deletions | additions       diff --git a/untitled.tex b/untitled.tex  index 0a34b06..352d786 100644  --- a/untitled.tex  +++ b/untitled.tex 
...
A characteristic feature of systems with episodic pulsing of hot fluids is the development of a thermal anomaly along the high permeability paths in which flow is focused. One example is the perturbation of the temperature field observed in the Mississippi Valley Type (MVT) mineralization districts that lie around the margins of major Palaeozoic sediment basins in the continental USA \citep{Sangster:1994ub}. Similar temperature anomalies have been reported for other sedimentary basins, for example to the south east of the Massif Central in France \citep{Charef:1988vt}. The anomaly is seen as a difference between the temperature of precipitation of hydrothermal minerals and that of the host rock at the time and depth of burial that the mineralization took place. Using simple thermal modelling Cathles and co-workers show that that the temperature difference is due to heat advection associated with episodic, rapid release of hot fluids from deeper regions of the basins \citep{Cathles:1983tj,CathlesIII:2005uo}. In these example the fluids are thought to originate from overpressured formation water in the compacting sedimentary basins. Importantly, the fluid velocities required to produce the thermal anomaly are more than 1000 times greater than could be produced by the steady subsidence, compaction, and dewatering of the basins \citep{Cathles:1983tj}. This suggests to us that the pulses result from a coupling between the pore fluid pressure and rock failure. We envisage that when pore fluid pressures approach lithostatic either mode I hydraulic fracturing or shear failure and development of dilation jogs along fault surfaces allows rapid dewatering of shales within the sediment pile. The fluid is channelled into high permeability aquifers located at the base of the basins where it flows outwards towards the basin margins.  Mineralization with MVT affinities occurs in the Peak District area of the southern Pennines in the UK. Here strata bound deposits (flats) of dominantly Pb-Zn and fluorite mineralization are closely associated with near vertical veins (scrins) that lie along strike-slip fault surfaces and fractures of Variscan age \citep{Quirk:1991uq}. As with the upper Mississippi valley sedimentary basins it is widely held that the mineralization results from basin scale migration of sedimentary formation waters \citep{ixer1993lead}. However, the driving force for, flow paths  and rates of fluid migration are poorly constrained. Opinion ranges from slow gravity driven flow as a result of tectonic uplift associated with the Variscan inversion \citep{Quirk:1991uq} to a seismic valve type process with rapid dewatering of the over-pressured basin fill triggered by fault activity \citep{Frazer:2014eh}. Evidence for a thermal anomaly associated with rapid advection of fluids is not conclusive. Fluid inclusion homogenization temperatures for fluorite and calcite span a wide range from <70$^{\circ}$ to >240$^{\circ}$C \citep{Atkinson:1983ua, Kendrick:2002vc}. Mineralization is thought to have occurred at depths between 1 and 2km \citep{Colman:1989vf}. Thus, assuming a geothermal gradient of 30$^{\circ}$C.km^{-1}, the fluid inclusion homogenization temperatures are at, or greater than the maximum expected host rock temperature at the time of mineralization. This suggests that fluid movement was rapid and therefore unlikely to be associated with slow, gravity driven flow or a gradual dewatering of the basin fill. There are questions, however, as to the reliability of some of the reported temperatures that are derived from fluid inclusion analysis. In the absence of very high heat flows through the base of the basins it is difficult to envisage how the very high temperatures of >240$^{\circ}$C or more are generated in with maximum depths on the order of four to five km. Moreover, Kendrick and co-workers report evidence of stretching, necking down and leakage in samples that show anomalously high temperatures \citep{Kendrick:2002vc}. To help us better understand the possible coupling between faulting and fluid flow in the Peak District we have used clumped isotope thermometry to determine the temperature at which a Variscan hydrothermal calcite vein precipitated. Clumped isotope thermometry is based on the fact that the rare, heavy isotopes of carbon (^{13}C) and oxygen (^{18}O) are ordered in the carbonate lattice. This is a result of the greater stability of the ^{13}C-^{18}O bond compared to bonds involving either no, or a single isotopic substitution. The degree of ordering is an inverse function of temperature. As temperature increases the isotopes tend towards a more random or stochastic distribution \citep{Eiler:2007vua}. Measurement of the degree of ordering allows us to estimate the temperature at which the distribution of isotopes in the calcite structure are locked in \citep{Ghosh:2006cn}. This is analogous to the concept of a closure temperature for radiogenic isotopes or for cation ordering in minerals. A key advantage of the method is that the temperature estimate is based on the distribution of carbon and oxygen isotopes within a single phase and not on the partitioning of oxygen isotopes between calcite and it’s parent fluid as in the conventional oxygen isotope geothermometer. Thus combining determination of the mineral precipitation temperature is decoupled from knowledge of the parent fluid oxygen isotope composition. Combining  the clumped isotope temperature (T($\Delta$_{47})) with the bulk oxygen isotope composition of the carbonate represented by it's $\delta^{13}$C value we can constrain the isotopic composition of the parent fluid. Two previous Recently two  studies have demonstrated the use of clumped isotopes to constrain the temperature and isotopic composiiton of fluids associated with faulting and fractures in the upper crust \citep{Swanson:2012gw, Bergman:2013ip}. Using these techniques we find: