Fractional crystallization

Title: Silicon isotope fractionation at high pressures and temperatures. Authors: Schauble, Edwin A.; Young, Edward D.; Ziegler, Karen; Shahar, Anat; Halliday, Alex N.; Bastian Georg, R. Publication: Geochimica et Cosmochimica Acta Supplement, Volume 73, p.A1169. ...

Major, trace element and K-Ar age determinations are reported for a suite from the Yamadağı volcanics in the Eastern Anatolia. The exposed rocks mainly consist of medium-potassium calc-alkaline basaltic andesites, andesites and dacites. Petrographical data exhibit disequilibrium mineral textures, such as resorption of the ferromagnesian phases, clinopyroxene-mantled orthopyroxene, and sieve-textured plagioclases. The Yamadağı volcanics have a calkalkaline character, and trace element characteristics exhibit that the volcanics resemble subduction zone volcanics and/or volcanics assimilated by continental crust. K/Ar age determinations show that the Yamadağı volcanics were formed during the 12 ± 0.5 -15 ± 0.5 Ma time interval. Geochemical characteristics of these volcanics can be attributed to complex petrogenetic processes, including magma mixing and crustal assimilation along with fractional crystallization.

intruded the Palaeogene lava field and older rocks in the vicinity of complex Loch Scridain, Isle of Mull, NW Scotland, has been investigated using mineral chemistry data together with whole-rock major and trace element and radiogenic Sr-Nd-Pb isotope data. Three distinct magma groups are present. Group I consists of aphyric tholeiitic INTRODUCTION

Very low frequency electromagnetic (VLF-EM) measurements were carried out in Wadi Isbayia area, south Sinai Peninsula,
to test the efficiency of the VLF-EM method in the exploration of sulphide mineralization in arid environments. The VLF-EM
field measurements, including tilt angle, real and imaginary components of the received VLF field, were carried out along
fifteen profiles covering a quartz monzonite bedrock. Interpretation of the VLF measurements, in the light of geological
information, has showed that sulphide minerals in the Wadi Isbayia area extend from the ground surface to a depth of about
200 m. However, the structural lineaments, especially faults, have controlled the distribution of the sulphide mineralization.
A few of polished sections for rock samples, collected from the sites of the VLF-EM anomalies in the study area, have been
prepared and examined by ore microscopy which confirmed the presence of pyrite and chalcopyrite as well as iron oxides,
disseminated in the quartz monzonite bedrock. These results showed that the VLF-EM method is an effective tool in the
exploration of sulphide minerals in the arid environments.

The Pedra Branca suite (2.75 Ga) is located in the Canãa dos Carajás domain in the southeastern Amazonia Craton. It diverges from typical TTG in mineralogical and geochemical terms, by the presence of hornblende and clinopyroxene and because it has a high content of HFSE (Zr, Y, Ti, and Nb). It belongs to the low-K subalkaline series, which varies from metaluminous to peraluminous, and are mostly calc and ferroan granitoids. Amphibole is calcic and classified as ferroan-edenite, and hastingsite. Plagioclase is mainly oligoclase. The Fe/(Fe + Mg) ratios found in the amphiboles indicate that these granitoids were formed under high to moderate fO 2 conditions. Geobarometric calculations suggest pressures between 9.3 and 71 Kbar for the origin and 4.8-53.4 Kbar for the emplacement. Geothermometric calculations suggest initial crystallization temperatures between 945 and 862°C, and the water content in the magma is estimated to be higher than 4 wt%. The magma source was defined as tholeiitic continental gabbro melted in an extensional setting (Carajás Rift) with geochemical features similar to diabase from Nova Canadá (PA). The Pedra Branca magma was originated by partial melting (~28%), leaving a residue with plagioclase (An40), hornblende, clinopyroxene, and may or may not have magnetite.

The Mesoarchean Na-granitoids exposed in the Rio Maria domain, southeastern Amazonian craton, are represented by tonalite-trondhjemite and leucogranodiorite-granite suites. The 2.98-2.92 Ga tonalite-trondhjemites are the most voluminous rock type in the Rio Maria domain and host 2.86 Ga leucogranodiorite-granite plutons. These rocks share common geochemical characteristics, such as relatively high Al 2 O 3 and Na 2 O and low Yb and Y contents, as well as the behavior of the REE. However, based on an extensive geochemical data set, it is possible to show that the leucogranodiorite-granites have higher K 2 O, Ba, Sr, and Rb and lower CaO contents than the tonalite-trondhjemites. The latter are compositionally similar to typical tonalite-trondhjemite-granodiorite (TTG) series and probably originated from partial melting of garnet amphibolites, derived from tholeiitic rocks or from metabasalts of the Identidade greenstone belt, at pressure conditions suitable to produce high, medium, and low La/Yb tonalite-trondhjemite groups. The leucogranodiorite-granites show geochemical affinity with the Transitional TTG of the Yilgarn craton and are related to the Hybrid granitoid group. The ambiguous geochemical character of the Rio Maria leucogranodiorite-granite suite, which shares some characteristics that are typical of the tonalite-trondhjemite rocks and others more commonly observed in the sanukitoid suites, may be related to complex processes involving TTG and sanukitoid magmas. The discrimination of these two Na-granitoid groups helps us estimate the true volume of TTG magmatism in the Rio Maria domain and in understanding the dynamics of petrogenetic processes in the terrane at the end of the Archean.

In the Mesoarchean Rio Maria granite-greenstone terrane, the leucogranodiorite-granite (LGdG) suites are mostly represented by the 2.87 Ga Guarantã suite which includes the Trairão and Azulona granodiorite and the Guarantã granite plutons. These granites originated around 50 m. y. after the 2.93 ± 0.1 Ga major TTG magmatic event and were approximately coeval with the sanukitoid suites (~2.87 Ga), potassic leucogranites (~2.86 Ga) and the younger TTGs (Água Fria trondhjemite; ~2.86 Ga). The rocks of the LGdG suites are characterised by strongly fractionated REE patterns, with either no Eu anomaly or slight negative Eu anomalies, and show enrichment in Ba and, to a lesser degree, in Sr compared with the other Archean granitoids of the RMGGT. The LGdG have strong geochemical affinity with the high-Ca granites or Transitional TTG of the Yilgarn craton. The different models proposed to explain the origin of these granites are still controversial and apparently are not able to explain the genetic processes and evolution of the LGdG of the RMGGT. The dual geochemical character of the LGdG suites that share some features typical of the TTGs with others more commonly observed in the sanukitoid suites, suggest a complex evolution for these granites and a possible genetic link between them and the mentioned suites. On the basis of modelling and geochemical data we deduced that the LGdG suites could be possibly derived from mixing between a Ba-and Sr-enriched granite magma and trondhjemitic liquids. The granite magmas participating in the mixture originated by fractional crystallization of 35% of a sanukitoid magma of granodioritic composition leaving a residue consisting of plagioclase (46.72%), hornblende (39.05%), clinopyroxene (10.36%), magnetite (3.12%), ilmenite (0.7%) and allanite (0.06%). The large compositional variations observed in the Guarantã suite can be apparently explained by mixing in different proportions between the granite and trondhjemitic liquids. This large spectrum of variation could be augmented if it is assumed that fractional crystallization played a significant role in the evolution of the liquids formed by mixing processes.

