0000000000222468
AUTHOR
Russell S. Harmon
Andean Cenozoic volcanic centers reflect basement isotopic domains
Isotopic data for Quaternary volcanic centers from lat 17.5° to 22°S in northern Chile provide evidence for crustal contributions to arc magma genesis in the central Andes and delineate basement domains. Crustal thickness, distance from trench, height of volcanic edifices above the seismically active subduction zone, and sediment supply to the trench are all constant along this segment of the arc. The only significant variable is crustal age (Paleozoic in the south, Proterozoic in the north). Pb isotopic compositions of Quaternary lavas in the northern sector are lower ( 206 Pb/ 204 Pb = 17.89-18.28) and Sr and O isotope ratios are less variable ( 87 Sr/ 86 Sr = 0.7058-0.7077, δ 18 O = +6.5…
The Nevados de Payachata volcanic region (18�S/69�W, N. Chile) II. Evidence for widespread crustal involvement in Andean magmatism
Volcanism extending over 11 Ma is represented in the rocks of the Nevados de Payachata region, culminating in the formation of two large composite stratocones within the last 500 000 years. Chemically distinct mafic magmas are erupted at a number of parasitic centers. These cannot be related to each other by crystal fractionation and do not appear to be direct parents for the differentiated suites of the composite cones. Two distinct trends are defined by the intermediate and evolved rocks; a high LILE (large ion lithophile element), TiO2 and Ce/Yb lineage among the youngest rocks (including the two major stratocones), and a more typical calc-alkaline trend among the older (>1 Ma) rock type…
Influence of crustal thickening on arc magmatism:, Nevados de Payachata volcanic region, northern Chile
Neogene through Pleistocene lava flows of the Nevados de Payachata region (lat 18°S) on the Altiplano of northern Chile fall into two discrete chemical groups defined by age and incompatible element concentrations. The Neogene suite (10.5-6.6 Ma) has trace element concentrations comparable to arc magmas erupted on thin crust in central Chile. Pleistocene lava flows (0.29-0 Ma) are enriched in incompatible elements relative to Neogene samples but have similar Sr, Nd, and Pb isotopic ratios. Incompatible element enrichment in mafic rocks reflects deep-crustal or subcrustal processes. Neogene volcanism in northern Chile immediately followed a period of intense crustal thickening. Uplift rates …