Fluid inclusions primary/secondary

Fluid inclusion data from our samples by Fluids Inc., not corrected for pressure. Data are for secondary inclusions second values for M. Modino are from primary inclusions. Secondary M. Modino inclusions contain hydrocarbons. Macigno fluid inclusion data are from quartz crystals. Rq values are averages of the number of samples in parentheses. 

Rare two-phase fluid inclusions e found in anker-ite and in calcite (Fig. 6H). They occur as isolated inclusions or in groups of a few inclusions with a random distribution. Owing to the scarcity of inclusions and to the lack of visible intracrystalline growth features in the carbonate cements, relationships between fluid inclusions and carbonate growth could not be evaluated. As a result, the primary or secondary origin of the inclusions studied cannot be ascertained. Microthermometric measurements are summarized in Table 2 and Fig. 7. 

Fig. 10. Frequency histogram of primary fluid inclusion homogenization temperatures reported for saddle dolomite. Horizontal arrows indicate literature sources that reported a range of values only. Data from Coniglio Williams-Jones (1992) are mostly from inclusions of secondary or indeterminate origin and are shown for comparison.

Fig. 11. Frequency histogram of final melting temperatures of primary fluid inclusions in saddle dolomite. Data from Coniglio Williams-Jones (1992) are mostly from inclusions of secondary or indeterminate origin and are shown for comparison. Horizontal arrows indicate literature sources that reported a range of values only. The upper x axis gives an expression of the measured temperatures as wt% NaCl eq., based on a pure H20-NaCl system (after Bodnar, 1993). The composition of seawater is indicated by the vertical dashed line (Tn, = -2.1 °C). The range of values in Shelton et al. (1992) include data from saddle dolomite and from other epigenetic dolomite varieties.

Fluid inclusions occur either as primary inclusions within the quartz of the silicified zone (I, 11 and III), or secondary inclusions in milky quartz of the silicified zone (I and II) 5 and 10 cm far from the intrusive contact. 

Inclusions may be classified as primary (formed during growth) or secondary (formed later). Primary fluid inclusions constitute samples of fluid in which the crystals grew. Secondary inclusions give evidence of later environments and are... 

Gong, S., Peng, P.A., Shuai, Y.H., Dai, J.X., Zhang, W.Z. (2008) Primary migration and secondary alteration of the Upper Paleozoic gas reservoir in Ordos Basin, China— application of fluid inclusion gases. Science in China Series D-Earth Sciences, 51,165-173. 

The fact that most metamorphic inclusions are secondary has led to the diffuse opinion that they are useless. Notwithstanding the evidence that they are an intrinsic part of the rock and have consequently to be studied, I see the problem in an entirely different way primary and secondary inclusions are exactly alike neither is "a priori" secure as any is liable to have suffered one of the many processes which may alter the representativity of the enclosed fluid, such as selective trapping, leakage, necking down or reaction with the host mineral. Therefore any fluid inclusion data must be compared with results derived independently by other methods. This is the point at which we are now, as many of these data became available in metamorphic petrology from experimentation or theoretical models. Only when some limiting conditions have been fulfilled may additional data be obtained and it comes then... 

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