Ph.D. / Preserved Archean crust dominantly recording lower temperature conditions (greenschist to amphibolites facies), the earliest widespread record of ultrahigh- temperature metamorphism occur in the Neoarchean. Considering that, collisional tectonic setting has been postulated as a possible tectonic scenario for the generation of ultrahigh-temperature metamorphism, sites where Archean cratons underwent collision can be potential sites for preservation of ultrahigh-temperature metamorphic granulites. The Limpopo Complex is a high-grade metamorphic terrain considered to have formed by collision in Neoarchean time between the Archean Kaapvaal and Zimbabwe cratons.Detailed petrographic and mineral chemical characterization of representative high Mg-Al granulites from the Southern Marginal Zone, Central Zone and the Northern Marginal Zone – forming the three subzones of the Limpopo Complex – was carried out. Evidence for the preservation of mineral assemblages considered diagnostic of ultrahigh- temperature metamorphic conditions, such as orthopyroxene+sillimanite±quartz, high-Al/(MgTs) orthopyroxene, sapphirine+quartz, spinel+quartz, corundum+quartz and antiperthite, are shown from these high Mg-Al granulites. Most of these mineral assemblages are reported for the first time from the Limpopo Complex. In addition, two unique textures are also reported – one, the discovery of corundum lamellar intergrowth with orthopyroxene from a high Mg-Al granulite from the Southern Marginal Zone, and second, the rare occurrence of sapphirine+quartz post dating orthopyroxene+sillimanite±quartz from two Mg-Al granulites from the Central Zone. Pressure-temperature calculations including representative P-T phase diagrams computed for the bulk compositions of the granulites studied clearly indicate ultrahigh- temperature conditions for all the three subzones. In contrast to two previous studies, one each for the Southern Marginal Zone (~950°C) and the Central Zone (~930°C), this study presents higher temperature estimates of ~1050 to ~1100°C for the three subzones. Together with examples of ultrahigh-temperature metamorphic conditions reported by the two previous studies, this study shows that the ultrahigh-temperature event reported here has affected the length and breadth of the three subzones of the Limpopo Complex. Further, the high-pressure conditions inferred from the early composition of orthopyroxene from the unique orthopyroxene-corundum intergrowth and the P-T phase diagrams computed for representative granulites from the three zones suggest a common high pressure event in all the three sub zones of the Limpopo Complex.

The Bafoussam area in west Cameroon is located within the Cameroon Neoproterozoic orogenic belt (north of the Congo craton) which is part of the Central African Fold Belt (CAFB).The evolution of the CAFB is related to the collision between the convergent West African craton, the São Francisco – Congo cratons and the Sahara Metacraton. The outcrop area stretches over a surface of ~1000 km2 and dominantly consists of granitoids which intruded wall-rocks of gneiss and migmatite during the Pan-African orogeny. The Bafoussam granitoid emplacement was influenced by the N 30 °E strike-slip shear zone in the prolongation of the Cameroon Volcanic Line, but also by the N 70 °E Central Cameroon Shear Zone. In the field, these two shear directions are expressed in the schistosity and foliation trajectories, fault orientation and the alignment of the volcanic cones as well. In the Bafoussam area, four types of granitoids can be distinguished, including: (i) the biotite granitoid, (ii) the deformed biotite granitoid, (iii) the mega feldspar granitoid, and (iv) the two-mica granitoid. These granitoids occur as elongated plutons hosting irregular mafic enclaves (amphibole-bearing, biotite-rich, and metagabbroic types) and are frequently cut by late pegmatites, aplite dykes and quartz veins. Petrographically, they range in composition from syenogranite (major), alkali-feldspar granite, granodiorite, monzogranite, quartz-syenite, quartzmonzonite to quartz-monzodiorite. Potassium feldspar, quartz, plagioclase and biotite are the principal phases, in cases accompanied by amphibole and accessory minerals such as apatite,zircon, monazite, titanite, allanite, ilmenite and magnetite. Sericite, epidote and chlorite are secondary minerals. In addition, the two-mica granitoid contains primary muscovite and sometimes igneous garnet. In the granitoids, potassium feldspar is orthoclase (microcline and orthoclase: Or81–97Ab19–3), and plagioclase is mainly oligoclase with some albite and andesine (An3–35Ab96–64).Biotite is Fe-rich (meroxene and lepidomelane, with some siderophyllite), having high Fe2+/(Fe2+ + Mg) ratios of 0.40–0.80. It is a re-equilibrated primary biotite and suggests calc-alkaline and peraluminous nature of the host granitoids. Amphibole is edenitic and magnesian hastingsitic hornblende, with high Mg/(Mg + Fe2+) ratios of 0.50–0.62. The evolution of the hornblende was dominated by the edenitic, tschermakitic, pargasitic and hastingsitic substitution types. Primary muscovite is iron-rich [Fe2+/(Fe2+ + Mg) = 0.52–0.82] and has experienced celadonite and paragonite substitutions. Igneous garnet is almandine–spessartine (XFe = 0.99 and XMn = 0.46–0.56). The euhedral grain shapes of garnet crystals and the absence of inclusions coupled with the high Mn and Fe2+contents (2.609–3.317 a.p.f.u and 2.646–3.277 