Aluminosilicates (kyanite, sillimanite and andalusite) are useful pressure-temperature (P-T)indicators that can form in a range of rock types through different mineral reactions, including thosethat involve partial melting. Their involvement in melting reactions means that the presence ofaluminosilicates in migmatite mineral assemblages can help to (broadly) constrain the P-T conditionsof melt formation, which then has implications for evaluating models of orogenic tectonics.Xenocrystic grains could lead to spurious tectonic interpretations, so being able to distinguishbetween different petrogenetic sources is important. Petrological and geochemical investigation ofmigmatite-hosted kyanite from Eastern Bhutan shows that kyanite petrogenesis may be constrainedby combining information from morphology, cathodoluminescence response, microtextural positionand geochemical zoning patterns. Mg, Ti, Ca, Fe, Cr and Ge concentrations provide diagnostic cluesthat distinguish sub-solidus kyanite from kyanite that crystallised directly from melt, or grewperitectically during muscovite dehydration reactions. The abundance of these elements in kyanite isalso strongly controlled by protolith composition, with considerable inter-sample variation observedin this sample set. LA-ICP-MS maps, especially of Cr/V, provide additional information aboutchanging geochemical environments during kyanite growth. These data and observations show thatmost kyanite is of xenocrystic origin in the analysed samples, and therefore that its presence does notnecessarily constrain the P-T conditions of the melt reaction(s). This finding has significantimplications for the interpretation of kyanite-bearing migmatites as representing early stages ofmelting during Himalayan evolution.

Mapping the age and trace element and Sm-Nd isotope compositions of monazite grains from a peraluminous Cretaceous granite using laser ablation-split stream analysis reveals a wide range in Nd isotope and rare earth element (REE) compositions within and between single grains. These data corroborate isotopic variability indicated by Hf isotope analysis of zircon in the same granite sample. The REE variations indicate that monazite grew during fractional crystallization. Hf and Nd isotopes indicate that the granitic magma was generated from at least two distinct Proterozoic sources of approximately the same age: one component that had highly radiogenic initial Hf-176/Hf-177 and Nd-143/Nd-144 and a second component that was notably less radiogenic. This study highlights the utility of in situ REE and Sm-Nd isotope data in monazite in magmatic systems. Further, it refines the zircon-based constraints on magmatic processes because of sensitivity of light REEs to fractional crystallization, lower probability of complications owing to inheritance, and smaller analytical volumes required.

The Old Woman-Piute Range Batholith (OWPB) in the Mojave Desert of south-eastern California is a suite of metaluminous and peraluminous Cretaceous granites that intrudes Proterozoic basement. The peraluminous Sweetwater Wash, Painted Rock and North Piute plutons were sampled to investigate geochemical heterogeneity. Zircon and monazite crystals were analysed for U–Pb & Lu–Hf and U–Pb & Sm–Nd isotopes, respectively, using the high-spatial resolution and the recently developed Laser Ablation Split Stream (LASS) approach. Inherited cores are widespread in zircon, limited in monazite, and yield U-Pb ages that range from 1800-1400 Ma, consistent with regional Proterozoic crustal building events. Zircon and monazite rims give a range of crystallisation ages between 70–75 Ma. The OWPB shows a large range in eHfi and eNdi in both inherited and magmatic populations, a characteristic that is derived primarily from the Proterozoic crustal source, but also influenced by the partial dissolution and preservation of inherited grains.

The Old Woman-Piute Range Batholith (OWPB) in the Mojave Desert of south-eastern California is a suite of metaluminous and peraluminous Cretaceous granites that intrudes a long-lived and complex Proterozoic basement. The OWPB consists of a number of discrete plutons that due to post-emplacement regional tilting expose deeper structural levels of the batholith to the south. The peraluminous Sweetwater Wash, Painted Rock and North Piute plutons were chosen for this study to investigate geochemical heterogeneity at the sample-, pluton- and batholith-scale. Samples taken show a magmatic differentiation sequence of two-mica granite to garnet-bearing granite to aplite. Zircon and monazite crystals were analysed for U–Pb & Hf and U–Pb & Sm–Nd isotopes respectively, by in situ LA-ICP-MS and LA-MC-ICPMS using the recently developed Laser Ablation Split Stream (LASS) approach. This high spatial-resolution approach allows a detailed assessment of geochemical changes in the magmatic system at a fine spatial and temporal scale. Additional zircon U–Pb data were collected by Q-LA-ICP-MS. The U–Pb data show widespread inheritance in zircon cores, yielding ages varying between ~1400 and ~1800 Ma, consistent with regional Proterozoic crustal building events. Only four monazite grains yield inherited cores ~1700 Ma, all of which are found in the Sweetwater Wash two-mica granites. Zircon and monazite rims give crystallisation ages between 70–75 Ma, with monazite rims typically slightly younger than the zircon rims from the same samples, and ages between samples and between plutons are within uncertainty of each other. The zircon and monazite crystals also preserve the Hf and Nd isotopic ratios of their crustal sources. Correct age determinations are crucial for this interpretation for monazite grains, illustrating the utility of the LASS technique in integrating two isotopic systems from the same ablation volume. The OWPB shows a large range in eHfi (young = -8.2– -19.2, old = -0.9– 8.4) and eNdi (young = -12.6 – -21.8, old = -0.8– -4.1) with the North Piute pluton being the most isotopically homogeneous. Isotopic data is consistent with derivation of the OWPB Batholith from the ancient crust into which it intrudes, which is spatially coincident with the inferred edge of Precambrian North America.