The rocks of 2.87 Ga Rio Maria sanukitoid suite of the eastern Amazonian craton include granodiorites, intermediate rocks, layered rocks and mafic enclaves. Their REE patterns and the behavior of Rb, Ba, Sr, and Y allowed the distinction of a granodioritic (granodiorite and intermediate rocks) and a monzonitic (mafic enclaves) sanukitoid series. Petrogenetic modeling indicated that the granodiorites and intermediate rocks are not related by fractional crystallization. The internal evolution of the intermediate rocks were leaded by fractionation of amphibole + biotite ± apatite, whereas the granodiorites evolved by fractionation of plagioclase + amphibole ± biotite. The layered rocks were probably derived from the granodiorite magma by an accumulation of 50% of amphibole (dark layer) and of 30% of amphibole ± plagioclase (gray layer). The petrogenesis of the Rio Maria suite required melting of a modified mantle extensively metasomatized by addition of about 30% TTG-like melt to generate the granodiorite (11% of melt) and intermediate magmas (14% of melt), and ~20% TTG-like melt in the case of mafic enclave magma (9% of melt). Modeling and geochemical data, particularly the behavior of Sr and Y, suggest that mafic enclave and granodiorite magmas were originated at different depths and should have mingled during their ascent and final emplacement. The modal and geochemical differences observed between the granodioritic and monzonitic sanukitoid series of Rio Maria are apparently a general feature of the Archean sanukitoids. This indicates the existence of at least two distinct sanukitoid series and suggests that the nature of the sanukitoid series is strongly dependent of the pressure of magma generation. Our results indicate that the sanukitoid magmas were originated in a two stage process. The envisaged model admits an active subduction tectonic setting in the Rio Maria terrane in between 2.98 and 2.92 Ga when the TTG magmas responsible by the mantle metasomatism were generated (first stage). At ~2.87 Ga, a tectonothermal event, possibly related to slab-break-off or due to the action of a mantle plume, induced the partial melting of the metasomatized mantle and generated the Rio Maria sanukitoid magmas (second stage).

The Archean granites exposed in the Mesorchean Rio Maria granite-greenstone terrane (RMGGT), southeastern Amazonian craton can be divided into three groups on the basis of petrographic and geochemical data. (1) Potassic leucogranites (Xinguara and Mata Surrão granites), composed dominantly of biotite monzogranites that have high SiO 2 , K 2 O, and Rb contents and show fractionated REE patterns with moderate to pronounced negative Eu anomalies. These granites share many features with the low-Ca granite group of the Yilgarn craton and CA2-type of Archean calc-alkaline granites. These granites result from the partial melting of rocks similar to the older TTG of the RMGGT. (2) Leucogranodioritegranite group (Guarantã suite, Grotão granodiorite, and similar rocks), which is composed of Ba-and Sr-rich rocks which display fractionated REE patterns without significant Eu anomalies and show geochemical affinity with the high-Ca granite group or Transitional TTG of the Yilgarn craton and the CA1-type of Archean calc-alkaline granites. These rocks appear to have been originated from mixing between a Ba-and Sr-enriched granite magma and trondhjemitic liquids or alternatively product of interaction between fluids enriched in K, Sr, and Ba, derived from a metasomatized mantle with older TTG rocks. (3) Amphibole-biotite monzogranites (Rancho de Deus granite) associated with sanukitoid suites. These granites were probably generated by fractional crystallization and differentiation of sanukitoid magmas enriched in Ba and Sr. The emplacement of the granites of the RMGGT occurred during the Mesoarchean (2.87e2.86 Ga). They are approximately coeval with the sanukitoid suites (w2.87 Ga) and post-dated the main timing of TTG suites formation (2.98e2.92 Ga). The crust of Rio Maria was probably still quite warm at the time when the granite magmas were produced. In these conditions, the underplating in the lower crust of large volumes of sanukitoid magmas may have also contributed with heat inducing the partial melting of crustal protoliths and opening the possibility of complex interactions between different kinds of magmas.

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Researched results on geochemistry of major, trace and isotopic elements from igneous formations in NE Vietnam area have established a Sodium alkaline igneous Province (Chi Nguyen et al., 2004), which consist of a chain of alkaline igneous formations: ijolite-melteigite-jacupirangite-nepheline syenite rocks from Pia Ma massif (Tuyen Quang) toward SE distance ~200km via Bang Phuc massif (Bac Kan), and then to Ngoi Biec one (Yen Bai) towards SW~ 250km, they created a assemblage of alkaline ultramafic-mafic and nepheline syenite rocks at Viet Bac Craton, that is a part of South China Platform margin. The research on petrogenesis of the above mentioned alkaline rocks show that: 1) Alkaline ultramafic -mafic rocks and nepheline syenite has a very high content of (Na 2 O+K 2 O) from (1.94-8.4%) to (9.62-16.7%), high Al 2 O 3 from (6.88-16.93%) to (17.2 -24.32%) belong to both alkaline ultramafic-mafic groups and nepheline syenite rock. The P 2 O 5 content of those 2 groups is very high (0.7-1.10%). Agpait Index (AI) of nepheline syenite rocks < 1, but Na > K and Ca, Mg contents is high, showing nepheline syenite is the miaskitic type. The total content of (REE+Y) varies from 164÷432ppm with Ce/Y=2.83÷6.64,(La/Sm) N =4.12,(Ce/Sm) N =2.64, (Yb/Lu) N = 1.27, Eu/Eu*= 0.1-0.28. However, the range isotope content of Sr and Nd in whole rocks of Pia Ma and that of Cho Don are different, in Pia Ma: 0.705846 ÷ 0.706419 and 0.511831 ÷ 0.511975 with value of ε Nd = -2.35 ÷ +0.12 belong to EM1-type and aged in 519 ± 40Ma (Early Cambrian); in Cho Don: 0.709893 ÷ 0.718356 and 0.511854 ÷ 0.512010 with value of ε Nd = -9.79 to -2.9 belong to EM2-type and aged in 231 ± 23 Ma (Late Triassic ). 2) The geochemical characteristics of trace elements and isotope from above rocks indicated that, have fractional crystallization of a mixed magma liquid with composition of nephelinite derived from partial melting of depleted mantle source. This magma source may intruded into crust at Pia Ma in Early Paleozoic (Paleohotspot trace) and then at Cho Don and Ngoi Biec in Late Triassic (Mesohotspot traces) as they pass over "hotspot" in mantle. Possibly, this hotspot reactivated in Eocen and by the way to open the East Sea. The movenment speed of South China Plate towards North is about 0,7-2,2 mm/year.

Fine-scale, telluric-electric geophysical profiling is the geophysical method of choice for locating buried, possibly mineralized granite cupolas at the Silsilah tin deposit (lat 26°06' N., long 42°40' E.; MODS 3262). This method is accurate, rapid, and inexpensive. In this study, it proved to be more accurate than the more costly and time-consuming induced-polarization technique. For this study, six traverses measured electrical fields (a qualitative measurement of rock resistivity) at 27 and 270 Hz across grounded electrodes spaced 50 m apart. Little difference was seen between the 27-and 270-Hz profiles, suggesting that only one frequency may be necessary for similar studies in the future. This method is able to identify and distinguish among unroofed granite cupolas, cupolas with their aplite-pegmatite carapaces intact, strong (quartz-rich) greisens, weak (relatively quartz-poor) greisens, dikes, faults, and pervasively argillized rock, such as that encountered at Silsilah.