a.p.f.u,respectively) and low Mg contents (0.012–0.038 a.p.f.u) clearly point to its plutonic origin. The Mn-depletion crystallization model is suggested for the origin of the analyzed garnet, i.e. initial crystallization of garnet inducing early decrease of Mn in the original melt. Aluminum-in-hornblende and phengite barometric estimates show that the granitoids crystallized at 4.2 ± 1.1 to 6.6 ± 1.0 kbar, corresponding to emplacement depths of 15–24 km.Zircon and apatite saturation temperature calibrations and hornblende–plagioclase thermometry yielded emplacement temperatures between 772 ± 41 and 808 ± 34 °C. Except the two-mica granitoid, the titanite–magnetite–quartz assemblage gives oxygen fugacities ranging from 10–17 to 10–13, suggesting that the granitoids were produced by an oxidized magma. Since the twomica granitoid lacks magnetite, it was originated from a magma under reducing conditions, below the quartz–fayalite–magnetite buffer. Fluid inclusions in quartz from hydrothermal veins are secondary in nature and are found in trails along healed microcracks or in clusters. Two types of fluid inclusion have been recognized, mixed aqueous–non-aqueous volatile fluid inclusions subdivided into aqueous-rich mixed and non-aqueous volatile-rich mixed fluid inclusions, and pure aqueous fluid inclusions.The non-aqueous volatile-rich mixed fluid inclusions are one-, two-, or three-phase inclusions, whereas the aqueous-rich mixed fluid inclusions are exclusively three-phase inclusions. Both have similar low to moderate salinities (1 to 10 equiv. wt. %). The total homogenization temperatures of the aqueous-rich mixed fluid inclusions are slightly lower than those of the nonaqueous volatile-rich mixed fluid inclusions, ranging from 150 to 250 °C and 170 to 300 °C,respectively. They contain nearly pure CO2, or CO2 with addition of 4.1–13.5 mole % CH4 as volatile constituents. Pure aqueous fluid inclusions are two-phase with lower total homogenization temperatures (130–150 °C) and salinities ranging from 3 to 8 equiv. wt. %. They display mixing salt system characteristics, having NaCl as the dominant salt and considerable amounts of other divalent cations. Aqueous-rich mixed fluid inclusions and pure aqueous fluid inclusions exhibit a low geothermal gradient value of 18 °C/km, whereas the non-aqueous volatiles-rich mixed fluid inclusions have a high density which correspond to high geothermal gradient of 68 °C/km. The studied granitoids are intermediate to felsic in compositions (56.9–74.6 wt. % SiO2)and have high contents of alkalis K2O (1.73–7.32 wt. %) and Na2O (1.25–5.13 wt. %) but low abundances in MnO (0.01–0.20 wt. %), MgO (0.10–3.97 wt. %), CaO (0.37–4.85 wt. %), P2O5(up to 0.90 wt. %). They display variable contents in TiO2 (0.07–0.91 wt. %), Fe2O3* (total Fe = 0.96–7.79 wt. %) and Al2O3 (12.0–17.6 wt. %) contents. The granitoids show a wide range of high-field-strength elements (HFSE) and large ion lithophile elements (LILE) contents, with felsic granitoids being enriched in HFSE and the intermediate granitoids displaying in contrast high LILE concentrations. They exhibit chemical characteristics of non-alkaline to mid-alkaline, alkali-calcic, calc-alkaline, K-rich to shoshonitic, ferriferous affinities. Chondrite-normalized rare earth element (REE) patterns are characterized by a strong enrichment in light compared to heavy REEs [(La/Sm)N = 3.23–9.65 and (Ga/Lu)N = 1.45–5.54, respectively], with small to significant negative Eu anomalies (Eu/Eu* = 0.28–1.08). Ocean ridge granites (ORG)normalized multi-elements spidergrams display typical collision-related granites pattern, with characteristic negative anomalies of Ba, Nb and Y, and positive anomalies in Rb, Th and Sm. The granitoids under study are genetically I-type granitoids (biotite granitoid, deformed biotite granitoid and mega feldspar granitoid) and one S-type granitoid (two-mica granitoid). The I-type granitoids are metaluminous (ASI: 0.70–1.00) or moderately peraluminous if highly fractionated (ASI: 1.01–1.06). The geochemistry and petrological features of these I-type granitoids argue for close genetic relationships and it is suggest that they originated from a single parent magma. The observed variability in mineralogy and major and trace element compositions in these granitoids are then the reflection of the fractional crystallization that evolved separation of plagioclase, biotite, K-feldspar and accessory minerals at the level of emplacement. The two mica S-type granitoid is exclusively peraluminous (ASI: 1.07–1.25) and classified as a peraluminous leucocratic granitoid or leucogranite. It is marked in its CIPW normative composition by the permanent presence of corundum, ranging between 0.12 and 3.03. The Bafoussam granitoids were emplaced in a syn- to post-collisional tectonic environment. The observed deformational features and the concentrations in Y, less than 40 ppm, confirm that they are related to an orogenesis. Whole-rock Rb–Sr isochrons defines an igneous crystallization ages of 540 ± 27 Ma for the biotite granitoid and 587 ± 41 Ma for the mega feldspar granitoid. These ages fit with the range of Pan-African granitoid ages (650–530 Ma) in West Cameroon and correspond to the Pan-African D2 deformation event in the Neoproterozoic Cameroon orogenic belt. The two-mica granitoid yields an older Rb–Sr isochron age of 663 ± 62 Ma which is considered to be probably a mixing age. The Nd–Sr isotopic compositions indicate that the