Valby van Schijndel | Helmholtz-Zentrum Potsdam (original) (raw)

Papers by Valby van Schijndel

Geological Society, London, Special Publications, Jan 5, 2023

We have found a new source of information about what lies beneath the Kalahari sands. The regions... more We have found a new source of information about what lies beneath the Kalahari sands. The regions known as the Kheis and Rehoboth Provinces were thought to be underlain by either an ~1800 Ma orogenic belt, or a northern branch of the ~1200 Ma Namaqua-Natal Province, now largely covered by Cretaceous to Recent sand. Glacial diamictites of the Permian Dwyka Group exposed at Rietfontein west of the Kalahari carry cobbles plucked from the bedrock by the ice sheet which covered the Gondwana supercontinent about 300 Ma ago. Microbeam U-Pb zircon dating of the granitic cobbles shows that they contain no evidence of crustal growth or orogeny at either 1800 or 1200 Ma. Rather they testify to the presence of 2500 to 2900 Ma Archean crust beneath the Kalahari, with a lesser ~2050 Ma component, coeval with the Bushveld complex of the Kaapvaal Craton to the east. The mafic cobbles are much younger and are related to intrusions of the 1.1 Ga Umkondo Large Igneous Province along the Kalahari Line. Oxygen isotope analyses of zircon from the cobbles and western Kaapvaal Craton granites show a surprising difference, supporting the lithostratigraphic evidence that the granite cobbles do not originate from as far east as the Kaapvaal Craton. All the cobbles are most likely derived from either the Kalahari Line or the Rehoboth Province, whereas origins in the Kheis Province and Kaapvaal Craton are considered unlikely. The possible existence of Archean crust in the Rehoboth Province has important implications not only for the tectonic framework and assembly of Southern Africa, but also for exploration for diamonds and other ore deposits.

Journal of South American Earth Sciences, Jul 1, 2023

Geological Society, London, Special Publications, May 31, 2023

The study of magmatic and metamorphic processes is challenged by geological complexities like geo... more The study of magmatic and metamorphic processes is challenged by geological complexities like geochemical variations, geochronological uncertainties and the presence/absence of fluids and/or melts. However, by integrating petrographic and microstructural studies with geochronology, geochemistry and phase equilibrium diagram investigations of different key mineral phases, it is possible to reconstruct insightful pressure–temperature–deformation–time histories. Using multiple geochronometers in a rock can provide a detailed temporal account of its evolution, as these geological clocks have different closure temperatures. Given the continuous improvement of existing and new in situ analytical techniques, this contribution provides an overview of frequently utilized petrochronometers such as garnet, zircon, titanite, allanite, rutile, monazite/xenotime and apatite, by describing the geological record that each mineral can retain and explaining how to retrieve this information. These key minerals were chosen as they provide reliable age information in a variety of rock types and, when coupled with their trace element (TE) composition, form powerful tools to investigate crustal processes at different scales. This review recommends best applications for each petrochronometer, highlights limitations to be aware of and discusses future perspectives. Finally, this contribution underscores the importance of integrating information retrieved by multi-petrochronometer studies to gain an in-depth understanding of complex thermal and deformation crustal processes.

Geological Society, London, Special Publications, 2011

Geological Society, London, Special Publications, Jul 7, 2023

Detrital heavy minerals have helped address geologically complex issues such as the nature and or... more Detrital heavy minerals have helped address geologically complex issues such as the nature and origin of the early terrestrial crust, the growth and evolution of the continental crust, and the onset of plate tectonics, together with palaeogeographic and supercontinent cycles reconstructions. With the advent of in situ analytical techniques and a more complete understanding of trace element behaviour in rock-forming and accessory minerals, we have now at our disposal a powerful suite of tools that we can apply to multiple proxies found as detrital minerals. These can be in situ dating, trace element or isotopic tracing applied to both mineral hosts and their inclusions. We opted to showcase minerals that occur as primary minerals in a wide range of rock compositions and that can provide reliable age information. Additionally, over recent decades their chemistries have been tested as proxies to understand crustal processes. These are zircon, garnet, apatite, monazite, rutile and titanite. We include an overview and provide some approaches to overcome common biases that specifically affect these minerals. This review brings together petrological, sedimentological and geochemical considerations related to the application of these detrital minerals in crustal evolution studies, highlighting their strengths, limitations and possible future developments.