For decades, radiometric dating has been used as primary evidence for determining the age of the earth, and its organic and inorganic material. Through much controversy, the greater part of the scientific community of geologists, astronomers, and other fields insist that the earth is billions of years old. However, this field of science needs to be addressed with caution, as the past is neither observable nor can the theory of the age of the earth be ascertained based on radiometric dating. According to the laws of empirical science, what is considered as scientific knowledge (i.e. fact) can only be determined by direct observation or experimentation within time based on evidence gathered from the real known world rather than upon mere theory or speculation. A scientific theory is often an inference derived by related observable processes, whereby a conjecture can be made, while the process pertaining to the theory is left unobserved or not directly tested. The endeavor of determining the age of the earth inherently fails the necessary conditions for empirical science. While radiometric dating can be utilized and its accuracy tested with regard to modern day organisms and geological matter with known ages, its accuracy has no absolute reference point, derived from empirical science, with regard to organisms and geological structures older than what may be confirmed through other means of empirical science. The use of modern day radiometric dating to determine the age of the earth and old entities is at best a scientific theory. Something that is observable in the modern age, namely, rates of radioactive decay of isotopes, is used to make broad and unobservable conjectures with no scientific "control" or known standard. This cannot be denied, regardless of the staunchness of scientists and geologists who insist upon an old earth. In what follows, the theory, methodology, assumptions, and flaws of radiometric dating will be discussed.

Diamonds from George Creek, Colorado, preserve complex intergrowth textures between two major growth generations: homogeneous diamond with yellow-buff cathodoluminescence (CL); and diamond with blue-green CL and local growth zonation. Secondary-ion mass spectrometry (SIMS) has revealed large variations in N concentration and C isotope composition within these diamonds. Even within single stones, N contents and δ13C values can vary from 0 to 750 ppm and 0 to −20‰ respectively. These variations are similar to those recorded elsewhere for entire diamond suites. The CL characteristics correlate directly with N: diamond with yellow-buff CL has uniform N contents, whereas the zoned diamond has bright blue CL bands with high N (50–750 ppm) and dark blue or green CL bands with low N (0–20 ppm). These bands are too narrow (10–5 µm) for analysis by IR spectroscopy. δ13C also varies between the two growth generations in any one diamond plate, and to a lesser extent within these generations, bu...

The Yichun topaz-lepidolite granite is the youngest and most evolved unit of the Yichun granitic complex, southern China, and is well known by virtue of the unusual development of Ta-Nb-Li mineralization and enrichment in cesium in a granite. Three petrographic zones are recognized from the bottom upward: K-feldspar-rich facies, albite-rich facies, and albite-and K-feldsparrich facies. The Cs contents increase with fractional crystallization of the magma, and reach a maximum in the middle part of the albite-rich facies (1709 ppm). Two principal carriers of Cs are observed in this facies: pollucite and the Cs-dominant analogue of polylithionite. In the middle part of this facies, both minerals occur as small inclusions within quartz or K-feldspar phenocrysts, indicative of a magmatic origin. However, in the upper part of this facies, pollucite appears interstitially among tabular crystals of albite around K-feldspar phenocrysts, suggesting that this type of pollucite postdates the rock-forming minerals, but formed prior to complete crystallization of the silicate melt. In addition, Cs-rich replacement zones typify the rim of lepidolite flakes in the groundmass. Lepidolite may contain up to 25.8 wt% Cs 2 O, or ~0.9 Cs apfu (based on O = 11). Such lepidolite may be considered a Cs-dominant analogue of polylithionite. According to their distribution and compositional characteristics, pollucite and the Cs-dominant analogue of polylithionite seem to have formed at the late-magmatic or magmatic to hydrothermal transition stage of evolution of the leucogranitic magma at Yichun.

The Late Archean Taihua complex, mainly composed of amphibolite and TTG and TTG-like gneisses, is volumetrically most important metamorphic rock suites scattered along the southern margin of the North China Craton (NCC). Zircon SHRIMP U-Pb dating shows two episodes (2765 ± 13 and 2723 ± 9 Ma) of Archean magmatism in the Lushan area with distinct geochemical features. The early (2765 ± 13 Ma) suite (TTG-like gneisses) has low-SiO 2 (52.5-66.1 wt%), high-Mg # (0.47-0.68), low HREE (Yb N = 3.0-5.4) and Y (8.07-13.9 ppm) with low to moderate (La/Yb) N (6.7-37.1) and Sr/Y (25.9-119.3). The younger (2723 ± 9 Ma) suite (TTG gneisses) has high-SiO 2 (63.5-74.3 wt%), low-Mg # (0.13-0.52), very low REE (Yb N < 1.8) and Y (<4 ppm) with a wide range of (La/Yb) N (5.2-86.6), Sr/Y (71.4-949) and showing Eu/Eu* > 1 (1.20-2.43). Both suites show pronounced negative Nb-Ta and Ti anomalies on the primitive mantle-normalized spidergram. The TTG-like gneiss suite has similar bulk-rock Nd and zircon Hf model ages (∼3.0 Ga) with ε Nd (t) > 0 (0.26-1.46), and is interpreted as resulting from melt of mantle interactions with the melts derived from partial melting of subducted ocean crust with a residual assemblage of garnet + clinopyroxene + rutile ± amphibole, which favors subducted slab model for the late Archean TTG. The TTG gneiss suite has abundant relic zircons (2.95-2.80 Ga) with ε Nd (t) < 0 (-1.31 to -0.23), which is best interpreted as derived from partial melting of thickened lower continental crust with a garnet-amphibolite residue (garnet + amphibole ± rutile). Significant high-pressure fractional crystallization (garnet ± amphibole) and accumulation (plagioclase) are also required in the petrogenesis. The Lushan amphibolite with nearly flat primitive mantle-normalized trace-element pattern is interpreted to represent early ocean crust metamorphism. These observations suggest a possible model of late Archean crustal accretion from ocean crust to continental terrain in the southern North China Craton.

Several types of granites including alkaline granites and alkali feldspar granites are distributed in the Karamaili tectonic belt of East Junggar, Xinjiang, China. Some medium-small tin deposits are located within or near the contact zones of the granitic intrusions. The alkaline granites share all the features commonly observed in peralkaline A-type granites. They contain alkalic mafic minerals such as riebeckite and aegirine; have high contents of SiO 2 , alkalis, Rb, Th, Zr, Hf, REE (except Eu), and high ratios of FeO*/MgO and Ga/Al; and show strong depletions in Ba, Sr, Eu in the spidergrams. Laser ablation-ICPMS U-Pb zircon geochronology indicates a crystallization age of ca. 305 Ma for the granites; TIMS analyses of the granites found high ε Nd (T) values of +5.9 to +6.5. Considering their geochemical features, alkaline granites most likely formed by fractional crystallization of granodioritic magmas, which were probably produced by partial melting of lower crustal basaltic to andesitic rocks formed from oceanic crustal materials that were deeply buried during late Paleozoic subduction and accretion. Six molybdenite samples from the Sareshike tin deposit in East Junggar yielded an isochron age of 307 ± 11 Ma (2σ) and a weighted mean model age of 306.5 ± 3.4 Ma, consistent with zircon U-Pb ages of the alkaline granites. Low Re contents (0.323-0.961 ppm) in the molybdenite suggest that they originated from crustal sources related to the alkaline granites. Considering their identical ages, close spatial distribution, and similar sources, we argue that the A-type granites have a genetic relationship with the tin mineralization, and that the same association may be important elsewhere.

