Two cryptic anatectic events within a syn-collisional granitoid from the Aracuai orogen (southeastern Brazil): Evidence from the polymetamorphic Carlos Chagas batholith

被引：44

作者：

Melo, M. G. ^{[1
,2
]}

Stevens, G. ^{[2
]}

Lana, C. ^{[1
]}

Pedrosa-Soares, A. C. ^{[3
]}

Frei, D. ^{[2
]}

Alkmim, F. F. ^{[1
]}

Alkmin, L. A. ^{[1
]}

机构：

[1] Univ Fed Ouro Preto, Escola Minas, Dept Geol, Appl Isotope Res Grp, Campus Univ Morro Cruzeiro S-N, BR-35400000 Ouro Preto, MG, Brazil

[2] Stellenbosch Univ, Dept Earth Sci, Ctr Crustal Petr, Private Bag X1, ZA-7602 Matieland, South Africa

[3] Univ Fed Minas Gerais, IGC CPMTC, Campus Pampulha, BR-31270901 Belo Horizonte, MG, Brazil

来源：

LITHOS | 2017年 / 277卷

关键词：

Multiple anatectic event; Garnet; Granulite facies metamorphism; Monazite and zircon dating; Aracual orogen; MINERAL EQUILIBRIA CALCULATIONS; PARTIAL MELTING EQUILIBRIA; WEST-CONGO OROGEN; SE BRAZIL; SOUTHERN BAHIA; PB AGES; U-PB; MAGMATISM; GRANULITE; SYSTEM;

D O I：

10.1016/j.lithos.2016.10.012

中图分类号：

P3 [地球物理学]; P59 [地球化学];

学科分类号：

0708 ; 070902 ;

摘要：

From the earliest (ca. 630 Ma) pre-collisional plutons to the latest (ca. 480 Ma) post-collisional intrusions, the Aracuai orogen (SE Brazil) records an outstanding succession of granite production events in space and time. The Carlos Chagas batholith (CCB) is the largest (similar to 14,000 km(2)) granitic body ascribed to the collisional plutonism (G2 supersuite) in the back-arc region of the Aracuai orogen, to the east of the Rio Doce magmatic arc. A wide range of monazite and zircon ages (> 725 Ma to ca. 490 Ma) have been found in CCB granites, recording a rich history of crustal recycling and inheritance, magmatic crystallization and anatexis. The CCB includes a dominant granite richer in garnet than in biotite, in which three mineral assemblages can be identified: 1) Qz + Pl + Kfs + Bt + Grt + Ilm +/- Rt; 2) Qz + Pl + Kfs + Bt + Grt + Ilm + Sil; and 3) Qz + Pl + Kfs + Bt + Grt + Ilm + Sil + Spl. Rocks which contain mineral assemblage 2 and 3 all contain two generations of garnet. Textural evidence for the presence of former melt, recognized in all studied CCB samples, includes: silicate melt inclusions in poikiloblastic garnet, pseudomorphed thin films of melt surrounding both generations of garnet, pseudomorphed melt pools adjacent to garnet and biotite, and plagioclase and quartz with cuspate-lobate shapes occurring among matrix grains. Both generations of garnet crystals (Grt(1) and Grt(2)) are unzoned in terms of major element concentration, contain small rounded inclusions of Ti-rich biotite and, in addition, the Grt(2) crystals also contain inclusions of remnant sillimanite needles. Microstructural evidence, in combination with mineral chemistry, indicates that the garnet crystals grew during two distinct metamorphic-anatectic events, as the peritectic products of fluid-absent melting reactions which consumed biotite, quartz and plagioclase, in the case of Grt(1), and which consumed biotite, quartz, plagioclase and sillimanite in the case of Grt(2). PT pseudosections calculated via Theriak-Domino, in combination with in situ UPb monazite and zircon dating, provide new constraints on the thermal evolution of the back-arc region of the Aracuai orogen. Data from assemblage 1 suggests PT conditions for the first granulite-facies metamorphic event (M1) at 790820 degrees C and 9.510.5 kbar, while the assemblage 2 records PT conditions for a second granulite-facies metamorphism (M2) of around 770 degrees C and 6.6 kbar. Monazite and zircon within garnets from the different assemblages give age peaks at 570550 Ma (M1) and 535515 Ma (M2), recording two anatectic events in the CCB during a single orogenic cycle. The PT conditions for these metamorphic events can be related to: i) M1, striking crustal thickening, probably involving thrusting of the magmatic arc onto the back-arc region; and ii) M2, decompression related to the gravitational collapse of the Aracuai orogen. (C) 2016 Elsevier B.V. All rights reserved.

引用

页码：51 / 71

页数：21