The following oxygen isotope data were measured on coexisting quartz and alumino
ID: 106401 • Letter: T
Question
The following oxygen isotope data were measured on coexisting quartz and aluminosilicate from Naxos Island (Greece). The data are from Putlitz et al. (2002). a. Compute Delta A-B (recall Delta_A-B = ~ delta^18 O_A - delta^18 O_A B) for each mineral pair (qtz-kyanite; quartz-sill) b. What is the general form of the relationship between Delta_A-B and temperature dependence for this temperature range (assess using 1/T)? c. Use your answers from (a) and (b) to make the appropriate plot for this temperature range and come up with an empirical relationship to describe the geothermometers. d. Use the geothermometers you derived to predict the difference you would find in the d^18 O_qtz and d^18 O_ky' for a metamorphic event that occurred at 730 degree C. What would the Delta_qtz-sill be for a metamorphic event at 800 degree C?Explanation / Answer
a.The del A-B value is calculated for each mineral pair as follows:-
For quartz-kyanite pair:-
9.65-(9.65*7.19)=-59.73
12.75-(12.75*10.27)=-118.19
13.05-(13.05*10.40)=-122.67
13.86-(13.86*10.80)=-135.828
13.86-(13.86*10.85)=-136.52
13.51-(13.51*10.93)=-134.15
13.09-(13.09*10.44)=-123.56
13.14-(13.14*10.48)=-124.56
12.56-(12.56*0)=0
13.23-(13.23*0)=0
14.47-(14.47-11.70)=-154.82
13.76-(13.76*0)=0
For quartz-sill pair:-
9.65*0=0
12.75*0=0
13.05*0=0
13.86*0=0
13.86*0=0
13.51*0=0
13.09-(13.09*10.32)=-121.99
13.14-(13.14*10.86)=-129.56
12.56-(12.56*9.82)=-110.77
13.23-(13.23*10.87)=-130.58
14.47*0=0
13.76-(13.76*11.31)=-141.86
b.The relationship between del A-B and temperature is estimated as follows:-
For quartz-kyanite pair,del A-B for first value=-59.73
Now 1/T=1/690=1.44×10^-3=0.00144
The neagtive sign is neglected and is=59.73 approximately =60
Now 60/0.00144=41.666
now 41.666/690=60
From the above calculations,we find that the temperature and del A-B value is inversely proportional.
c.From the estimated values of a and b the temperature is plotted along x axis and del A-B value is plotted along y axis and the relation is inversely proportional to each other.
d.The del A-B value in case of quartz-sill pair at 800degrees would nearly be equal to -140 as it is roughly estimated from the table.
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