More than half the patients with rectal cancer present with locally advanced rectal disease at diagnosis with a high risk of recurrence. Preoperative chemoradiotherapy and standardized radical surgery with total mesorectal excision have been established as the 'gold standard' for treating these patients. Pathological staging using the ypTNM classification system to decide on adjuvant chemotherapy (ACT) is widely used in clinical practice, but the delivery of ACT is still controversial, as many discrepancies persist in the conclusions of different trials, due to heterogeneity of the inclusion criteria between studies, lack of statistical power, and variations in preoperative and adjuvant regimens. In 2014, a meta-analysis of four randomized phase-III trials (EORTC 22921, I-CNR-RT, PROCTOR-SCRIPT, CHRONICLE) failed to demonstrate any statistical efficacy of fluorouracil (5FU)-based ACT. Three recent randomized trials aimed to compare 5FU with 5FU plus oxaliplatin-based chemotherapy. Two of them (ADORE, CAO/ARO/AIO-04) appeared to find a disease-free survival benefit for patients treated with the combination therapy. Thus, while awaiting new data, it can be said that, as of 2015, patients with yp stage I tumors or histological complete response derived no benefit from adjuvant therapy. On the other hand, the FOLFOX chemotherapy regimen should be proposed for

CHAPTER 1 Table 1. Summary of Hypotheses for the Origin of Andesites GENERAL HYPOTHESIS SPECIFIC PROPOSAL P a rtia l melting of mantle Generation of 'andesitic liq u id s ' with p e rid o tite . small degrees of p a rtia l melting a t high fH20 (

CHAPTER 1 Table 1. Summary of Hypotheses for the Origin of Andesites GENERAL HYPOTHESIS SPECIFIC PROPOSAL P a rtia l melting of mantle Generation of 'andesitic liq u id s ' with p e rid o tite . small degrees of p a rtia l melting a t high fH20 (

The Cenozoic Mormon Mountain Volcanic Field (MMVF) of northern Arizona is situated in the transition zone between the Basin and Range and the Colorado Plateau. It is composed of alkalic to sub-alkalic basalts and calcalkalic andesites, dacites, and rhyodacites. Despite their spatial and temporal association, the basalts and the calcalkalic suite do not seem to be co-genetic. The petrogenesis of primitive MMVF basalts can be explained as the result of different degrees of partial melting of a relatively homogenous, incompatible element-enriched peridotitic source. The variety of evolved basalt types was the result of subsequent fractional crystallization of olivine, spinel, and clinopyroxene from the range of primitive basalts. Crustal contamination seems to have occurred, but affected only the highly incompatible element abundances. The formation of MMVF calcalkalic rocks is most readily explained by small to moderate amounts of partial melting of an amphibolitic lower crust. This source is LREE-enriched but depleted in Rb and relatively unradiogenic Sr (SVSr/S6Sr ~0.7040). Calcalkalic rhyodacites may also be derived from andesitic parents by fractional crystallization. The overall petrogenesis of the MMVF complex is the result of intra-plate volcanism where mantle-derived magmas intrude and pass through thick continental crust.

Flg. 1. Optical photographs of melt inclusions. (A) Two remelted inclusions showing glass (g) trapped M. L. Rivers and S. R. Sunon, Dcpamnent of Applied sciena, ~~k h ~~~~ ~~~i ~~~l ~~b ~~~~~, upton, NY in quartz (q) and an associated vapor bubble (b). (8) In a leaked glassy inclusion, a capillary connects 11973. the low-H,O glass and a vapor bubble to the outside of the host quartz. (C) Devitrified inclusions in quartz can be heated and cooled to produce remelted inclusions (D) that are hydrous and contain several *To whom comspondence should be addressed. small vapor bubbles.

Glass Mountain, California, consists of > 50 km 3 of high-silica rhyolite lavas and associated pyroclastic deposits that erupted over a period of > 1 my preceding explosive eruption of the Bishop Tuff and formation of the Long Valley caldera at 0.73 Ma. These "minimum-melt" rhyolites yield Fe-Ti-oxide temperatures of 695-718~ and contain sparse phenocrysts of plagioclase + quartz + magnetite + apatite + sanidine, biotite, ilmenite, allanite, and zircon. Incompatible trace elements show similar or larger ranges within the Glass Mountain suite than within the Bishop Tuff, despite a much smaller range of major-element concentrations, largely due to variability among the older lavas (erupted between 2.1 and 1.2 Ma). Ratios of the most incompatible elements have larger ranges in the older lavas than in the younger lavas (1.2-0.79 Ma), and concentrations of incompatible elements span wide ranges at nearly constant Ce/Yb, suggesting that the highest concentrations of these elements are not the result of extensive fractional crystallization alone; rather, they are inherited from parental magmas with a larger proportion of crustal partial melt. Evidence for the nature of this crustal component comes from the presence of scarce, tiny xenocrysts derived from granitic and greenschist-grade metamorphic rocks. The wider range of chemical and isotopic compositions in the older lavas, the larger range in phenocryst modes, the eruption of magmas with different compositions at nearly the same time in different parts of the field, and the smaller volume of individual lavas suggest either that more than one magma body was tapped during eruption of the older lavas or that a single chamber tapped by all lavas was small enough that the composition of its upper reaches was easily affected by new additions of crustal melts. We interpret the relative chemical, mineralogical, and isotopic homogeneity of the younger Glass Mountain lavas as reflecting eruptions from a large, integrated magma chamber. The small number of eruptions between 1.4 and 1.2 Ma may have allowed

San Antonio Volcano, in the Tacaná Volcanic Complex, erupted ~1950 yr. B.P., with a Pelean type eruption that produced andesitic pyroclastic surges and block-and-ash flows destroying part of the volcano summit and producing a horse-shoe shaped crater open to the SW. Between 1950 and 800 yr B.P. the eruption continued with effusive andesites followed by a dacite lava flow and a summit dome, all from a single magma batch. All products consist of phenocrysts and microphenocrysts of zoned plagioclase, amphibole, pyroxene, magnetite ± ilmenite, set in partially crystallized groundmass of glass and microlites of the same mineral phases, except for the lack of amphibole. Included in the andesitic blocks of the block-and-ash flow deposit are basaltic andesite enclaves with elongated and ellipsoidal forms and chilled margins. The enclaves have intersertal textures with brown glass between microphenocrysts of plagioclase, hornblende, pyroxene, and olivine, and minor proportions of phenocrysts of plagioclase, hornblende, and pyroxene. A compositional range obtained of blocks and enclaves resulted from mixing between andesite (866 °C ± 22) and basaltic andesite (enclaves, 932 °C ± 22), which may have triggered the explosive Pelean eruption. Vestiges of that mixing are preserved as complex compositional zones in plagioclase and clinopyroxene-rich reaction rims in amphibole in the andesite. Whole-rock chemistry, geothermometry, experimental petrology and modeling results suggest that after the mixing event the eruption tapped hybrid andesitic magma (≤900 °C) and ended with effusive dacitic magma (~825 °C), all of which were stored at ~200 MPa water pressure. A complex open-system evolution that involved crustal end-members best explains the generation of effusive dacite from the hybrid andesite. Amphibole in the dacite is rimmed by reaction products of plagioclase, orthopyroxene, and Fe-Ti oxides produced by decompression during ascent. Amphibole in the andesite, however, lacks such rims. Because the andesite was at 866 ± 22 °C and the dacite was at ~825 °C, the reaction rims indicate that the andesitic magma ascended at 0.023 m s -1 during the explosive phase of the eruption, whereas the dacitic magma rose more slowly at ~0.002-0.004 m s -1 .

