Influence of basement rocks on fluid evolution during multiphase deformation: the example of the Estamariu thrust in the Pyrenean Axial Zone
<p>Calcite veins precipitated in the Estamariu thrust during two tectonic events are studied in order to (i) decipher the temporal and spatial relationships between deformation and fluid migration in a long-lived thrust and (ii) determine the influence of basement rocks on the fluid chemistry...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-11-01
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| Series: | Solid Earth |
| Online Access: | https://se.copernicus.org/articles/11/2257/2020/se-11-2257-2020.pdf |
| Summary: | <p>Calcite veins precipitated in the Estamariu thrust during
two tectonic events are studied in order to (i) decipher the temporal and
spatial relationships between deformation and fluid migration in a
long-lived thrust and (ii) determine the influence of basement rocks on the
fluid chemistry during deformation. Structural and petrological observations
constrain the relative timing of fluid migration and vein formation, whilst
geochemical analyses (<span class="inline-formula"><i>δ</i><sup>13</sup>C</span>, <span class="inline-formula"><i>δ</i><sup>18</sup>O</span>,
<span class="inline-formula"><sup>87</sup>Sr∕<sup>86</sup>Sr</span>, clumped isotope thermometry, and elemental composition)
applied to the related calcite cements and host rocks indicate the fluid
origin, pathways, and extent of fluid–rock interaction. The first tectonic
event, recorded by calcite cements Cc1a and Cc2, is attributed to the Alpine
reactivation of the Estamariu thrust. Analytical data indicate that these
cements precipitated from heated meteoric fluids (temperatures in the range
of 50 to 100 <span class="inline-formula"><sup>∘</sup></span>C) that had interacted with basement rocks
(<span class="inline-formula"><sup>87</sup>Sr∕<sup>86</sup>Sr</span> <span class="inline-formula"><i>></i></span> 0.71) before upflowing through the thrust
zone. The second tectonic event, attributed to the Neogene extension, is
characterized by the reactivation of the Estamariu thrust and the formation
of normal faults and shear fractures sealed by calcite cements Cc3, Cc4, and
Cc5. Analytical data indicate that cements Cc3 and Cc4 precipitated from
hydrothermal fluids (temperatures between 130 and 210 <span class="inline-formula"><sup>∘</sup></span>C
and between 100 and 170 <span class="inline-formula"><sup>∘</sup></span>C, respectively) that had
interacted with basement rocks (<span class="inline-formula"><sup>87</sup>Sr∕<sup>86</sup>Sr</span> <span class="inline-formula"><i>></i></span> 0.71) and
been expelled through fault zones during deformation. In contrast, cement
Cc5 probably precipitated from meteoric waters that likely percolated from
the surface through small shear fractures.</p>
<p>The comparison between our results and already published data in other
structures from the southern Pyrenees suggests that regardless of the origin
of the fluids and the tectonic context, basement rocks have a significant
influence on the fluid chemistry, particularly on the <span class="inline-formula"><sup>87</sup>Sr∕<sup>86</sup>Sr</span>
ratio. Accordingly, the cements precipitated from fluids that have
interacted with basement rocks have significantly higher <span class="inline-formula"><sup>87</sup>Sr∕<sup>86</sup>Sr</span>
ratios (<span class="inline-formula"><i>></i></span> 0.710) with respect to those precipitated from fluids
that have interacted with the sedimentary cover (<span class="inline-formula"><i><</i></span> 0.710), which
involves younger and less radiogenic rocks.</p> |
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| ISSN: | 1869-9510 1869-9529 |