Abstract
Isotopic and geochemical data delineate passive margin, rift and active margin cycles in northwestern South America since ~623 Ma, spanning from the Iapetus Wilson Cycle. Ultramafic and mafic rocks record rifting associated with the formation of the Iapetus Ocean during 623–531 Ma, while the initiation of subduction of the Iapetus and Rheic oceans is recorded by continental arc plutons that formed during 499–414 Ma, with alternating compressive and extensional stages. Muscovite 40Ar/39Ar dates suggest there may have been a phase of Carboniferous metamorphism, although this remains tentative. A Passive margin was modified by active margin magmatism that started at ~294 Ma and culminated with collisional tectonics that signaled the final stages of the amalgamation of western Pangaea. Early Pangaea fragmentation included back-arc rifting during 245–216 Ma, leading to a Pacific active margin that spanned from 213–115 Ma. Trench retreat accelerated during 144–115 Ma, forming a highly attenuated continental margin prior to the collision of the Caribbean Large Igneous Province at ~75 Ma.
Highlights
Northwestern South America is a relict fragment of Gondwana and its northern and western margins preserve a punctuated record spanning from the opening of the Iapetus Ocean to its interaction with the thickened Caribbean Plate
The older Palaeozoic arc sequences are geographically dismembered and most exposures occur in inboard regions of northwestern South America (~499–414 Ma and 296–250 Ma; Mérida Andes and the Santander Massif, and minor occurrences in the Cordillera Central) during the subduction of Iapetan and Rheic oceanic lithosphere, and in crustal blocks that are dispersed throughout the cordilleras Real (Ecuador) and Central (Colombia), and isolated blocks in Venezuela
Assuming insignificant strike-slip displacement, this implies that Jurassic magmatism initiated far from the trench at ~213 Ma, and these rocks are currently exposed within the Mérida Andes, Santander Massif (Figures 1 and 3) and in the southern Cordillera Central [19,44]
Summary
Thermochronological constraints are provided by apatite U-Pb and 40Ar/39Ar muscovite dates, and lower-T thermochronometers including fission track and (U-Th)/He data These data are compiled into a series of summary figures and identify periods of continental rift-related magmatism associated with the Central Iapetus Magmatic Province and the disassembly of Panotia in the period ~623–531 Ma, Triassic back-arc riftto-drift magmatism in the period ~245–216 Ma, heralding the early disassembly of Pangaea, and failed rifting during hyperextension of the Pacific margin in the Early Cretaceous starting in ~145 Ma. The older Palaeozoic arc sequences are geographically dismembered and most exposures occur in inboard regions of northwestern South America (~499–414 Ma and 296–250 Ma; Mérida Andes and the Santander Massif, and minor occurrences in the Cordillera Central) during the subduction of Iapetan and Rheic oceanic lithosphere, and in crustal blocks that are dispersed throughout the cordilleras Real (Ecuador) and Central (Colombia), and isolated blocks in Venezuela. With the exception of small porphyry-type intrusions, a significant magmatic hiatus throughout northwestern South America in the period 414–294 Ma is accounted for by the transfer of the rifted conjugate Triassic margin from Gondwana to Laurentia during the Triassic
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