Major, trace element and isotopic data for mafic to peralkaline silicic volcanic rocks from the northern sector of the main Ethiopian rift are discussed with the aim of placing constraints on processes of magma genesis and evolution and to present models for magma plumbing systems of rift volcanoes. Basalts straddle the subalkaline-alkaline boundary and exhibit important variations of incompatible element abundances and ratios. Silicic rocks consist of dominant pantellerites and minor comendites and trachytes, although some volcanoes along the rift shoulders consist entirely or predominantly of trachytes. Rocks with intermediate compositions are very scarce. Mafic and silicic rocks exhibit similar values as some basalts for many incompatible element and radiogenic isotopic ratios. Geochemical and petrological modelling shows that the most likely petrogenetic process for rift magmatism is a derivation of rhyolites from basalts by dominant fractional crystallisation occurring at shallow depths. Variations of incompatible element ratios and radiogenic isotopes in the basalts suggest heterogeneous sources and significant interaction with the crust. In contrast, the role of crustal assimilation during evolution of silicic magmas is negligible. It is suggested that large amounts of basalts were emplaced both into the lower continental crust, and at shallow depths. Shallow level fractional crystallisation generated zoned magma chambers with rhyolitic melts accumulating at the top, and mafic magmas ponding at the bottom. Volcanic activity was fed preferentially by the upper rhyolitic layer, whereas mafic magmas were erupted only accidentally, when extensional faults intersected the bottom of shallow reservoirs or tapped directly the deep magma chambers. The presence of trachytic volcanoes along the rift shoulders could result from clinopyroxene-dominated high-pressure basalt fractionation, which did not allow melts to reach rhyolitic compositions. Satellite imagery and field studies reveal the occurrence of a large number of caldera collapses in the main Ethiopian rift, suggesting that several magma chambers have been formed at shallow depths, possibly favoured by block tilting and strike-slip faulting. This explains the huge amounts of silicic rocks along the northern Ethiopian rift. The occurrence of huge magma reservoirs is also supported by positive gravity anomalies detected by previous studies beneath several silicic volcanic centres.

After the IUGS definition (Le Maitre et al., 1989), ankaramite is a porphyritic melanocratic basanite with abundant phenocrysts of pyroxene and olivine. These rocks were firstly defined by Lacroix (1916), in their type locality of Ankaramy, at Ampasindava, Madagascar. Ocurrences of ...

Duhem&#x27;s Theorem applied to igneous systems has stimu-lated petrologists to examine simultaneously the extensive and intensive propenies of the system. Simultaneous solu-tion of equations for material balance and thermodynamic equilibrium in a closed magma-system, at known ...

The Gföhl Unit is the largest migmatite terrain of the Variscan orogenic root domain in Europe. Its genesis has been until now attributed to variable degrees of in situ partial melting. In the Rokytná Complex (Gföhl Unit, Czech Republic) there is a wellpreserved sequence documenting the entire migmatitization process on both outcrop and regional scales. The sequence starts with (i) banded orthogneiss with distinctly separated monomineralic layers, continuing through (ii) migmatitic mylonitic gneiss, (iii) schlieren migmatite characterised by disappearance of monomineralic layering and finally to (iv) felsic nebulitic migmatite with no relics of the original banding. While each type of migmatite shows a distinct whole-rock geochemical and Sr-Nd isotopic fingerprint, the whole sequence evolves along regular, more or less smooth trends for most of the elements. Possible mechanisms which could account for such a variation are that the individual migmatite types (i) are genetically unrelated, (ii) originated by equilibrium melting of a single protolith, (iii) formed by disequilibrium melting (with or without a small-scale melt movement) or (iv) were generated by melt infiltration from external source. The first scenario is not in agreement with the field observations and chemistry of the orthogneisses/migmatites. Neither of the remaining hypotheses can be ruled out convincingly solely on whole-rock geochemical grounds. However in light of previously obtained structural, petrologic and microstructural data, this sequence can be interpreted as a result of a process in which the banded orthogneiss was pervasively, along grain boundaries, penetrated by felsic melt derived from an external source. In terms of this melt infiltration model the individual migmatites can be explained by different degrees of equilibration between the bulk rock and the passing melt. The melt infiltration can be modelled as an open-system process, characterised by changes of the total mass/volume and accompanied by gains/losses in many of the major-and trace elements. The modelling of the mass balance resulted in identification of a component added by a heterogeneous nucleation of feldspars, quartz and apatite from the passing melt. This is in line with the observed presence of new albitic plagioclase, K-feldspar and quartz coatings as well as resorption of relict feldspars. At the most advanced stages (schlieren and nebulitic migmatites) the whole-rock trace-element geochemical variations document an increasing role for fractional crystallization of the K-feldspar and minor plagioclase, with accessory amounts of monazite, zircon and apatite.

A suite of peralkaline trachytes from Longonot volcano, Kenya, which erupted during the last 6000 years, has been analysed for major and trace elements, Pb and Nd isotopes, and U-Th-Ra disequilibria. The lavas are divided into three stratigraphic groups of trachytes (Lt 2 a, Lt 2 b and Lt 3 ), and hybrid lavas, designated LMx 1 and LMx 2 , which, respectively, pre-date and post-date the Lt 2 lavas. Major and trace elements are consistent, with up to 37% within-group fractional crystallization of predominantly alkali feldspar. The parental magma for the different trachyte groups had a more mafic composition-probably hawaiitic. Nd and Pb isotopes show minimal variation, both within and between magma groups, and indicate that up to 10% comendite magma from the neighbouring Olkaria volcanic field may have intermixed with the Longonot magma. ( 230 Th/ 238 U) disequilibria indicate that limited U/Th fractionation occurred during the past 10 kyr, whereas ( 226 Ra/ 230 Th) disequilibria reflect the effect of alkali feldspar fractionation >8 kyr ago in the Lt 2 a lavas, between 3 and 7 kyr ago in the Lt 2 b lavas and in the past 3 kyr for the Lt 3 lavas. ( 226 Ra/ 230 Th) disequilibria in the Lt 2 b lavas are interpreted using a model that combines the equations of radioactive decay and in-growth with Rayleigh crystallization to give fractionation rates of about 0Á2 Â 10 À4 /year for the evolution of hawaiite to trachyte, but more rapid rates of up to 3 Â 10 À4 /year for fractionation within the trachyte sequence. ( 226 Ra/ 230 Th) from two whole-rockalkali feldspar pairs are interpreted to show the crystals formed at 5800 years BP (Lt 2 b) and 2800 years BP (Lt 3 ), implying that phenocryst formation continued almost up to the time of eruption. The results strongly indicate that fractionated magmas can be stored for periods on the order of 1000-2500 years prior to eruption, whereas other magmas were erupted as fractionation was proceeding.

