Basin formation by thermal subsidence of accretionary orogens

Abstract

Additional information:Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Response to referees of Holt et al.We thank the three referees for their extremely helpful comments on the submitted paper, and appreciate the time that must have been needed. We have paid close attention to their suggestions, and feel that the revised paper greatly benefits from the constructive criticism. We take each referee's comments in turn, below, and offer a point-by-point account of how we have addressed them in the revised version. Our responses are preceded by the # symbol and are in italics.1. Five basins were chosen for the analysis. Why were these basins chosen? The main goal of this paper is to show that a lithosphere cooling model is a fundamental process in accretionary orogens. Therefore, the choice of the case studies needs to be carefully justified to show that these are 'typical' basins (i.e., there are no special conditions that could lead to a subsidence pattern similar to that of the cooling model). This is done in places in the manuscript, but it should be more explicit. At the moment, it isn't clear if the five basins are representative of accretionary orogens or if they were chosen because they fit the cooling model. 2. The cooling model is only vaguely described and no quantitative details are provided. Perhaps there should be a separate section with a conceptual description of the cooling model -why is it expected that accretionary crust has a thin initial lithosphere, what maintains the thin lithosphere, and what happens to cause the lithosphere to start to cool? It is stated that this model is different from a mantle delamination model (top of pg 4), but the 'alternate' mechanism for creating thin lithosphere is not clearly described. #Text has been added to explain the cooling model in section 2. There is also a longer description of why accretionary crust starts with thin mantle lithosphere in the Introduction. Both of these items were first described in Holt et al (2010): the only reason they were not originally given more length in this paper is that we thought readers would prefer a terse version of the material!In addition, the actual numerical values used in the cooling model need to be given. Readers are referred to the Holt et al. (2010) paper, but it isn't clear how this method was applied to the current study. For example: Do all regions start with a 20 km thick mantle lithosphere or does this vary (as implied on pg 15, line ~18: "an unusually thin initial lithosphere…is required")? How was crustal thickness var...

U-PB zircon tuff geochronology from the Karoo Basin, South Africa: implications of zircon recycling on stratigraphic age controls

“…The Ecca and Beaufort Groups of the late CarboniferousJurassic Karoo Supergroup accumulated as a flysch-tomolasse style succession within the Karoo Basin, a tectonically subsiding basin developed in the Gondwanan cratonic interior (Catuneanu et al 2002;Tankard et al 2009;Holt et al 2015). The northeast-southwest elongate basin is bounded by the Cape Fold Belt to the west and south (Figure 1) that contains three clastic depositional areas: the Tanqua, Laingsburg, and Ripon depocentres.…”

Crustal structure, gravity anomalies, and subsidence history of the Parnaíba cratonic basin, Northeast Brazil

“…For example, Armitage and Allen [2010] speculated, assuming a rift origin, that at the low strain rates implied by the longevity of cratonic basin subsidence, extension may be accommodated in some diffusive manner, such that it is not resolved in seismic imaging. However, as discussed by Holt et al [2015], analogue models [Bellahsen et al, 2003] and field observations [Mazzarini et al, 2004] suggest that at low strain rates, extension is more likely to become localized on fewer, large faults. Therefore, it appears that an extensional origin is inconsistent with Parnaíba Basin seismic structure, and an alternative mechanism must be responsible for basin subsidence and possibly cratonic basins in general [e.g., Stel et al, 1993;Hamdani et al, 1991Hamdani et al, , 1994Sleep, 2009;Holt et al, 2010Holt et al, , 2015McKenzie and Priestley, 2016].…”

“…However, as discussed by Holt et al . [], analogue models [ Bellahsen et al ., ] and field observations [ Mazzarini et al ., ] suggest that at low strain rates, extension is more likely to become localized on fewer, large faults. Therefore, it appears that an extensional origin is inconsistent with Parnaíba Basin seismic structure, and an alternative mechanism must be responsible for basin subsidence and possibly cratonic basins in general [e.g., Stel et al ., ; Hamdani et al ., , ; Sleep , ; Holt et al ., , ; McKenzie and Priestley , ].…”

“…Hartley and Allen [], Klein [], and Allen and Armitage [] have reviewed the processes that have been proposed to explain cratonic basin formation. Most studies have focused on developing geodynamical models in order to explain their tectonic subsidence and the main processes can be summarized as follows: (1) thermal subsidence following lithosphere extension, thinning, and cooling; lithospheric accretion and cooling above a subduction mantle wedge; or erosion, thinning and cooling following crust and lithosphere thickening [e.g., Sleep , ; Sleep et al ., ; Ahern and Mrkvicka , ; Nunn and Sleep , ; Sleep , ; Kadima Kabongo et al ., ; Holt et al ., , ; Lucazeau et al ., ; McKenzie and Priestley , ]; (2) lithospheric folding caused by far‐field in‐plane stresses [e.g., Lambeck , , ; DeRito et al ., ; Cloetingh , ]; (3) dense loads produced by metamorphic phase changes or cooling of igneous intrusions within the lower crust and/or mantle lithosphere [e.g., Haxby et al ., ; Nunn and Aires , ; Fowler and Nisbet , ; Klein , ; Baird et al ., ; Naimark and Ismail‐Zadeh , ]; and (4) dynamic topography driven by large‐scale mantle convection or isolated convective instabilities [e.g., Middleton , ; Hartley and Allen , ; Downey and Gurnis , ].…”

“…A buried load model is consistent with seismic data, which suggest that the Moho is as deep or deeper beneath the basin center than its flanks and accounts for at least part of the tectonic subsidence through a viscoelastic stress relaxation that occurs in the lithosphere following load emplacement.Recent heat flow and seismic tomographic studies [e.g., Koptev and Ershov, 2011;Priestley and McKenzie, 2013] reveal that most cratonic basins are located above regions of thick (thermally defined) lithosphere. Although a few basins, such as Murzuq and Ghadames in North Africa, appear to have formed above young, thin, lithosphere [Holt et al, 2015], plate reconstructions [Cannon et al, 2014] show that most are located on old, thick lithosphere far from plate boundaries. [1994], Klein [1995], and Allen and Armitage [2011] have reviewed the processes that have been proposed to explain cratonic basin formation.…”