Arc-scale temporal histories of the Cordilleran orogen

MORITZ KIRSCH; SCOTT R. PATERSON; FLORIAN WOBBE; ANA MARIA MARTINEZ ARDILLA; BENJAMIN L. CLAUSEN; PABLO H. ALASINO

Congreso; Goldschmidt; 2015

Magmatic activity in continental arcs is known to vary in a non-steady state manner, the mechanisms for which are a matter of ongoing discussion. Of particular importance is the question to what extent episodic magmatism in continental arcs is governed by external factors (e.g., plate motions) andinternal factors (e.g., feedback processes in the upper plate). In order to test existing models for magmatic episodicity, which are mostly based on temporally and spatially limited records, this study uses large datasets of geochronological, geochemical, and plate kinematic data to document thePaleozoic to Mesozoic development of the Cordilleran orogen in eight transects from British Colombia to Patagonia. The temporal distribution of U/Pb bedrock and detrital zircon ages, used as a proxy for timing of magmatic accretion, shows that some minima and maxima are nearly synchronous for thousands of km along the arc. Some age patterns are characterized by a periodicity of 50?80 Ma, suggesting a cyclic controlling mechanism. Other magmatic lulls or flare-ups find no equivalent in adjacent sectors, indicating that either discrete events or variable lag times also may be important in governing magmatic activity in continental arcs. Magma composition in Mexico, the Peninsular Ranges, and the Sierra Nevada varies episodically and proportionally with the temporal record of arc activity. During flare-up events, there is an increase in Sm/Yb, indicating deeper melting, and a decrease in εNdi, suggesting a higher degree of crustalassimilation. Geochemical scatter also increases during the initiation of flare-up events. Plate kinematic data provide a means of evaluating mantle heat input. The correlation between plate convergence rate and magmatic accretion variesfor each sector, suggesting that different flare-ups or lulls likely reflect variable combinations of processes.