SDLRC: Dr. Paddy Lawless highlights the 2019 Technical Reference Best Reads
Dr. Paddy Lawless Highlights Favorites from the 2019 Technical References
Patricia Sheahan asked Dr. Paddy Lawless in early 2020 if he would review the 2019 Sheahan Diamond Literature Technical Reference Compilation and highlight those he found most interesting and worthwhile. Dr. Lawless was Divisional Geologist for De Beers/Anglo American in 1974-2004 during which he was also Resident Geologist for the Finsch Diamond Mine. He resides in South Africa where he runs a consultancy called Dr Paddy Lawless & Associates. He developed a selection strategy and reduced the 936 technical references to a short list presented below along with his selection criteria. Many thanks to Dr. Lawless for this monumental effort!
Criteria used to Select References classified as Most Valuable References for 2019 from Pat Sheahan's admirable lists.
Obviously all the references could not be obtained, nor consulted, nor read.
Methodology used had to be Subjective;
Method was initially "negatively-based"': - i.e. Rather than look for the stand-outs, identified those likely not to be selected for reading.
~ Took the list of 936 references submitted and eliminated references perceived not to be of general or global interest;
~ Eliminated those which were locality-specific, i.e. of geographically local interest;
~ eliminated those which were likely to be very-discipline-specific; e.g. vacancies in atomic lattices;
~ Eliminated those which were Conference/Symposia/Meetings Abstracts of 1 to 2 pages length;
~ Eliminated Theses as unlikely to be read unless requiring specifics on the subject - often papers by the student, the supervisor(s) and others are published from thesis findings.
First pass reduced list to 624 references;
Second pass reduced list to 323 references which were colour-coded by category i.e., e.g. Diamonds, Lithosphere, Kimberlites, Mantle etc.
Reviewing these lists clearly indicated the subjectivity of the selector.
These categories were then further colour coded by "value", in descending order.
A further two passes or rounds of eliminations were made within categories.
The second of these passes was ruthless, using the criteria:
~ of most relevance to all involved in kimberlite and diamond research;
~ likely to be correct based on the selector's knowledge of the authors and their previous papers.
The final list of 9 references contains seven (7) on diamond genesis and two (2) on kimberlites.
A further two were selected as 'reserves', one on continental mantle and one on silicate inclusions in sub-lithospheric diamonds.
Three references on 50 years of plate tectonics, Pangea and the Upper Mantle by one of the Pioneers, Xavier le Pichon et al. are deemed to be very worthy of inclusion but are not specific to diamond and kimberlites per se.
Three further Abstract References all on diamonds were also selected as worthwhile reading, but might not have sufficient details.
Some of these latter references are perceived to be the same material reworked for different journals.
If only one has to be selected then it has to be the Shirey, Smit and 27 others on "Diamonds and the Mantle Geodynamics of Carbon; Deep Mantle Carbon and Evolution from the Diamond Record".
Dr. Paddy Lawless' Favorites from the Technical References in the 2019 Sheahan Diamond Literature Compilation
Abstract: Carbon is one of the most important elements on our planet, which led the Geological Society of London to name 2019 the Year of Carbon. Diamonds are a main host for carbon in the deep earth and also have a deeper origin than all other gemstones. Whereas ruby, sapphire, and emerald form in the earth's crust, diamonds form many hundreds of kilometers deep in the earth's mantle. Colored gemstones tell scientists about the crust; gem diamonds tell scientists about the mantle. This makes diamonds unique among gemstones: Not only do they have great beauty, but they can also help scientists understand carbon processes deep in the earth. Indeed, diamonds are some of the only direct samples we have of the earth's mantle. But how do diamonds grow in the mantle? While Hollywood's depiction of Superman squeezing coal captured the public's imagination, in reality this does not work. Coal is a crustal compound and is not found at mantle pressures. Also, we now know that diamond does not prefer to form through direct conversion of solid carbon, even though the pressure and temperature conditions under which diamond forms have traditionally been studied experimentally as the reaction of graphite to diamond. Generally, two conditions are needed for diamond formation:?Carbon must be present in a mantle fluid or melt in sufficient quantity, and the melt or fluid must become reduced enough so that oxygen does not combine with carbon (see below). But do diamonds all grow by the same mechanism? What does their origin reveal about their growth medium and their mantle host rock? Surprisingly, diamonds do not all form in the same way, but rather they form in various environments and through varying mechanisms. Through decades of study, we now understand that diamonds such as the rare blue Hope, the large colorless Cullinan, and the more common yellow "cape" diamonds all have very different origins within the deep earth.
