期刊
JOURNAL OF SOUTH AMERICAN EARTH SCIENCES
卷 86, 期 -, 页码 38-53出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jsames.2018.06.004
关键词
Geochronology; Geochemistry; Punta del Este Terrane; Ophiolite
资金
- Fundacao de Amparo a Pesquisa do Estado do Rio Grande do Sul (FAPERGS) [PqG 10/1509-0]
- Conselho Nacional de Desenvolvimento Cientifico e Tecnologic (CNPq) [PQ 305853/2010-4]
This paper presents the first Rb-Sr isotopic geochemistry study and SHRIMP zircon U-Pb dating in the Arroio Grande Ophiolite (southeasternmost Dom Feliciano Belt in Brazil), an extension of the Uruguayan Punta del Este Terrane. The metamafic units of the ophiolite show Sr-87/(86) Sr ratios ranging from 0.7036 to 0.7070 (recalculated at 630 Ma), which suggest a MORE magmatic source for the amphibolite protoliths and a volcanic magmatic arc source (with possible crustal contamination) for the metagabbro protoliths. Together, these features suggest a supra-subduction zone origin for these rocks, corroborating previous studies based on bulk-rock chemistry. In the metaultramafics, the( 87)Sr/(86) Sr-630 ratio of the chloritite sample (0.7152) is comparable to that of the Tres Figueiras granite (0.7139), a syn-kinematic peraluminous granite related to the Ayrosa Galvao-Arroio Grande Shear Zone (which also affected the southern portion of the ophiolite, where the studied samples are located). The emplacement of the latter granite could be responsible for the metasomatism of the former serpentinites, generating talc- and chlorite-rich reaction zones. The SHRIMP U-Pb analysis of twelve chloritite zircons strengthens that assumption, as zircons with ca. 610-585 Ma (the age of the granite) were found in association with metasomatic microtextures. Zircon ages ranging from ca. 2000 to 660 Ma were also found in the chloritite. These latter ages are analogous to those found in the metasiliciclastic rocks that envelop the metaultramafic rocks of the ophiolite, so that the chloritite probably represents a blackwall reaction zone between (i) a former serpentinite, (ii) the Tres Figueiras granite, and (iii) metasiliciclastic rocks. Additionally, we perform a SHRIMP U-Pb dating in a quartz-syenite melt, which are related to a tonalitic intrusion within the metasedimentary unit (the Matarazzo Marbles) of the ophiolite. The obtained concordia age of 640 Ma constrains the minimum age of ophiolitic melange emplacement, as the tonalitic intrusion is related to continental arc magmatism (Pinheiro Machado Intrusive Suite).
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据