Abstract Monazite–xenotime thermometry is a potentially powerful technique for understanding the evolution of Earth systems. While a rich set of experimental and empirical datasets are available for monazite–xenotime equilibria, five different thermometric calibrations yield significantly different results, making this technique difficult to apply in practice. To clarify best practices for monazite–xenotime thermometry, a compilation of published compositional data for monazite and xenotime with independently determined pressure–temperature conditions is evaluated. For each existing thermometer, we examine how closely estimated temperatures match independent empirical temperatures and consider how best to calculate monazite end-members for each thermometer. Monazite–xenotime thermometry is applied to samples from the Northern Highlands Terrane of northern Scotland, which experienced amphibolite–upper greenschist facies metamorphism and penetrative deformation during the Scandian orogeny. Thermometry data in conjunction with U–Pb dating define relatively slow regional cooling across the Scandian thrust nappes. Thermometry data closely match quartz c -axis fabric-based deformation thermometry across the structurally lower nappes, suggesting that monazite and xenotime record the timing and temperature of penetrative deformation and shearing. The data suggest that ductile deformation in the hinterland nappes of the Scandian orogen in Scotland occurred as late as 415–410 Ma.

Abstract Low concentrations of Na, Ca, K, Fe, Mg and Al in quartzite commonly prevent the crystallization of index metamorphic minerals, inhibiting the obtainability of thermobarometric calculations. Quartzite typically contains quartz, zircon and rutile; therefore, single-element thermometers, such as Zr-in-rutile, may be applied. We investigate changes in trace-element composition of rutile from quartzite through increasing metamorphic conditions. Studied samples derive from a quartzite package (Luminárias Nappe, Minas Gerais, Brazil) where previous thermobarometric constraints on metapelites showed an increasing metamorphic grade southwards, from high-pressure lower amphibolite facies (580°C; 0.9 GPa) to eclogite facies (630°C; 1.4 GPa). Rutile from the lower-grade facies samples show a large spread in Zr concentrations, with the highest values corresponding to temperature estimates higher than metamorphic conditions affecting those units, and thus interpreted as inherited detrital signatures. A narrower spread in Zr concentration is observed in rutile grains from the higher-grade facies, and estimated Zr-in-rutile temperatures agree with previous thermobarometric constraints. Therefore, we show that at 630°C, Zr contents in detrital rutile from quartzites re-equilibrate. The comparison between the quartzite- and metapelite-hosting rutile grains from the same area shows that the resetting of the geothermometer in the latter seems to occur at slightly lower temperatures (∼50°C lower).

Abstract The Neoarchean to Paleoproterozoic Betsiboka Suite of Madagascar mainly consists of granitoid orthogneiss and migmatite variably metamorphosed to amphibolite and granulite facies during the late Neoproterozoic. New U–Pb zircon data yield emplacement ages of 2512 ± 17, 2507 ± 17, 2493 ± 14 and 2485 ± 16 Ma. Zircon δ 18 O data indicate involvement of the continental crust during magma genesis. Mostly positive ε Hf ( t ) values plot slightly below the depleted-mantle curve. The isotopic data favour mixing between an older Archean crustal source and a juvenile depleted-mantle source. Possible local crustal candidates for the older component in the exposed Malagasy basement are Neoarchean mafic gneisses in the Tsaratanana Complex and the c. 3200 Ma Nosy Boraha orthogneiss in the Antongil Domain. The new isotopic data support interpretations from previous studies investigating the genesis of Tonian plutonic rocks advocating crustal melting of a Mesoarchean crustal source in the Antananarivo Domain. In addition, detrital zircon in the Proterozoic Ambatolampy Group and Itremo Group probably had a local source with the same isotopic composition as the Betsiboka Suite. Our study demonstrates the significance of multi-isotopic data from zircon for constraining the sources of detrital zircon grains in sedimentary provenance studies.

Abstract The Choquequirao Formation is a >3 km-thick amphibolite-grade succession that outcrops in the Central Andes of southern Peru. To constrain its age and tectonostratigraphic setting, detrital zircon and metamorphic zircon, titanite, and rutile U–Pb isotopic analyses were conducted. Mantle-derived c. 640 Ma detrital zircons constrain the maximum age of the lower part of the succession and 550–490 Ma metamorphic zircon domains constrain its minimum age. The absence of early Paleozoic detrital zircons suggests that deposition predated early Paleozoic orogenesis in southwestern Gondwana. The close similarity of detrital zircon age spectra to those from sediments deposited on the Arequipa basement suggests that the Choquequirao Formation was deposited on the Arequipa Terrane. Metamorphic titanite dates are highly overdispersed, yet they overlap with c. 460 Ma peak metamorphism recorded by metamorphic zircon. Pb-loss pathways displayed by metamorphic titanite have a lower intercept that overlaps with c. 325 Ma metamorphic rutile, which corresponds to Hercynian orogenesis. A poorly constrained upper intercept of c. 510 Ma may correspond to Pampean and/or early Famatinian orogenesis. We interpret the Cryogenian–Ediacaran Choquequirao Formation as having been deposited during the opening of the Palaeo-Iapetus (Puncoviscana–Clymene) Ocean between eastern Arequipa and southern Kalahari prior to the subsequent collision with southwestern Amazonia during the Pampean Orogeny.