Lithos, Dec 1, 2021

A multidisciplinary approach to the study of collisional orogenic belts can improve our knowledge... more A multidisciplinary approach to the study of collisional orogenic belts can improve our knowledge of their geodynamic evolution and may suggest new tectonic models, especially for (U)HP rocks inside the accretionary wedge. In the Western Alps, wherein nappes of different origin are stacked, having recorded different metamorphic peaks at different stages of the orogenic evolution. This study focuses on the External (EPZ) and Internal (IPZ) ophiolitic units of the Piedmont Zone (Susa Valley, Western Alps), which were deformed throughout four tectonometamorphic phases (D1 to D4), developing different foliations and cleavages (S1 to S4) at different metamorphic conditions. The IPZ and EPZ are separated by a shear zone (i.e. the Susa Shear Zone) during which a related mylonitic foliation (SM) developed. S1 developed at high pressure conditions (Epidote-eclogite vs. Lawsonite-blueschist facies conditions for IPZ and EPZ, respectively), as suggested by the composition of white mica (i.e. phengite), whereas S2 developed at low pressure conditions (Epidote-greenschist facies conditions in both IPZ and EPZ) and is defined by muscovite. White mica defining the SM mylonitic foliation (T1) is mostly defined by phengite, while the T2-related disjunctive cleavage is defined by fine-grained muscovite. The relative chronology inferred from meso-and micro-structural observations suggests that T1 was nearcoeval respect to the D2, while T2 developed during D4. A new set of radiometric ages of the main metamorphic foliations were obtained by in situ Ar/Ar dating on white mica. Different generations of white mica defining S1 and S2 foliations in both the IPZ and EPZ and SM in the SSZ, were dated and two main groups of ages were obtained. In both IPZ and EPZ, S1 foliation developed at ~46-41 Ma, while S2 foliation developed at ~40-36 Ma and was nearly coeval with the SM mylonitic foliation (~39-36 Ma). Comparison between structural, petrological and geochronological data allows to define time of coupling of the different units and consequently to infer new tectonic implications for the exhumation of meta-ophiolites of the Piedmont Zone within axial sector of the Western Alps.

Journal of African Earth Sciences, Nov 1, 2014

The Hohewarte Metamorphic Complex has been variously correlated with the Abbabis Complex, Kamanja... more The Hohewarte Metamorphic Complex has been variously correlated with the Abbabis Complex, Kamanjab Inlier and the Rehoboth inlier, which is better studied. The Hohewarte Metamorphic Complex is wholly surrounded by the Damara Sequence that experienced peak orogenesis at circa 550 Ma. The Damaran cover has been thrusted over the Hohewarte gneisses, producing subhorizontal fabrics. The Hohewarte Metamorphic Complex was already accreted onto the Kalahari craton during Damaran peak orogenesis. The Hohewarte Metamorphic Complex is composed of a variety of gneisses, ranging from amphibolites, quartz-feldspathic gneiss, plagioclase-rich striped gneisses that enclose two varieties of augen gneiss; a felsic K-feldspar-augen gneiss and an augen gneiss with plagioclase and K-feldspar augens in a matrix of biotite and hornblende rich matrix, occurring mainly to the east of the complex. To the northeast in the Seeis inlier, occurs a medium-grained granitic gneiss with a weak foliation. To the west occurs the ubiquitous banded quartz-feldspar-biotite gneisses, that were intruded by megacrystic granites that are now gneisses. The whole complex has been deformed with two deformations prior to the Damaran orogeny. The fabrics in the gneisses are vertical to subhorizontal, whereas the Damaran cover rocks show a distinct ENE trending fabrics with a consistent dip of 30-45°to the NW. Four samples were selected for single zircon U-Pb dating to establish the age relations; the amphibolite unit within the quartzo-feldspathic gneiss records an age of 1758 ± 10 Ma; the felsic augen gneiss yielded an age of 1290 ± 10 Ma. The megacrystic K-feldspar gneiss yielded an age of 1168 ± 38 Ma, whereas the granitic gneiss gave the youngest age of 1061 ± 10 Ma. eHf model ages show that all the Hohewarte Metamorphic Complex gneisses plot close to the CHUR and posses very primitive crustal signatures and have not been recycled much in the crust. A depleted mantle source is suggested for their origin.

