Band 106, Heft 9

We present >500 zircon δ 18 O and Lu-Hf isotope analyses on previously dated zircons to explore the interplay between spatial and temporal magmatic signals in Zealandia Cordillera. Our data cover ~8500 km 2 of middle and lower crust in the Median Batholith (Fiordland segment of Zealandia Cordillera) where Mesozoic arc magmatism along the paleo-Pacific margin of Gondwana was focused along an ~100 km wide, arc-parallel zone. Our data reveal three spatially distinct isotope domains that we term the eastern, central, and western isotope domains. These domains parallel the Mesozoic arc-axis, and their boundaries are defined by major crustal-scale faults that were reactivated as ductile shear zones during the Early Cretaceous. The western isotope domain has homogenous, mantle-like δ 18 O (Zrn) values of 5.8 ± 0.3‰ (2 St.dev.) and initial ε Hf (Zrn) values of +4.2 ± 1.0 (2 St.dev.). The eastern isotope domain is defined by isotopically low and homogenous δ 18 O (Zrn) values of 3.9 ± 0.2‰ and initial ε Hf values of +7.8 ± 0.6. The central isotope domain is characterized by transitional isotope values that display a strong E-W gradient with δ 18 O (Zrn) values rising from 4.6 to 5.9‰ and initial ε Hf values decreasing from +5.5 to +3.7. We find that the isotope architecture of the Median Batholith was in place before the initiation of Mesozoic arc magmatism and pre-dates Early Cretaceous contractional deformation and transpression. Our data show that Mesozoic pluton chemistry was controlled in part by long-lived, spatially distinct isotope domains that extend from the crust through to the upper mantle. Isotope differences between these domains are the result of the crustal architecture (an underthrusted low-δ 18 O source terrane) and a transient event beginning at ca. 129 Ma that primarily involved a depleted-mantle component contaminated by recycled trench sediments (10–20%). When data showing the temporal and spatial patterns of magmatism are integrated, we observe a pattern of decreasing crustal recycling of the low-δ 18 O source over time, which ultimately culminated in a mantle-controlled flare-up. Our data demonstrate that spatial and temporal signals are intimately linked, and when evaluated together they provide important insights into the crustal architecture and the role of both stable and transient arc magmatic trends in Cordilleran batholiths.

Part V of the evolutionary system of mineralogy explores phases produced by aqueous alteration, metasomatism, and/or thermal metamorphism—relicts of ancient processes that affected virtually all asteroids and that are preserved in the secondary mineralogy of meteorites. We catalog 166 historical natural kinds of minerals that formed by alteration in the parent bodies of chondritic and non-chondritic meteorites within the first 20 Ma of the solar system. Secondary processes saw a dramatic increase in the chemical and structural diversity of minerals. These phases incorporate 41 different mineral-forming elements, including the earliest known appearances of species with essential Co, Ge, As, Nb, Ag, Sn, Te, Au, Hg, Pb, and Bi. Among the varied secondary meteorite minerals are the earliest known examples of halides, arsenides, tellurides, sulfates, carbonates, hydroxides, and a wide range of phyllosilicates.