Tholeiite basalts from 60~ to 65~ on the Mid-Atlantic Ridge were melted and recrystallized at atmospheric pressure in a CO2-H2 gas mixture. Seven basalts are from the Langjokull-Thingvellir volcanic zone and the Reykjanes Peninsula of Iceland and nine are from the Reykjanes Ridge. The crystallization sequence in both Iceland and Reykjanes Ridge basalts with (Total Fe as FeO)/(Total Fe as FeO+ MgO) [F/F+M] less than 0.6 is olivine, plagioclase, clinopyroxene. Chromian spinel crystallizes before plagioclase in one Iceland and one Reykjanes Ridge basalt with F/F+M less than 0.57. Chemical differences of the two groups of basalts (lower SiO2 and higher alkalis in Iceland basalts) can not simply be a result of low pressure fractional crystallization. Liquidus temperatures of the seven Iceland basalts decreases from 1,230~ to 1,170~ as the F/F+M of the rock increases from 0.52 to 0.70. The liquidus temperatures of the Reykjanes Ridge basalts are about 10 ~ C lower than those of the Iceland basalts for the same F/F + M value. The profile of measured liquidus temperatures from 65 ~ N on Iceland to 60 ~ N on the Reykjanes Ridge has a minimum value at 63.2 ~ N on the Reykjanes Ridge just south of Iceland. Model calculations of the pressure of phenocryst crystallization indicate that olivine and plagioclase in Langjokull basalts could have equilibrated between 2.0 and 6.2 kb (200 to 620 MPa). Phenocryst assemblages in Reykjanes Ridge basalts at 60 ~ N could have crystallized together at greater than 2 kb (200 MPa) and probably less than 8 kb (800 MPa). A minimum in the equilibrium pressure of phenocryst crystallization occurs between 62.9 ~ and 64~ and coincides with the minimum in the experimentally determined liquidus temperatures. The more extensive fractionation at low pressure in this area could be related to the shift of the Mid-Atlantic Ridge axis along the

We analyzed the Steinbach IVA stony-iron meteorite using scanning electron microscopy (SEM), electron microprobe analysis (EMPA), laser ablation inductively-coupled-plasma mass spectroscopy (LA-ICP-MS), and modeling techniques. Different and sometimes adjacent low-Ca pyroxene grains have distinct compositions and evidently crystallized at different stages in a chemically evolving system prior to the solidification of metal and troilite. Early crystallizing pyroxene shows evidence for disequilibrium and formation under conditions of rapid cooling, producing clinobronzite and type 1 pyroxene rich in troilite and other inclusions. Subsequently, type 2 pyroxene crystallized over an extensive fractionation interval. Steinbach probably formed as a cumulate produced by extensive crystal fractionation (~60-70% fractional crystallization) from a high-temperature (~1450-1490 °C) silicate-metallic magma. The inferred composition of the precursor magma is best modeled as having formed by ≥30-50% silicate partial melting of a chondritic protolith. If this protolith was similar to an LL chondrite (as implied by O-isotopic data), then olivine must have separated from the partial melt, and a substantial amount (~53-56%) of FeO must have been reduced in the silicate magma. A model of simultaneous endogenic heating and collisional disruption appears best able to explain the data for Steinbach and other IVA meteorites. Impact disruption occurred while the parent body was substantially molten, causing liquids to separate from solids and oxygen-bearing gas to vent to space, leading to a molten metal-rich body that was smaller than the original parent body and that solidified from the outside in. This model can simultaneously explain the characteristics of both stony-iron and iron IVA meteorites, including the apparent correlation between metal composition and metallographic cooling rate observed for metal.

The petrography and mineral and bulk chemistries of silicate inclusions in Sombrerete, an ungrouped iron that is one of the most phosphate-rich meteorites known, was studied using optical, scanning electron microscopy (SEM), electron microprobe analysis (EMPA), and secondary ion mass spectrometry (SIMS) techniques. Inclusions contain variable proportions of alkalic siliceous glass (~69 vol% of inclusions on average), aluminous orthopyroxene (~9%, Wo 1-4 Fs 25-35 , up to ~3 wt% Al), plagioclase (~8%, mainly An 70-92 ), Cl-apatite (~7%), chromite (~4%), yagiite (~1%), phosphaterich segregations (~1%), ilmenite, and merrillite. Ytterbium and Sm anomalies are sometimes present in various phases (positive anomalies for phosphates, negative for glass and orthopyroxene), which possibly reflect phosphate-melt-gas partitioning under transient, reducing conditions at high temperatures. Phosphate-rich segregations and different alkalic glasses (K-rich and Na-rich) formed by two types of liquid immiscibility. Yagiite, a K-Mg silicate previously found in the Colomera (IIE) iron, appears to have formed as a late-stage crystallization product, possibly aided by Na-K liquid unmixing. Trace-element phase compositions reflect fractional crystallization of a single liquid composition that originated by low-degree (~4-8%) equilibrium partial melting of a chondritic precursor. Compositional differences between inclusions appear to have originated as a result of a "filter-press differentiation" process, in which liquidus crystals of Cl-apatite and orthopyroxene were less able than silicate melt to flow through the metallic host between inclusions. This process enabled a phosphoran basaltic andesite precursor liquid to differentiate within the metallic host, yielding a dacite composition for some inclusions. Solidification was relatively rapid, but not so fast as to prevent flow and immiscibility phenomena. Sombrerete originated near a cooling surface in the parent body during rapid, probably impact-induced, mixing of metallic and silicate liquids. We suggest that Sombrerete formed when a planetesimal undergoing endogenic differentiation was collisionally disrupted, possibly in a breakup and reassembly event. Simultaneous endogenic heating and impact processes may have widely affected silicate-bearing irons and other solar system matter. b "Na-glass" and "K-glass" counts include glass-rich mesostases that contain orthopyroxene crystallites and minor phosphate and plagioclase. c Average weighted by count area. d Includes Na-K-glass 17, 18, 6, 14) and Na-glass (other objects). e Plagioclase-glass intergrowths (spongy plagioclase). f P-rich segregations (phosphate-rich arcs and orb). g Mixed phase composed of an intergrowth of at least two phases, possibly Ti-oxide + pyroxene.

The textures and mineral chemistries of silicate inclusions in the Udei Station (IAB) and Miles (fractionated IIE) iron meteorites were studied using optical and electron microscopy, SEM, EMPA, and LA-ICP-MS techniques to better understand the origin of silicate-bearing irons. Inclusions in Udei Station include near-chondritic, basaltic/gabbroic, feldspathic orthopyroxenitic, and harzburgitic lithologies. In Miles, most inclusions can be described as feldspathic pyroxenite or pyroxeneenriched basalt/gabbro. The trace-element compositions of both orthopyroxene and plagioclase grains are similar in different lithologies from Udei Station; whereas in different inclusions from Miles, the compositions of orthopyroxene grains are similar, while those of clinopyroxene, plagioclase, and especially Cl-apatite are variable. Orthopyroxene in Miles tends to be enriched in REE compared to that in Udei Station, but the reverse is true for plagioclase and clinopyroxene. The data can be explained by models involving partial melting of chondritic protoliths, silicate melt migration, and redox reactions between silicate and metal components to form phosphate. The extent of heating, melt migration, and phosphate formation were all greater in Miles. Silicates in Miles were formed from liquids produced by $30% partial melting of a chondritic precursor brought to a peak temperature of $1250 °C. This silicate melt crystallized in two stages. During Stage 1, crystallizing minerals (orthopyroxene, clinopyroxene, chromite, and olivine) were largely in equilibrium with an intercumulus melt that was evolving by igneous fractionation during slow cooling, with a residence time of $20 ka at $1150 °C. During Stage 2, following probable re-melting of feldspathic materials, and after the silicate "mush" was mixed with molten metal, plagioclase and phosphate fractionally crystallized together during more rapid cooling down to the solidus. In Udei Station, despite a lower peak temperature (<1180 °C) and degree of silicate partial melting ($3-10%), silicate melt was able to efficiently separate from silicate solid to produce melt residues (harzburgite) and liquids or cumulates (basalt/gabbro, feldspathic orthopyroxenite) prior to final metal emplacement. Olivine was generally out of equilibrium with other minerals, but orthopyroxene and plagioclase largely equilibrated under magmatic conditions, and clinopyroxene in basalt/gabbro crystallized from a more evolved silicate melt. We suggest that a model involving major collisional disruption and mixing of partly molten, endogenically heated planetesimals can best explain the data for IAB and fractionated IIE silicate-bearing irons. The extent of endogenic heating was different (less for the IABs), and the amount of parent body disruption was different (scrambling with collisional unroofing for the IAB/IIICD/winonaite body, more complete destruction for the fractionated IIE body), but both bodies were partly molten and incompletely differentiated at the time of impact. We suggest that the post-impact secondary body for IAB/ IIICD/winonaite meteorites was mineralogically zoned with Ni-poor metal in the center, and that the secondary body for fractionated IIE meteorites was a relatively small melt-rich body that had separated from olivine during collisional break-up.

