Apatite from NWA 10153 and NWA 10645 : the key to deciphering magmatic and fluid evolution history in Nakhlites

Apatites from Martian nakhlites NWA 10153 and NWA 10645 were used to obtain insight into their crystallization environment and the subsequent postcrystallization evolution path. The research results acquired using multi-tool analyses show distinctive transformation processes that were not fully completed. The crystallization history of three apatite generations (OH-bearing, Cl-rich fluorapatite as well as OH-poor, F-rich chlorapatite and fluorapatite) were reconstructed using transmission electron microscopy and geochemical analyses. Magmatic OH-bearing, Cl-rich fluorapatite changed its primary composition and evolved toward OH-poor, F-rich chlorapatite because of its interaction with fluids. Degassing of restitic magma causes fluorapatite crystallization, which shows a strong structural affinity for the last episode of system evolution. In addition to the three apatite generations, a fourth amorphous phase of calcium phosphate has been identified with Raman spectroscopy. This amorphous phase may be considered a transition phase between magmatic and hydrothermal phases. It may give insight into the dissolution process of magmatic phosphates, help in processing reconstruction, and allow to decipher mineral interactions with hydrothermal fluids

Two stages of Late Carboniferous to Triassicmagmatism in the Strandja Zone of Bulgaria and Turkey

Although Variscan terranes have been documented from the Balkans to the Caucasus, the southeastern portion of the Variscan Belt is not well understood. The Strandja Zone along the border between Bulgaria and Turkey encompasses one such terrane linking the Balkanides and the Pontides. However, the evolution of this terrane, and the Late Carboniferous to Triassic granitoids within it, is poorly resolved. Here we present laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) U–Pb zircon ages, coupled with petrography and geochemistry from the Izvorovo Pluton within the Sakar Unit (Strandja Zone). This pluton is composed of variably metamorphosed and deformed granites which yield crystallization ages of c. 251–256 Ma. These ages are older than the previously assumed age of the Izvorovo Pluton based on a postulated genetic relationship between the Izvorovo Pluton and Late Jurassic to Early Cretaceous metamorphism. A better understanding of units across the Strandja Zone can now be achieved, revealing two age groups of plutons within it. An extensive magmatic episode occurred c. 312–295 Ma, and a longer-lived episode between c. 275 and 230 Ma. Intrusions associated with both magmatic events were emplaced into pre-Late Carboniferous basement, and were overprinted by Early Alpine metamorphism and deformation. These two stages of magmatism can likely be attributed to changes in tectonic setting in the Strandja Zone. Such a change in tectonic setting is likely related to the collision between Gondwana-derived terranes and Laurussia, followed by either subduction of the Palaeo-Tethys Ocean beneath Laurussia or rifting in the southern margin of Laurussia, with granitoids forming in different tectonic environments

Variscan magmatic evolution of the Strandja Zone (Southeast Bulgaria and Northwest Turkey) and its relationship to other North Gondwanan margin terranes

The Strandja Zone, straddling the border between Bulgaria and Turkey, is often assigned to either the Balkanide or the Pontide thrust belts of the Alpine orogen in the Black Sea region. Previous studies have considered this zone, which originated on the North Gondwanan margin, as part of a Late Carboniferous to Triassic magmatic arc associated with the subduction of the Paleo-Tethys Ocean beneath Eurasia. Magmatism has been regarded as representing one continuous or two separate stages occurring under different tectonic settings. We present new LA-ICP-MS U-Pb zircon ages together with field, petrographic and geochemical studies of variably deformed granites from the Sakar Batholith and Levka Pluton of the Sakar Unit in the Strandja Zone. The new U-Pb ages from Sakar Batholith (ca. 306 Ma) and Levka Pluton (ca. 319 Ma) demand a re-evaluation of previously published U-Pb crystallisation ages from these magmatic bodies. The U-Pb age reported for the Levka Pluton also provides an upper age limit for the timing of Variscan metamorphism. The Late Carboniferous to Early Permian magmatic evolution of the Strandja Zone displays a strong resemblance to that of the Sredna Gora Zone. Both units, probably together with Serbo-Macedonian Metamorphic Complex and Sakarya Zone, were part of the metamorphic core of the Variscan Orogen