The timing and mechanisms of continental crust formation represent major outstanding questions in the Earth sciences. Extinct-nuclide radioactive systems offer the potential to evaluate the temporal relations of a variety of differentiation processes on the early Earth, including crust formation. Here, we, investigate the whole-rock W-182/W-184 and Na-142/(144) Nd ratios and zircon Delta O-17 values of a suite of well-studied and lithologically-homogeneous meta-igneous rocks from the Acasta Gneiss Complex, Northwest Territories, Canada, including the oldest-known zircon-bearing rocks on Earth. In the context of previously published geochemical data and petrogenetic models, the new Nd-142/Nd-144 data indicate that formation of the Hadean-Eoarchean Acasta crust was ultimately derived from variable sources, both in age and composition. Although 4.02 Ga crust was extracted from a nearly bulk-Earth source, heterogeneous it Nd-142 signatures indicate that Eoarchean rocks of the Acasta Gneiss Complex were formed by partial melting of hydrated, Hadean-age mafic crust at depths shallower than the garnet stability field. By similar to 3.6 Ga, granodioritic-granitic rocks were formed by partial melting of Archean hydrated mafic crust that was melted at greater depth, well into the garnet stability field. Our W-182 results indicate that the sources to the Acasta Gneiss Complex had homogeneous, high-mu W-182 on the order of +10 ppm- a signature ubiquitous in other Eoarchean terranes. No significant deviation from the terrestrial mass fractionation line was found in the triple oxygen isotope (O-16-O-17-O-18) compositions of Acasta zircons, confirming homogeneous oxygen isotope compositions in Earth's mantle by 4.02 Ga. Crown Copyright (C) 2018 Published by Elsevier B.V. All rights reserved.

The advancement of science depends upon developing classification protocols that systematize natural objects and phenomena into "natural kinds"-categorizations that are conjectured to represent genuine divisions in nature by virtue of playing central roles in the articulation of successful scientific theories. In the physical sciences, theoretically powerful classification systems, such as the periodic table, are typically time independent. Similarly, the standard classification of mineral species by the International Mineralogical Association's Commission on New Minerals, Nomenclature, and Classification relies on idealized chemical composition and crystal structure, which are time-independent attributes selected on the basis of theoretical considerations from chemical theory and solid-state physics. However, when considering mineral kinds in the historical context of planetary evolution, a different, time-dependent classification scheme is warranted. We propose an "evolutionary" system of mineral classification based on recognition of the role played by minerals in the origin and development of planetary systems. Lacking a comprehensive theory of chemical evolution capable of explaining the time-dependent pattern of chemical complexification exhibited by our universe, we recommend a bootstrapping approach to mineral classification based on observations of geological field studies, astronomical observations, laboratory experiments, and analyses of natural samples and their environments. This approach holds the potential to elucidate underlying universal principles of cosmic chemical complexification.

The Tamarack Intrusive Complex (1105 +/- 1.2 Ma), in northeastern Minnesota, occurs within the Midcontinent rift system and hosts potentially economic Ni-Cu-(PGE) mineralization. The system represents "conduit-style" mineralization and with 1.3 wt % Ni, 0.7 wt % Cu, 0.3 ppm Pt, and 0.25 ppm Pd, is similar in many aspects to the Eagle deposit in Michigan. Sulfur, O, and Os isotopes have been used to evaluate the role of crustal contamination in promoting sulfide liquid saturation. All of the types of mineralization in the Tamarack Intrusive Complex are characterized by delta S-34 values between -0.2 and 2.8 parts per thousand, values that are not strongly anomalous relative to uncontaminated mantle values near 0 parts per thousand. The values are very similar to those from the Eagle deposit, but contrast sharply with values of disseminated sulfides in intrusions of the Duluth Complex and Crystal Lake Gabbro, which may be as elevated as 17 parts per thousand. Initial Os-187/Os-188 ratios in the Tamarack intrusive Complex are between 4 and 44% higher than the same ratio of the undepleted primitive mantle at 1105 Ma and correspond to gamma Os values for all magmatic sulfide types from the Tamarack Intrusive Complex ranging from 10 to 92. These values are consistent with crustal contamination but for S, the isotopic ratios are remarkably lower than those from mineralization in the Duluth Complex, where initial Os-187/Os-188 ratios are more than 110% higher than that of primitive mantle and gamma os values may be in excess of 1,000. Olivine from an unmineralized but sparsely serpentinized portion of the Tamarack Intrusive Complex has O isotope compositions from 5.2 to 5.5 parts per thousand, indicating a fraction of a percent crustal contamination of the parental magma.

