Although Earth has a convecting mantle, ancient mantle reservoirs that formed within the first 100 Ma of Earth’s history (Hadean Eon) appear to have been preserved through geologic time. Evidence for this is based on small anomalies of isotopes such as182W,142Nd, and129Xe that are decay products of short-lived nuclide systems. Studies of such short-lived isotopes have typically focused on geological units with a limited age range and therefore only provide snapshots of regional mantle heterogeneities. Here we present a dataset for short-lived182Hf−182W (half-life 9 Ma) in a comprehensive rock suite from the Pilbara Craton, Western Australia. The samples analyzed preserve a unique geological archive covering 800 Ma of Archean history. Pristine182W signatures that directly reflect the W isotopic composition of parental sources are only preserved in unaltered mafic samples with near canonical W/Th (0.07 to 0.26). Early Paleoarchean, mafic igneous rocks from the East Pilbara Terrane display a uniform pristine µ182W excess of 12.6 ± 1.4 ppm. Fromca. 3.3Ga onward, the pristine182W signatures progressively vanish and are only preserved in younger rocks of the craton that tap stabilized ancient lithosphere. Given that the anomalous182W signature must have formed byca. 4.5 Ga, the mantle domain that was tapped by magmatism in the Pilbara Craton must have been convectively isolated for nearly 1.2 Ga. This finding puts lower bounds on timescale estimates for localized convective homogenization in early Earth’s interior and on the widespread emergence of plate tectonics that are both important input parameters in many physical models.

Significance Due to active plate tectonics, there are no direct rock archives covering the first ca. 500 million y of Earth’s history. Therefore, insights into Hadean geodynamics rely on indirect observations from geochemistry. We present a high-precision 182 W dataset for rocks from the Kaapvaal Craton, southern Africa, revealing the presence of Hadean protocrustal remnants in Earth’s mantle. This has broad implications for geochemists, geophysicists, and modelers, as it bridges contrasting 182 W isotope patterns in Archean and modern mantle-derived rocks. The data reveal the origin of seismically and isotopically anomalous domains in the deep mantle and also provide firm evidence for the operation of silicate differentiation processes during the first 60 million y of Earth’s history.

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Knowledge of pressure-temperature-time (P-T-t) evolution of Archean high-grade (deep crustal) metamorphic rocks is important for deciphering the nature of Archean tectonic processes. However, exposures of such rocks are limited in the present rock record. Here, we study a suite of high-grade, mafic rocks that are present along a crustal-scale shear zone (called the Mercara Shear Zone) between two Archean terrains of India, the Coorg block and the Dharwar Craton. Given that the Mercara Shear Zone is dated to be Mesoarchean, these shear zone rocks are well suited to elucidate Archean orogenic processes. Petrological investigation shows that these mafic rocks are characterized by a granulitic assemblage of orthopyroxene, clinopyroxene, plagioclase, quartz, amphibole ± garnet, and with accessory phases such as apatite, ilmenite, magnetite and rutile in some cases. We distinguish the investigated rocks into low-Mg and high-Mg varieties based on their whole rock composition as well as their mode of occurrence in the field and mineral chemistry. This difference in the bulk composition led to different reaction histories – for example, the low-Mg mafic granulites underwent partial melting while high-Mg granulites were less fertile. Combining these observations with the results of geothermobarometry, phase equilibria modelling, geochronology (U-Pb in zircon and Lu-Hf garnet geochronology) and diffusion modeling, we have reconstructed a multi-stage P-T-t history for these rocks. The first phase (Stage 1) is represented by granulite-grade metamorphism at ~750 – 900 °C and 8 – 13 kbar during ~3100 Ma (with uncertainties permitting a timing as recent as ~2700 Ma), after which they resided at T < 500 °C, likely at lower crustal levels (Stage 2). Subsequently, these rocks were reheated to a T of 700 – 750 °C at 7 – 10 kbar at ~2400 Ma (Stage 3) and then again cooled down to ~500 – 600 °C at 6 – 8 kbar (Stage 4). Application of diffusion chronometry shows that: (1) the cooling rates of these granulites at high temperatures (> 600 °C) varied in the range of 25 – 50 °C/Ma, and (2) the rocks resided for a long duration (~500 million years) at the Stage 2 metamorphic conditions i.e., at T < 500 °C. We infer that such a protracted, high-T metamorphic history involving at least two heating pulses, and the relatively slow cooling rates on the order of 10’s °C/Ma are consistent with the operation of peel-back styled orogenesis (an embryonic form of plate tectonics) on an early hotter Earth (Mesoarchean to Palaeoproterozoic). Moreover, the controls of bulk rock compositions on reaction histories provide a mechanism for intracrustal differentiation and generating Mg-rich, refractory material that may have eventually formed the lower continental crust over a protracted and pulsed thermal evolution spanning several hundred million years.