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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 67 (1983)

Issue: 4. (April)

First Page: 692

Last Page: 705

Title: Deciphering Fracturing and Fluid Migration Histories in Northern Appalachian Basin

Author(s): J. Edward Tillman (2), H. L. Barnes (3)


An integrated structural and geochemical analysis of mineralized faults and fractures revealed that the most widespread fracture systems in the northern Appalachian basin resulted from two periods of post-Alleghenian deformation. Fluid inclusion homogenization measurements on calcite samples from pre-, syn-, and post-kinematic structural settings bracketed the temperature ranges (predominantly a function of depth of burial) for each period of fracturing. The first period of deformation produced northwest, west-northwest, and east-northeast fractures and related faults that experienced recurrent strike-slip movements during a cooling event from 176° to 120°C (349° to 248°F). This cooling episode was associated with the waning of an elevated thermal grad ent attained during dewatering caused by late Paleozoic burial metamorphism (at depths of 3 to 3.5 km [9,800 to 11,500 ft]). Later normal faulting reopened the earlier strike-slip fault zones during subsequent cooling of the system from 112°C (234°F) to below 76°C (169°F). This second cooling stage resulted from the 1 to 2 km (3,300 to 6,600 ft) of uplift and erosion that occurred throughout the eastern United States during the Cretaceous. The ubiquitous occurrence of carbonate, silicate, and sulfide epigenetic mineralization in many environments allows for widespread application of the dating techniques demonstrated in this study. Basic to this approach is the analysis of mineral assemblages deposited during increases in hydrothermal circulation resulting from enhanc d permeability associated with periods of faulting and fracturing. The presence of different mineral assemblages (representing a range of ages and crystallization environments) on various generations of brittle structures, provides a means for developing detailed faulting and circulation histories, and the determination of approximate, as well as precise relative ages for each event.

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