scholarly journals Ultrahigh-temperature granulite-facies metamorphism and exhumation of deep crust in a migmatite dome during late- to post- orogenic collapse and extension in the central Adirondack Highlands (New York, USA)

Geosphere ◽  
2021 ◽  
Author(s):  
Ellen P. Metzger ◽  
Mary L. Leech ◽  
Michael W. Davis ◽  
Jackson V. Reeder ◽  
Brandon A. Swanson ◽  
...  
Keyword(s):  
New York ◽  
Phase Equilibrium ◽  
Granulite Facies ◽  
Gneiss Dome ◽  
Granulite Facies Metamorphism ◽  
Equilibrium Modeling ◽  
Crustal Rocks ◽  
Ultrahigh Temperature ◽  
Uht Metamorphism ◽  
Shrimp Zircon Geochronology

This study combines field observations, mineral and whole-rock geochemistry, phase equilibrium modeling, and U-Pb sensitive high-resolution ion microprobe (SHRIMP) zircon geochronology to investigate sillimanite-bearing felsic migmatites exposed on Ledge Mountain in the central Adirondack Highlands (New York, USA), part of an extensive belt of mid-crustal rocks comprising the hinterland of the Mesoproterozoic Grenville orogen. Phase equilibrium modeling suggests minimum peak metamorphic conditions of 960–1025 °C and 11–12.5 kbar during the Ottawan orogeny—significantly higher pressure-temperature conditions than previously determined—followed by a period of near-isothermal decompression, then isobaric cooling. Petrography reveals abundant melt-related microstructures, and pseudosection models show the presence of at least ~15%–30% melt during buoyancy-driven exhumation and decompression. New zircon data document late Ottawan (re)crystallization at ca. 1047 ± 5 to 1035 ± 2 Ma following ultrahigh-temperature (UHT) metamorphism and anatexis on the retrograde cooling path. Inherited zircon cores give a mean date of 1136 ± 5 Ma, which suggests derivation of these felsic granulites by partial melting of older igneous rocks. The ferroan, anhydrous character of the granulites is similar to that of the ca. 1050 Ma Lyon Mountain Granite and consistent with origin in a late- to post-Ottawan extensional environment. We present a model for development of a late Ottawan migmatitic gneiss dome in the central Adirondacks that exhumed deep crustal rocks including the Snowy Mountain and Oregon anorthosite massifs with UHT Ledge Mountain migmatites. Recognition of deep crustal meta-plutonic rocks recording UHT metamorphism in a migmatite gneiss dome has significant implications for crustal behavior in this formerly thickened orogen.

scholarly journals Supplemental Material: Ultrahigh-temperature granulite-facies metamorphism and exhumation of deep crust in a migmatite dome during late- to post-orogenic collapse and extension in the central Adirondack Highlands (New York, USA)

2021 ◽  
Author(s):  
E.P. Metzger ◽  
et al. ◽  
M.L. Leech
Keyword(s):  
New York ◽  
Granulite Facies ◽  
Granulite Facies Metamorphism ◽  
Deep Crust ◽  
Honestly Significant Difference ◽  
Significant Difference ◽  
Facies Metamorphism ◽  
Text Figure ◽  
Tukey Honestly Significant Difference ◽  
Ultrahigh Temperature

<div>Text S1: Supplemental text. Figure S1: Cathodoluminescence images for all analyzed zircon grains. Figure S2: REE spider plots for zircon. Figure S3: Tukey honestly significant difference (HSD) for the timing of anatexis. Table S1: Cathodoluminescence images for all analyzed zircon grains. Table S2. Grossular content of garnet used to calculate the 95% confidence intervals for isopleth modeling in Figure 13. <br></div>

scholarly journals Supplemental Material: Ultrahigh-temperature granulite-facies metamorphism and exhumation of deep crust in a migmatite dome during late- to post-orogenic collapse and extension in the central Adirondack Highlands (New York, USA)

2021 ◽  
Author(s):  
E.P. Metzger ◽  
et al. ◽  
M.L. Leech
Keyword(s):  
New York ◽  
Granulite Facies ◽  
Granulite Facies Metamorphism ◽  
Deep Crust ◽  
Honestly Significant Difference ◽  
Significant Difference ◽  
Facies Metamorphism ◽  
Text Figure ◽  
Tukey Honestly Significant Difference ◽  
Ultrahigh Temperature

