriru region, situated in the SW Amazon Craton, Mato Grosso, Brazil, is composed of two main domains: (1) an area of undeformed bimodal volcanic rocks and (2) an area of deformed granitic–gneissic–migmatite rocks that also include a small occurrence of slightly deformed rhyolite. The undeformed domain is composed of felsic to mafic flows and volcanoclastic sediments; the felsic flows are essentially explosive deposits classified as ignimbrites, however flows lava occurs interlayed. The compositions of ignimbrites and associated felsic lava are rhyodacite to dacite. The mafic volcanics are phaneritic, fine-grained, and are often strongly hydrothermally altered. Unaltered samples have tholeiitic to transitional compositions and have within-plate petrologic and geochemical characteristics. The felsic volcanics are enriched in light REE, show a negative Eu anomaly, and are depleted in heavy REE. The trace elements indicate a post-collisional environment. U–Pb data on single zircon grains from the volcanic sequence yield ages between 1770±6Ma and 1778±6Ma. ?Nd(t) values range from −1.4 to +1.5 (t=1.75Ga), and the TDM model ages range from 2.02 to 2.16Ga.