Fluid Inclusion Microthermometry
The determination of temperatures of phase changes within fluid inclusions during heating and cooling of samples is termed microthermometry. The technique is invaluable for discovering the temperatures at which minerals form, the thermal history a rock has experienced, and the compositions of the fluids that traversed a rock in its history. The fundamental principles upon which microthermometry is based are the principles of phase equilibria introduced in Chapter 3. And, as explained in Chapter 6, it is best to first spend a considerable amount of time and effort to characterize the fluid inclusion petrography prior to attempting microthermometry. This chapter elucidates useful philosophical approaches and important practical procedures that, if learned and employed, will ensure successful and efficient microthermometric studies. Also, phase changes for some simple but potentially applicable fluid systems common in the diagenetic realm will be described.
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The past decade has revealed significant advantages to using fluid inclusions as a means of understanding the physical and chemical history of fluids in sedimentary basins, but it also has revealed important limitations which have required that a new approach must be employed to effectively use fluid inclusions. This book is divided into six sections: (1) what fluid inclusions are and what geologic history they are capable of recording; (2) basic phase equilibria that must be known to understand the behavior of pore fluids and fluid inclusions in nature; (3) the question of validity of using fluid inclusions as records of ancient diagenetic systems is dealt with in such a way that the questions commonly asked about the limitations of the technique are addressed; (4) hot to conduct a fluid inclusion study, a new petrographically based approach for conducting fluid inclusion research that is followed by methods that allow for the interpretation of compositions of pore fluids that existed in sedimentary rocks, and methods of geothermometry and geobarometry; (5) selected case histories that are designed specifically to give practice in evaluating fluid inclusion data from the diagenetic realm; and (6) a summary of the arsenal of analytical techniques that may be applied to fluid inclusions to develop additional constraints on fluid inclusion composition.