Xenocrysts and xenoliths in Upper Cretaceous pyroclastics on Mount Carmel (northern Israel) represent a series of similar magma-fluid systems at different stages of their evolution, recording a continuous decrease in oxygen fugacity ( f O2 ) as crystallization proceeded. Corundum coexisting with Fe-Mg-Cr-Al spinels, other Fe-Mg-Al-Na oxides, and Fe-Ni alloys in apparent cumulates crystallized at f O2 values near the iron-wüstite (IW) buffer ( f O2 = IW±1) and is zoned from high-Cr cores to lower-Cr rims, consistent with fractional crystallization trends. The reconstructed parental melts of the cumulates are Al-Cr-Fe-Mg oxides with ca. 2 wt% SiO 2 . Corundum in other possible cumulates that contain Cr-Fe (Fe 45 wt%) alloys has low-Cr cores and still lower-Cr rims. Corundum coexisting with Cr 0 ( f O2 = IW-5) in some possible cumulates has low-Cr cores, but high-Cr rims (to >30% Cr 2 O 3 ). These changes in zoning patterns reflect the strong decrease in the melting point of Cr 2 O 3 , relative to Al 2 O 3 , with decreasing f O2 . The electron energy loss spectroscopy (EELS) analyses show that all Cr in corundum that coexists with Cr 0 is present as Cr 3+ . This suggests that late in the evolution of these reduced melts, Cr 2+ has disproportionated via the reaction 3Cr 2+ (melt) → 2Cr 3+ (Crn) + Cr 0 . The most Cr-rich corundum crystallized together with β-alumina phases including NaAl 11 O 17 (diaoyudaoite) and KAl 11 O 17 (kahlenbergite) and β″-alumina phases; residual melts crystallized a range of (K,Mg) 2 (Al,Cr) 10 O 17 phases with the kahlenbergite structure. The parental melts of these assemblages appear to have been Al-Cr-K-Na-Mg oxides, which may be related to the Al-Cr-Fe-Mg oxide melts mentioned above, through fractional crystallization or liquid immiscibility. These samples are less reduced ( f O2 from IW to IW-5) than the assemblages of the trapped silicate melts in the more abundant xenoliths of corundum aggregates ( f O2 = IW-6 to IW-10). They could be considered to represent an earlier stage in the f O2 evolution of an “ideal” Mt. Carmel magmatic system, in which mafic or syenitic magmas were fluxed by mantle-derived CH 4 +H 2 fluids. This is a newly recognized step in the evolution of the Mt. Carmel assemblages and helps to understand element partitioning under highly reducing conditions.

Zoned plagioclase crystals are often interpreted as proxies for magmatic history because the mineral is present in most silicic magmas and has compositional sensitivity to magmatic conditions (pressure, temperature, and composition) with slow internal diffusion that preserves compositional zones. Changes in growth rates and crystal dissolution present challenges to quantitatively relating time to particular zoning patterns. The numerical model SNGPlag uses Rhyolite MELTS to determine the equilibrium phase assemblage and compositions for a user-defined magma composition experimentally determined instantaneous nucleation and growth rates, and reasonable dissolution rates to examine plagioclase crystallization and population dynamics through time. The model tracks the numbers, sizes, morphologies, and compositional zoning of plagioclase crystals through time in response to changes in pressure, temperature, and volume or mass inputs. Model results show that significant fractions of time are functionally missing from the crystal record because of effectively zero growth rates or erased from the record through dissolution; in some instances, those processes can together remove >>50% of time from the crystal record. The results show that temperature- (or pressure-) cycling alone will not produce substantial compositional zoning but that the addition of new magma is required to grow complexly zoned phenocrysts. Comparison of the input pressure-temperature-time series with compositional transects shows that the crystal record is biased toward more recent intervals and periods of decreasing temperature (i.e., neither the peak temperatures nor intervals of prolonged, cool storage are favored). Crystallization (or dissolution during heating) acts to return magmas to near-equilibrium crystal fractions within hundreds of days.

