TY - JOUR
T1 - U-Pb zircon geochronology and tectonostratigraphy of southern Liverpool Land, East Greenland
T2 - Implications for deformation in the overriding plates of continental collisions
AU - Johnston, Scott M.
AU - Hartz, Ebbe H.
AU - Brueckner, Hannes K.
AU - Gehrels, George E.
N1 - Funding Information:
Funding for field work in Greenland was supported by the Norwegian Science Council through the Petromaks program and a “Centre of Excellence” grant to Physics of Geological Processes. Aka Lynge and Luc Mehl are thanked for assistance with field logistics and field work. Post-doctoral support for Johnston while at the University of Arizona was supported by NSF EAR 044387 and 0732436 awarded to Gehrels. This manuscript benefitted from two detailed anonymous reviews. Appendix A
PY - 2010/9
Y1 - 2010/9
N2 - The East Greenland Caledonides formed in the overriding plate as Baltica was subducted westward beneath Laurentia from 460 to 360. Ma, and offer a unique opportunity to investigate lower crustal deformation in the overriding plates of continental collisions. Field work and new zircon geochronology from gneisses in southern Liverpool Land, exposed in the hinterland ~. 100. km east of the nearest Caledonian gneisses, define three tectonostratigraphic units that are, from the bottom up, the eclogite. +. peridotite-bearing Tværdal complex and the granulite-facies Jættedal complex in the footwall of the top-N Gubbedalen shear zone, and the Hurry Inlet granite and associated paragneiss screens in its immediate hangingwall. Zircons from Tværdal complex gneisses yield metamorphic rims that cluster in age from 409 to 401. Ma and overgrow magmatic cores of 1674 and 1665. Ma in two samples, and range from ~. 1800-1000. Ma in a third sample. In contrast, zircons from three samples in the Jættedal complex and two samples in the paragneiss screens of the Hurry Inlet granite yield metamorphic rims that cluster in age from 438 to 417. Ma with Archean-Early Neoproterozoic detrital cores. A cross-cutting granitic dike in the Jættedal complex yields an age of 394. Ma. Archean-Early Neoproterozoic detrital zircons associated with ~. 440-420. Ma metamorphism in the Liverpool Land paragneisses suggests correlation with the Krummedal sequence and the Hagar Bjerg thrust sheet of Laurentian affinity. 1670. Ma cores in the Tværdal complex, and ~. 400. Ma eclogite-facies metamorphism, allow correlation of the Tværdal complex with the Western Gneiss Region in Norway, and it may therefore be of Baltican affinity. Furthermore, the contact between the older Jættedal complex with the younger Tværdal complex requires the existence of a structure, named the Ittoqqortoormiit shear zone herein, which juxtaposed these rocks prior to the initiation of normal-sense slip along the Gubbedalen shear zone. This work provides geochronologic evidence for continental underplating of the overriding plate by the subducting plate during orogenesis, and supports models for high-pressure exhumation in continental collisional settings that identify separate structures associated with initial emplacement in the lower-middle crust and subsequent upper-crustal exhumation.
AB - The East Greenland Caledonides formed in the overriding plate as Baltica was subducted westward beneath Laurentia from 460 to 360. Ma, and offer a unique opportunity to investigate lower crustal deformation in the overriding plates of continental collisions. Field work and new zircon geochronology from gneisses in southern Liverpool Land, exposed in the hinterland ~. 100. km east of the nearest Caledonian gneisses, define three tectonostratigraphic units that are, from the bottom up, the eclogite. +. peridotite-bearing Tværdal complex and the granulite-facies Jættedal complex in the footwall of the top-N Gubbedalen shear zone, and the Hurry Inlet granite and associated paragneiss screens in its immediate hangingwall. Zircons from Tværdal complex gneisses yield metamorphic rims that cluster in age from 409 to 401. Ma and overgrow magmatic cores of 1674 and 1665. Ma in two samples, and range from ~. 1800-1000. Ma in a third sample. In contrast, zircons from three samples in the Jættedal complex and two samples in the paragneiss screens of the Hurry Inlet granite yield metamorphic rims that cluster in age from 438 to 417. Ma with Archean-Early Neoproterozoic detrital cores. A cross-cutting granitic dike in the Jættedal complex yields an age of 394. Ma. Archean-Early Neoproterozoic detrital zircons associated with ~. 440-420. Ma metamorphism in the Liverpool Land paragneisses suggests correlation with the Krummedal sequence and the Hagar Bjerg thrust sheet of Laurentian affinity. 1670. Ma cores in the Tværdal complex, and ~. 400. Ma eclogite-facies metamorphism, allow correlation of the Tværdal complex with the Western Gneiss Region in Norway, and it may therefore be of Baltican affinity. Furthermore, the contact between the older Jættedal complex with the younger Tværdal complex requires the existence of a structure, named the Ittoqqortoormiit shear zone herein, which juxtaposed these rocks prior to the initiation of normal-sense slip along the Gubbedalen shear zone. This work provides geochronologic evidence for continental underplating of the overriding plate by the subducting plate during orogenesis, and supports models for high-pressure exhumation in continental collisional settings that identify separate structures associated with initial emplacement in the lower-middle crust and subsequent upper-crustal exhumation.
KW - Continental underplating
KW - Crustal exhumation
KW - East Greenland Caledonides
KW - Liverpool Land
KW - Small-volume U-Pb geochronology
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U2 - 10.1016/j.epsl.2010.07.003
DO - 10.1016/j.epsl.2010.07.003
M3 - Article
AN - SCOPUS:77956009562
SN - 0012-821X
VL - 297
SP - 512
EP - 524
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
IS - 3-4
ER -