Abstract: The age of something is fundamental. Humans, animals, wine, cars, and antiques are viewed and understood in the context of their age. So it is with rocks and minerals. A geologist needs to know the age of rocks to construct the geologic history of an area. In the field, relative ages can be determined by cross-cutting relationships (the younger rock "cuts" across the older rock) or superposition (the younger rock overlies the older rock). To determine the absolute ages of rocks and minerals such as diamond, scientists measure naturally occurring radioactively decaying elements. Absolute ages are free of any knowledge of relative age relations to any other geological material. This is known as the science of geochronology...(no abstract, full article)
Abstract: "Super-deep" diamonds are thought to have a sub-lithospheric origin (i.e., below ~300 km depth) because some of the mineral phases entrapped within them as inclusions are considered to be the products of retrograde transformation from lower-mantle or transition-zone precursors. CaSiO3-walstromite, the most abundant Ca-bearing mineral inclusion found in super-deep diamonds, is believed to derive from CaSiO3-perovskite, which is stable only below ~600 km depth, although its real depth of origin is controversial. The remnant pressure (Pinc) retained by an inclusion, combined with the thermoelastic parameters of the mineral inclusion and the diamond host, allows calculation of the entrapment pressure of the diamond-inclusion pair. Raman spectroscopy, together with X-ray diffraction, is the most commonly used method for measuring the Pinc without damaging the diamond host. In the present study we provide, for the first time, a calibration curve to determine the Pinc of a CaSiO3-walstromite inclusion by means of Raman spectroscopy without breaking the diamond. To do so, we performed high-pressure micro-Raman investigations on a CaSiO3-walstromite crystal under hydrostatic stress conditions within a diamond-anvil cell. We additionally calculated the Raman spectrum of CaSiO3-walstromite by ab initio methods both under hydrostatic and non-hydrostatic stress conditions to avoid misinterpretation of the results caused by the possible presence of deviatoric stresses causing anomalous shift of CaSiO3-walstromite Raman peaks. Last, we applied single-inclusion elastic barometry to estimate the minimum entrapment pressure of a CaSiO3-walstromite inclusion trapped in a natural diamond, which is ~9 GPa (~260 km) at 1800 K. These results suggest that the diamond investigated is certainly sub-lithospheric and endorse the hypothesis that the presence of CaSiO3-walstromite is a strong indication of super-deep origin.
Abstract: Kimberlites are the main source of natural gem-quality diamonds. The intrepid diamond explorer faces three major problems. First, finding a small, usually less than 300 m diameter, kimberlite, which is often highly weathered. Second, evaluating the quantity of diamonds within a kimberlite that often consists of multiple phases of intrusive and extrusive kimberlite, each with potentially different diamond grades. Third, evaluating the rough diamonds, the value of which is dependent on carat-weight, shape, colour, and clarity. Modern advances in mantle petrology, geophysics, geochemistry, geomorphology, and geostatistics now complement historical exploration knowledge and aid in selecting prospective target areas, resource estimation, and evaluating kimberlite-hosted diamond deposits.
Abstract: Hypabyssal kimberlites are subvolcanic intrusive rocks crystallised from mantle-derived magmas poor in SiO2 and rich in CO2 and H2O. They are complex, hybrid rocks containing significant amounts of mantle-derived fragments, primarily olivine with rare diamonds, set in a matrix of essentially magmatic origin. Unambiguous identification of kimberlites requires careful petrographic examination combined with mineral compositional analyses. Melt inclusion studies have shown that kimberlite melts contain higher alkali concentrations than previously thought but have not clarified the ultimate origin of these melts. Because of the hybrid nature of kimberlites and their common hydrothermal alteration by fluids of controversial origin (magmatic and/or crustal), the composition of primary kimberlite melts remains unknown.
IN: Deep carbon: past to present, Orcutt, Daniel, Dasgupta eds., pp. 89-128.
Abstract: The science of studying diamond inclusions for understanding Earth history has developed significantly over the past decades, with new instrumentation and techniques applied to diamond sample archives revealing the stories contained within diamond inclusions. This chapter reviews what diamonds can tell us about the deep carbon cycle over the course of Earth's history. It reviews how the geochemistry of diamonds and their inclusions inform us about the deep carbon cycle, the origin of the diamonds in Earth's mantle, and the evolution of diamonds through time.
Abstract: Real-time tracking during diamond anvil cell experiments indicates reaction rates may control the unusual depth distribution of the extremely rare diamonds that form deep within Earth's mantle.
