Terrestrial heat flow above the Andean Subduction Zone in Bolivia and Peru

Abstract

We report 35 new and 9 revised terrestrial heat flow measurements overlying the Andean subduction zone in Bolivia and Peru. The measurement sites are distributed in the Andean Cordillera, the Altiplano, the sub‐Andean ranges, and the sedimentary platform and basins to the east of the Andes. They fall in the distance range 75–900 km from the Peru‐Chile trench. Sites in the Peruvian Cordillera have a mean heat flow of 41 mW m−2, whereas those in the Bolivian Cordillera and Altiplano average 84 mW m−2. The sub‐Andean ranges and the adjacent sedimentary platform have a mean heat flow of 50 mW m−2. The higher heat flow of the Bolivian Cordillera and Altiplano lies to the east of Quaternary volcanoes along the Bolivia‐Chile border and in southernmost Peru and thus can be recognized as a “back arc” heat flow high. Neither Quaternary volcanism nor high heat flow are present in central and northern Peru. This contrasting along‐strike pattern correlates with the variable angle of subduction of the Nazca plate beneath the region. Beneath Bolivia the subduction is at about 30°–35°, whereas beneath Peru it is subhorizontal and may be providing a cold underplate to the overlying Peruvian lithosphere. Extensive Miocene volcanism in Peru suggests, however, that heat flow in Peru 10 Ma ago was likely similar to that in Bolivia in the present day and implies a change in subduction and a rapid diminution of heat flow in Peru over the past 10 Ma. Imbrication of cold oceanic lithosphere beneath Peru, analogous to that beneath western British Columbia, may provide a mechanism for rapid reduction of the heat flow.

Heat-Flow Studies in the Peru Trench Subduction Zone

“…Thus, low heat flow may extend to the coast. There are few heat-flow data in the Andes of central and northern Peru, where a long volcanic gap exists, and they are low, 17 to 55 mW/m 2 , except for one value, 196 mW/m 2 Henry and Pollack, 1988). It is important to obtain more data to determine whether the high heat flow is a local anomaly.…”

“…Just before subduction, i.e., seaward of the trench axis, heat flow is extremely . Circles represent the previous data (Von Von Herzen and Uyeda, 1963;Henry and Pollack, 1988). Closed and open triangles are the data obtained during the MW8506 cruise and a cruise of the Jean-Charcot in 1986 (J.…”

“…However, no heat-flow data were reported off the coast of Peru after the Risepac expedition, while a considerable amount of geophysical and geological data were collected in the Peru-Chile Trench area under the Nazca Plate Project (Woollard and Kulm, 1981). On land, about 30 heat-flow values were obtained from the Peruvian coast to the Andes in Peru and Bolivia Watanabe et al, 1980;Henry and Pollack, 1988) and more than 50 values were determined in the sedimentary platform and basins to the east of the Andes (Ocola, 1985;Henry and Pollack, 1988). However, most of these values are concentrated in areas near the northern and southern ends of Peru, and it was difficult to construct a profile of the heat flow from the trench to the Andes in central Peru.…”

Thermal regime of fold and thrust belts—an application to the Bolivian sub Andean zone

“…Thermal profiles through various mountain belts (data source: Pollack et al, 1993). Sclater et al, 1970, Uyeda and Watanabe, 1982, Henry and Pollack, 1988Springer and Forster 1998) overlain on a digital elevation map. Box: periodic setting evidenced by filtering of topographical high frequencies.…”

Electrical and Thermal Anomalies in the Central Andean Subduction Zone

“…For latitudes below 23°S, the assumed values of Q s are based on data compiled by HENRY and POLLACK (1988) and GIESE (1993), they are summarized in Table 1. A Q s value of 30 mWm −2 is assumed at sites 1 and 2, which is considered to be representative of that flat subduction zone.…”