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Zinc isotopes in primitive magmatic rocks have been used recently to interrogate the origins of mantle heterogeneity. Of special interest are the high ¿66Zn values obtained for OIBs and continental alkali basalts, and this signature hints at recycled carbon-bearing oceanic crust (including carbonate sediments) in their mantle sources. Other studies argue however that large ¿66Zn fractionation results from the melting process, based on correlations between the degree of partial melting and ¿66Zn of basaltic to komatiitic lavas. To further explore the utility of zinc in the study of deep volatile cycles, we investigate the ¿66Zn of kimberlites and lamproites from southern Africa. These rocks formed by H2O-CO2 fluxed partial melting of metasomatized peridotite at >180 km depths, and their contrasting Sr-Nd-Hf isotopic compositions indicate distinct sources near the lithosphere-asthenosphere boundary. Both magma types contain notable amounts of carbonates with mantle-like ¿13C values. In keeping with the discrete Sr-Nd-Hf isotope groupings, kimberlites and lamproites have different ¿66Zn compositions, with mean values of 0.33±0.07¿ (n=22) and 0.25±0.06¿ (n=18), respectively. They have low zinc concentrations (64±35 and 51±29 ppm), more similar to MORBs (64±25 ppm) than to OIBs (120±40 ppm). Given that the degree of partial melting is equally low for kimberlites and lamproites (<1%), our study provides evidence for significant zinc isotope heterogeneity in the deep upper mantle. Modelling shows that the kimberlite and lamproite zinc systematics fit with near-solidus melting of asthenospheric and refractory cratonic peridotites, respectively. The alkali-metasomatic components required to explain the petrology of lamproites do not influence the zinc systematics of carbonated mantle melts, probably owed to the compatible nature of zinc in mineralogically exotic metasomes. Although the origins of kimberlites and OIBs are frequently compared because of their apparent link to

A new high-precision Ar-40/Ar-39 anorthoclase feldspar age of 176.7 +/- 0.5 Ma (2-sigma) reveals that small-volume alkaline basaltic magmatism occurred at the rifted SW margin of the Baltic Shield in Scania (southern Sweden), at a time of global plate reorganization associated with the inception of Pangea supercontinent break-up. Our combined elemental and Sr-Nd-Hf-Pb isotope dataset for representative basanite and nephelinite samples (>8 wt.% MgO) from 16 subvolcanic necks of the 30 by 40 km large Jurassic volcanic field suggests magma derivation from a moderately depleted mantle source (Sr-87/(86)Sri = 0.7034-0.7048; epsilon Nd-i = +4.4 to +5.2; epsilon Hf-i = +4.7 to +8.1; Pb-206/(204)Pbi = 18.8-19.5). The mafic alkaline melts segregated from mixed peridotite-pyroxenite mantle with a potential temperature of similar to 1400 degrees C at 2.7-4.2 GPa (similar to 90-120 km depths), which places ultimate melt generation within the convecting upper mantle, provided that the lithosphere-asthenosphere boundary beneath the southern Baltic Shield margin was at <= 100 km depth during Mesozoic-Cenozoic rifting. Isotopic shifts and incompatible element enrichment relative to Depleted Mantle reflect involvement of at least 20% recycled oceanic lithosphere component (i.e., pyroxenite) with some minor continent-derived sediment during partial melting of well-stirred convecting upper mantle peridotite. Although pargasitic amphibole-rich metasomatized lithospheric mantle is excluded as the main source of the Jurassic magmas from Scania, hydrous ultramafic veins (i.e., hornblendite) may have caused subtle modifications to the compositions of passing sublithospheric melts. For example, modeling suggests that the more radiogenic Hf (epsilon Hf-i = +6.3 to +8.1) and Pb (Pb-206/Pb-204(i) = 18.9-19.5) isotopic compositions of the more sodic and H2O-rich nephelinites, compared with relatively homogenous basanites (epsilon Hf-i = +4.7 to +6.1; Pb-206/Pb-204(i) = 18.8-18.9), originate fro