The Weekeroo Station IIE iron meteorite contains a variety of felsic and mafic inclusions enclosed in an FeNi-metal host. Petrographic, EMP, and SIMS data suggest that the petrogenesis of the silicates was complex, and included differentiation, remelting, FeO-reduction, and dynamic mixing of phases. Differentiation produced a variety of olivine-free inclusion assemblages, ranging from pyroxene ϩ plagioclase ϩ tridymite with peritectic compositions, to coarse orthopyroxene, to plagioclase ϩ tridymite and its glassy equivalent. Individual phases have similar trace-element abundances and patterns, despite large variations in inclusion textures, modes, and bulk compositions, probably as a result of mechanical separation of pre-existing phases in an impact event that dynamically mixed silicates with the metallic host. Traceelement data imply that augite and plagioclase grains in different inclusions crystallized from the same precursor melt, characterized by relatively unfractionated REE abundances of ϳ20 -30 ϫ CI-chondrites except for a negative Eu anomaly. Such a precursor melt could have been produced by ϳ2-5% equilibrium partial melting of an H-chondrite silicate protolith, or by higher degrees of partial melting involving subsequent fractional crystallization. Glass appears to have formed by the remelting of pre-existing plagioclase and orthopyroxene, in a process that involved either disequilibrium or substantial melting of these phases. During remelting, silicate melt reacted with the FeNi-metal host, and FeO was reduced to Fe-metal. Following remelting and metal-silicate mixing, inclusions apparently cooled at different rates in a near-surface setting on the parent body; glass-or pigeonite-bearing inclusions cooled more rapidly (Ն2.5°C/hr between 1000 -850°C) than pigeonite-free, largely crystalline inclusions. The results of this study point to two likely models for forming IIE iron meteorites, both involving collision between an FeNi-metal impactor and either a differentiated or undifferentiated silicate-rich target of Hchondrite affinity. Each model has difficulties and it is possible that both are required to explain the diverse IIE group.

This study presents the results of mineral chemistry data of Meso-Cenozoic volcanic rocks of Livingston, Robert and Ardley islands (South Shetland Arc, Antarctica). These rocks include basalts and basaltic andesites that exhibit pilotaxitic, intergranular, and intersertal textures. Glomeroporphyritic clusters consist of phenocrysts of plagioclase, augite, and Ti-magnetite or only plagioclase. The rocks are composed of plagioclase, augite, olivine, Ti-magnetite, and ilmenite phenocrysts. Geochemistry studies indicate that these rocks are rich in Al 2 O 3 , Rb, Ba, Sr, and show enrichment in LREE relative to HREE. The Ni, Cr, Co, and MgO contents are lower than primary compositions, and demonstrate that these magmas are evolved. Mineral chemistry indicates that the volcanic rocks belong to the calc-alkaline series typical of island arcs. Plagioclase crystals are mostly bytownite and labradorite in Livingston and Robert islands. Nevertheless, some Robert Island phenocrysts are of anorthite composition. The plagioclase of volcanic rocks of Ardley Island is only labradorite. Augite is the main mafic phase (Wo 23-48 , En 40-58 , Fs 9-21 ) in all studied islands. Olivine shows a chrysolite composition. Oxide phases are represented by Ti-magnetite and ilmenite. The evaluation of whole-rock geochemistry and mineral chemistry supports the hypothesis of fractional crystallization for the evolution of the rocks of Livingston, Robert, and Ardley islands. Geothermometry for olivine-clinopyroxene pairs suggests a crystallization temperature of 962°C ± 10°C (1 bar) and of 965°C ± 10°C (500 bars).

Volcanic rocks that make up Faial Island, Central Azores, consist of four volcanostratigraphic units, with ages between 730 ka and the present. Lavas range from alkali basalts to trachyandesites and belong to the alkaline-sodic series. The oldest unit is the Ribeirinha Volcanic Complex, generally characterized by low MgO contents. The Cedros Volcanic Complex is composed of basalts to benmoreites with low MgO contents. The Almoxarife Formation represents fissure flows, containing MgO contents similar to to slightly higher than those of the underlying Cedros Volcanic Complex. The youngest unit, the Capelo Formation, consists of mafic rocks with MgO values higher than those of the other units. Bulk-rock major and trace element trends suggest that differentiation of the three earliest units were dominated by fractional crystallization of plagioclase ± clinopyroxene ± olivine ± titanomagnetite. Capelo bulk-rock compositions are the most primitive, and are related to a period when volcanic activity was fed by deep magmatic chambers, and melts ascended more rapidly. Comparison among geochemical patterns of the trace elements suggests a strong similarity between the lavas from Faial and Pico islands. Corvo Island volcanism contrasts with the geochemistry of Faial and Pico lavas, reflecting its strong K and Rb depletion, and Th, U, Ta, Nb, La, and Ce enrichment. Absence of the Daly gap in the Faial volcanics is attributed to early crystallization of Ti-Fe oxides. The probable source of the Faial magma coincides with the MORB-FOZO array, which implies the presence of ancient recycled oceanic crust in the mantle source. Ratios of incompatible trace elements suggest the similarity of Corvo volcanic rocks with magmas derived from HIMU sources, whereas the Faial and Pico volcanic rocks could have been produced from sources very close to EMII-type OIB.

Oligo-Miocene Bagh-e-Khoshk granitoid stock is intruded into the Eocene volcanic rocks in the southeastern part of the Urumieh-Dukhtar Magmatic assemblage in Iran. The granitoids are mainly consisting of diorite, quartz diorite and granodioritic rock types. They are metaluminous to slightly peraluminous, medium to high K calc-alkaline, with SiO2 ranging from 50.2 to 66 wt.%. The major elements mostly define linear trends and negative slopes with increasing of SiO2, while K2O is positively correlated with silica. There is a higher content of Ba, Rb, Nb and Zr elements with increasing SiO2, whereas Sr shows an opposite behavior. Primordial mantle-normalized multi-element patterns show enrichment in LILE relative to HFSE with distinctive Nb, Ta, Ti negative anomalies. These signatures are typical of subduction related magmas that formed in an active continental margin. The high Ba/La Ba/TiO2, Ba/Nb and Th/Nb ratios emphasizes the significant involvement of fluids during subduction processes. The chondrite-normalized REE patterns of the Bagh-e-Khoshk granitoids show an enrichment in light REEs ((La/Yb)n = 3.84, 7.41), very slightly HREE fractionation patterns ([Gd/Yb]n=1.26–1.83)  and small positive Eu anomalies (EuN/EuN* = 1.01, 1.44) in diorites. Whole-rock Sm–Nd isotope analysis give εNd values (+2.91 to +3.29) and Sr ratios (0.7046–0.7053). The geochemical characteristics, positive εNd and low Sr ratios of the Baghe-Khoshk granitoids suggest their formation from partial melting of the mantle wedge source, at pressures below the garnet stability field, modified by fluids during subduction processes.