I-type granitoids have been produced by partial melting of a tonalite–granodiorite source in the lower crust. This is supported by their initial 87Sr/86Sr(600 Ma) ratios (0.705–0.709) and by their WNd(600 Ma) values (0.2 to –6.3, mainly < 0). The two-mica granitoid was generated by partial melting of a greywacke-dominated source involving biotite-limited, biotite dehydration melting. Chemical data of the two-mica granitoid that support this hypothesis are low CaO/Na2O (0.11–0.38) and Sr/Ba (0.20–0.30), the high Rb/Sr (2.26–7.00), the high initial 87Sr/86Sr(600 Ma) ratios ranging from 0.708 to 0.720, the large range in Al2O3/TiO2 (47–204) and the negative WNd(600 Ma) values (–9.9 to –14.0). Moreover,the higher initial 87Sr/86Sr(600 Ma) ratios of the two-mica granitoid are consistent with an upper crust origin. The depleted mantle Nd model ages (TDM) of 1.3–2.3 Ga indicate that the studied granitoids originated by partial melting of Paleoproterozoic and Mesoproterozoic crust, with limited mantle-derived magma contribution. The high initial 87Sr/86Sr(600 Ma) ratios of these granitoids coupled with the wide negative WNd(600 Ma) values strongly suggest a very long residence time in the crust of their protoliths before the melting event. The petrologic signatures of the Bafoussam granitoids are similar to those described in other Pan-African belts of western Gondwanaland such as the neighbouring provinces of Nigeria and the Central African Republic, as well as in the Borborema Province of northeastern Brazil. This supports the previous hypothesis that the Central African fold Belt including Cameroon, Nigeria and the Central African Republic provinces has a continuation in Brazil. / Die Region Bafoussam im westlichen Kamerun ist Teil des "Cameroon Neoproterozoic orogenic belt" (nördlich des Kongo Kratons), welcher zum "Central African Fold Belt" (CAFB)gehört. Die Entstehung des CAFB hängt ursächlich mit der Kollision zwischen dem konvergierenden Westafrikanischen Kraton, dem Sao Francisco – Kongo Kraton und dem Sahara Megakraton zusammen. Die untersuchten Gesteine, im wesentlichen Granitoide, die während der pan-afrikanischen Orogenese in Migmatite und Gneisse intrudierten, sind auf einer Fläche von ca. 1000 km2 aufgeschlossen. Die Platznahme der Bafoussam Granitoide wurde zum einen durch die N 30 °E verlaufende transversale Störungszone entlang der Verlängerung der "Cameroon Volcanic Line" beeinflusst, zum anderen durch die N 70 °E verlaufende "CentralCameroon Shear Zone". Im Gelände finden diese beiden Richtungen Ausdruck in der Schieferung und Foliation der Gesteine, der Orientierung von Störungen, sowie der Anordnung von vulkanischen Kegeln.Das untersuchte Gebiet in der Umgebung von Bafoussam beherbergt vier Typen von Granitoiden: (i) Biotit-Granitoid, (ii) deformierter Biotit-Granitoid, (iii) Mega-Feldspat-Granitoid und (iv) Zwei-Glimmer-Granitoid. Generell sind die Granitoide als ausgelängte Plutone mit eingeschlossenen Enklaven von Mafiten (amphibolführende, biotitreiche und metagabbroide Typen) aufgeschlossen und werden teilweise von jüngeren Quarz-, Pegmatit- und Aplitdykes durchzogen. Petrographisch reichen die Granitoide von dominierendem Syenogranit über Alkali-Feldspat-Granit, Granodiorit, Monzogranit, Quarz-Syenit, Quarz-Monzonit bis zu Quarz-Monzodiorit. Hauptgemengteile sind Kalifeldspat, Quarz, Plagioklas und Biotit, die zusammen mit teilweise vorhandenem Amphibol und Akzessorien wie Apatit, Zirkon, Monazit,Titanit, Allanit, Ilmenit und Magnetit auftreten. Serizit, Epidot und Chlorit sind Sekundärminerale. Der Zwei-Glimmer-Granitoid enthält zusätzlich primären Muskovit und gelegentlich magmatischen Granat. Die Granitoide enthalten als Kalifeldspat generell Orthoklas (Mikroklin und Orthoklas:Or81–97Ab19– 3), Plagioklas ist hauptsächlich Oligoklas mit etwas Albit und Andesin (An3–35Ab96–64). Biotit ist Fe-reich (Meroxene und Lepidomelan mit etwas Siderophyllit) mit hohen Fe2+/(Fe2++ Mg) Verhältnissen zwischen 0.40–0.80. Es handelt sich um reequilibrierten primären Biotit, der ein kalk-alkalines, peraluminöses Ausgangsgestein für die Granitoide anzeigt. Amphibol ist edenitische und magesium-hastingsitische Hornblende mit hohem Mg/(Mg + Fe2+) Verhältnis von 0.50–0.62. Die Entstehung der Hornblende wurde durch edenitische, tschermakitische,pargasitische und hastingsitische Substitutionen bestimmt. Primärer Muskovit ist eisenreich [Fe2+/(Fe2+ + Mg) = 0.52–0.82] und hat Celadonit- und Paragonit-Substitutionen erfahren. Granat ist Almandin-Spessartin (XFe = 0.99 und XMn = 0.46–0.56). Die idiomorphe Ausbildung des Granats und das Fehlen von Einschlüssen in Kombination mit hohen Mn und Fe2+ Gehalten(2.609–3.317 a.p.f.u und 2.646–3.277 a.p.f.u) und niedrigen Mg-Gehalten (0.012–0.038 a.p.f.u)liefern deutliche Hinweise für den plutonischen Ursprung des Granats. Für die Sprossung des Granats wird das Mn-Verarmungsmodell angenommen; danach wächst initialer Granat, was eine frühe Mn-Verarmung der Schmelze zur Folge hat. Aluminium-in-Hornblende- und Phengit-barometrische Abschätzungen zeigen, dass die Granitoide bei 4.2 ± 1.1 bis 6.6 ± 1.0 kbar kristallisierten, was einer Platznahmetiefe von 15–24 km entspricht. Temperaturbestimmungen über die Zirkon- und Apatit-Sättigung und Hornblende-Plagioklas Thermometrie ergeben Platznahmetemperaturen von 772 ± 41 bis 808 ± 34 °C. Mit Ausnahme des Zwei-Glimmer-Granitoids liefert die Paragenese Titanit-Magnetit-Quarz eine Sauerstoff-Fugazität zw. 10-17 und 10-13, was