A new high-precision Ar-40/Ar-39 anorthoclase feldspar age of 176.7 +/- 0.5 Ma (2-sigma) reveals that small-volume alkaline basaltic magmatism occurred at the rifted SW margin of the Baltic Shield in Scania (southern Sweden), at a time of global plate reorganization associated with the inception of Pangea supercontinent break-up. Our combined elemental and Sr-Nd-Hf-Pb isotope dataset for representative basanite and nephelinite samples (>8 wt.% MgO) from 16 subvolcanic necks of the 30 by 40 km large Jurassic volcanic field suggests magma derivation from a moderately depleted mantle source (Sr-87/(86)Sri = 0.7034-0.7048; epsilon Nd-i = +4.4 to +5.2; epsilon Hf-i = +4.7 to +8.1; Pb-206/(204)Pbi = 18.8-19.5). The mafic alkaline melts segregated from mixed peridotite-pyroxenite mantle with a potential temperature of similar to 1400 degrees C at 2.7-4.2 GPa (similar to 90-120 km depths), which places ultimate melt generation within the convecting upper mantle, provided that the lithosphere-asthenosphere boundary beneath the southern Baltic Shield margin was at <= 100 km depth during Mesozoic-Cenozoic rifting. Isotopic shifts and incompatible element enrichment relative to Depleted Mantle reflect involvement of at least 20% recycled oceanic lithosphere component (i.e., pyroxenite) with some minor continent-derived sediment during partial melting of well-stirred convecting upper mantle peridotite. Although pargasitic amphibole-rich metasomatized lithospheric mantle is excluded as the main source of the Jurassic magmas from Scania, hydrous ultramafic veins (i.e., hornblendite) may have caused subtle modifications to the compositions of passing sublithospheric melts. For example, modeling suggests that the more radiogenic Hf (epsilon Hf-i = +6.3 to +8.1) and Pb (Pb-206/Pb-204(i) = 18.9-19.5) isotopic compositions of the more sodic and H2O-rich nephelinites, compared with relatively homogenous basanites (epsilon Hf-i = +4.7 to +6.1; Pb-206/Pb-204(i) = 18.8-18.9), originate fro

Proterozoic basins in cratonic India, referred to as "Purana Basins", cover about 20% of the Archean basement of the subcontinent. Although the stratigraphy of most of these basins has been well established, it is only recently that radiometric age constraints have been obtained for some of the sedimentary sequences. This study provides new data for two of the Purana Basins in southern India using SHRIMP U-Pb analysis of detrital zircons. For the Pranhita-Godavari Basin, an age limit of 709. Ma is provided for the age of deposition of the Sullavai Group. This prolongs the duration of Proterozoic sedimentation to approximately one billion years (ca. 1700-709. Ma) and establishes the Venkatpur Sandstones of Sullavai Group as the youngest Purana Basin succession identified in India so far. A major zircon provenance age peak at about 1000. Ma, and zircon ages between 800 and 750. Ma, are correlated with major tectonothermal events in the Eastern Ghats Mobile Belt (EGMB) and intrusion of granites and associated pegmatites at that time. The main provenance area of the Venkatpur Sandstones is interpreted to be the EGMB, with subordinate supply of sediments from the Eastern Dharwar craton. It is suggested that portions of the EGMB must have been an integral part of Peninsular India at the time of deposition of these sediments. For the Cuddapah Basin, new U-Pb detrital zircon age constraints are provided for the Nallamalai Group sediments (Bairenkonda Quartzites within the Nallamalai Fold Belt), the youngest population of which yielded an age of ca. 1550. Ma. This age is similar to the emplacement age of the Vinukonda Granite (1589. ±. 4.4. Ma) in the Nellore Schist Belt. This suggests that the Nellore Schist Belt was a source region for the Bairenkonda Quartzites and that deposition continued until at least 1550. Ma. A high-precision Archean age (ca. 3366. Ma) for a detrital zircon grain indicates the presence of Paleoarchean components within the sediment source region. Pr