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Microstructural Investigation of Variscan Late-Collisional Granitoids (Asinara Island, NW Sardinia, Italy): New Insights on the Relationship Between Regional Deformation and Magma Emplacement

In the framework of the geological mapping of sheet “n. 425—Asinara Island” (NW Sardinia, Italy) of the Italian National Geological Mapping Project (CARG Project), three late- to post-collisional Variscan intrusive units are recognized: (i) Castellaccio Unit; (ii) Punta Sabina Unit; and (iii) sheeted dyke complex. Granitoid rocks from these intrusive units intruded into the medium- to high-grade metamorphic micaschist and paragneiss and the migmatitic complex. A range of deformation microstructures from sub-magmatic to low-temperature subsolidus conditions are recognized. The main observed microstructures are represented by chessboard patterns in quartz and by feldspar sub-grain rotation dynamic recrystallization, indicative of deformation at high-temperature conditions (T > 650 °C). Solid-state high-temperature deformations (T > 450 °C) are provided by feldspar bulging, myrmekites, quartz grain boundary migration and sub-grain rotation dynamic recrystallization. Low-temperature sub-solidus microstructures (T < 450 °C) consist of quartz bulging, mica kinks, and feldspar twinning and bending. These features highlight that the three intrusive units recorded tectonic stresses, which affected the granitoids during cooling without developing a strong penetrative meso/microstructural fabric, as observed in other sectors of the Variscan orogen. The complete sequence of deformation microstructures, recorded in all intrusive units, suggests a weak but still ongoing deformation regime during granitoid emplacement in the Variscan orogen of northwestern Sardinia. These observations are similar to the features highlighted in other sectors of the southern Variscan belt and suggest a complex interplay between transpressional-induced exhumation of the middle/deep crust and magma intrusion.

Ketersediaan
#
Perpustakaan BIG (Eksternal Harddisk) 550
429
Tersedia
Informasi Detail
Judul Seri
Geosciences
No. Panggil
550
Penerbit
Switzerland : MPDI.,
Deskripsi Fisik
25 hlm PDF, 7.626 KB
Bahasa
Inggris
ISBN/ISSN
2076-3263
Klasifikasi
550
Tipe Isi
text
Tipe Media
-
Tipe Pembawa
online resource
Edisi
Vol.15, Issue 3, March 2025
Subjek
Structural analysis
deformation microstructures
late-Variscan magmatism
CARG Project
ductile deformation of granitoids
Sardinia
Info Detail Spesifik
Geosciences
Pernyataan Tanggungjawab
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Lampiran Berkas
  • Microstructural Investigation of Variscan Late-Collisional Granitoids (Asinara Island, NW Sardinia, Italy): New Insights on the Relationship Between Regional Deformation and Magma Emplacement
    In the framework of the geological mapping of sheet “n. 425—Asinara Island” (NW Sardinia, Italy) of the Italian National Geological Mapping Project (CARG Project), three late- to post-collisional Variscan intrusive units are recognized: (i) Castellaccio Unit; (ii) Punta Sabina Unit; and (iii) sheeted dyke complex. Granitoid rocks from these intrusive units intruded into the medium- to high-grade metamorphic micaschist and paragneiss and the migmatitic complex. A range of deformation microstructures from sub-magmatic to low-temperature subsolidus conditions are recognized. The main observed microstructures are represented by chessboard patterns in quartz and by feldspar sub-grain rotation dynamic recrystallization, indicative of deformation at high-temperature conditions (T > 650 °C). Solid-state high-temperature deformations (T > 450 °C) are provided by feldspar bulging, myrmekites, quartz grain boundary migration and sub-grain rotation dynamic recrystallization. Low-temperature sub-solidus microstructures (T < 450 °C) consist of quartz bulging, mica kinks, and feldspar twinning and bending. These features highlight that the three intrusive units recorded tectonic stresses, which affected the granitoids during cooling without developing a strong penetrative meso/microstructural fabric, as observed in other sectors of the Variscan orogen. The complete sequence of deformation microstructures, recorded in all intrusive units, suggests a weak but still ongoing deformation regime during granitoid emplacement in the Variscan orogen of northwestern Sardinia. These observations are similar to the features highlighted in other sectors of the southern Variscan belt and suggest a complex interplay between transpressional-induced exhumation of the middle/deep crust and magma intrusion.
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