The South Safaga area, Central Eastern Desert of Egypt, comprises an undeformed Dokhan Volcanic suite, which is temporally and spatially associated with immature clastic sediments belonging to the Hammamat Group. Undeformed high level leucogranite intrusions and dykes have invaded these volcanic rocks whereas relatively more deformed lithologies, represented by a syn-tectonic metavolcano-sedimentary association and an I-type tonalite-granodiorite underlie them. The Dokhan Volcanic suite consists of two units: (1) a mafic unit composed of basalt, basaltic andesite, andesite, dacite and their pyroclastic equivalents, (2) a felsic unit of rhyodacite and rhyolite composition in addition to welded flow tuffs. The chemical data of the entire suite show general trends of increasing contents of incompatible elements (K 2 O, Rb, Nb, Y, and Th), and decreasing contents of elements compatible with clinopyroxene, feldspars, and magnetite (e.g. MgO, Fe 2 O 3 * , Al 2 O 3 , CaO, TiO 2 , Ni, Sr, and Ba) with increasing SiO 2 . Although these variations are consistent with closed system fractional crystallization processes, the slightly wide variation of Rb/Zr and La/Sm in the felsic volcanics may indicate random crustal contamination during the evolution of these rocks. Normalized trace element patterns show enrichment in LILEs (Rb, Ba, K, Th, and Ce) relative to HFSEs (Nb, Zr, P, and Ti) and are very similar to calc-alkaline subduction-related rocks from orogenic belts. However, the stratigraphic position of the Dokhan Volcanic rocks in relation to the major structural features and tectono-metamorphic events in the Eastern Desert of Egypt suggests that these rocks post-date active subduction. They were emplaced during a post-orogenic extensional collapse event that follows continental collision during late stages of the late Neoproterzoic Pan-African crustal evolution. Major and trace element arc signature of these rocks indicate partial melting of a lithospheric mantle enriched during a previous long subduction event in the Arabian-Nubian Shield. Further investigation of the regional significance of the Dokhan Volcanic rocks and their associated clastic sediments shows that the extensional episode during which these rocks were formed is a regional one.

Three distinctive metaluminous granitic suites have been identi®ed from the Pan-African belt of the Kab Amiri area, Eastern Desert, Egypt. These are: 1) a trondhjemitetonalite suite, 2) a calc-alkaline granodiorite suite, and 3) an alkali leucogranite suite. The trondhjemite-tonalite and the granodiorite suites resemble I-type granitoids whereas the alkali leucogranites display A-type characteristics. Geochemical attributes and ®eld aspects indicate that three independent magmas, at different tectonic stages of the Pan-African crustal growth, are required to explain the origin of these granitoid suites. Rocks of the trondhjemite-tonalite suite correspond to granites of the arc stage and possess a narrow range of SiO 2 with low K 2 O, Sr, Rb, Ba, Nb and Zr. Its composition is consistent with 20±30% partial melting of a primitive low-K tholeiitic source, similar to the early formed tholeiitic metavolcanics of the Egyptian basement. The granodiorite suite belongs to the collision stage and displays higher K 2 O, Rb, Ba, and Sr. Its magma was derived by 30±40% partial melting of LILE-enriched ma®c island arc crust. The presence of abundant microdiorite enclaves in the trondhjemite-tonalite and the granodiorite suites suggests that mantle-derived ma®c magma played an important role in their petrogenesis, acting as a heat source for melting via underplating and=or intrusion. The A-type leucogranites are post-collision highly fractionated granites. They exhibit low Al 2 O 3 , MgO, CaO, TiO 2 , Sr, and Ba and high Rb, Nb, Y. The wide chemical variations within this suite are consistent with its evolution by fractional crystallization of plagioclase, K-feldspar, amphibole, Fe±Ti oxides, and apatite from a ma®c magma. The parent magma was originated in the upper mantle due to crustal attenuation associated with extension in the late stage of the Pan-African crustal evolution.

The Upper Proterozoic volcanism of northwestern Africa is characterized by the predominance of calc-alkaline rocks. Volcanics with tholeiitic affinities and alkali basalts are rare. The geochemistry and the relative proportions of calc-alkaline rocktypes in the Silet zone (Algeria) and the Ouarzazate formation (Morocco) are similar to those of recent island arc suites where basalts are most abundant while in the Tassendjanet and Gara Akofo zones (Algeria) they resemble contintal margin volcanic suites with a predominance of andesites. The volcanic rocks have undergone low-grade metamorphism which strongly affected alkali and alkali-earth elements and also to a smaller degree, the less mobile elements such as REE, Zr, Hf, Nb, and P. The geochemistry of the calc-alkaline rocks point to a complex origin involving low-pressure fractional crystallization, crustal contamination and derivation from a source already enriched in LILE.

The Francistown plutonic rocks at the southwestern margin of the Zimbabwe craton consist of three igneous suites: Sanukitoid, Tonalite-Trondhjemite-Granite (TTG) suites and High-K granites. The TTG suite is subdivided into High Aluminum-TTG (HA-TTG) and Low Aluminum-TTG (LA-TTG) sub-suites. Their Rb-Sr isotope systems were partially homogenized by post-crystallization thermo-tectonic events, in which hydrothermal solutions and migmatization played an important role. Therefore, the Rb-Sr isochron age of 2427±54 Ma can only be regarded as a lower limit to the Francistown plutonic rock age. The large errors in the Sm-Nd isochron dates of Francistown granitoids indicate that these dates are not really constrained. In this study we compared the rock types of Francistown and adjacent areas, adopting the precise U, Th-Pb single zircon SHRIMP ages from the Vumba area as references. For TTG and Sanukitoid suites, the age we adopted is ca. 2.7 Ga, which is close to their depleted-mantle Sm-Nd model ages (T DM ). For High-K granites, the age adopted is ca. 2.65 Ga, which is also close to their Sm-Nd isochron age. The highest e Nd t values of Sanukitoids and TTG are +2.1 and +2.3, respectively. The positive e Nd t values and trace element geochemistry support partial melting of a depleted mantle and young oceanic crust for the genesis of Sanukitoid and the TTG suites respectively. The lowest e Nd t values of Sanukitoids and TTGs are À1.0 and À1.1, respectively, indicating contamination by continental crust, up to 10 and 14%, respectively. The e Nd t values of TTG decrease with decreasing Al 2 O 3 and Sr contents and increasing Eu negative anomalies (Eu*-Eu), suggesting that the TTG magmas underwent a coupled fractionation crystallization and crustal contamination, and that the LA-TTG was the product of the fractionation and contamination of the HA-TTG subsuite. In contrast, negative e Nd t values for the High-K granites (from À0.4 to À3.5) indicate the involvement of LA-TTG and some materials from an old continental crust in their genesis. The products of partial melting of both oceanic and continental crusts at the south-western margin of the Zimbabwe craton occurred within a short time interval (from 2.7 to 2.65 Ga ago) suggesting that the Francistown plutonic rocks were formed in a active continental margin environment, where a young ocean plate (Limpopo oceanic plate) subducted underneath an old continental plate (Zimbabwe craton).