<div>Text S1: Supplemental text. Figure S1: Cathodoluminescence images for all analyzed zircon grains. Figure S2: REE spider plots for zircon. Figure S3: Tukey honestly significant difference (HSD) for the timing of anatexis. Table S1: Cathodoluminescence images for all analyzed zircon grains. Table S2. Grossular content of garnet used to calculate the 95% confidence intervals for isopleth modeling in Figure 13. <br></div>

scholarly journals Supplemental Material: Ultrahigh-temperature granulite-facies metamorphism and exhumation of deep crust in a migmatite dome during late- to post-orogenic collapse and extension in the central Adirondack Highlands (New York, USA)

2021 ◽  
Author(s):  
E.P. Metzger ◽  
et al. ◽  
M.L. Leech
Keyword(s):  
New York ◽  
Granulite Facies ◽  
Granulite Facies Metamorphism ◽  
Deep Crust ◽  
Honestly Significant Difference ◽  
Significant Difference ◽  
Facies Metamorphism ◽  
Text Figure ◽  
Tukey Honestly Significant Difference ◽  
Ultrahigh Temperature

<div>Text S1: Supplemental text. Figure S1: Cathodoluminescence images for all analyzed zircon grains. Figure S2: REE spider plots for zircon. Figure S3: Tukey honestly significant difference (HSD) for the timing of anatexis. Table S1: Cathodoluminescence images for all analyzed zircon grains. Table S2. Grossular content of garnet used to calculate the 95% confidence intervals for isopleth modeling in Figure 13. <br></div>

Petrology and geochronology of cordierite bearing assemblages from the Wanni Complex – Sri Lanka

2020 ◽  
Author(s):  
Nikolaus Lechner ◽  
Christoph Hauzenberger ◽  
Marcel Masten ◽  
Dominik Sorger ◽  
G.W.A. Rohan Fernando
Keyword(s):  
Sri Lanka ◽  
Rock Type ◽  
Granulite Facies ◽  
Granulite Facies Metamorphism ◽  
Pan African ◽  
Basement Rocks ◽  
The Matrix ◽  
The Common ◽  
Group 2 ◽  
Uht Metamorphism

&lt;p&gt;Based on differences in metamorphic grade and isotope model ages, the basement rocks of Sri Lanka can be subdivided from NW to SE into the Wanni Complex (WC), the Highland Complex (HC) and the Vijayan Complex (VC) (Milisenda et al. 1994). The UHT conditions of the HC were studied extensively and are well constrained whereas data from the WC and VC are less abundant. Only few recent petrological and geochemical work has been done especially along the WC&amp;#8211;HC boundary which is still ill-defined (Kitano et al. 2018; Wanniarachchi &amp; Akasaka 2016). Due to the common occurrence of migmatites, pyroxene bearing gneisses, and cordierite bearing metapelites/paragneisses, the WC clearly experienced granulite facies metamorphism. However, PT conditions are lower compared to the HC. In this study, U-Th-Pb monazite dating combined with a petrological study including phase equilibria modelling and thermobarometry was conducted focusing on cordierite bearing migmatic biotite gneisses located at the WC&amp;#8211;HC boundary in the West of Sri Lanka. The HC underwent UHT metamorphism at 580-570Ma (Sajeev et al. 2010), the main metamorphic phase of the VC is dated with 580Ma. (Kr&amp;#246;ner et al., 2013). With U-Th-Pb monazite ages of around 530 Ma, the cordierite bearing assemblages from the WC are significantly younger (Wanniarachchi &amp; Akasaka 2016). The predominantly felsic but also mafic peraluminous migmatic ortho- and paragneisses comprising the mineral assemblage cordierite + garnet + biotite + plagioclase + k-feldspar + quartz + ilmenite + magnetite + spinel + sillimanite &amp;#177; orthopyroxene and contain monazite (+ zircon &amp;#177; xenotime) as garnet inclusions (Group1) and in the matrix (Group2). Group1 monazite ages cluster around 575&amp;#177;5 Ma and 561&amp;#177;5 Ma whereas ages of Group 2 cluster at 550&amp;#177;3 and 527&amp;#177;3. Based on ages and textural occurrence of monazite we suggest that two thermal events at ca. 550-575 Ma and ca. 530-550 Ma are recorded in this rock type indicating a complex evolution during the late stage of the Pan-African orogeny. PT conditions range from 700&amp;#8211;900&amp;#176;C and from 5&amp;#8211;8 kbar with a decreasing north-south gradient. Further geochronological investigations are needed to relate either to the older or the younger overprint to the main metamorphic phase of the WC.&lt;/p&gt;&lt;p&gt;Kitano, I., Osanai, Y., Nakano, N., Adachi, T., &amp; Fitzsimons, I. C. W. (2018). Journal of Asian Earth Sciences, 156, 122&amp;#8211;144.&lt;/p&gt;&lt;p&gt;Kr&amp;#246;ner, A., Rojas-Agramonte, Y., Kehelpannala, K. V. W., Zack, T., Hegner, E., Geng, H. Y., &amp;#8230; Barth, M. (2013). Precambrian Research, 234, 288&amp;#8211;321.&amp;#160;&lt;/p&gt;&lt;p&gt;Milisenda, C. C., Liewa, T. C., Hofmanna, A. W., &amp; K&amp;#246;hler, H. (1994). Precambrian Research, 66(1&amp;#8211;4), 95&amp;#8211;110.&lt;/p&gt;&lt;p&gt;Sajeev, K., Williams, I. S., &amp; Osanai, Y. (2010). Geology, 38(11), 971&amp;#8211;974.&lt;/p&gt;&lt;p&gt;Wanniarachchi, D. N. S., &amp; Akasaka, M. (2016). Journal of Mineralogical and Petrological Sciences, 111(5), 351&amp;#8211;362.&lt;/p&gt;

