Geological map of the ultra-high pressure Brossasco-Isasca unit (Western Alps, Italy)

• Published in: Journal of maps Vol. 8; no. 4; pp. 465 - 472
• Main Authors: Compagnoni, Roberto, Rolfo, Franco, Groppo, Chiara, Hirajima, Takao, Turello, Robertino
• Format: Journal Article
• Language: English
• Published: Routledge 01-01-2012
• Subjects: Dora-Maira Massif; ultra-high pressure metamorphism (UHPM); Western Alps
• ISSN: 1744-5647; 1744-5647
• DOI: 10.1080/17445647.2012.744367

In the southern Dora-Maira Massif, Western Alps, slivers of continental crust with similar lithologies, but recrystallized during the Alpine orogeny at different peak-P conditions, are exposed. They include the Brossasco-Isasca Unit (BIU) where coesite was first discovered in continental crust. A new 1:20,000-scale geologic map and related cross-sections of the whole BIU and adjoining units is presented, in which the most significant features useful to infer the pre-Alpine history and the Alpine tectonic and metamorphic evolution, are summarized. Thanks to detailed petrography and petrology, the geologic map shows the precise location of ultra-high pressure (UHP) minerals (such as coesite), and the locations of the most significant mineral assemblages (such as kyanite + jadeite). This innovative approach is used to distinguish the BIU from the adjacent units. Relict pre-Alpine structures (such as igneous intrusive contacts with basement xenoliths and metagranitoids) are summarized in a sketch illustrating the geologic setting of the UHP metamorphic unit as inferred before the Alpine orogeny.