darauf schliessen lässt, dass die Granitoide einem oxidierten Magma entstammen. Da dem Zwei-Glimmer-Granitoid Magnetit fehlt, entstand er aus einem Magma unter reduzierenden Bedingungen unterhalb des Quarz-Fayalit-Magnetit Puffers. Fluideinschlüsse in Quarz aus hydrothermalen Gängen sind sekundärer Natur und als Spuren entlang verheilter Mikrorisse oder als Cluster zu finden. Zwei Sorten von Fluideinschlüssen wurden unterschieden, gemischte wässrige-nicht-wässrige volatile Fluideinschlüsse, die wiederum in wässrige gemischte und nicht-wässrige volatilreiche gemischte Fluideinschlüsse unterteilt werden und zweitens rein wässrige Einschlüsse. Die nichtwässrigen volatilreichen gemischten Fluideinschlüsse sind ein-, zwei-, oder drei-phasige Einschlüsse. Beide Sorten besitzen ähnlich niedrige bis mittlere Salinitäten (1 bis 10 equiv. wt.%). Die Homogenisierungstemperatur der wässrigen gemischten Fluideinschlüsse ist geringfügig niedriger als die der nicht-wässrigen volatilreichen, mit Werten zw. 150 bis 250 °C bzw. 170 bis 300 °C. Sie enthalten nahezu reines CO2, oder CO2 mit 4.1–13.5 mol % CH4 als flüchtigen Bestandteil. Reine wässrige Fluideinschlüsse sind zwei-phasig mit niedrigerer Homogenisierungstemperatur (130–150 °C) und Salinitäten zw. 3 und 8 equiv. wt. %. Sie zeigen Salzmischungscharakteristika mit NaCl als dominantem Salz sowie gewissen Mengen an anderen divalenten Kationen. Wässrige gemischte Fluideinschlüsse und reine wässrige Einschlüsse zeigen einen niedrigen geothermalen Gradienten von 18 °C/km, wohingegen nichtwässrige gemischte Fluideinschlüsse eine hohe Dichte aufweisen, was einem hohen geothermalen Gradienten von 68 °C/km entspricht. Die untersuchten Granitoide besitzen eine intermediäre bis saure Zusammensetzung(56.9–74.6 wt. % SiO2) und zeigen hohe Alkali-Gehalte (K2O = 1.73–7.32 wt. %, Na2O = 1.25–5.13 wt. %), aber niedrige Gehalte an MnO (0.01–0.20 wt. %), MgO (0.10–3.97 wt. %), CaO(0.37–4.85 wt. %) und P2O5 (bis zu 0.90 wt. %), zudem besitzen sie variable Gehalte an TiO2(0.07–0.91 wt. %), Fe2O3* (total Fe = 0.96–7.79 wt. %) und Al2O3 (12.0–17.6 wt. %). Die Granitoide zeigen ein weites Spektrum bezogen auf ihren Gehalt an high-field-strenght elements(HFSE) und large-ion-litophile elements (LILE), wobei saure Granitoide an HFSE angereichert sind und intermediäre Granitoide hohe Konzentrationen von LILE aufweisen. Die Granitoide zeigen chemische Signaturen nicht-alkaliner bis mittel-alkaliner, alkali-kalziumreicher, kalkalkaliner,K-reicher bis shoshonitischer und eisenreicher Magmatite. Chondrit-normalisierte Seltene Erden Element (SEE)-Verteilungsmuster sind durch eine starke Anreicherung der leichten SEE [(La/Sm)N = 3.23–9.65] verglichen mit schweren SEE [(Ga/Lu)N = 1.45–5.54]gekennzeichnet sowie durch geringe bis signifikante negative Eu Anomalien (Eu/Eu* = 0.28–1.08). Auf die Zusammensetzung von Ocean Ridge Granit (ORG) normalisierte Multielement-Spiderdiagramme zeigen Verteilungsmuster, die typisch sind für Granite aus Kollisionsorogenen,mit charakteristischen negativen Anomalien von Ba, Nb und Y sowie positiven Anomalien von Rb, Th, Sm. Die untersuchten Granitoide sind genetisch I-Typ Granitoide (Biotit-Granitoid, deformierter Granitoid und Mega-Feldspat-Granitoid) mit einem S-typ Granitoid (Zwei-Glimmer-Granitoid). Die I-Typ Granitoide sind metaluminös (ASI: 0.70–1.00) oder schwach peraluminös bei starker Fraktionierung (ASI: 1.01–1.06). Die geochemischen und petrologischen Merkmale dieser I-Typ Granitoide sprechen für eine enge genetische Verwandtschaft der Gesteine untereinander und lassen somit eine einzige Quelle als Ausgangsmagma vermuten. Die beobachteten Unterschiede in der Mineralogie und in Haupt- und Spurenelementzusammensetzung spiegeln somit die fraktionierte Kristallisation wieder, welche für die Trennung von Plagioklas, Biotit, K-Feldspat und Akzessorien während der Platznahme verantwortlich ist. Der S-Typ Zwei-Glimmer-Granitoid ist ausschliesslich peraluminös (ASI:1.07–1.25) und wird als peraluminöser leukokrater Granitoid oder Leukogranit klassifiziert. In der normativen CIPW Zusammensetzung ist er durch die durchgehende Präsenz von Korund gekennzeichnet, mit Werten zw. 0.12 und 3.03. Die Platznahme der Bafoussam Granitoide fand in einem tektonischen syn- bis post-Kollisions-Umfeld statt. Die beobachteten Deformationsmerkmale und die Konzentration an Y mit Werten meist unter 40 ppm bestätigen, dass die Granitoide mit einer Orogenese verbunden sind. Rb–Sr Gesamtgesteins-Isochronen ergeben ein Kristallisationsalter von 540 ± 27 Ma für den Biotit-Granitoid und 587 ± 41 Ma für den Mega-Feldspat-Granitoid. Diese Alter entsprechen denen anderer pan-afrikanischer Granitoide (650–530 Ma) in West-Kamerun und stimmen mit dem pan-afrikanischen D2 Deformationereignis im "Cameroon Neoproterozoic Orogenic Belt" überein. Der Zwei-Glimmer Granitoid liefert ein Rb–Sr Isochronenalter von 663 ± 62 Ma, was wahrscheinlich als Mischungsalter zu deuten ist. Die Zusammensetzung der Nd–Sr Isotope zeigt an, dass die I-Typ Granitoide durch partielles Schmelzen einer tonalitisch-granodioritischen Quelle entstanden sind. Dies wird gestützt durch ihr initiales 87Sr/86Sr Verhältnis (0.705–0.709) sowie durch ihre WNd(600 Ma) Werte(0.2 bis –6.3, meist <0). Der Zwei-Glimmer-Granitoid entstand durch partielles Aufschmelzen einer Grauwacken-dominierten Quelle mit Biotit-Entwässerungs-Schmelzen. Chemische Daten des Zwei-Glimmer-Granitoids, die diese Hypothese bestätigen, sind niedrige CaO/Na2O (0.11–0.38) und Sr/Ba (0.20–0.30) Gehalte, hohe Rb/Sr (2.26–7.00) Gehalte, sowie die grosse Spanne im Al2O3/TiO2 Verhältnis (47–204) und negative WNd(600 Ma) Werte (–9.9 bis –14.0). Desweiteren sprechen die höheren initialen 87Sr/86Sr(600 Ma) Verhältnissse des Zwei-Glimmer-Granitoids für einen Urspung aus der oberen Kruste. Die Nd-Modellalter eines verarmten Mantels (TDM) von 1.3–2.3 Ga geben Hinweise auf die Entstehung der untersuchten Granitoide durch partielles Aufschmelzen paläozoischer und mesoproterozoischer Kruste, mit eingeschränkter Zufuhr von Mantelmagma. Die hohen initialen 87Sr/86Sr(600 Ma) Werte der Granitoide, verbunden mit negativen WNd(600 Ma) Werten sprechen stark dafür, dass der Protolith dieser Granitoide eine sehr lange Zeit in der Kruste verbrachte, bevor es zum Schmelzereignis kam. Die petrologischen Signaturen der Bafoussam Granitoide ähneln denen von bereits beschriebenen Granitoiden des pan-afrikanischen Gürtels in West-Gondwana, z. B. aus den angrenzenden Provinzen von Nigeria und der Zentral Afrikanischen Republik sowie der Borborema Provinz im nordöstlichen Brasilien. Dies unterstützt die Hypothese, dass der "Central African Fold Belt" von Kamerun, Nigeria und der Zentral Afrikanischen Provinz seine Fortsetzung in Brasilien findet.

The issue of granite petrogenesis plays a key role in our overall understanding of the growth and differentiation of continents, as well as in our ability to unravel the tectonic histories of orogenic belts. Granites are ubiquitous magmatic products found in almost all tectonic settings: oceanic and continental rifts (i.e., plagiogranites - extreme basalt differentiates), active continental margins (e.g,. the granitic batholiths of central and southern Andes), continent-continent collision zones (e.g., the orogenic batholiths of the Himalayas, Western Anatolia), post-collisional settings (e.g., the Variscan provinces of Europe), complex within-plates settings (e.g., Limmo massif, Afar, Ethiopia). Furthermore, granitoids are characterized by considerable petrological and geochemical heterogeneity, as they can form from a vast array of sources: sediments (e.g., pelites, arkoses, psammites), metamorphic rocks (e.g., (mica)schists, gneisses, etc.), and igneous rocks (e.g. andesites, dacites, tonalites, etc.). Aside from fertile sources (i.e., protoliths), granite petrogenesis is dependent upon two critical parameters: temperature (to promote melting of the protoliths) and water availability - either as freely available aqueous solutions/vapors (e.g., water input in subduction zones); or water released via dehydration melting of hydrous minerals (e.g., micas, amphiboles). The presence of water in protoliths depresses the melting temperature of mineral components and provides the environment for redistribution of chemical components. Understanding the origins of granitic rocks presents unique challenges, given that in many of the tectonic settings where granites are encountered, it is clear that their modes of formation can involve a spectrum of igneous and metamorphic processes that are not readily accessible for examination, either through the study of modern environments or via analogy to "classical" localities. The petrogenesis and emplacement of granites in post-collisional tectonic settings is one of the thornier challenges, as these rocks appear to be derived via thermal and magmatic processes within highly deformed and compositionally diverse continental crust for which we lack a clear understanding. A number of unconventional and difficult-to-test mechanisms have been posited to drive crustal heating, melting, and subsequent pluton post-collisional emplacement. Although large volumes of granitic magmas have been emplaced in post-collisional settings, the complexities of the processes active in such settings make it challenging to put forward testable models that effectively combine available geochemical, petrologic, and geophysical data. Models for granite genesis away from plate margins (by means of crustal thickening, thermal blanketing, and internal heating from radioactive decay of 40K, 230Th, 235U, and 238U; delamination of the crustal lithosphere and juxtaposition of hot mantle melts at the base of the crust; underplating of mantle melts; or slab brake-off and upwelling of mantle melts) have been successfully applied in comparatively young orogenic regions, such as the Himalayas, the Carpathians, and Turkey. These models have proven challenging to employ in older orogenic belts, given their sometimes intricate tectonic and metamorphic histories, and the loss of pertinent evidence due to the effects of post-emplacement tectonic reworking, and often extensive alteration and erosion. A series of ancient but fresh, age-correlative granitic plutons are exposed in Alpine nappes on the flanks of the Carpathians Mountains in southwestern Romania. These granites, all mapped as intruding the Neoproterozoic basement of the Danubian tectonic terrane, were emplaced during the post-collisional stages of two world-scale orogenies: an older, Pan-African event (~600 Ma) and a younger, Variscan event (~330- 280 Ma). My dissertation is focused on the study of late Variscan post-collisional plutons and associated sub-volcanic dykes, as they are tremendous tools for understanding and quantifying the mantle-crust interaction in post-collisional environments and the overall evolution of the continental crust during the Variscan orogeny. Originally believed