The metamorphic rocks from the Torres del Paine contact aureole (Patagonia, Chile) show field, petrographic, and geochemical evidence for small amounts of igneous fluid infiltration due to the solidification of the granite complex. Hydrogen isotope ratios (D/H) in the contact aureole first decrease while approaching the intrusion and subsequently increase toward the granite contact. Initial decrease with metamorphic grade is due to preferential loss of the 2 H isotopes due to Rayleigh fractionation during prograde dehydration reactions. The infiltration of high-δD fluids from the intrusion increases δD within the last 150 m. In contrast, ( 18 O/ 16 O) ratios show no systematic changes, indicating that neither oxygen loss by Rayleigh fractionation nor oxygen exchange by fluid infiltration was significant enough to dominate original variations seen in the oxygen isotope ratio of the protolith. Calculated volume of fluid using the position of the hydrogen isotope exchange front gives a relatively low time-integrated fluid flux of about 4 m 3 /m 2 at the contact for the igneous fluid. These small amounts of fluid flux are in agreement with whole rock oxygen isotope data that are not affected in the contact aureole. Chlorine content of metamorphic biotite crystals, in contrast to oxygen isotopes, supports infiltration of igneous fluids. Indeed, relatively high-Cl concentrations in biotite were measured in some samples close to the intrusion (up to 0.2 wt%), while chlorine concentrations in biotite are constant everywhere else in the entire contact aureole, having low concentrations (0.01–0.06 wt%). The absence of a well-marked Rayleigh fractionation trend in Cl concentrations with increasing metamorphism is surprising since chlorine strongly fractionates into the fluid. This is best explained by slow diffusive exchange of chlorine in biotite in the cooler outer aureole. Hence recrystallization of biotite would be required to modify its Cl composition. Biotite grains from samples close to the intrusion with high-Cl content also have lower Ti content (0.4 pfu) than biotite (0.5 pfu) from other samples containing biotite with lower Cl content located at the same distance from the contact. Since Ti content in biotite is a function of temperature, this is a good indication that magmatic fluid infiltration started post peak, early during cooling of the metamorphic rocks. Episodes of fluid flow appear to have been nearly continuous during cooling as evidenced by numerous retrogression textures, such as secondary muscovite (above 470 °C) or chlorite + muscovite intergrowth after cordierite or biotite (slightly below 470 °C). This might be related to crystallization of subsequent batches of granites or the onset of minor fluid convection during cooling of the aureole. Nevertheless, only minor secondary muscovite has been found, and fresh cordierite is present throughout the aureole confirming small amounts of fluid infiltration. The time-integrated fluid flux computed from the hydrogen isotope exchange front is two orders of magnitude lower than values computed for metacarbonate in many other contact aureoles, suggesting low permeabilities of pelitic rocks. In conclusion, Cl contents and hydrogen isotope compositions of hydrous minerals provide a sensitive tool to identify small fluid-rock interaction events, much more sensitive than oxygen isotope compositions of the whole rock or minerals.

The shock stages of 14 L6 ordinary chondrites are estimated using the random X‑ray diffraction patterns of polished thin section samples and the in-plane rotation method. The mean lattice strains and grain size factors for olivine and orthopyroxene are determined from the analyses based on the Williamson–Hall plots, which depict the tangent Bragg angle and integral breadth β. The lattice strain in olivine, ε Ol , is distributed from ~0.05% to ~0.25%, while that in orthopyroxene, ε Opx , is distributed from ~0.1 to ~0.4%, where we selected the isolated peaks of olivine and orthopyroxene. The olivine peaks have Miller indices of (130), (211), (222), and (322), while the orthopyroxene peaks have Miller indices of (610), (511), (421), (631), and (12.1.2). The intercept for integral breadth β 0 O1  and β 0 O p x $\beta_{0}^{\text {O1 }}\, \text{and} \,\beta_{0}^{O \mathrm{px}}$for the Williamson–Hall plots correlates with the grain size of the constituent minerals. The grain size is proportional to the inverse of β 0 since the β intercept increases with the shock stage. Introducing a new parameter, –ε/log β 0 for olivine (0.04–0.16) and orthopyroxene (0.07–0.32) reveals a clear relationship between them: –ε Opx /log β 0 O p x = $\beta_{0}^{\mathrm{Opx}}=$–0.01+ 2.0 − ε 01 / log ⁡ β 0 O 1 $\left(-\varepsilon^{01} / \log \beta_{0}^{O 1}\right)$(R > 0.9). In addition, the isolated peak of plagioclase (2̅01) systematically changes as the shock stage increases, suggesting the progress of amorphization (maskelynitization). Another parameter, ( I /FWHM) Pl(2̅01) reveals additional relationships: − ε O l / log ⁡ β 0 O l = $-\varepsilon^{\mathrm{Ol}} / \log \beta_{0}^{\mathrm{Ol}}=$0.14(±0.01) − 5.2 × 10 −5 (±5.7 × 10 −6 ) × ( I /FWHM) Pl(2̅01) , and − ε O p x / log ⁡ β 0 O p x = $-\varepsilon^{\mathrm{Opx}} / \log \beta_{0}^{\mathrm{Opx}}=$0.25(±0.04) − 8.9 × 10 −5 (±2.6 × 10 −5 ) × 10 –5 × ( I /FWHM) Pl(2̅01) . These three parameters systematically change with the shock stage, suggesting that they are suitable shock barometers. The present method is useful to evaluate the shock stage of L6 chondrites and potentially enables quantitative shock stage classification for stony meteorites.

