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This paper provides an overview of the role that geochemistry plays in petroleum systems analysis, and how this can be used to derive constraints on the key elements and processes that give rise to a successful petroleum system. We discuss the history of petroleum geochemistry before reflecting on the next frontier in geochemical applications in hydrocarbon systems. We then review the individual contributions to this Special Publication. These papers present new geochemical techniques that allow us to develop a more systematic understanding of critical petroleum system elements; including the temperature and timing of source-rock deposition and maturation, the mechanisms and timescales associated with hydrocarbon migration, trapping, storage and alteration, and the impact of fluid flow on reservoir properties. Finally, we provide a practical example of how these different geochemical techniques can be integrated to constrain and generate a robust understanding of the prolific Paleozoic petroleum system of the Bighorn Basin.

Tektites are natural glasses formed as a result of melting and quenching of distally ejected terrestrial material upon hypervelocity (>11 km/s) impact on Earth. Some tektites contain inclusions of lechatelierite (nearly pure SiO_2 glass; 99-100 wt. % SiO_2), generally thought to be the amorphous relicts of partially digested quartz grains [1]. This study exploits the presence of these local heterogeneities to extract information about tektite thermal histories by investigating chemical diffusion between molten silica inclusions and surrounding peraluminous felsic melt in natural tektites and experimental analogues.

Much of our knowledge about the early Solar System comes from the study of CV3 meteorites, in particular Allende. Hydrothermal alteration is recognized as an important, ubiquitous process within these rocks (e.g. [1]). Nevertheless, we know little regarding the nature of these fluids. Volatile element abundances in phosphates from carbonaceous chondrites could constrain relative fugacities of H_2O, HF and HCl in the fluid present during metasomatism in primitive planetesimals.

The Moon has been thought to have a bulk planetary water content < 1 ppb [1]. Recent ion microprobe analyses have shown that lunar samples contain up to 7000±1000 ppm OR (reported as equivalent H_20) in apatite and 4-46 ppm in igneous glass [2-6]. These studies suggest that the mantle sources of at least some lunar magmas contain from 64 ppb to 200 ppm [4-6]. Sharp et al. [6] report an apparently contradictory observation -that ^(37)Cl values of lunar samples vary from -1 to 24%o, with an upper extreme they argue demands devolatilization of anhydrous melts. We examine this issue further through measurements of water content, δ^(37)Cl, and δD of apatite from lunar meteorites MIL 05035, NWA 2977, and Dhofar 458.

Magmatic volatiles influence igneous phase equilibria, eruptive behavior, atmospheric composition, and climate. Several lines of evidence suggest that Mars is rich in halogens and S relative to Earth. However, magmatic volatile abundances and their effects on magmatic processes on Mars are controversial. Here we examine igneous apatites in SNC meteorites as indicators of magmatic volatile abundances.

Young basalts from Kilauea, on the big island of Hawai’i, frequently feature visually striking, white, orange and blue coatings, consisting of a 10-50 μm layer of amorphous silica, capped, in some cases, by a ~1 μm layer of Fe-Ti oxide [1]. The coatings provide an opportunity to study the early onset of acid-sulfate weathering, a process common to many volcanic environments. Silicon isotopes fractionate with the precipitation of clays and opaline silica, and have been demonstrated to be an indicator of weathering intensity [2,3]. Here we report in situ measurements of δ^(30)_Si of the silica coatings and their implications for coating formation.

Apatite incorporates several volatile elements (including S, as SO_4 ^(2-)) and can provide a record of magmatic volatile evolution. Recent measurements of volatiles in apatite from Apollo sample 14053.241 revealed 300-450 ppm S. Although many lunar melts have sufficient S for sulfide saturation, the observed S content of lunar apatite is surprising because lunar samples (especially 14053) are highly reduced (≤ IW) and are thus expected to contain little SO_4 ^(2-). One possibility is that there are micro-environments in late-stage lunar melts that are more oxidized than one would infer from conditions recorded by other components of these rocks. Alternatively, it may be that S^(2-) substitutes for F+Cl+OH in lunar apatite: S^(2—)bearing apatite has been synthesized, but to our knowledge has not been observed in nature.