to be Proterozoic in age, zircon U/Pb dating showed that the plutons are much younger (Chapter 1 - Post-collisional Late Variscan magmatism in the Danubian domain (South Carpathians, Romania) documented by zircon U/Pb LA-ICP-MS) and correspond to the latest stages of the Variscan orogeny, as recorded elsewhere in the European Variscan provinces. The granitic plutons are relatively small and are generally concordant with the structures preserved by the country rocks. The extraordinary petrological and geochemical heterogeneities, even at pluton scale (Chapter 2 - Petrology and geochemistry of the Late Variscan post-collisional Furătura granitic pluton South. Carpathian Mts. (Romania)) argue against unique protoliths and simple evolutionary processes (e.g., closed-system fractional crystallization; anatexis). Trace elemental data for the Furătura pluton shows that the melts were formed in equilibrium with a garnet-amphibole restite, under pressure-temperature conditions deeper than the plagioclase stability field, implying that the melting took place at depths in excess of 40 km in the continental crust. Stable and radiogenic isotope data suggest that a protolith was of (possibly enriched) mantle affinities, and that the melts were subsequently contaminated in various degrees by deep crustal lithologies. In comparison, other post-collisional Variscan plutons from the Danubian domain (Chapter 4 - The role of the continental crust and lithospheric mantle in Variscan post-collisional magmatism - insights from Muntele Mic, Ogradena, Cherbelezu, Sfârdinu, and Culmea Cernei plutons (Romanian Southern Carpathians)) have trace elemental compositions that suggest they were formed at different levels in the crust, under P-T conditions corresponding to both garnet-amphibole and plagioclase stability fields. Some of the plutons lack mantle geochemical signatures and their isotopic compositions are indicative of substantial involvement of both lower- and upper-crustal rocks in their formation and subsequent evolution. On the other hand, plutons emplaced during the same time interval and most likely in close geographical proximity have trace elemental and isotopic compositions indicating strong input from previously enriched mantle components which experienced various degrees of assimilation fractionation-crystallization and/or assimilation of continental crust material during their evolution. This variability in both protoliths and processes responsible for the formation of the granites, coupled with the presence of mantle signatures in late-orogenic post-collisional melts are strong evidence to support delamination as means of providing both the mantle-derived input and energy required for generation of granitoids in the crust. The pronounced variation in petrological and chemical compositions of synchronous plutons suggests that delamination in the Danubian domain was not a single, large scale event that affected the entire crust, but rather a collection of disparate, spatially and chronologically limited event, that affected the Variscan crust during the latest stages of the orogeny. This hypothesis is further tested on a series of sub-volcanic dykes (the Motru Dyke Swarm) crosscutting the entire Danubian basement (Chapter 3 - Post-collisional magmatism associated with Variscan orogeny in the Danubian Domain (Romanian Southern Carpathians): the Motru Dyke Swarm). Initially, the emplacement age of these dykes was assumed as "pre-Silurian" but our mapping has showed that they intrude components of the Danubian domain that shared a documented common history not earlier than the Carboniferous. Furthermore, the dykes are in intrusive relationship with two of the Danubian Variscan plutons, thus arguing for an early Permian emplacement age. Geochemical data show extraordinary heterogeneities in the dykes' composition and record both mantle and crust involvement in their formation. The dykes were emplaced at much shallower depths in the crust, as compared with the granitic plutons. Still, their isotopic compositions clearly indicate that they sampled both lower- and upper-crustal compositions during their evolution. This means that after the crustal thickening episodes that define continent-continent collisions, during the latest stages of the Variscan orogeny, the crust became progressively thinner, as a way to compensate for its metastable state. Thinning of the crust is greatly favored by delamination of the lithosphere. A delamination event, which usually postdates the cessation of continental collision or prolonged crustal shortening, involves the geologically rapid foundering of negatively buoyant lithosphere comprised of mantle and (potentially) lower crust into underlying hotter and less dense asthenosphere. Such a process will remove the lithospheric mantle (and potentially segments of the lower crust) along pre-existing lineaments or mechanical flaws, and juxtapose hot upwelling asthenosphere against the base of the crust, leading to partial melting. Field, petrological, and geochemical data presented in my dissertation document pronounced variations in the overall composition of synchronous plutons and dykes, and further suggest that delamination in the Danubian domain was an active process. This bears great importance in our understanding of the evolution of the crust and argues that mantle-crust interactions are responsible for the generation of continental crust even in the latest stages of an orogen.

