Ancient heat flow and crustal thickness at Warrego rise, Thaumasia highlands, Mars: Implications for a stratified crust

Abstract

a b s t r a c tHeat flow calculations based on geological and/or geophysical indicators can help to constrain the thickness, and potentially the geochemical stratification, of the martian crust. Here we analyze the Warrego rise region, part of the ancient mountain range referred to as the Thaumasia highlands. This region has a crustal thickness much greater than the martian average, as well as estimations of the depth to the brittle-ductile transition beneath two scarps interpreted to be thrust faults. For the local crustal density (2900 kg m À3) favored by our analysis of the flexural state of compensation of the local topography, the crustal thickness is at least 70 and 75 km at the scarp locations. However, for one of the scarp locations our nominal model does not obtain heat flow solutions permitting a homogeneous crust as thick as required. Our results, therefore, suggest that the crust beneath the Warrego rise region is chemically stratified with a heat-producing enriched upper layer thinner than the whole crust. Moreover, if the mantle heat flow (at the time of scarp formation) was higher than 0.3 of the surface heat low, as predicted by thermal history models, then a stratified crust rise seems unavoidable for this region, even if local heatproducing element abundances lower than average or hydrostatic pore pressure are considered. This finding is consistent with a complex geological history, which includes magmatic-driven activity.

Depth of faulting and ancient heat flows in the Kuiper region of Mercury from lobate scarp topography

“…Crustal heat sources abundances are based on preliminary surface measure ments of Th and K performed with the MESSENGER Ganuna-Ray Spectrometer (GRS) (Peplowsky et al, 2011). Indeed, previous works have pointed out the importance of taking into account crustal heat sources in this kind of calculations, since the obtained surface heat flow increases with the proportion of heat sources within the crust (Ruiz et al, 2006(Ruiz et al, , 2009. Finally, we discuss the implications of our results for the history of Mercury.…”

“…In addition, our surface heat flow estimations can be used to place constraints on the thickness of the mercurian crust (Ruiz et al, 2008(Ruiz et al, , 2009. If the crustal heat production rates assumed previously are representative for the bulk of the crust, then crustal contribution to the surface heat flow is given by multiplying H by the crustal thickness, and therefore an upper limit on the crustal thickness is imposed by the condition of non-negative mantle heat flow.…”

The thermal evolution of Mars as constrained by paleo-heat flows

“…Also, the condition of non-negative sublithospheric heat flow is imposed for calculations using lithospheric heat sources. A negative sublithospheric heat flow could occur if assumed litho spheric HPE abundances are higher than the actual ones for a par ticular region (for example, the crust could be stratified, with a HPE-poor lower crust; see Ruiz et al, 2006bRuiz et al, , 2009. If the sublitho spheric heat flow is negative, then the thermal profile is adjusted to enforce zero sublithospheric heat flow and permit a ductile strength higher than 10 MPa at the base of the mechanical litho sphere.…”

“…Surface heat flows obtained from lithospheric strength are high er, for a fixed Te or BOT depth, if lithospheric radioactive heat sources are included in the calculations than if purely thermal gra dients are used (see Ruiz et al, 2006aRuiz et al, , 2008Ruiz et al, , 2009). Thus, we calcu late surface heat flow upper limits by including HPE in the crust and the mantle lithosphere, whereas lower limits are obtained by using zero lithospheric heat sources.…”

“…Previous works estimated surface heat flows for diverse regions and epochs of Mars from the effective elastic thickness of the lith osphere (Solomon and Head, 1990;Anderson and Grimm, 1998;Zuber et al, 2000;Nimmo, 2002;Kiefer, 2004;McGovern et al, 2002McGovern et al, , 2004Grott et aI., 2005;Ruiz et aI., 2006aRuiz et aI., ,b, 2008Ruiz et aI., , 2010Kronberg et al, 2007;Ruiz, 2009;Dohm et al, 2009a;Ritzer and Hauck, 2009) or from the depth to the brittle-ductile transition (BDT) beneath large thrust faults ( Schultz and Watters, 2001;Grott et al, 2007;Ruiz et al, 2008Ruiz et al, , 2009; such heat flow estimates cor respond to the time when the lithosphere was loaded or faulted.…”