Many aspects of the Earth’s early sulfur cycle, from the origin of mass anomalous fractionations to the scale and degree of biological involvement, remain poorly understood. We have been studying the nature of multiple sulfur isotope (^(32)S, ^(33)S, and ^(34)S) signals using a novel combination of scanning high-resolution low-temperature superconductivity SQUID microscopy and secondary ion mass spectrometry (SIMS) techniques in a suite of samples from distal slope and basinal environments adjacent to a major Late Archean-age (~2.6-2.52 Ga) carbonate platform. Coupled with petrography, these techniques allow us to interrogate, at the same microscopic scale, the complex history of mineralization in samples containing diverse sulfide-bearing mineral components. Because of a general lack of Archean sulfate minerals, we focused our analyses on early diagenetic pyrite nodules, precipitated in surface sediments. This allows us to assay fractionations by controlling for isotope mass balance.

Acid leachates and residues of primitive meteorites have revealed large variations in ^(54)Cr relative to terrestrial composition [1–9]. Despite two decades of extensive search, the nature of the carrier of ^(54)Cr excesses is still uncertain. Ion probes offer the opportunity to address directly this question by measuring ^(54)Cr/^(52)Cr ratios in individual grains [10–13].

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Insoluble organic matter (IOM), the main organic constituent in chondrites, has been extensively studied after HF/HCl isolation techniques. Bulk isotopic compositions and elemental ratios show variations between chondrite groups, whereas they are quite homogeneous within each class [1]. Recent isotopic measurements by ion probes have revealed that IOM is heterogeneous at the sub-micron scale [2,3]. Does this heterogeneity reflect parent body evolution or reactions in the gas phase prior to accretion? To answer this question, we have studied in situ organic matter in Orgueil (CI), Tagish Lake, Murchison (CM), Cold Bokkeveld (CM), Allende (CV), Renazzo (CR) and Chainpur (LL) by NanoSIMS imaging. We have determined D/H ratios and chemical composition (C, H and N contents) of organic particles in the matrices of these meteorites.

Carbonate minerals observed in primitive meteorites are products of either terrestrial weathering or aqueous alteration in the early solar system. Most of the carbonate minerals in carbonaceous chondrites occur primarily as isolated grains in matrix, as crosscutting veins, or as replacement minerals in chondrules [e.g., 1, 2]. A few calcium-aluminum-rich inclusions (CAIs) have been reported containing carbonate minerals as well [2, 3]. The C and O isotopes of carbonates in carbonaceous chondrites, mostly measured by stepwise extraction of bulk samples with phosphoric acid [4–7], are largely distinctive from those of terrestrial carbonates, whereas textural and petrographic evidence indicates that some carbonates in primitive meteorites are terrestrial in origin [2]. This study attempts to investigate from the aspect of C isotope the origin of rare carbonate minerals in some CAIs. If of extraterrestrial origin, carbonates in CAIs can provide important information and constraints on the ubiquitous aqueous alteration process in the early solar system.

During our nano-mineralogy investigation of the Allende meteorite, we discovered a unique corundum-rich cluster of irregular micrometer-sized refractory grains in a type IA chondrule. The presence of relatively oxidized (rutile) and highly reduced (a new mineral Ti_2O_3, khamrabaevite) phases in the same cluster reflects distinctly different environments prior to incorporation of the cluster into the chondrule. To our knowledge, this is the first occurrence of such a cluster. Investigation of phases that are clearly exotic to the host chondrule and may predate its formation can provide not only important constraints on the materials present when chondrules formed and the enviroments within or outside the Protoplanetary disk, but also on the chondrule formation event. Herein we report our prelimary results on the mineralogy of these grains and the overall petrology of their host chondrule.