This thesis investigates the morphological, chemical and growth characteristics of zircon mineral in relation with the granitoid petrology. Physical and chemical variations recorded within zircon crystals during evolution of the Central Anatolian Granitoids are discussed. The thesis focuses on twelve granitoid samples from the Ekecikdag, Aga&ccedil / &ouml / ren and Terlemez regions from western part of central Anatolia. These granitoids are differentiated into S- and H-type granitoids on the basis of field, petrographical and whole-rock geochemical aspects. In granitoids concerned, zircon is associated with biotite, allanite and plagioclase, and zircon populations mainly comprise P- and S-type zircon crystals, with rare G-, L- and J-types. Typology method combined with cathodoluminescence imaging revealed that S- and H-type granitoids show intrusive aluminous autochthonous and hybrid character, respectively. Zircons generally have euhedral to subhedral cores exhibiting zoning, although sometimes faint, but inherent and embayed cores also exist. Large scale, first order, and/or small-scale second order oscillatory zoning and effects of late stage recrystallization are observed within zircon crystals. Multi-corrosion zones within zircons are characterized by sharp changes in crystal forms with decreased Zr and Si, and increased U, Th and REE+Y contents, beside infrequent increase in Hf, Sc, Ta, Ti, Ca, Al and Fe elements. These zones are interpreted to be formed by transient heating of the resident felsic magma due to mafic melt contribution, at the time of mixing/mingling processes of the H-type granitoids, and then zircons re-grow in magma source reflecting a mafic character. Corrosion stages within zircons of S-type granitoids, on the other hand, were probably formed by mantle-derived melts producing heat for resorption of zircons without direct contribution.

The aim of this study is to investigate the petrography, geochemistry and evolution of quartz-tourmaline-rich rocks occurring in a wide breccia zone within the Late Cretaceous Kerkenez Granitoid (Central Anatolian Crystalline Complex (CACC), Turkey). The approximately 40-m wide main breccia zone has a NE-SW trend and is characterized by intense cataclastic deformation. The breccia zone can be traced several kilometers towards the west and generally occurs as tourmaline-filled faults and 1mm-30cm-thick veins within the granitoid. On the basis of mineralogical and textural features, rocks within this zone are defined as tourmaline veins, tourmaline-breccias and quartz-tourmaline rocks. These rocks are generally composed of quartz, tourmaline and granitic fragments. Petrographical investigations and electron-microprobe analyses indicate that, there are three optically and chemically different tourmaline generations. From oldest to youngest, the tourmalines are classified as blue pleochroic feruvites, blue-green pleochroic schorls and green-light green pleochroic schorls. The chemistry of the tourmalines suggests that these tourmalines crystallized from boron rich fluids derived from an evolving magma. Consequently, the quartz tourmaline-breccia zone is considered to have formed by the injection of overpressured boron rich fluids into faults and fractures present within the Kerkenez Granitoid. Fluid-filled faults and fractures were sealed by quartz-tourmaline crystallization. This led to further fractionation in the magma, new fluid pressure accumulations, reactivation of faults and crystallization of different tourmaline generations. Tourmaline-breccia zones are scarce in the literature and the presence of such rocks within the CACC is first reported in this study.

Beypazari Granitoid is a low temperature and shallow-seated batholite intruded the Tepek&ouml / y metamorphic rocks of the Central Sakarya Terrane. Composition of the granitoid varies from granite to diorite. The granitoid is unconformably overlain by Palaeocene and Eocene rock units. Thus the age is probably Late Cretaceous. The Beypazari Granitoid comprises mafic microgranular enclaves. The granitoid mainly consists of quartz, plagioclase, orthoclase and minor amphibole, biotite, chlorite, zircon, sphene, apatite, and opaque minerals. Plagioclase shows sericitation whereas biotite and hornblende, chloritization. Holocrystalline and hypidiomorphic are characteristic textures of the granitoid. Geochemically, the Beypazari Granitoid is calc-alkaline, metaluminous and I-type. REE data indicate that it may have been generated from a source similar to the upper continental crust. The trace element data of the Beypazari Granitoid suggest a volcanic arc tectonic setting. The possible mechanism of Beypazari granitoid is the northdipping subduction of Neo-Tethyan northern branch under Sakarya continent during Late Cretaceous. The Beypazari Granitoid may be related with Galatean volcanic arc granitoids.

The aim of this study is to extract information about mineral distribution and percentages of Oymaaga&ccedil / granitoid (Beypazari-Ankara) by using remote sensing techniques. Two methods are applied during the studies which are spectral analysis and Crosta techniques. Spectral measurements are done for fresh and weathered samples collected at 32 locations. Mineral percentages are calculated using spectral mixture analysis for each sample by considering main, accessory and secondary mineral content of granodiorite. A total of 10 endmembers for fresh samples and 15 for weathered samples are used. USGS spectral library data is utilized through the analyses. For Crosta technique (image analysis) the multispectral ASTER satellite image is used. Five alteration minerals are discriminated and their maps are generated during this analysis. Interpretation and comparison of the results of both methods and testing these results with the existing petrographical and geochemical data indicate that: 1) according to the results of both spectral analyses and Crosta technique a zonation is not observed in the granitoid, 2) comparison of the results for alteration minerals of these two analyses are partly compatible but not exactly similar, 3) Results of spectral analysis do not fit geochemical nor modal analyses because of inconsistency of the data sets.