Abstract: Earth Scientists have two ways of examining and mapping the structure and composition of the subcontinental lithospheric mantle (SCLM): geophysical surveys, and studies of mantle samples from volcanic rocks or exposed terranes. Interpretation of both types of data requires an understanding of some basic strengths and limitations of each approach.
Geochemistry International, Vol. 57, 9, pp. 964-972.
Abstract: The paper describes mineralogical characteristics of SiO2 inclusions in sublithospheric diamonds, which typically have complicated growth histories showing alternating episodes of growth, dissolution, and postgrowth deformation and crushing processes. Nitrogen contents in all of the crystals do not exceed 71 ppm, and nitrogen is detected exclusively as B-defects. The carbon isotope composition of the diamonds varies from d13? = -26.5 to -6.7‰. The SiO2 inclusions occur in association with omphacitic clinopyroxenes, majoritic garnets, CaSiO3, jeffbenite, and ferropericlase. All SiO2 inclusions are coesite, which is often associated with micro-blocks of kyanite in the same inclusions. It was suggested that these phases have been produced by the retrograde dissolution of primary Al-stishovite, which is also evidenced by the significant internal stresses in the inclusions and by deformations around them. The oxygen isotope composition of SiO2 inclusions in sublithospheric diamonds (d18O up to 12.9‰) indicates a crustal origin of the protoliths. The negative correlation between the d18O of the SiO2 inclusions and the d13C of their host diamonds reflects interaction processes between slab-derived melts and reduced mantle rocks at depths greater than 270 km.
Gems & Gemology, Sixth International Gemological Symposium Vol. 54, 3, 1p. Abstract p. 272-3.
Africa, Sierra Leone
Abstract: Diamond ages are obtained from radiogenic isotopic analysis (Rb-Sr, Sm-Nd, Re-Os, and Ar-Ar) of mineral inclusions (garnet, pyroxene, and sulfide). As diamonds are xenocrysts that cannot be dated directly, the ages obtained on mineral inclusions provide a unique set of interpretive challenges to assure accuracy and account for preexisting history. A primary source of geological/mineralogical uncertainty on diamond ages is any process affecting protogenetic mineral inclusions before encapsulation in the diamond, especially if it occurred long before diamond formation. In practical application, the isotopic systems discussed above also carry with them inherent systemic uncertainties. Isotopic equilibrium is the essential condition required for the generation of a statistically robust isochron. Thus, isochron ages from multiple diamonds will record a valid and accurate age when the diamond-forming fluid promotes a large degree of isotopic equilibrium across grain scales, even for preexisting ("protogenetic") minerals. This clearly can and does occur. Furthermore, it can be analytically tested for, and has multiple analogues in the field of dating metamorphic rocks. In cases where an age might be suspect, an age will be valid if its regression uncertainties can encompass a known and plausible geological event (especially one for which an association exists between that event and the source of diamond-forming fluids) and petrogenetic links can be established between inclusions on the isochron. Diamonds can be dated in six basic ways: 1. model ages 2. radiogenic daughter Os ages (common-Os-free) 3. single-diamond mineral isochrons 4. core to rim ages 5. multiple single-diamond isochron/array ages 6. composite isochron/array ages Model ages (1) are produced by the intersection between the evolution line for the inclusion and a reference reservoir such as the mantle. The most accurate single-diamond age is determined on a diamond with multiple inclusions (3). In this case an internal isochron can be obtained that not only establishes equilibrium among the multiple grains but also unequivocally dates the time of diamond growth. With extreme luck in obtaining the right diamond, concentric diamond growth zones visible in UV fluorescence or cathodoluminescence can sometimes be shown to constrain inclusions to occur in the core of the diamond and in the exterior at the rim. These single grains can be extracted to give a minimum growth time (4) for the diamond. In optimal situations, multiple inclusions are present within single growth zones, in single diamonds, allowing internal isochrons to be constructed for individual growth zones in single diamonds. If enough diamonds with inclusions can be obtained for study, valid ages for diamond populations can be obtained on multiple single-diamond ages that agree (5) or on composited, mineralogically similar inclusions to give an average age (6).
Abstract: Type IIb diamonds, those defined as having trace amounts of substitutional boron, are prized for their blue colors. The famous Hope diamond is a perfect example. Besides their boron content, these rare diamonds are also characterized by their general lack of nitrogen. Little is known about how type IIb diamonds form, but they are especially intriguing because boron is often regarded as a crustal element whose presence in mantle-derived diamonds is unexpected. Despite interest in type IIb diamonds as a potential geochemical tracer of mantle processes, minimal research progress has been made to date. They are simply so rare and their color so highly valued that sample access is problematic. Even when access to type IIb diamonds is granted, these diamonds are typically free of mineral or fluid inclusions that might illuminate their geological significance (e.g. Gaillou et al. 2012; King et al. 1998).
