Mafic slab melt contributions to Proterozoic massif-type anorthosites
Duncan S Keller1, Cin-Ty A Lee1, William H Peck2
1Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005, USA.
Science Advances
|August 14, 2024
Summary
Massif-type anorthosites formed from mafic melts originating from altered oceanic crust. This study links their formation to subduction processes beneath continental margins, explaining their temporal restriction.
Area of Science:
- Geology
- Petrology
- Isotope Geochemistry
Background:
- Massif-type anorthosites are large, enigmatic plagioclase-rich intrusions emplaced into Earth's crust.
- Their formation, primarily between 1 and 2 billion years ago, is debated, with hypotheses including mantle melting, lower crustal melting, and arc magmatism.
- Previous research has not reached a consensus on parental magmas or the reasons for their temporal restriction.
Purpose of the Study:
- To investigate the origin of parental magmas for massif-type anorthosites.
- To understand the temporal restriction of massif-type anorthosite formation.
- To elucidate the tectonic setting of anorthosite massif emplacement.
Main Methods:
- Analysis of B, O, Nd, and Sr isotopes.
- Bulk chemistry analysis.
- Petrogenetic modeling.
Main Results:
- The Marcy and Morin anorthosites, key North American examples, originated from magmas with significant input from mafic melts derived from altered oceanic crust.
- Boron isotope signatures indicate the involvement of subducted slab lithologies, such as serpentinite.
- The findings suggest a genetic link between anorthosite formation and subduction processes.
Conclusions:
- Massif-type anorthosites formed beneath convergent continental margins.
- Extensive melting of subducted or subducting slabs provided the parental magmas.
- Anorthosite massif formation is linked to Earth's thermal and tectonic evolution, specifically during periods of significant subduction activity.
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