Naslov
Transition from regional to contact metamorphism in the area of Torres del Paine (Southern Chile) – insights from the clay mineralogy perspective

Autori
Süssenberger, A ; Schmidt, S. Th ; Šegvić, Branimir ; Baumgartner, L

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, ostalo

Skup
8th Mid-European Clay Conference

Mjesto i datum
Košice, Slovačka, 04.07.2016. - 08.07.2016

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
contact and regional metamorphism, illite-smectite, Torres del Paine

Sažetak
Clay minerals are used as metamorphic indicators of low-grade conditions due to their compositional variation and degree of ordering. The extent of chloritization and illitization is generally considered to be a function of temperature, which is related to burial depth, circulation of hydrothermal fluids, proximity of igneous bodies and/or deformation processes. The contact aureole surrounding the Torres del Paine intrusive complex (TPIC) is located in the Magallanes Basin at 51°S latitude. It exhibits excellent conditions to investigate the clay mineral reaction processes taking place during and after the emplacement of the intrusion. The thermal history observed in the Magallanes Basin is due to regional burial, deformation and contact metamorphism. Preliminary results dated the fold-and-thrust belt formation at around 60 Ma under regional anchizonal metamorphic conditions. The Miocene TPIC was emplaced into the Cretaceous Cerro Toro and Punta Barrosa formations between 12.59 and 12.43 Ma [1, 2, 3]. This study investigates the gradual change in clay mineralogy and rock fabric in relation to the distance to the TPIC in order to understand the thermal effects within the several 100 m wide contact aureole. A set of 20 samples were collected in profiles towards the contact aureole, as well as in selected spots surrounding the intrusion. The temperature conditions are estimated based on crystallinity indices, the maturity of organic material and the evolution of mineral paragenesis. Mineral identification and quantification is being done by XRD, SEM, and QEMSCAN. The initial regional metamorphic conditions, prior to the emplacement of the TPIC, are anchizonal with temperatures between 220 and 270°C. Contact metamorphic samples depict minimum temperatures of 330°C. The regional metamorphic anchizonal shale paragenesis consists of albite, chlorite and illite (dominant clay phases). Chlorite shows considerable chemical variations which can be assigned to the presence of a detrital high-T chamosite and an authigenic low-T clinochlore as well as mixed-layer chlorite (clinochlore) -smectite. Illite appears either as pure illite or mixed-layer illite (90%)/smectite. The gradual change to contact metamorphic samples is initiated by a pattern of decreasing expandability of illite and chlorite layers. Contact metamorphic chlorites and illites are characterized by small variations in their chemical composition due to the complete transformation/disappearance of interlayers and the chemical equilibration of detrital grains.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

POVEZANOST RADA