University, Diss., 2007--Frankfurt (Main). / Zsfassung in engl. und dt. Sprache.

Thesis (MSc (Geography and Environmental Studies))--University of Stellenbosch, 2005. / 81 Leaves printed on single pages i-xi, preliminary pages and numbered pages 1- 70. Includes bibliography, list of tables and list of figures. / Digitized at 300 dpi color PDF format (OCR), using KODAK i 1220 PLUS scanner. / ENGLISH ABSTRACT: Geological field mapping is often limited by logistical and cost constraints as well as the scope and extent of observations possible using ground-based mapping. Remote sensing offers, among others, the advantages of an increased spectral range for observations and a regional perspective of areas under observation. This study aimed to determine the accuracy of a collection of image classification techniques when applied to ASTER reflectance data. Band rationing, the Crosta Technique, Constrained Energy Minimization, Spectral Correlation Mapping and the Maximum Likelihood Classifier were evaluated for their efficiency in detecting and discriminating between greenstone and granitoid material. The study area was the Archaean Barberton Greenstone Belt in the eastern Mpumalanga Province, South Africa. ASTER reflectance imagery was acquired and pre-processed. Training and reference data was extracted from the image through visual inspection and expert knowledge. The training data was used in conjunction with USGS mineral spectra to train the five classification algorithms using the ERDAS's software package. This resulted in abundance images for the target materials specified by the training data. The Maximum Likelihood Classifier produced a classified thematic map. The reference data was used to perform a rigorous classification accuracy assessment procedure. All abundance images were thresholded to varying levels, obtaining accuracy statistics at every level. In so doing, threshold levels could be defined for every abundance image in such a way that the reliability of the classification was optimized. For each abundance image, as well as for the output map of the Maximum Likelihood Classifier, user's- and producer's accuracies as well as kappa statistics were derived and used as comparative measures of efficiency between the five techniques. This information was also used to assess the spectral separability of the target materials. The Maximum Likelihood Classifier outperformed the other techniques significantly, achieving an overall classification accuracy of 81.1% and an overall kappa value of 0.748. Greenstone rocks were accurately discriminated from granitoid rocks with accuracies between 72.9% and 98.5%, while granitoid rocks showed very poor ability to be accurately distinguished from each other. The main recommendations from this study are that thermal infrared and gamma-ray data be considered, together with better vegetation masking and an investigation into object orientated techniques. / AFRIKAANSE OPSOMMING: Geologiese veldkartering word algemeen beperk deur logistiese en koste-verwante faktore, sowel as die beperkte bestek waartoe waarnemings met veld-gebasseerde tegnieke gemaak kan word. Afstandswaarneming bied, onder andere, 'n vergrote spekrale omvang vir waarnemings en 'n regionale perspektief van die area wat bestudeer word. Hierdie studie was gemik daarop om die akkuraatheid van 'n versameling beeld-klassifikasie tegnieke, toegepas op ASTER data, te bepaal. Bandverhoudings, die Crosta Tegniek, "Constrained Energy Minimization", Spektrale Korrellasie Kartering, en Maksimum Waarskynlikheid Klassifikasie is evalueer op grond van hul vermoë om groensteen en granitoied-rotse op te spoor en tussen hulle te onderskei. Die studiegebied was die Argalese Barberton Groensteengordel in die oostelike Mpumalanga Provinsie in Suid Afrika. 'n ASTER refleksie beeld is verkry, waarop voorverwerking uitgevoer is. Opleidings- en verwysingsdata is van die beeld verkry deur visuele inspeksie en vakkundige kennis. Die opleidingsdata is saam met VSGO mineraalspektra gebruik om die vyf klassifikasie algoritmes met behulp van die ERDAS sagteware pakket op te lei. Die resultaat was volopheidsbeelde vir die teikenmateriale gespesifiseer in die opleidingsdata. Die Maksimum Waarskynlikheid algoritme het 'n geklassifiseerde tematiese beeld gelewer. Met behulp van die verwysingsdata is 'n streng akkuraatheidstoetsing prosedure uitgevoer. Vir alle volopheidsbeelde is 'n reeks drempelwaardes gestel, en by elke drempelwaarde is akkuraatheidsstatistieke afgelei. Op hierdie manier kon 'n drempelwaarde vir elke volopheidsbeeld vasgestel word sodat die drempelwaarde die betroubaarheid van die klassifikasie optimeer. Vir elke volopheidsbeeld, asook vir die tematiese kaart verkry van die Maksimum Waarskynlikheid klassifikasie, is gebruikers- en produsent-akkuraathede en kappa statistieke bereken. Hierdie waardes is gebruik as vergelykende maatstawwe van akkuraatheid tussen die vyf tegnieke, asook van die spektrale skeibaarheid van die onderskeie teikenmateriale. Die Maksimum Waarskynlikheid klassifikasie het die beste resultate gelewer, met 'n algehele klassifikasie akkuraatheid van 81.1%, en 'n gemiddelde kappa waarde van 0.748. Groensteenrotse kon met hoë akkuraathede van tussen 72.9% en 98.5% van granitoiedrotse onderskei word, terwyl granitoiedrotse 'n swak vermoë getoon het om van mekaar onderskei te word. Die belangrikste aanbevelings vanuit hierdie studie is dat termiese uitstralingdata asook gamma-straal data geimplimenteer word. Beter verwydering van plantegroei en 'n studie na die lewensvatbaarheid van objekgeorienteerde metodes word ook aanbeveel.

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