Despite the predominately mafic character of martian surface rocks, silica-rich materials have long been predicted to occur on Mars; recently, those predictions have been validated. CRISM spectra from numerous regions of Mars have revealed H_2O and OH-bearing phases most consistent with amorphous silica. Additionally, the detection of high-silica materials at Home Plate by MER Spirit implied aqueous alteration and leaching in a volcanic environment [3]. In order to fully understand the environments in which silica-rich materials are formed on Mars, it is useful to study silica in analogous terrestrial settings. We focus on silica and Fe-Ti oxide coatings in the Ka’u Desert on the island of Hawaii, an analog to Mars characterized by low levels of rainfall and strong acid-sulfate alteration processes [4]. Many formation mechanisms for these coatings have been proposed, including dissolution of wind-blown tephra [5], leaching of volcanic glass [6], and vapor deposition [7]. We focus on a suite of samples from the 1974 Kilauea pahoehoe flow, collected in 2003. The chemistry and morphology of these coatings were previously presented [8]. Here we present new morphological, spectral and isotopic analyses of the coating suite. The goal of the study is to characterize the coatings and their formation mechanism and describe the implications for silica mobility on Mars.

The short-lived radionuclide ^(36)Cl decays to either ^(36)Ar (98.1%, β-) or ^(36)S (1.9%, ε and β+), with a half life of 3.01 × 10^5 yr [1]. Recent study has shown that ^(36)S anomalies from the decay of ^(36)Cl exist in sodalite (Na_8Al_6Si_6O_(24)Cl_2) of some Ningqiang CAIs and Allende CAIs and chondrule [2–5], but not in sodalite in other CAIs from Allende or Vigarano [6, 7]. In this study, we have expanded the search for ^(36)S anomalies in primitive ordinary chondrites.

Aqueous alteration of primitive meteorites is among the earliest and the most widespread geological processes in the solar system. A better understanding of these processes would help us constrain the early evolution condition of the solar system and test models of thermal and chemical evolution of planetesimals. In this study, we extended our previous work on CM chondrites by further applying carbonate clumped isotope thermometry to other types of carbonaceous chondrites (GRO 95577, CR1; Orgueil, CI; and Tagish Lake, ungrouped type 2) to determine the conditions of their aqueous alteration. Carbonate in GRO 95577 is almost exclusively calcite; both Orgueil and Tagish Lake contain complex mixtures of several carbonates, which necessitated stepped phosphoric acid digestion to separately analyze calcite, dolomite/ankerite and breunnerite. CO_2 gases derived from these acid digestions are exceptionally rich in sulfur and organic contaminants. While so far no consistent evidence suggests their influences on Δ_(47) after extensive purification, we are continuing working on this issue.

Analysis of the compositions of crystals and melt inclusions from a suite of 40 gabbroic and wehrlitic nodules in a single eruptive body provides a record of concurrent mixing and crystallization of melts under NE Iceland. The crystals in the nodules have a similar range of compositions to those found as phenocrysts in the flow, and many of the nodules may have been generated by crystallization of a magma with a similar composition to that of the host flow. While plagioclase is only present in nodules where the average forsterite content of olivines is 0.8 GPa and is in agreement with estimates of crystallization pressures for the host basalt. The relationship between the compositional variability of melt inclusions and the forsterite content of the host olivine is revealed by REE analyses of over 120 melt inclusions. The degree of variability in REE concentrations and REE/Yb ratios decreases with falling forsterite content of the host olivine, as expected if melt mixing and fractional crystallization are operating together. The standard deviation of the REEs falls by a factor of ~4 between Fo90 and Fo87. This change in olivine composition can be produced by crystallization of 20% which occurs on cooling of ~50°C. The relative rates of mixing, cooling and crystallization may provide constraints upon the dynamics of magma bodies. The oxygen isotopic composition of olivines from the nodules and phenocrysts is highly variable (δ18O from 3.3–5.2 per mil) and shows little correlation with the forsterite content of the olivine. The full range of oxygen isotope variation is present in olivines with Fo89–90, and the low δ18O signal is associated with melts of high Mg# and La/Yb. Such geochemical relationships cannot be produced by assimilation of low Mg# crustal materials alone, and may reflect oxygen isotopic variation within the mantle source. The geochemistry of the melt inclusions and their host crystals can be accounted for by fractional melting of a mantle source with variable composition, followed by concurrent mixing and crystallization beneath the Moho.