Gems & Gemology, Sixth International Gemological Symposium Vol. 54, 3, 1p. Abstract p. 274.
Africa, South Africa, Angola
deposit - Cullinan, Lulo
Abstract: Many of the world's largest and most valuable gem diamonds exhibit an unusual set of physical characteristics. For example, in addition to their conspicuously low nitrogen concentrations, diamonds such as the 3,106 ct Cullinan (type IIa) and the Hope (type IIb, boron bearing) tend to have very few or no inclusions, and in their rough state they are found as irregular shapes rather than as sharp octahedral crystals. It has long been suspected that type IIa and IIb diamonds form in a different way than most other diamonds. Over the past two years, systematic investigation of both type IIa and IIb diamonds at GIA has revealed that they sometimes contain rare inclusions from unique geological origins. Examination of more than 130 inclusion-bearing samples has established recurring sets of inclusions that clearly show many of these diamonds originate in the sublithospheric mantle, much deeper in the earth than more common diamonds from the cratonic lithosphere. We now recognize that type IIa diamonds, or more specifically, diamonds with characteristics akin to the historic Cullinan diamond (dubbed CLIPPIR diamonds), are distinguished by the occurrence of ironrich metallic inclusions. Less frequently, CLIPPIR diamonds also contain inclusions of majoritic garnet and former CaSiO3perovskite that constrain the depth of formation to within 360--750 km. The inclusions suggest that CLIPPIR diamonds belong to a unique paragenesis with an intimate link to metallic iron in the deep mantle (Smith et al., 2016, 2017). Similarly, findings from type IIb diamonds also place them in a "superdeep" sublithospheric mantle setting, with inclusions of former CaSiO3 perovskite and other high-pressure minerals, although the iron-rich metallic inclusions are generally absent (Smith et al., 2018). Altogether, these findings show that high-quality type II gem diamonds are predominantly sourced from the sublithospheric mantle, a surprising result that has refuted the notion that all superdeep diamonds are small and nongem quality. Valuable information about the composition and behavior of the deep mantle is cryptically recorded in these diamonds. CLIPPIR diamonds (figure 1) confirm that the deep mantle contains metallic iron, while type IIb diamonds suggest that boron and perhaps water can be carried from the earth's surface down into the lower mantle by plate tectonic processes. In addition to being gemstones of great beauty, diamonds carry tremendous scientific value in their unique ability to convey information about the interior of our planet.
Tectonics, doi.org/10.1029 / 2018TC005350 27p. Pdf
Abstract: I suggest that the Earth Sciences in the mid-1950's entered a state of supercooling where the smallest input could lead to the simultaneous crystallization of new ideas. I joined in 1959 the Lamont Geological Observatory, one of the hotbeds where the Plate Tectonic revolution germinated. This paper is not an exhaustive history from an unbiased outside observer. It is a report of one of the participants who interacted with quite a few of the main actors of this revolution and who, fifty years later, revisits these extraordinary times. I emphasize the state of confusion and contradiction but also of extraordinary excitement in which we, earth scientists, lived at this time. I will identify several cases of what I consider to be simultaneous appearances of new ideas and will describe what now appear to be incomprehensible failures to jump on apparently obvious conclusions, based on my own experience.
Abstract: We show that the peripheral Pangea subduction zone closely followed a polar great circle. We relate it to the band of faster-than-average velocities in lowermost mantle. Both structures have an axis of symmetry in the equatorial plane. Assuming geologically long term stationarity of the deep mantle structure, we propose to use the axis of symmetry of Pangea to define an absolute reference frame. This reference frame is close to the slab remnants and NNR frames of reference but disagrees with hot spots based frames. We apply this model to the last 400 Myr. We show that a hemispheric supercontinent appeared as early as 400 Ma. However, at 400 Ma, the axis of symmetry was situated quite far south and progressively migrated within the equatorial plane that it reached at 300 Ma. From 300 to 110-100 Ma, it maintained its position within the equatorial plane. We propose that the stationarity of Pangea within a single hemisphere surrounded by subduction zones led to thermal isolation of the underlying asthenosphere and consequent heating as well as a large accumulation of hot plume material. We discuss some important implications of our analysis concerning the proposition that the succession of supercontinents and dispersed continents is controlled by an alternation from a degree one to a degree two planform.