The results of a coupled, in situ laser ablation-inductively coupled
plasma-mass spectrometry (LA-ICP-MS) U-Pb study on zircon and
geochemical characterization of the Eastern Cordilleran intrusives of
Peru reveal 1.15 Ga of intermittent magmatism along central Western
Amazonia, the Earth's oldest active open continental margin. The eastern
Peruvian batholiths are volumetrically dominated by plutonism related to
the assembly and breakup of Pangea during the Paleozoic-Mesozoic
transition. A Carboniferous-Permian (340-285 Ma) continental arc is
identified along the regional orogenic strike from the Ecuadorian border
(6 degrees S) to the inferred inboard extension of the
Arequipa-Antofalla terrane in southern Peru (14 degrees S). Widespread
crustal extension and thinning, which affected western Gondwana
throughout the Permian and Triassic resulted in the intrusion of the
late- to post-tectonic La Merced-San Ramon-type anatectites dated
between 275 and 220 Ma, while the emplacement of the southern Cordillera
de Carabaya peraluminous granitoids in the Late Triassic to Early
Jurassic (220-190 Ma) represents, temporally and regionally, a separate
tectonomagmatic event likely related to resuturing of the
Arequipa-Antofalla block. Volcano-plutonic complexes and stocks
associated with the onset of the present Andean cycle define a
compositionally bimodal alkaline suite and cluster between 180 and 170
Ma. A volumetrically minor intrusive pulse of Oligocene age (ca. 30 Ma)
is detected near the southwestern Cordilleran border with the Altiplano.
Both post-Gondwanide (30-170 Ma), and Precambrian plutonism (691-1123
Ma) are restricted to isolated occurrences spatially comprising less
than 15% of the Eastern Cordillera intrusives. Only one remnant of a
Late Ordovician intrusive belt is recognized in the Cuzco batholith
(446.5 +/- 9.7 Ma) indicating that the Famatinian arc system previously
identified in Peru along the north-central Eastern Cordillera and the
coastal Arequipa-Antofalla terrane also existed inboard of this
parautochthonous crustal fragment. Hitherto unknown occurrences of late
Mesoproterozoic and middle Neoproterozoic granitoids from the
south-central cordilleran segment define magmatic events at 691 +/- 13
Ma, 751 +/- 8 Ma, 985 +/- 14 Ma, and 1071-1123 +/- 23 Ma that are
broadly coeval with the Braziliano and Grenville-Sunsas orogenies,
respectively. Our data suggest the existence of a continuous orogenic
belt in excess of 3500 km along Western Amazonia during the formation of
Rodinia, its ``early'' fragmentation prior to 690 Ma, and support a
model of reaccretion of the Paracas-Arequipa-Antofalla terrane to
western Gondwana in the Early Ordovician with subsequent detachment of
the Paracas segment in form of the Mexican Oaxaquia microcontinent in
Middle Ordovician. A tectonomagmatic model involving slab detachment,
followed by underplating of cratonic margin by asthenospheric mantle is
proposed for the genesis of the volumetrically dominant Late Paleozoic
to early Mesozoic Peruvian Cordilleran batholiths.