The North-East Greenland Caledonides record a complex history of crustal thickening and extension during the Paleozoic collision of Baltica with Laurentia. We divide the southern portion of the orogen (70°N–76°N) into three plates separated by low-angle fault systems that are interpreted as extensional detachments superimposed on, and perhaps coeval with, the thrust geometry of the orogen. From structurally lowest to highest, the plates include amphibolite-facies Archean to Paleoproterozoic orthogneiss and lesser paragneiss that retain relics of Devonian high-pressure metamorphism, migmatitic Mesoproterozoic metasedimentary rocks with Silurian leucogranites and lesser orthogneiss at amphibolite-facies conditions, and low-grade Neoproterozoic to Ordovician sedimentary rocks. Individual detachments are characterized by superposition of cataclastic features on mylonitic fabrics, and they record progressive deformation that accommodated exhumation. The extensional faults define two detachment systems that evolved at different crustal levels during two episodes of movement. The upper detachment system, which separates the upper and middle plates, exhumed the midcrustal rocks after ca. 420 Ma. Extension was contemporaneous with crustal thickening and closely followed leucogranite emplacement. The structure may be analogous to the South Tibetan detachment system in the present-day Himalayas. Continental Old Red Sandstone deposition began in the Eifelian, closely following high-pressure metamorphism in the lower plate at ca. 405 Ma. The lower detachment was probably active at some depth below the evolving Devonian basins. The lower detachment system brought lower-plate metamorphic rocks to shallower crustal levels after 400 Ma, excising the overlying extensional system. This second period of extension was similar in timing and style to extension in the Scandinavian Caledonides. Displacement on the younger detachments, which exhumed lower-plate rocks, was broadly syncollisional, as indicated by the overlap in age with ultrahigh-pressure metamorphism in the north at 365–350 Ma, and it may have been synchronous with young thrusts that emplaced high-pressure lower-plate rocks over the foreland and with strike-slip faults in the hinterland. Conversion to extension, accommodated by high-angle brittle faulting in the Carboniferous (after 345 Ma), may mark the final transition to plate divergence that ultimately led to continental rifting.

The Caledonian orogen of North-East Greenland hosts numerous mineral occurrences related to (1) pre-Caledonian crystalline complexes (Pb-Zn skarn type); (2) Neoproterozoic basins (strata-bound copper); (3) Caledonian granites (vein-type gold, silver, tungsten, arsenic, and antimony); and (4) late Caledonian extensional structures (vein base metal ± silver). Sr, Pb, and Sm-Nd isotope analyses of scheelite (CaWO 4 ) indicate a heterogeneous, probably local, source for tungsten, and Sr isotopic data support a genetic link to Caledonian magmatic activity. Pb isotopes indicate mixing of Pb derived from late waning-stage fluids from the granites and from interaction with wall rocks. Sm-Nd isotopic data for the investigated scheelites indicate that a portion of the rare earth elements was derived from fluids that had interacted with both Archean-Paleoproterozoic crystalline basement and Mesoproterozoic-Neoproterozoic sedimentary rocks. Mineral occurrences associated with fault zones and late Caledonian veins all show a genetic relationship with Caledonian granite emplacement. Sm-Nd isotopic data from scheelite define an errorchron with a slope corresponding to 382 ± 39 Ma (mean square of weighted deviates [MSWD] = 2.6) and an initial 143 Nd/ 144 Nd value of 0.511642 ± 0.000049. This indicates emplacement during the latest stages or even subsequent to emplacement of most Caledonian granites around 425 Ma. The initial Nd isotopic ratio defined by the scheelite Sm-Nd isotopic correlation line is identical within error to the values of S-type granitoids. The multi-isotope studies indicate that tungsten may have been deposited from fluids associated with Caledonian granites, which provided heat sources for local hydrothermal circulation cells. Forced into faults, thrusts, and fractures, the fluids were trapped by dominantly Ca-rich sediments.