Repeated S–I–A-type granite trilogy in the lachlan orogen and geochemical contrasts with a-type granites in Nigeria: implications for petrogenesis and tectonic discrimination

Collins, William J., Huang, Hui Qing, Bowden, Peter, and Kemp, A. I.S. (2020) Repeated S–I–A-type granite trilogy in the lachlan orogen and geochemical contrasts with a-type granites in Nigeria: implications for petrogenesis and tectonic discrimination. Geological Society Special Publication, 491 (1). pp. 53-76.

[img] PDF (Published version) - Published Version
Restricted to Repository staff only

View at Publisher Website: https://doi.org/10.1144/SP491-2018-159
15


Abstract

The classical S–I–A-type granites from the Lachlan Orogen, SE Australia, formed as a tectonic end-member of the accretionary orogenic spectrum, the Paleozoic Tasmanides. The sequence of S-to I-to A-type granite is repeated at least three times. All the granites are syn-extensional, formed in a dominantly back-arc setting behind a single, stepwise-retreating arc system between 530 and 230 Ma. Peralkaline granites are rare. Systematic S–I–A progressions indicate the progressive dilution of an old crustal component as magmatism evolved from arc (S-type) to proximal back-arc (I-type) to distal back-arc (A-type) magmatism. The alkaline and peralkaline A-type Younger granites of Nigeria were generally hotter and drier than the Lachlan A-type granites and were emplaced into an anhydrous Precambrian basement during intermittent intracontinental rifting. This geodynamic environment contrasts with the distal back-arc setting of the Lachlan A-type granites, where magmatism migrated rapidly across the orogen. Tectonic discrimination diagrams are inappropriate for the Lachlan granites, placing them in the wrong settings. Only the peralkaline Narraburra suite of the Lachlan Orogen fits the genuine ‘within-plate’ setting of the Nigerian A-type granites. Such discrimination diagrams require re-evaluation in the light of an improved modern understanding of tectonic processes, particularly the role of extensional tectonism and its geodynamic drivers.

Item ID: 67367
Item Type: Article (Research - C1)
ISSN: 0305-8719
Copyright Information: © 2019 The Author(s). Published by The Geological Society of London. All rights reserved.
Research Data: https://doi.org/10.6084/m9.figshare.c.4490117
Date Deposited: 16 Apr 2021 03:53
FoR Codes: 37 EARTH SCIENCES > 3703 Geochemistry > 370304 Organic geochemistry @ 30%
37 EARTH SCIENCES > 3705 Geology > 370511 Structural geology and tectonics @ 70%
More Statistics

Actions (Repository Staff Only)

Item Control Page Item Control Page