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In the Upper Pedraforca thrust sheet in the Southern Pyrenees, replacive dolomite occurs in the Jurassic carbonates (Rd1) and Lower Cretaceous sedimentary breccias and carbonates (Rd2). Dolomite crystals are red-dull to non-luminescent, subhedral, 15–400 μm in size, and show idiotopic and hypidiotopic textures. The replacive dolostones are cut by fracture-filling dolomite cement (Dc1 and Dc2). Dc1 precipitated in bed-perpendicular fractures and consisted of red-luminescent saddle crystals of 250–700 μm. Dc2 precipitated between breccia clasts and in bed-parallel fractures and composed of non- to red-luminescent saddle crystals of 250 μm and 2 mm in size, respectively. The 87Sr/86Sr ratio of Rd1 (0.707816) is higher than that of Jurassic–Cretaceous seawater, suggesting siliciclastic inputs, whereas the ratios of Rd2 (from 0.707366 to 0.707604) are within the range of the Late Jurassic–Early Cretaceous seawater. The bell-shaped to almost flat REE + Y patterns of Rd1 and Rd2 and the positive Y and Gd anomalies reflect marine influence. The Y/Ho ratios of 52.75–44.91 reflect intermediate values between the composition of marine carbonates and detritic sediments. The absence of positive Eu anomalies discards high-temperature dolomitization. Fracture-filling dolomites have temperatures of 149.4 ± 12.5 °C and δ18Ofluid of + 11.2 ± 1.1 ‰ VSMOW for Dc1 and 124.7 ± 6.2 °C and + 7.1 ± 0.7 ‰ VSMOW for Dc2, reflecting the influence of formation brines possibly interacting with the Triassic evaporites. Rd1 and Rd2 share a common origin and age with shallow burial dolostones from the North Pyrenean Zone. Contrarily, fracture-filling dolomites in the Southern Pyrenees precipitated from formation brines, whereas deep-crustal and mantle-derived fluids (from 250 to > 300 °C) were also identified in the Northern Pyrenees. These differences are interpreted as higher crustal thinning in the North Pyrenean Zone than in the Southern counterpart, facilitating the occurrence of deep-sourced fluids and high-temperature/low-pressure metamorphism.

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Origin of the Jurassic and Early Cretaceous Dolomitization in the Southern Pyrenees: Comparison with the North Pyrenean Zone

  • 会议论文

  • 发表日期：

    2025年

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  • David Cruset,
  • Anna Travé,
  • Jaume Vergés,
  • Irene Cantarero,
  • Daniel Muñoz-López,
  • Mar Moragas,
  • Vinyet Baqués

摘要

In the Upper Pedraforca thrust sheet in the Southern Pyrenees, replacive dolomite occurs in the Jurassic carbonates (Rd1) and Lower Cretaceous sedimentary breccias and carbonates (Rd2). Dolomite crystals are red-dull to non-luminescent, subhedral, 15–400 μm in size, and show idiotopic and hypidiotopic textures. The replacive dolostones are cut by fracture-filling dolomite cement (Dc1 and Dc2). Dc1 precipitated in bed-perpendicular fractures and consisted of red-luminescent saddle crystals of 250–700 μm. Dc2 precipitated between breccia clasts and in bed-parallel fractures and composed of non- to red-luminescent saddle crystals of 250 μm and 2 mm in size, respectively. The 87Sr/86Sr ratio of Rd1 (0.707816) is higher than that of Jurassic–Cretaceous seawater, suggesting siliciclastic inputs, whereas the ratios of Rd2 (from 0.707366 to 0.707604) are within the range of the Late Jurassic–Early Cretaceous seawater. The bell-shaped to almost flat REE + Y patterns of Rd1 and Rd2 and the positive Y and Gd anomalies reflect marine influence. The Y/Ho ratios of 52.75–44.91 reflect intermediate values between the composition of marine carbonates and detritic sediments. The absence of positive Eu anomalies discards high-temperature dolomitization. Fracture-filling dolomites have temperatures of 149.4 ± 12.5 °C and δ18Ofluid of + 11.2 ± 1.1 ‰ VSMOW for Dc1 and 124.7 ± 6.2 °C and + 7.1 ± 0.7 ‰ VSMOW for Dc2, reflecting the influence of formation brines possibly interacting with the Triassic evaporites. Rd1 and Rd2 share a common origin and age with shallow burial dolostones from the North Pyrenean Zone. Contrarily, fracture-filling dolomites in the Southern Pyrenees precipitated from formation brines, whereas deep-crustal and mantle-derived fluids (from 250 to > 300 °C) were also identified in the Northern Pyrenees. These differences are interpreted as higher crustal thinning in the North Pyrenean Zone than in the Southern counterpart, facilitating the occurrence of deep-sourced fluids and high-temperature/low-pressure metamorphism.