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Abstract The northern Andes of southern Colombia contain a rich geologic history recorded by Proterozoic to Cenozoic metamorphic, igneous, and sedimentary rocks. The region plays a pivotal role in understanding the evolution of topography in northwestern South America and the development of large river systems, such as the Amazon, Orinoco, and Magdalena rivers. However, understanding of the basement framework has been hindered by challenging access, security concerns, tropical climate, and outcrop scarcity. Further, an insufficient geochronologic characterization of Andean basement complicates provenance interpretations of adjacent basins and restricts understanding of the paleogeographic evolution of southern Colombia. To address these issues, this paper presents a zircon U-Pb geochronological dataset derived for 24 bedrock samples and 19 modern river samples. The zircon U-Pb results reveal that the Eastern Cordillera of southern Colombia is underlain by basement rocks that originated in various tectonic events since ca. 1.5 Ga, including the accretion of discrete terranes. The oldest rocks, found in the Garzon Massif, are high-grade metamorphic rocks with contrasting Proterozoic protolith crystallization ages. Whereas the SW part of the massif formed during the Putumayo Orogeny (ca. 1.2–0.9 Ga), we report orthogneisses for the NE segment with protoliths formed at ca. 1.5 Ga, representing the NW continuation of the Rio Negro Jurena province of the Amazonian Craton. In contrast, crystalline rocks of the Central Cordillera primarily consist of Permian–Triassic (ca. 270–250 Ma) and Jurassic–Cretaceous (ca. 180–130 Ma) igneous rocks formed in a magmatic arc. In southernmost Colombia, the Putumayo Mountains mainly consist of Jurassic–Cretaceous (180–130 Ma) plutonic and volcanic rocks. Furthermore, we analyzed the heavy mineral abundances in modern river sands in southern Colombia (spanning 1°N–5°N) and found that key minerals such as garnet and epidote can be utilized to trace high-grade metamorphic and igneous lithologies, respectively, in the river catchments. The differentiation of basement ages for separate tectonic provinces, combined with heavy mineral abundances in modern sands, can serve as unique fingerprints in provenance analyses to trace the topographic and exhumational evolution of different Andean regions through time.
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This content will become publicly available on April 1, 2026
Age of Skarn Formation and Meteoric Water Infiltration in the Willsboro–Lewis Wollastonite District (Adirondack Highlands, New York)
Abstract The Willsboro–Lewis wollastonite district occurs along the margin of the 1.15-Ga Marcy anorthosite massif in the Adirondack Highlands (New York) and records mineralogical and isotopic evidence for formation in the anorthosite’s low-pressure metamorphic contact aureole. Wollastonite–garnet–pyroxene gneisses in the ~25-km-long, 1.5-km-thick skarn belt are mined for wollastonite and are intercalated with massive garnetite and pyroxene ± garnet skarns, all of which have low oxygen isotope ratios indicating circulation of heated meteoric water and relatively shallow depths above the brittle–ductile transition during their formation. Anorthosite, skarns, and country rocks were all variably deformed and recrystallized at depths of 25 to 30 km during the 1.09- to 1.02-Ga Ottawan phase, and locally altered during the 1.01- to 0.98-Ga Rigolet phase, of the Grenvillian orogeny. This study examined rare zircon in low-δ18O skarn rocks to constrain the timing of surface-derived meteoric water infiltration. Zircon was dated, and trace elements were measured by laser-ablation ICPMS, and oxygen isotopes were measured by ion microprobe, yielding a spectrum of ages and oxygen isotope ratios reflecting the polymetamorphic history of these rocks. Most samples are dominated by metamorphic zircon having Ottawan or Rigolet 207Pb/206Pb ages and are in high-temperature oxygen isotopic equilibrium with host wollastonite, garnet and/or pyroxene. Several samples contain igneous zircon with disturbed U–Pb isotope systematics, reflecting some combination of new zircon growth and recrystallization during subsequent metamorphism. Relict 1150–1140 Ma ages are preserved in some zircon cores, which are taken as the ages of igneous zircon incorporated during skarn formation or from protoliths. Some of these 1150 to 1140 Ma cores preserve the low-δ18O record of interaction with meteoric water. Ages seen in the Willsboro–Lewis skarns reproduce the span of igneous, disturbed and metamorphic ages in Adirondack anorthosite, and point to contemporaneous anorthosite emplacement, meteoric water circulation and skarn formation at ca. 1150 Ma. This result is consistent with shallow emplacement of the Marcy anorthosite massif during crustal thinning related to the collapse of the 1.19- to 1.14-Ga Shawinigan orogeny, and that granulite facies overprinting was a later tectonic event.
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- Award ID(s):
- 2004618
- PAR ID:
- 10597740
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Journal of Petrology
- Volume:
- 66
- Issue:
- 4
- ISSN:
- 0022-3530
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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