Precambrian Research, Jul 1, 2017

We report the results of combined U-Pb and Lu-Hf isotope analyses of detrital and metamorphic zir... more We report the results of combined U-Pb and Lu-Hf isotope analyses of detrital and metamorphic zircon grains from a variety of metavolcano-sedimentary rocks of the Dwalile Supracrustal Suite (DSS) from the ca. 3.66 to 3.20 Ga Ancient Gneiss Complex (AGC) in Swaziland. The results indicate that the DSS is made up by Palaeo-and Mesoarchaean rocks which have been affected by a polymetamorphic overprint and became tectonically assembled during the Neoarchaean. The oldest Dwalile rocks were formed during a phase of felsic to intermediate volcanism at ca. 3.46 Ga, and are derived from the same magma source as the Tsawela Gneisses. Based on the combined U-Pb-Hf isotope data, two groups of metasedimentary rocks can be distinguished: an older Dwalile Group I that is similar in age to the Hooggenoeg and Kromberg Formations (3.46-3.40 Ga), but with a different source area. A younger Dwalile Group II is coeval with the Fig Tree and possibly Moodies Groups (<3.23 Ga) and the data suggest there was a similar provenance. The U-Pb-Hf isotope data and petrological observations demonstrate that the DSS was affected by three stages of metamorphic overprint: an event at 3.23 Ga, pervasive amphibolite-facies metamorphism at 3.15 Ga, and low-P granulite-facies metamorphism at 2.99 Ga. Metamorphic zircon in the amphibolitefacies rocks resulted from new growth in aqueous fluids at 3.15 Ga, whereas in the granulite-facies rocks new zircon was formed in the presence of melt. The 3.23 Ga event coincides with the last significant metamorphic overprint documented in the Barberton Greenstone Belt (BGB), whereas as two younger events are restricted to the AGC. The data support the model suggesting amalgamation between the AGC and BGB terranes at ca. 3.23 Ga. In addition, they require crustal thickening in the AGC terrane at ca. 3.15 Ga, causing Barrovian-type metamorphism in the DSS and granulite-facies metamorphism in the Luboya-Kubuta Terrane. Low-P granulite-facies metamorphism at ca. 2.99 Ga is most likely related to crustal extension during the onset of Pongola Basin rifting, causing mantle upwelling, mafic magmatism, and heat transfer from the mantle into the thinned crust.

Geological Society, London, Special Publications

The investigation of key minerals including zircon, apatite, titanite, rutile, monazite, xenotime... more The investigation of key minerals including zircon, apatite, titanite, rutile, monazite, xenotime, allanite, baddeleyite and garnet can retain critical information about petrogenetic and geodynamic processes and may be utilized to understand complex geological histories and the dynamic evolution of the continental crust. They act as small but often robust petrochronological capsules and provide information about crustal evolution, from local processes to plate tectonics and supercontinent cycles. They offer us insights into processes of magmatism, sedimentation, metamorphism and alteration, even when the original protolith is not preserved. In situ techniques have enabled a more in-depth understanding of trace element behaviour in these minerals within their textural context. This has led to more meaningful ages for many stages of geological events. New developments of analytical procedures have further allowed us to expand our petrochronological toolbox while improving precision an...

Geological Society, London, Special Publications

Journal of South American Earth Sciences

Analytical procedures Zircon separation and imaging Sample preparation (including crushing, sievi... more Analytical procedures Zircon separation and imaging Sample preparation (including crushing, sieving, magnetic separation with a strong hand magnet) for samples TAC1, TAC2 and BREN1 was done at the Universidad Nacional de Salta in Argentina. This was followed by magnetic separation using a Frantz® magnetic separator (frontal angle 10°, side angle 10°, current 1.2 A) and density separation using Sodium Polytungstate (SPT) and Diiodomethane (DI). The samples were hand-picked under a binocular microscope, mounted in epoxy and polished. The zircons were examined by backscatter electron (BSE) and cathodoluminescence (CL) imaging to determine different age domains and to avoid cracks and metamict zones. The imaging was done using a JEOL JXA-8200 electron microprobe, at the University of Potsdam.

Lithos, 2021

South African Journal of Geology, 2016

The Palaeoproterozoic Hartley Formation in the Olifantshoek Group was deposited in one of the rif... more The Palaeoproterozoic Hartley Formation in the Olifantshoek Group was deposited in one of the rift-related Waterberg (sensu lato) red bed basins which formed on the Kaapvaal Craton after the 2.05 Ga Bushveld intrusions and coeval thermal event. The age of these basins is not well constrained due to the shortage of directly dateable rock types. The Hartley Formation contains rare quartz-porphyry lavas interbedded with the dominant basalts and these provide the means to date the formation by analyses of zircon. In this work zircon from one sample has been dated by six Th-U-Pb methods, namely Laser Ablation ICP Quadrupole Mass Spectrometry, Laser Ablation ICP High-resolution Mass Spectrometry, Laser Ablation ICP Multicollector Mass Spectrometry U-Pb (also Lu-Hf), Nordsim Ion probe U-Pb and Th-Pb; and Krogh method ID-TIMS. Our precise ages give a combined age of 1915.2 ± 1.1 Ma. Including one published ion probe date from the only other known occurrence of quartz porphyry, the results only agree if the quoted analytical errors are increased by 20%, which gives a combined result of 1915.6 ± 1.4 Ma. This is considered a reliable, precise and accurate age for the Hartley Formation and supersedes the published Kober method 207Pb/206Pb age of 1928 ± 4 Ma. The new Lu-Hf zircon data, supported by published whole rock Sm-Nd and Rb-Sr data, suggests that both the dominant basalts and the rare quartz porphyries of the Hartley Formation were derived from mafic source rocks which had been in the crustal domain from Archaean times. By contrast with the intracratonic rifts of the other Waterberg Basins, the Olifantshoek Supergroup reflects the development of a western passive margin as the Archaean Kaapvaal Craton rifted and drifted. This was followed by accretion of the Rehoboth Province along the Kalahari Line, accompanied by the development of the east-vergent Kheis Province thrust complex. This created a larger cratonic block against which the 1.2 Ga collisions of Namaqua-Natal terranes impacted. The Kheis Province now yields ~1.17 Ma cooling ages, reflecting the Namaqua collisions, but the true age of the Kheis event is still enigmatic.