A new indentation-based method was developed that will impact and facilitate the elastic property measurements of rocks and minerals, especially those possessing unusual deformation behavior, including brittle materials and those with complex architectures. The novel feature employed is a metallic film that uniformly transfers the load from the indenter tip to the sample. The film also absorbs the damage caused by the penetrating indenter, shielding the material from highly localized deformation that can impact its response to loading. Many geologically relevant materials have resisted traditional indentation testing because they are either brittle in nature or possess highly anisotropic architectures, such as layered or lamellar structures. In both cases, the highly localized deformation from direct indentation significantly affects the indenter unloading stiffness, from which the elastic properties are determined. The indirect indentation method developed here has demonstrated accurate determination of the elastic properties of many common geological materials as well as materials that have resisted elastic characterization such as galena and talc.

The Helukou deposit, with proven reserves of 33 752 t WO 3 , is one of the newly exploited medium-scale tungsten (W) deposits in the Guposhan ore field, Nanling Range of South China. Skarn-type and less abundant altered granite-type tungsten orebodies were identified in this deposit. The ore mineralization in this district was a product of two-stage magmatism, as shown by LA-ICP-MS U-Pb dating of zircons and Re-Os dating of molybdenite. The former yielded U-Pb ages of 184.0 ± 3.6 Ma (MSWD = 0.15) and 163.8 ± 1.5 Ma (MSWD = 0.41) for fine-grained biotite granite and muscovite granite, respectively, as well as a U-Pb age of 181.5 ± 2.1 Ma (MSWD = 0.75) for zircon grains from altered granite-type tungsten ore. The latter yielded molybdenite Re-Os ages of 183.5 ± 2.8 Ma (without MSWD owing to a limited number of samples) and 163.4 ± 2.8 Ma (MSWD = 0.71) for altered granite-type and skarn-type tungsten deposits, respectively. Thus, two separate tungsten mineralization events occurred during the Early Jurassic and Middle Jurassic. Trace-element compositions suggest that scheelite I was controlled by the coupled substitution reactions of 2Ca 2+ = Na + + REE 3+ and Ca 2+ + W 6+ = Nb 5+ + REE 3+ , whereas scheelite II was controlled by the coupled reactions of 2Ca 2+ = Na + + REE 3+ and 3Ca 2+ = ◻Ca + 2REE 3+ (where ◻ is a site vacancy). High Mo and low Ce contents suggest that both scheelite I and scheelite II were precipitated from oxidizing magmatic-hydrothermal fluids. Based on the mineral assemblage of the altered granite-type ores and geochemical characteristics of scheelite I [i.e., negative Eu anomalies (0.02–0.05; mean = 0.03 and STD = 0.01), and high 87 Sr/ 86 Sr ratios (0.70939–0.71932; mean = 0.71345 and STD = 0.00245)], we infer that fluid-rock interaction played an important role in modifying Early Jurassic ore-forming fluids. Scheelite II exhibits a geochemical composition [i.e., 87 Sr/ 86 Sr ratios (0.70277–0.71471; mean = 0.70940 and STD = 0.00190), Eu anomalies (0.14–0.55; mean = 0.26 and STD = 0.09), and Y/Ho ratios (16.1–33.7; mean = 27.9 and STD = 2.91)] similar to that of the Middle Jurassic Guposhan granites, suggesting inheritance of these features from granite-related magmatic-hydrothermal fluids. These results provide new insights into the two-stage magmatic and metallogenic history of the Nanling Range during the Jurassic Period.

