Metamorphic history of riebeckite- and aegirine-augite-bearing high-pressure–low-temperature blocks within the Siuna Serpentinite Mélange, northeastern Nicaragua

Abstract

The Siuna Serpentinite Mélange (SSM) is a subduction-zone-related complex that contains diverse blocks of igneous and sedimentary origin, overprinted by various metamorphic conditions. The SSM is located at the southern border of the Chortís block and marks the boundary between continental and oceanic crusts in the western margin of the Caribbean Plate. The serpentinite matrix mainly consists of lizardite/chrysotile, Cr-rich spinel, and relict orthopyroxene that suggest a harzburgitic protolith and an upper mantle supra-subduction zone origin. Blocks within the southern and central regions range from Jurassic pelagic sediments to mafic/intermediate igneous rocks that are metamorphosed to various degrees, ranging from prehnite-pumpellyite/greenschist to likely blueschist facies (e.g. riebeckite-bearing metashale) conditions. In contrast, the northern section encloses almost exclusively epidote-amphibolite facies metabasite blocks, and minor micaand chlorite-rich rocks of metasomatic origin, respectively. Some of the epidote-amphibolite blocks contain relic garnet-rich zones embedded in an amphibole-rich matrix. The garnets appear to record two generations of growth and contain mineral inclusions such as amphibole, apatite, titanite, aegirine-augite, and quartz. Thermobarometric estimates for the garnet-rich zones and epidote-amphibolite-rich matrix suggest a prograde blueschist facies at~1.2 GPa and 400-450°C, an eclogite facies metamorphic peak at 1.5-1.7 GPa and 565-614°C, and a post-peak epidote-amphibolite facies metamorphism. These pressure and temperature estimates indicate a classical clockwise PT path that has been observed in many palaeo-subduction zone environments worldwide. Phengite Ar-Ar dating of mica-rich rock yields 140 Ma and suggests an Early Cretaceous exhumation along the southern edge of the continental Chortís block.

Record of massive upwellings from the Pacific large low shear velocity province

“…4; ref. 67) and by the ages of collision events recorded in the Middle American region6869. The lithospheric plates were constructed through time by adding/removing oceanic crust to the major continents and terranes.…”

Paleomagnetism and Geochronology of the Early Cretaceous Dipilto Batholith (NW Nicaragua): Chortís Block Large Rotation With Respect to SW North America

“…Several reviews of Mexican tectono-stratigraphic terranes and complexes include Campa and Coney (1983), Keppie (2004), Ortega-Gutiérrez et al (2018), and Sedlock et al (1993). Since Early Cretaceous time the Chortís block has interacted with the following terranes and complexes ( Figure 1a): (1) Oaxaca, with Grenville (1300-990 Ma) basement consisting mainly of granulite facies (Solari et al, 2003, and others); (2) Mixteco, with a Paleozoic polymetamorphic basement, comprising diverse metamorphic and igneous suites of Ordovician to Early Triassic ages (Ortega-Gutiérrez et al, 1999; and others); (3) Juárez, consisting of a Mesozoic sequence of low to medium-grade phyllites and schist, and some MORB Andjić et al, 2018;Campa & Coney, 1983;Centeno-García, 2017;Fitz-Díaz et al, 2018;Flores et al, 2015;Sedlock et al, 1993). In dotted lines, the classical models that position the Chortís block juxtaposed south of Mexico (x) and with a separation angle (y) Rogers, Mann, Scott, & Patino, 2007).…”

“…It collided with the Chortís block in Late Cretaceous time (Rogers, Mann, Emmet, & Venable, 2007;Venable, 1994). The Siuna Terrane has a record of multiple metamorphic episodes including the Siuna Serpentinite Mélange with blueschist facies blocks, a metamorphic peak of eclogite facies, and a post-peak (epidote) of amphibole facies, with an Ar-Ar in phengite exhumation age of~140 Ma (Flores et al, 2015). This sequence, typical of a paleosubduction zone (Flores et al, 2015) is cut by intermediate dikes and plutons (K-Ar age of~75 to 60 Ma; Venable, 1994).…”

“…(a) Tectonic and geological frameworks of southwestern Mexico and Central America (based on Andjić et al, ; Campa & Coney, ; Centeno‐García, ; Fitz‐Díaz et al, ; Flores et al, ; Rogers, Mann, & Emmet, ; Sedlock et al, ). In dotted lines, the classical models that position the Chortís block juxtaposed south of Mexico ( x ) and with a separation angle ( y ) (Molina‐Garza et al, ; Rogers, Mann, Scott, & Patino, ).…”

Rapid vertical motions and formation of volcanic arc gaps: Plateau collision recorded in the forearc geological evolution (Costa Rica margin)

“…In the past 20 years, the careful study of igneous and associated sedimentary rocks unveiled the existence of a terrane puzzle in Costa Rica. The MCOT was accreted to the southern margin of the Chortis Block (continental terranes; Rogers et al, 2007) during an earliest Cretaceous arcarc collision Flores, 2009;Flores et al, 2015). The blocks consist of variously metamorphosed arc and oceanic floor lithologies, including radiolarites of Late Triassic and Jurassic age.…”