Information-rich attributes of minerals reveal their physical, chemical, and biological modes of origin in the context of planetary evolution, and thus they provide the basis for an evolutionary system of mineralogy. Part III of this system considers the formation of 43 different primary crystalline and amorphous phases in chondrules, which are diverse igneous droplets that formed in environments with high dust/gas ratios during an interval of planetesimal accretion and differentiation between 4566 and 4561 Ma. Chondrule mineralogy is complex, with several generations of initial droplet formation via various proposed heating mechanisms, followed in many instances by multiple episodes of reheating and partial melting. Primary chondrule mineralogy thus reflects a dynamic stage of mineral evolution, when the diversity and distribution of natural condensed solids expanded significantly.

Geological pathways for the recycling of Earth's surface materials into the mantle are both driven and obscured by plate tectonics(1-3). Gauging the extent of this recycling is difficult because subducted crustal components are often released at relatively shallow depths, below arc volcanoes(4-7). The conspicuous existence of blue boronbearing diamonds (type IIb)(8,9) reveals that boron, an element abundant in the continental and oceanic crust, is present in certain diamond-forming fluids at mantle depths. However, both the provenance of the boron and the geological setting of diamond crystallization were unknown. Here we show that boron-bearing diamonds carry previously unrecognized mineral assemblages whose high-pressure precursors were stable in metamorphosed oceanic lithospheric slabs at depths reaching the lower mantle. We propose that some of the boron in seawater-serpentinized oceanic lithosphere is subducted into the deep mantle, where it is released with hydrous fluids that enable diamond growth(10). Type IIb diamonds are thus among the deepest diamonds ever found and indicate a viable pathway for the deep-mantle recycling of crustal elements.

Minerals preserve records of the physical, chemical, and biological histories of their origins and subsequent alteration, and thus provide a vivid narrative of the evolution of Earth and other worlds through billions of years of cosmic history. Mineral properties, including trace and minor elements, ratios of isotopes, solid and fluid inclusions, external morphologies, and other idiosyncratic attributes, represent information that points to specific modes of formation and subsequent environmental histories-information essential to understanding the co-evolving geosphere and biosphere. This perspective suggests an opportunity to amplify the existing system of mineral classification, by which minerals are defined solely on idealized end-member chemical compositions and crystal structures. Here we present the first in a series of contributions to explore a complementary evolutionary system of mineralogy-a classification scheme that links mineral species to their paragenetic modes.

Ancient rock samples are limited, hindering the investigation of the processes operative on the Earth early in its history. Here we present a detailed study of well-exposed crustal remnants in the central Slave craton that formed over a 1 billion year magmatic history. The tonalitic-granodioritic gneisses analysed here are broadly comparable to common suites of rocks found in Archean cratons globally. Zircon Hf isotope data allow us to identify a major change positive epsilon Hf starting at similar to 3.55 Ga. The crust production processes and spatial distribution of isotopic compositions imply variable interaction with older crust, similar to the relationships seen in modern tectonic settings; specifically, long-lived plate margins. A majority of the Slave craton might have been formed by a similar mechanism.

Neoproterozoic West African diamonds contain sulfide inclusions with mass-independently fractionated (MIF) sulfur isotopes that trace Archean surficial signatures into the mantle. Two episodes of subduction are recorded in these West African sulfide inclusions: thickening of the continental lithosphere through horizontal processes around 3 billion years ago and reworking and diamond growth around 650 million years ago. We find that the sulfur isotope record in worldwide diamond inclusions is consistent with changes in tectonic processes that formed the continental lithosphere in the Archean. Slave craton diamonds that formed 3.5 billion years ago do not contain any MIF sulfur. Younger diamonds from the Kaapvaal, Zimbabwe, and West African cratons do contain MIF sulfur, which suggests craton construction by advective thickening of mantle lithosphere through conventional subduction-style horizontal tectonics.