Isotopic analysis of water released by vacuum heating of hydrous minerals and sub-marine basaltic glasses indicates that they vary in δD_(SMOW) between ca. +10 and -115 per mil (e.g., [1]). However, with few exceptions variations within that range are not well correlated with other geochemical and geologic properties and it is debated whether they reflect isotopic heterogeneity in the mantle, fractionations produced during ascent to the surface, or sub-solidus alteration. This ambiguity is at least partly due to the large sample size and slow rate of conventional analyses, which precludes linking isotopic ranges to grain-scale petrographic variables or constructing large data bases (many 10’s of samples) in a reasonable period of time. Ion microprobe methods provide one solution to these problems, although they suffer from analytical uncertainties nominally 5 to 10 times worse than conventional measurements and large fractionations that can be a source of systematic error.

Variations of oxygen isotope ratios in arc-related lavas can constrain the contributions of subducted crustal igneous rocks, sediments, and fluids to the sub-arc mantle. We have measured oxygen isotope ratios in 72 arc and back-arc lavas from five ocean–ocean subduction zone systems using laser-fluorination analyses of olivine and other phenocrysts and glass. Eighty percent of our samples have {delta}18O values for any given phase (olivine, plagioclase, glass, or biotite) within 0·2{per thousand} of the average value for that phase in upper-mantle peridotites and mid-ocean ridge basalt (MORB); the range for each phase is

The stable isotopic geochemistry of carbonates in SNC meteorites constrains both the characteristics of martian volatile reservoirs and the origin of secondary mineralization in these samples. We here report new ion microprobe measurements of ^(18)O/^(16)O in carbonates and related phases in ALH 84001, supported with major-, minor-, and trace-element data on the same materials.

The temperature of formation of carbonates in ALH 84001 provide a test of the hypothesis that they contain features produced by ancient martian life [1], and contributes to our understanding of the global budgets of martian volatiles. We have determined the micrometer-scale distribution of O and C isotope ratios in carbonate concretions, enstatite, and SiO_2 in ALH 84001 by ion microprobe as a means of constraining the range of possible temperatures of fluid-rock interaction [2]. The principal results are: (1) Carbonate δ^(18)O is 9.5-20.6‰, SMOW, significantly expanding the range from bulk analysis. The magnesite rim is higher in δ^(18)O than Ca-rich (0.07 ≤ X_(ca) ≤ 0.13) cores. (2) Variations in δ^(18)O occur over length scales as small as 50 µm. (3) Interiors of fractured orthopyroxene that hosts carbonate are homogeneous to within ±1‰. (4) Secondary SiO_2 has a δ^(18)O of 20.4‰. These data are inconsistent with mutual O isotope equilibrium among carbonate and silicate minerals and indicate either fine-scale mineral-mineral equilibrium at a range of temperatures ≤ 300°C or a failure to attain mineral-mineral equilibrium. Mineralogical evidence for disequilibrium supports the latter interpretation. Our δ^(18)O values for carbonates have been confirmed by two studies [3], and extended to compositions of carbonate not found in our sample.

Oxygen isotope ratios in phenocrysts from ocean island basalts (OIB) can place constraints on the origins of their mantle sources. Values of δ^(18)O in olivines from alkali basalts from Pitcairn Island (which have the extreme "EM1" signature based on radiogenic isotopes) are equal to those of olivines from average mantle peridotite (based on studies of mantle xenoliths and the MORB source region) . This result suggests that the amount of recycled continental sediment in Pitcairn Island EM1 sources is less than ~0.75%. Based on studies of olivine phenocrysts, the sources of both the plume component of Hawaiian lavas and of all measured Juan Fernandez ("PHEM") samples also have oxygen isotope compositions indistinguishable from average upper mantle peridotite. If these OIB sources come from the lower mantle, it is implied to have an oxygen isotope ratio similar to the upper mantle. Low ^(18)O/^(16)O olivines from some Hawaiian lavas are associated with a more MORB-like He and radiogenic isotope component, possibly recycled but also consistent with contamination from the base of the modern Pacific plate.