BACK TO THE SOURCE A combined trace elemental and multi-isotopic approach to provenance pre-colonial Caribbean jade artefacts: Implications for mobility and exchange networks

The determination of trace element (TE) abundances and multi-isotopic compositions (IC) of artefacts is a powerful tool that provides valuable information about their origin, manufacturing technology and authenticity. Such studies allow to conclude about the circulation of goods, past human interaction and ancient mobility networks. This dissertation aims to untangle the circulation of objects made of jade in the pre-colonial Caribbean through a multi-disciplinary approach employing development of a novel minimally-invasive sampling technique to generate geochemical and archaeological data sets and their interpretation with statistical modelling. To geochemically fingerprint objects stored in private and public institutions, very sensitive, ideally portable and non-invasive analytical techniques are demanded. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) allows determination of major, minor and TE abundances in a quasi-non-destructive manner with limits of qualification/quantification (LOD and LOQ) in the lower ppb to sub-ppb range. Since LA-ICPMS is a laboratory-based bench set-up, it is neither accessible for cultural heritage objects which are immobile, nor to objects which exceed the dimensions of the closed ablation cell. To circumvent these limitations and to enable the analyses of isotope ratios, an analytical procedure involving an offline laser ablation sampling strategy was developed. This dissertation reports on the further optimization, validation and application of the 532 nm portable LA sampling technique with subsequent low-blank geochemical analyses. The method allows minimally-invasive in situ sampling of cultural heritage objects made of various materials, regardless of their mobility, geometry or size, leaving cone to cylinder shaped ablation pits with the diameter of hair, invisible to the naked eye, and hence maintaining the integrity of the archaeological/art object. Low-blank geochemical clean lab procedures, TE and strontium (Sr) and neodymium (Nd) analyses using quadrupole ICPMS and thermal ionisation mass spectrometry (TIMS) produced accurate, precise and reproducible data. The method was validated by taking ten ablations (25 to 40 µg) per sample of a USGS reference basalt glass and twenty ablations (50 to 80 µg) per sample of a natural jade slab. The outcome demonstrated that Sr and Nd isotope variability can be resolved in natural samples within the fourth decimal, which is sufficient to determine the provenance or authenticity. The laser system was applied to collect material from 88 pre-colonial jade artefacts unearthed from Early to Late Ceramic Age (400 BC to AD 1500) sites on Cuba (CU), the Dominican Republic (DR), St. John, St. Thomas, St. Croix, St. Vincent and Grenada. Samples (< 40 µg) were prepared for low-blank ICPMS and TIMS analyses. Furthermore, destructive (cut-offs of < 5g) geochemical analyses of 19 artefacts retrieved from the Late Ceramic Age (AD 750 to AD 1600) Playa Grande site in the northern DR, was conducted. An extensive geochemical jade source rock database (n=101) was created from the only know sources in the Caribbean, Guatemala (GM), CU and the DR. TE abundances and Sr, lead (Pb), and Nd IC were determined by conventional geochemical clean lab procedures on sample aliquots (approximately 80 mg of whole rock powder) with subsequent analyses by quadrupole ICPMS, TIMS, and MC-ICPMS. The geochemical fingerprints of the laser ablated artefacts were interpreted in reference to the jade source rock database using logistic multi-class regression models. The predicted artefact provenances in GM, CU and the DR, led to the conclusion that Caribbean pre-colonial Indigenous societies were linked with each other in a more complex manner than previously assumed. Vast trade and mobility networks spanning over > 4000 km, connecting Caribbean islands with the Mesos- and South American mainland, including linchpin settlements with highly specialised workshops serving as important distribution centres, stimulated and boosted the exchange and mobility of goods, humans and ideas.