Contact vs Regional Metamorphism in the Area of Torres Del Paine (Southern Chile) – Combining Raman Spectroscopy and Clayinvestigations

Süssenberger, Annette; Schmidt, Susanne Theodora; Šegvić, Branimir; Baumgartner, Lukas P.

doi:10.1130/abs/2016am-285464

Cited by 2 publications

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“…Sample 14-72 originated from the hanging wall above the thrust ramp, similar to the position of sample 14-1, and it records the thrust activity of the Río Nutria thrust. Thermal influence due to the Miocene Torres del Paine intrusive complex is considered to be unlikely, since the contact metamorphic zone is limited to a very narrow (<1.2 km) corridor surrounding the intrusion (Bodner, 2013;Süssenberger et al, 2016Süssenberger et al, , 2017. The interpretation of the <0.2 μm ages for samples within the Cerro Toro Formation (14-15, 14-21, 14-29, 14-35, 14-38, 14-46, 14-55, 14-63, and 14-75) is less evident and needs to be considered in light of the whole K-Ar database.…”

Section: (2) Early Campanian (Ca 80 Ma)-illite Growth During Diagenementioning

confidence: 99%

Timing and thermal evolution of fold-and-thrust belt formation in the Ultima Esperanza District, 51°S Chile: Constraints from K-Ar dating and illite characterization

et al. 2017

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K-Ar dating on synkinematically formed illite in low-grade metamorphic pelites was used to set new time constraints on the development of the Patagonian retroarc fold-andthrust belt caused by the subduction of the Antarctic plate beneath the South American plate. The combined use of illite crystallinity (Kübler index), polytype quantification, and K-Ar dating of illite fractions (<0.2, <2, and 2-6 μm) is a powerful tool in constraining the missing time gap between the emergent foldand-thrust belt formation and early Miocene uplift of the Magallanes Basin. Four distinct periods of illite growth were identified based on their K-Ar ages and degree of regional metamorphism: (1) early Cenomanian (98 Ma) illite crystallization, (2) widespread early Campanian (ca. 80 Ma) long-lasting burial illitization processes under anchizonal metamorphic conditions, (3) a significant period of illite formation in the early Paleocene (ca. 60 Ma), and (4) a late stage of illite growth in the early Eocene (55-46 Ma) under epizonal conditions. Based on K-Ar fine fraction ages and Kübler index values, we propose to subdivide the internal domain along the Río Nutria and Río Rincon thrust into a thrust zone with maximum rock uplift in the west and a foreland-vergent imbricate thrust zone in the east. The earliest indication for the emergent fold-and-thrust belt formation in the hinterland is documented in a metapelitic clast (sample 14-9, <2 μm) within the Upper Cretaceous Cerro Toro conglomerate, which yielded a K-Ar cooling age of 98.3 ± 1.2 Ma and an epizonal Kübler index value of 0.24 Δ°2Ɵ. After a certain period of geological quiescence, an interval of major thrusting and rock uplift occurred between ca. 60 and 46 Ma. The west-dipping Río Nutria and Río Rincon thrusts record the onset of fold-andthrust belt activity, which can be placed close to 60 Ma. In the western part of the internal domain, thrusts remained active, and associated structural uplift is recorded until 46 Ma by K-Ar illite cooling ages. Flexural subsidence driven by thrust sheet loading in the internal domain was responsible for the eastward migration of the foreland depocenter and a rapid increase in sedimentation rate along the monoclinal belt. Our results prove a synchronous onset of thickskinned thrusting between 49°S and 55°S and suggest constant convergence rates of the Patagonian arc against the adjacent South American continental margin. Time-averaged exhumation rates along the Río Rincon anticline (54.6-22 Ma) and along the Río Nutria thrust (46.5-22 Ma) suggest rather low exhumation rates of 1.6-1.2 mm/yr (maximum). The low exhumation rates link back to constantly low subduction rates, resulting in a period of geological quiescence between 46.5 and 22 Ma.

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Section: (2) Early Campanian (Ca 80 Ma)-illite Growth During Diagenementioning

confidence: 99%

Timing and thermal evolution of fold-and-thrust belt formation in the Ultima Esperanza District, 51°S Chile: Constraints from K-Ar dating and illite characterization

et al. 2017

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“…The maximum ambient temperature of the metasediments prior to the emplacement of the TPI was between 240 and 260 • C and related to regional low-grade metamorphism (Süssenberger et al, 2016(Süssenberger et al, , 2018b. The regional anchizonal metamorphic degree is recorded by the maturity of organic matter, chlorite temperatures, and illite "crystallinities" (Süssenberger et al, 2018a, b, c).…”

Section: Geological Settingmentioning

confidence: 99%

Reaction progress of clay minerals and carbonaceous matter in a contact metamorphic aureole (Torres del Paine intrusion, Chile)

Süssenberger

Schmidt

et al. 2020

Eur. J. Mineral.

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Abstract. This study reports on reaction processes in a transition zone from contact to regional metamorphism by using Raman spectroscopy on carbonaceous matter (RSCM), illite “crystallinity” (Kübler index, KI), chlorite geothermometry, and thermal modeling. The thermal effect due to the emplacement of the Torres del Paine intrusion (TPI, assembly time of ca. 150 kyr) had different consequences for inorganic and organic compounds of the host rock. The thermal alteration of the pre-intrusive regional metamorphosed host rock is documented by elevated RSCM temperatures, high-temperature chlorite generations, and the appearance of epidote and retrograde Fe-rich chlorite. Microprobe analysis on chlorite indicates incomplete re-equilibration as evidenced by various chlorite populations of individual contact metamorphic samples. This study indicates that the maturity of organic matter is the most reliable and unequivocal indicator on timescales of several thousand years to determine the lateral extension of the TPI contact aureole. Raman geothermometry reveals that the lateral extension of the contact-influenced zone expands up to a distance of 1.5 km and, thus, expands to ca. 1.1 km further out than the macroscopically mappable hornfels contact aureole. The best match between measured (Raman geothermometry) and calculated (thermal modeling) ΔTmax values (ΔT=54 ∘C) is achieved with a total intrusion assembly time of 150 kyr, a magmatic temperature of 800 ∘C, a two-batch model (batch repose time of 10 kyr) with five pulses per batch, short heating durations (3 kyr), and long pulse repose times (15 kyr).

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Contact vs Regional Metamorphism in the Area of Torres Del Paine (Southern Chile) – Combining Raman Spectroscopy and Clayinvestigations

Cited by 2 publications

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Timing and thermal evolution of fold-and-thrust belt formation in the Ultima Esperanza District, 51°S Chile: Constraints from K-Ar dating and illite characterization

Timing and thermal evolution of fold-and-thrust belt formation in the Ultima Esperanza District, 51°S Chile: Constraints from K-Ar dating and illite characterization

Reaction progress of clay minerals and carbonaceous matter in a contact metamorphic aureole (Torres del Paine intrusion, Chile)

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