Deformation history of the eclogite‐ and jadeitite‐bearing mélange from North Motagua Fault Zone, Guatemala: insights in the processes of a fossil subduction channel

Abstract

In Guatemala, along the northern side of the Motagua Valley, a mélange consisting of blocks of eclogite and jadeitite set in a metaserpentinitic and metasedimentary matrix crops out. The metasedimentary rocks display a complex deformation history that includes four tectonic phases, from D1 to D4. The D1 phase occurs only as a relic and is characterized by a mineral assemblage developed under pressure temperature (P-T) conditions of 1.00-1.25 GPa and 206-2638C. The D2 phase, characterized by isoclinal folds, schistosity and mineral/stretching lineation, developed at P-T conditions of 0.70-1.20 GPa and 279-4098C. The following D3 and D4 phases show deformations developed at shallower structural levels. Whereas the D1 phase can be interpreted as the result of underplating of slices of oceanic lithosphere during an intraoceanic subduction, the following phases have been acquired by the mélange during its progressive exhumation through different mechanisms. The deformations related to the D2 and D3 phases can be regarded as acquired by extrusion of the mélange within a subduction channel during a stage of oblique subduction. In addition, the structural evidences indicate that the coupling and mixing of different blocks occurred during the D2 phase, as a result of flow reverse and upward trajectory in the subduction channel. By contrast, the D4 phase can be interpreted as related to extension at shallow structural levels. In this framework, the exhumationrelated structures in the mélange indicate that this process, probably long-lived, developed through different mechanisms, active in the subduction channel through time.

Metamorphic evolution of lawsonite eclogites from the southern Motagua fault zone, Guatemala: insights from phase equilibria and Raman spectroscopy

“…The NMFZ mélange has been thrust northward over the Chuacús complex, consisting of amphibolite facies gneiss with rare relict eclogite (Ortega‐Gutiérrez et al. , 2004; Marroni et al. , 2009; Ratschbacher et al.…”

“…, 2011). In contrast, the SMFZ mélange has been thrust southward over the very low‐grade metasedimentary rocks (San Diego phyllite) of the Chortís basement (Marroni et al. , 2009; Ratschbcher et al.…”

“…The northern MFZ (NMFZ) me´lange includes blocks of zoisite eclogite that are mostly retrogressed to garnet amphibolite, whereas the SMFZ me´lange hosts blocks of pristine lawsonite eclogite and blueschist (Harlow et al, 2004;Tsujimori et al, 2005Tsujimori et al, , 2006b. The NMFZ me´lange has been thrust northward over the Chuacu´s complex, consisting of amphibolite facies gneiss with rare relict eclogite (Ortega-Gutie´rrez et al, 2004;Marroni et al, 2009;Ratschbacher et al, 2009), and is interpreted as either the basement of the Maya block (e.g. Harlow et al, 2004;Brueckner et al, 2009) or an allochthonous terrane accreted to the south of the Maya block along the Baja Verapaz shear zone (e.g.…”

“…Ortega-Gutie´rrez et al, 2007;Ortega-Obrego´n et al, 2008;Solari et al, 2011). In contrast, the SMFZ me´lange has been thrust southward over the very lowgrade metasedimentary rocks (San Diego phyllite) of the Chortı´s basement (Marroni et al, 2009;Ratschbcher et al, 2009). The tectonic relationship between the two high-P me´langes has been a matter of debate.…”

“…3. Beccaluva et al, 1995;Ortega-Gutie´rrez et al, 2007;Marroni et al, 2009) Primary fluid inclusions are common in omphacite crystals (Tsujimori et al, 2006a). Laser Raman analysis shows the fluid inclusions are dominantly H 2 O, but their salinity has not been determined due to their small size.…”