Reply to Comment by Z. Şen,İ. Sönmez,and H. Tatli

Mathematical Geosciences -     

Replies to Comment by K. Bratvedt,E. Bølviken,T. Gimse,H. Holden,L. Holden,and R. Knarud

Mathematical Geosciences -     

Reply to ‘Comment on “The beginnings of hydrous mantle wedge melting” by Till et al.’ by Green, Rosenthal and Kovacs

The comment of Green et al. debates the interpretation of the temperature of the H₂O-saturated peridotite solidus and presence of silicate melt in the experiments of Till et al. (Contrib Mineral Petrol 163:669–688, 2012) at <1,000?°C. The criticisms presented in their comment do not invalidate any of the most compelling observations of Till et al. (Contrib Mineral Petrol 163:669–688, 2012) as discussed in the following response, including the changing minor element and Mg# composition of the solid phases with increasing temperature in our experiments with 14.5?wt% H₂O at 3.2?GPa, as well as the results of our chlorite peridotite melting experiments with 0.7?wt% H₂O. The point remains that Till et al. (Contrib Mineral Petrol 163:669–688, 2012) present data that call into question the H₂O-saturated peridotite solidus temperature preferred by Green (Tectonophysics 13(1–4):47–71, 1972; Earth Planet Sci Lett 19(1):37–53, 1973; Can Miner 14:255–268, 1976); Millhollen et al. (J Geol 82(5):575–587, 1974); Mengel and Green (Stability of amphibole and phlogopite in metasomatized peridotite under water-saturated and water-undersaturated conditions, Geological Society of Australia Special Publication, Blackwell, pp 571-581, 1989); Wallace and Green (Mineral Petrol 44:1–19, 1991) and Green et al. (Nature 467(7314):448–451, 2010).     

Carboxylic acid anions in formation waters,San Joaquin Basin and Louisiana Gulf Coast,U.S.A.—Implications for clastic diagenesis. Reply to discussion by P.D. Lundegard and L.S. Land

MacGowan and Surdam (1990a) suggested some modifications to the model of Lundegard and Land (1989) to make it more geologically and geochemically reasonable. The predictive power of such a geochemical model is wholly dependent on the species modeled and the constants used; any model that excludes important species or important thermodynamic data, or one that couples certain reactions in an unrealistic way, may produce results which are not geologically or geochemically reasonable (W. K. Harrison, pers. commun., 1988; Y. K. Kharaka, pers. commun., 1991). We have long recognized that, under early-burial diagenetic conditions, aluminosilicate hydrolysis generally controls formation water pH (Surdam and Eugster, 1976; Mariner and Surdam, 1970; Taylor and Surdam, 1981) and that, during intermediate burial, either aqueous CO₂ or CAA species (in the absence of aqueous S species or other weak conjugate acid-base pairs) will dominate formation water alkalinity and control pH (Surdam et al., 1989c). We reassert that the model of Lundegard and Land (1989) does not take into account the relative importance of PCO₂ and of concentrations of both Ca²⁺ and CAA and their relative organic metal complexes to carbonate mineral stability in sandstones in the zone of intermediate burial clastic diagenesis (cf. the models of Surdam et al., 1984 and Surdam and Crossey, 1985). The usefulness of such models is predicted on the completeness of the model and the use of the best, most accurate thermodynamic data. Also, geologically realistic concentrations of critical species are required for reasonable modeling to be done. Although their model is vigorously defended in the discussion of Lundegard and Land, 1989, Lundegard and Land, 1993, we continue to disagree that their analysis of their model conditions are either geologically or geochemically satisfying.We agree with the fundamental approach and philosophy of Lundegard and Land, 1989, Lundegard and Land, 1993. It is of the utmost importance to determine from experimental, geochemical, petrographic, and geological data what the controls on pH and alkalinity in formation waters are, as well as the exact thermodynamic speciation of aqueous moieties and the stability of detrital and authigenic minerals. Lundegard and Land (1993) raise an additional point about CAA reaction with carbonate minerals in shales, although Fisher and Lewan (1989), Lewan (1989) and MacGowan and Surdam (1990b) have demonstrated that CAA generated in shale likely migrate in the oil phase along incipient shale microfractures to the sandstone reservoir, and thus are likely to not react much with the shale. Finally, we agree with Lundegard and Land that these areas require much additional experimental and field analysis, and petrographic study.     

Reply to ‘Comment on “The beginnings of hydrous mantle wedge melting” by Till et al.’ by Stalder

The comment of Stalder raises three main concerns regarding the interpretation of the experiments presented by Till et al. (2012): (1) our inability to uniquely distinguish between high-pressure hydrous silicate melt and solute-rich aqueous fluid leads to the incorrect interpretation of phase relations, (2) the temperature interval over which hydrous melting takes places is inordinately large and contrary to expectations, and/or (3) the possibility that the system may be above the second critical end point (SCEP) in this H₂O-rich silicate system has been insufficiently discussed. In this reply, we provide clarification on these concerns and argue that with the extent of knowledge available today, the chemical characteristics of our experimental products at 3.2 and 4?GPa evince the presence of a silicate melt at temperatures <1,000?°C and we are below the SCEP in the peridotite–H₂O system at the P–T conditions of our experiments. If in fact the quench observed in our experiments does represent that of a supercritical (SC) fluid, then our data suggest Mg and Fe are highly soluble in SC fluids at the P–T conditions of the base of the mantle wedge below arc volcanoes. Therefore, our results would require a significant change in thinking about the chemical compositional characteristics of SC fluids.     

Reply to “Reply to comments on defining biominerals and organominerals: Direct and indirect indicators of life [Perry et al., Sedimentary Geology, 201, 157–179]” by R.S. Perry and M.A. Sephton: [Sedimentary Geology 213 (2009) 156]

This is a reply to R.S. Perry and M.A. Sephton's “Reply to comments on defining biominerals and organominerals: direct and indirect indicators of life [Perry et al., Sedimentary Geology, 201, 157–179]” [Sedimentary Geology 213 (2009) 156].     

Reply to discussion on “Guidelines on the use of inverse velocity method as a tool for setting alarm thresholds and forecasting landslides and structure collapses” by F. Bozzano,P. Mazzanti,and S. Moretto

■■■The paper “Discussion to: Guidelines on the use of inverse velocity method as a tool for setting alarm thresholds and forecasting landslides and structure collapses by T. Carlà, E. Intrieri, F. Di Traglia, T. Nolesini, G. Gigli and N. Casagli” by Bozzano et al. brings forward new considerations on an issue of extreme concern in landslide risk management. To this day, the ability to predict catastrophic landslide failures from slope surface displacements is a problem dictated more by practical constraints rather than by theoretical uncertainties. In this sense, the development of data interpretation practices is crucial. This short reply provides a few further insights with regard to this subject, also in the context of the recently published literature.     

Reply to comments by Henry N. Pollack and David S. Chapman on “Spherical harmonic analysis of Earth’s conductive heat flow”

Pollack and Chapman, hereafter referred to as P&C, argue that: (1) errors arising from lack of quality control in the IHFC database are not important and not properly documented, (2) resolution of spatial patterns in global heat flux distribution should not be represented by spherical harmonics and (3) heat flow in young oceanic crust and global heat loss are better represented by a contested 1-D cooling model than by the data. We disagree and provide additional information that may help clear up such misunderstandings. We also mention briefly the results of a new improved thermal model of the lithosphere that satisfactorily reproduces the main features identified in observational data sets of heat flow and ocean floor bathymetry. Thus, there is no reason to invoke the ad hoc hypothesis of large-scale hydrothermal circulation in the ocean crust.