TY - JOUR
T1 - Recent crustal foundering in the Northern Volcanic Zone of the Andean arc
T2 - Petrological insights from the roots of a modern subduction zone
AU - Bloch, Elias
AU - Ibañez-Mejia, Mauricio
AU - Murray, Kendra
AU - Vervoort, Jeffrey
AU - Müntener, Othmar
N1 - Funding Information:
We are grateful to Diane Wilford and Charles Knaack for assistance with the Lu?Hf analyses, and to Jibamitra Ganguly, Lukas Baumgartner and Carmala Garzione for insightful discussions. We also wish to thank Carlos Borrero and Hugo Murcia for assistance in the field, and David Coblentz and Gaspar Monsalve for kindly providing the geoid and crustal thickness models, respectively, used in Fig. 1. Critical feedback from two anonymous reviewers led to substantial improvement of this manuscript, and we thank Michael Bickle for his editorial handling of this article. Lu?Hf analyses were funded by NSF grant no. EAR-1016189 to Jibamitra Ganguly. M.I.M. benefited from a W.O. Crosby post-doctoral fellowship at the Massachusetts Institute of Technology, which was also used to fund portions of this research.
Funding Information:
We are grateful to Diane Wilford and Charles Knaack for assistance with the Lu–Hf analyses, and to Jibamitra Ganguly, Lukas Baumgartner and Carmala Garzione for insightful discussions. We also wish to thank Carlos Borrero and Hugo Murcia for assistance in the field, and David Coblentz and Gaspar Monsalve for kindly providing the geoid and crustal thickness models, respectively, used in Fig. 1 . Critical feedback from two anonymous reviewers led to substantial improvement of this manuscript, and we thank Michael Bickle for his editorial handling of this article. Lu–Hf analyses were funded by NSF grant no. EAR-1016189 to Jibamitra Ganguly. M.I.M. benefited from a W.O. Crosby post-doctoral fellowship at the Massachusetts Institute of Technology , which was also used to fund portions of this research.
Publisher Copyright:
© 2017 Elsevier B.V.
PY - 2017/10/15
Y1 - 2017/10/15
N2 - Periodic loss of the lower lithosphere into the convecting mantle due to gravitational instability is postulated to be a major mechanism for lithosphere recycling in orogenic zones, but unequivocal petrologic evidence of this process is elusive. The Granatifera Tuff, located in the Mercaderes–Rio Mayo area of the southern Colombian Andes, contains a wide variety of crustal and mantle xenoliths. Here we focus on the thermobarometry and Lu–Hf isotope systematics of crustal garnet clinopyroxenite xenoliths, the results of which offer the first evidence of recent, and likely active, crustal foundering in the Northern Volcanic Zone of the Andean arc. We find that most of these xenoliths equilibrated between 60–80 km depths, ∼7–27 km below the seismically determined Moho in this region, and that at least one crustal garnet clinopyroxenite re-equilibrated at depths exceeding 95 km. A second garnet clinopyroxenite equilibrated at ∼150 km depths, and is either foundered lithospheric material or the product of reaction between peridotite and a mobile component (either silicic melt or fluids) at >4 GPa. All of the investigated garnet clinopyroxenites are negatively buoyant relative to the upper mantle asthenosphere. The presence of minor amounts of secondary amphibole and orthopyroxene, coupled with the lack of major-element retrograde zonation in primary phases within these xenoliths, indicates that these rocks were rapidly transported to, and briefly resided at, shallow depths before eruption. Lu–Hf ages from two garnet clinopyroxenites and one garnet–clinopyroxene hornblendite are <5 Ma, and approximate the time at which these xenoliths were transported to shallow depths prior to eruption. A large-magnitude positive geoid anomaly and relatively low mean surface elevations indicate that the gravitationally unstable crustal root is still largely attached to the overriding crust in this part of the Northern Volcanic Zone. Thermobarometric calculations indicate that the lowermost crust in this region is a partial melt zone, and we argue that rheological weakening in the presence of melt has led to the foundering of relatively small parcels of gravitationally unstable crustal material, which the Mercaderes xenoliths document, without catastrophic removal of the crustal root.
AB - Periodic loss of the lower lithosphere into the convecting mantle due to gravitational instability is postulated to be a major mechanism for lithosphere recycling in orogenic zones, but unequivocal petrologic evidence of this process is elusive. The Granatifera Tuff, located in the Mercaderes–Rio Mayo area of the southern Colombian Andes, contains a wide variety of crustal and mantle xenoliths. Here we focus on the thermobarometry and Lu–Hf isotope systematics of crustal garnet clinopyroxenite xenoliths, the results of which offer the first evidence of recent, and likely active, crustal foundering in the Northern Volcanic Zone of the Andean arc. We find that most of these xenoliths equilibrated between 60–80 km depths, ∼7–27 km below the seismically determined Moho in this region, and that at least one crustal garnet clinopyroxenite re-equilibrated at depths exceeding 95 km. A second garnet clinopyroxenite equilibrated at ∼150 km depths, and is either foundered lithospheric material or the product of reaction between peridotite and a mobile component (either silicic melt or fluids) at >4 GPa. All of the investigated garnet clinopyroxenites are negatively buoyant relative to the upper mantle asthenosphere. The presence of minor amounts of secondary amphibole and orthopyroxene, coupled with the lack of major-element retrograde zonation in primary phases within these xenoliths, indicates that these rocks were rapidly transported to, and briefly resided at, shallow depths before eruption. Lu–Hf ages from two garnet clinopyroxenites and one garnet–clinopyroxene hornblendite are <5 Ma, and approximate the time at which these xenoliths were transported to shallow depths prior to eruption. A large-magnitude positive geoid anomaly and relatively low mean surface elevations indicate that the gravitationally unstable crustal root is still largely attached to the overriding crust in this part of the Northern Volcanic Zone. Thermobarometric calculations indicate that the lowermost crust in this region is a partial melt zone, and we argue that rheological weakening in the presence of melt has led to the foundering of relatively small parcels of gravitationally unstable crustal material, which the Mercaderes xenoliths document, without catastrophic removal of the crustal root.
KW - Andes
KW - delamination
KW - foundering
KW - Lu–Hf
KW - Northern Volcanic Zone
KW - xenoliths
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U2 - 10.1016/j.epsl.2017.07.041
DO - 10.1016/j.epsl.2017.07.041
M3 - Article
AN - SCOPUS:85027675354
VL - 476
SP - 47
EP - 58
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
SN - 0012-821X
ER -