Precambrian Research, 2015

This work investigates a number of gabbro-granite hybrid rocks exposed in the Great Escarpment be... more This work investigates a number of gabbro-granite hybrid rocks exposed in the Great Escarpment between the coastal Namib desert and the inland plateau of Namibia. They form part of the tectonostratigraphic Konkiep Terrane which lies between the Mesoproterozoic Namaqua-Natal Province and largely Palaeoproterozoic Rehoboth Province in southern Africa. Microbeam U-Pb and Lu-Hf analyses of zircon were used to investigate the geochronology of these rocks which have previously been assigned to the Mooirivier Metamorphic Complex or the Kairab Formation. The oldest hybrid rocks at Neuhof Valley are U-Pb dated at 1359 ± 6 Ma and cut by 1347 ± 8 Ma unfoliated granite dykes, but have the youngest Lu-Hf crustal residence ages between 1690 and 1430 Ma. Together with nearby volcanic rocks of the 1333 ± 6 Ma Neuhof and 1327 ± 10 Ma Welverdiend Formations which we dated, they are thought to reflect rifting of the Rehoboth Province followed by the ocean development (by seafloor spreading) phase of the Namaqua Wilson Cycle. The hybrid rocks at Goede Hoop Foothills are U-Pb dated at 1230 ± 6 Ma with a number of xenocrysts up to 1532 Ma. Similar hybrid rocks at Hauchabfontein have 20-30 Ma younger U-Pb ages of 1211 ± 19 Ma and 1202 ± 7 Ma (two samples), they formed by gabbro intruding an 1195 ± 5 Ma granite (within error but older from field relations) and contain many xenocrysts with U-Pb ages 1755 ± 29 Ma (n = 7), 1367 and 1260 ± 17 Ma (n = 24). All the Goede Hoop Foothills and Hauchabfontein hybrid rocks have old Lu-Hf crustal residence ages from 1935 to 2000 Ma and one sample up to 2320 Ma, reflecting involvement of Palaeoproterozoic Rehoboth Province crust. This 1230 to 1200 Ma group of hybrid rocks corresponds in age to the arc magmatism recognised in the Namaqua-Natal Province to the west and south of the Konkiep Terrane. The hybrid rocks probably formed during the closure of the Namaqua Ocean by eastward subduction under the Rehoboth Province, corresponding to the previously proposed Rehoboth Magmatic Arc and forming the Konkiep Terrane by massive intrusions into the margin of the Rehoboth Province. The hybrid rocks we investigated in the Konkiep Terrane are thus related to the rifting phase and the pre-collisional subduction phase of the Namaqua Wilson Cycle. The Arc-related magmatism ended abruptly at 1200 Ma as the Namaqua-Natal terranes were assembled by collisions and subduction ceased. We did not find evidence for the 1200 to 1150 Ma post-collisional metamorphic cycle and magmatism which prevailed in the adjacent Grünau Terrane of the Namaqua Province, suggesting that the Konkiep Terrane did not experience crustal thickening during the Namaqua collision and terrane assembly. An undeformed felsic lava at Sukses which we dated at 1105 ± 10 Ma corresponds in age to the Langberg Formation in the Rehoboth Terrane. It is coeval with the Keimoes Suite of post-tectonic intrusions and younger Koras lavas in the Namaqua-Natal Province and these ∼1100 Ma rocks all extend the area of the plume-related Umkomdo Large Igneous Province documented on the Kaapvaal Craton. This part of the Konkiep Terrane originated in the Rehoboth Province and was then modified by magmatic intrusions coupled to the evolution of the Namaqua Natal Province.

Geological Society, London, Special Publications, Jan 5, 2023

Journal of South American Earth Sciences, Jul 1, 2023

Geological Society, London, Special Publications, May 31, 2023

Geological Society, London, Special Publications, 2011

Geological Society, London, Special Publications, Jul 7, 2023

Lithos, Dec 1, 2021

Journal of African Earth Sciences, Nov 1, 2014

Precambrian Research, Jul 1, 2017

Geological Society, London, Special Publications

Journal of South American Earth Sciences

Lithos, 2021

South African Journal of Geology, 2016

Precambrian Research, 2015