期刊
GEOLOGICAL MAGAZINE
卷 159, 期 11-12, 页码 2020-2035出版社
CAMBRIDGE UNIV PRESS
DOI: 10.1017/S0016756822000371
关键词
calcite vein; fibrous vein; mudrock; EBSD; SEM-CL
资金
- Shell International Exploration and Production B.V
A study on calcite veins in the Marcellus Formation reveals that the veins were formed through a combination of continuous fibrous growth and punctuated fracture-opening increments. The continuous growth is due to pressure-solution creep, while the incremental opening is caused by overpressured, mineral-saturated fluid. The study provides insights into the formation mechanism and deformation conditions of calcite veins.
Calcite veins are common in organic-rich mudrocks, but their genesis and ability to transmit fluids are debated. A combined microstructural and isotopic investigation of an array of calcite veins recovered in core from the Marcellus Formation reveals that the veins grew via a combination of continuous fibrous growth and punctuated fracture-opening increments. Continuous opening is the result of pressure-solution creep and involves no mechanical fracturing, but rather the growth of a pressure fringe around a pre-existing, sealed fracture. In contrast, incremental opening is accomplished by overpressured, mineral-saturated fluid, which repeatedly ruptures the rock at the cement / host-rock interface. Punctuated growth increments occurred repeatedly throughout an otherwise protracted, continuous growth history, indicating that the present structures preserve hybrid deformation conditions between brittle, fluid-assisted cracking and plastic strain. Stable isotopic signatures match those of a regional opening-mode fracture set that formed in response to catagenetic fluid overpressures amid a tectonically imposed (Alleghanian) stress field. It is concluded that calcite veins form as opening-mode hydraulic fractures and are susceptible to increments of brittle reactivation, even while inelastic growth processes widen and fill the veins with fibrous cement.
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