The genesis of the Dabaoshan stratabound base metal deposit has remained in dispute since its discovery. Scheelite is commonly present in both the Cu-S orebody and adjacent porphyry-style Mo-W mineralization and can provide insights into the hydrothermal history. In the stratabound Cu-S orebodies, there are three stages of mineralization: early-stage, Cu-(W), and late-stage. Two types of scheelite (here referred to as SchA and SchB) are identified in the Cu-(W) mineralization stage. SchA is anhedral and disseminated in massive sulfide ores. It coexists with chalcopyrite and replaces the preexisting arsenic-bearing pyrite. SchA exhibits chaotic cathodoluminescent (CL) textures and contains abundant mineral inclusions, including pyrite, chalcopyrite, arsenopyrite, uraninite, and minor REE-bearing minerals. Chemically, SchA displays middle REE (MREE)-enriched patterns with negative Eu anomalies. SchB occurs in veins crosscutting the stratabound orebodies and shows patchy textures in CL images. Based on CL texture, SchB is subdivided into SchB1 and SchB2. SchB1 is CL-dark and occasionally shows oscillatory zoning, whereas SchB2 is CL-bright and relatively homogeneous. Chemically, SchB1 has a high-U content (mean = 552 ppm) and REE patterns varying from MREE-enriched to MREE-depleted. In contrast, SchB2 is depleted in U (mean = 2.5 ppm) and has MREE-enriched patterns. Compared with SchB, SchA is significantly enriched in Ba. Scheelite in the stratabound orebodies has similar Y/Ho ratios and trace-element characteristics as Sch3 in the Dabaoshan porphyry system. In situ U-Pb dating of hydrothermal apatite, collected from the Sch3-bearing veins in the footwall of stratabound orebodies, yielded a mineralization age of 160.8 ± 1.1 Ma. Zircon from the Dabaoshan granite porphyry yielded a U-Pb age of 161.8 ± 1.0 Ma. These two ages are consistent within uncertainty, suggesting that the ore-forming fluid responsible for tungsten mineralization in the stratabound orebodies was derived from the porphyry system. When fluid emanating from the deep porphyry system encountered the overlying Lower Qiziqiao Formation and stratabound orebodies, replacement reactions resulted in dramatic variations in physiochemical conditions (e.g., decrease in f O2 , increase in Ca/Fe, As, Ba). During this process, U 6+ was reduced to U 4+ , and As and Ba were leached out of the preexisting pyrite and host rock. Fluid-rock interactions triggered a rapid discharge of fluids, forming SchA with chaotic CL textures and abundant inclusions, but uniform REE patterns. SchB (characterized by patches with different chemical characteristics) may have been formed from repeated injection of ascending fluids into fractures crosscutting the pre-existing massive sulfide ores. We propose that Jurassic porphyry Mo-W mineralization contributed to tungsten mineralization in the stratabound orebodies. Considering that Cu and W mineralization are genetically related, not only in the footwall but also in the stratabound orebodies, we infer that Cu in the stratabound orebodies was locally sourced from the Jurassic porphyry mineralization.

