Figure 3. Forward modeling of scalar magnetic anomalies of six Magsat tracks across Tibet (locations shown in Fig. 1). All blocks have model susceptibility of 0.015 cgs (unless otherwise noted). Surrounding white areas have zero susceptibility. Thick black line across top of each model is average elevation along ground tracks of modeled pair of orbits (vertical exaggeration is 46x). BS is Banggong suture. Average satellite altitudes for each pair of orbits are similar, thus limiting continuation differences in anomaly amplitude (orbit 400 = 493 km, 323 = 467 km, 1574 = 355 km, 77 = 386 km, 492 = 518 km, 415 = 498 km). Because of filtering effects, anomaly amplitudes in Figure 1 are less than Figure 3.
 
 

Tibetan satellite magnetic low: Evidence for widespread melt in the Tibetan crust?

Accepted to Geology, 1999

Doug Alsdorf Institute for Computational Earth System Science, University of California, Santa Barbara, California, 93106, USA

Doug Nelson Department of Earth Sciences, Syracuse University, Syracuse, New York, 13244, USA

ABSTRACT

The Tibetan plateau is associated with a pronounced satellite magnetic low. Forward modeling of this anomaly demonstrates that the crust underlying the Tibetan plateau is weakly magnetic compared to the crust on either side, and that the boundaries of the weakly magnetic region coincide closely with the topographic edges of the plateau (Himalaya, Kun Lun). As there are no obvious changes in the bulk magnetization of the crust associated with the principal terrane boundaries within the plateau (Banggong and Yarlung-Zangbo sutures), the low likely manifests hot crust beneath Tibet. Forward modeling of the magnetic anomaly with simple assumptions suggests that the Curie isotherm is likely to reside in the upper crust across the Tibetan plateau (~15 km depth), implying that granite minimum melt temperature (~600-650 °C) is also achieved in the upper crust across the plateau (~16-18 km depth). This inference is consistent with the shallow depth extent of earthquakes in Tibet, and with the recent suggestion that melt may be areally widespread within the Tibetan crust.