Extreme thermal metamorphism associated with Gondwana assembly: Evidence from sapphirine-bearing granulites of Rajapalayam, southern India

2019 ◽  
Vol 132 (5-6) ◽  
pp. 1013-1030 ◽  
Author(s):  
Shan-Shan Li ◽  
Richard M. Palin ◽  
M. Santosh ◽  
E. Shaji ◽  
T. Tsunogae
Keyword(s):  
Granulite Facies ◽  
Prolonged Heating ◽  
Crustal Block ◽  
Lithospheric Extension ◽  
Spatially Distributed ◽  
Peak Metamorphism ◽  
Ultrahigh Temperature ◽  
T Path ◽  
Uht Metamorphism

Abstract The Madurai block is the largest composite crustal block in the Southern Granulite terrane of India, where granulite-facies rocks metamorphosed at ultrahigh-temperature (UHT) conditions occur in several localities. Here, we investigated UHT rocks from Rajapalayam, in the southern domain of the Southern Granulite terrane, using integrated thermobarometry and in situ monazite geochronology to precisely constrain the nature and timing of this extreme metamorphism and its implications for regional tectonics. Conventional thermobarometry and petrological phase equilibrium modeling reveal prograde pressure-temperature (P-T) conditions at 0.75–1.2 GPa and &lt;900 °C, followed by peak/postpeak UHT metamorphism at 0.72–0.82 GPa and 1025–1050 °C, and retrograde reequilibration at 0.72–0.80 GPa and 875–895 °C. The granulites thus record a clockwise P-T path defining geothermal gradients of 1200–1500 °C/GPa at peak metamorphism, indicating the presence of an extreme thermal perturbation in the middle to lower continental crust. In situ monazite dating indicates prograde metamorphism at 607–585 Ma, peak metamorphism at 546–543 Ma, and retrograde cooling and exhumation at 539–483 Ma. As such, the entire tectonothermal cycle was complete within ∼120 m.y., although temperatures exceeding 900 °C were likely sustained for at least 30 m.y. Such extreme thermal events preserved in geological terranes worldwide are commonly associated with lithospheric extension, although our data show that prolonged heating can occur during continental convergence instead, supporting inferences made by thermomechanical models. Thus, supercontinent formation may act as a driver for spatially distributed UHT tectonometamorphism, as shown by the episodic records in geological history. The age of peak metamorphism constrained here was synchronous with UHT metamorphism in other localities in the Southern Granulite terrane, Sri Lanka, Madagascar, and Antarctica, indicating their correlation with the final amalgamation of eastern Gondwana at ca. 550 Ma.

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