Since the first applications in the geosciences (~ 1985) and the first successful dating of zircons (1993, 1995), LA-ICP-MS has become a standard method for the analysis of major and trace elements as well as numerous isotope systems (e.g., Li, B, Sr, Sm-Nd, Lu-Hf, U-Th-Pb) in minerals, glasses and other solids.

Speed, relatively low cost, versatility, high spatial resolution (10-50 µm) and sufficient to better precision often make LA-ICPMS superior to competing methods. The most successful application, U-Th-Pb zircon geochronology has led to an exponential increase in scientific publications in this field between 2000 and 2020.

This article aims to give an overview of the developments of the last 10 years in the field of U-Pb dating of carbonates, garnets, sulphates, as well as various oxide and other silicate minerals. The complexity of the analysis, problems, the possible potential of these methods and the precision, accuracy and significance of the dates/ages compared to those of zircons are discussed.

What are the methodological challenges of the near future? Will methodological developments in LA-ICP-MS analysis be driven by technical advancements in analytical equipment or active science teams?

In-situ Rb-Sr dating using laser ablation (LA) systems coupled to inductively coupled plasma (ICP) – reaction cell mass spectrometers (MS/MS) is an emerging geochronological tool. This analytical setup uses reaction gases to allow the reaction of targeted masses. ⁸⁷Rb and ⁸⁷Sr can for example be separated chemically to avoid the isobaric overlap during mass-spectrometric analysis. In-situ Rb-Sr LA-ICP-MS/MS dating has until now successfully been applied to date magmatic, metamorphic and tectonic events as well as ore formation processes. In addition, it has huge potential for sedimentology and stratigraphy.

Here, we present case studies of in-situ Rb-Sr LA-ICP-MS/MS dating of detrital minerals (mica and feldspar) and glauconite. We focus on (1) the analytical routine, (2) data reduction and age calculation strategy and (3) interpretation of in-situ Rb-Sr age data. In addition, we demonstrate advantages of volume-coupled major and trace element data collected from the same laser spots. This data can for example be used as indicator of alteration and as multi-proxy tool for provenance studies.

The number of zircon age studies being published from all regions of the planet is consistently growing, as is for continental or global zircon ages databases. Unfortunately, a considerable amount of such data is often not utilized for future studies after their publication. Consequently, there is a considerable amount of valuable data that is waiting to be discovered for further use that could reach much further than reconstructing supercontinent cycles. An initial compilation of pre-Mesozoic zircon age data (N>5000, n>275000) characterizes the circum-Atlantic (s.l.) zircon provinces. Despite having compiled an initial zircon age database, further effort is necessary to reach the required sample density for mapping the age spectra of (meta)igneous host rocks and primary sediment flux in appropriate statistical, spatial and temporal frameworks. Nonetheless, this is a primary goal that will allow for more precise palaeogeographic reconstructions of terrane configurations in conjunction with additional data. To date, the zircon age database permits the identification of the primary zircon provinces and some sub-provinces at a reasonable terrane-scale resolution. The database also identifies distinct zircon age populations that can be used as "unique identifiers", e.g. to distinguish the western and the eastern parts of Cadomia or the role of the Kunene Intrusive Complex in southern Africa. Additionally, the presented compilation outlines the key zircon age provinces in large parts of the circum-Atlantic. Therefore, this study aims to present an initial impression of typical zircon age patterns found in the aforementioned areas at certain periods of time.

The erosional debris of the poorly exposed Paleo- and Mesoproterozoic mobile belts of Amazonia (Terra Amazonica Orogen, 2-1 Ga, TAO-1) eventually accumulated in the orogenic basins of the central proto-Andean Terra Australis Orogen (TAO-2, 0.65-0.2 Ga), offering an abundant indirect source of information.

From newly constructed U-Pb, Hf and O isotope zircon data bases we derived that in TAO-1 eHf(t) values define 3 cycles between 2-1 Ga from strongly unradiogenic to radiogenic values. After the dispersal of Rodinia, TAO-2 registers one large similar cycle. In accretionary orogens, such trends indicate the progressive removal of lower crust and lithospheric mantle of the upper plate during subduction and their replacement by new radiogenic crust.

d¹⁸O data show a flat d¹⁸O trend at 6.3‰ over the first 800 Myr of TAO-1, increasing to elevated values around 7.3‰ during collision with Laurentia. Contrastingly, d¹⁸O of TAO-2 trends from 8‰ to more mantle-like values just below 7‰. The different trends show that anatectic intracrustal recycling played only a subordinate role in the generation of new crust during TAO-1. However, there is a correspondence between the O and Hf isotope trends in TAO-2 towards more juvenile compositions through time.

Global d¹⁸O data showed gradually increasing d¹⁸O after 2.5 Ga indicating the progressive hydration and intracrustal recycling of the continental crust after the Archean. Our data register the sudden appearance of d¹⁸O values up to 10‰ at the Archean-Proterozoic transition indicating that Amazonia had experienced intracrustal recycling at an accretionary margin already in the Late Archean.

The Rosenhof Member is part of the Lower Cambrian Fish River Subgroup of the Nama Group in southern Namibia (Groß Aub Formation). The sediments of the Nama Group are deposited in two basins, the northern Zaris Subbasin and the southern Witpütz Subbasin. Both are separated by the Osis Arch, a basement updoming (Germs, 1974; Grotzinger and Miller, 2008). While the basal two Nama subgroups are influenced by these two basins and their paleorelief, the uppermost Fish River Subgroup sediments overstep the Osis Arch and cover previous deposits with an unconformity. Deposits of the Fish River Subgroup are represented by Lower Cambrian shales and sandstones (e.g. Grotzinger and Miller, 2008).

The sandstones of the Rosenhof Member show distinct sedimentary patterns that allow the interpretation as fluvial deposits originating from the north (e.g. Geyer, 2005). They were deposited after the final collision of the Kalahari Craton (south) and the Congo Craton (north) that created the Damara Orogen. The latter is discussed as a major sedimentary source area for the studied deposits covering southern Namibia (Kalahari Craton). For this purpose, the Rosenhof Member was sampled and studied at various locations, covering occurrences from its northern outcrops until its most southern ones. This sample set allows the study of changes in the sedimentary pattern of a particular member over an area of about 300 km.

This talk presents sedimentary structures combined with heavy mineral analyses (U-Pb on zircon and apatite) and discusses possible sedimentary source areas, as well as sedimentary mixing and homogenisation.