Schreibersite, (Fe,Ni) 3 P, the most abundant cosmic phosphide, is a principal carrier of phosphorus in the natural Fe-Ni-P system and a likely precursor for prebiotic organophosphorus compounds at the early stages of Earth’s evolution. The crystal structure of the mineral contains three metal sites allowing for unrestricted substitution of Fe for Ni. The distribution of these elements across the structure could serve as a tracer of crystallization conditions of schreibersite and its parent celestial bodies. However, discrimination between Fe ( Z = 26) and Ni ( Z = 28) based on the conventional X-ray structural analysis was for a long time hampered due to the proximity of their atomic scattering factors. We herein show that this problem has been overcome with the implementation of area detectors in the practice of X-ray diffraction. We report on previously unknown site-specific substitution trends in schreibersite structure. The composition of the studied mineral encompasses a Ni content ranging between 0.03 and 1.54 Ni atoms per formula unit (apfu): the entire Fe-dominant side of the join Fe 3 P-Ni 3 P. Of 23 schreibersite crystals studied, 22 comprise magmatic and non-magmatic iron meteorites and main group pallasites. The near end-member mineral (0.03 Ni apfu) comes from the pyrometamorphic rocks of the Hatrurim Basin, Negev desert, Israel. It was found that Fe/Ni substitution in schreibersite follows the same trends in all studied meteorites. The dependencies are nonlinear and can be described by second-order polynomials. However, the substitution over the M 2 and M 3 sites within the most common range of compositions (0.6 < Ni <1.5 apfu) is well approximated by a linear regression: Ni( M 2) = 0.84 × Ni( M 3) – 0.30 apfu (standard error 0.04 Ni apfu). The analysis of the obtained results shows a strong divergence between the variation of unit-cell parameters of natural schreibersite and those of synthetic (Fe,Ni) 3 P. This indicates that Fe/Ni substitution trends in the mineral and its synthetic surrogates are different. A plausible explanation might be related to the differences in the system equilibration time of meteoritic schreibersite (millions of years) and synthetic (Fe,Ni) 3 P (~100 days). However, regardless of the reason for the observed difference, synthetic (Fe,Ni) 3 P cannot be considered a structural analog of natural schreibersite, and this has to be taken into account when using synthetic (Fe,Ni) 3 P as an imitator of schreibersite in reconstructions of natural processes.

A continuously increasing number of research groups are adopting elastic geobarometry for retrieving pressures and temperatures of entrapment of inclusions into a host from both natural and experimental samples. However, a few misconceptions of some of the general concepts underlying elastic geobarometry are still widespread. One is the difference between various approaches to retrieve the residual pressures and residual strains from Raman measurements of inclusions. In this paper, the estimation of uncertainties and the validity of some general assumptions behind these methods are discussed in detail, and we provide general guidelines on how to deal with inclusion strain, measurements, inclusion pressure, and their uncertainties.

Cuadros et al. (2019) used a wide range of data from dioctahedral and trioctahedral Fe 3+ -bearing, 2:1 phyllosilicates to propose a model describing how tetrahedral occupancy by Fe 3+ takes place in both dioctahedral and trioctahedral 2:1 phyllosilicates. The partition coefficient approach (Decarreau and Petit 2014) focusing on the distribution of Al 3+ and Fe 3+ between octahedral and tetrahedral sites of dioctahedral smectites has been disregarded in the study of Cuadros et al. (2019). This approach was applied here on the set of data from Cuadros et al. (2019). The partition coefficient value linked to the distribution of Al 3+ and Fe 3+ between octahedral and tetrahedral sites determined from natural and synthetic dioctahedral smectites applies well to trioctahedral phyllosilicates too. Data from synthetic iron-rich 2:1 smectites also fit well with both Cuadros et al. (2019) and Decarreau and Petit (2014) models.

The model of Fe 3+ distribution between octahedra and tetrahedra in dioctahedral smectites by Decarreau and Petit (2014) used data from infrared analysis. From their own and other general evidence, the resulting data are likely to be affected by significant uncertainty. This aside, their model has limited application because it is based on synthetic smectites containing only Si, Al, and Fe 3+ .

This New Mineral Names has entries for 11 new species, including bohuslavite, fanfaniite, ferrierite-NH 4 , feynmanite, hjalmarite, kenngottite, potassic-richterite, rockbridgeite-group minerals (ferrirockbridgeite and ferrorockbridgeite), rudabányaite, and strontioperloffite.