Search results for "Diorite"
showing 10 items of 19 documents
Age, geodynamic setting, and mantle enrichment processes of a K-rich intrusion from the Meissen massif (northern Bohemian massif) and implications fo…
1997
The plutonic complex of the Meissen massif (northern margin of the Bohemian massif) comprises dioritic to mainly monzonitic and granitic rocks. The diorite to monzonite intrusions show major and trace element patterns typical for shoshonitic series. The chemical signatures of less crustally contaminated diorites are similar to arc-related shoshonitic rocks derived from continental lithospheric mantle (CLM) sources previously enriched by subduction of altered oceanic crust. Laser step heating 40Ar/39Ar analyses on actinolitic to edenitic amphiboles from geographically different occurrences of the monzonitic intrusion yielded concordant plateau ages as well as total gas ages ranging from 329.…
Source composition, fractional crystallization and magma mixing processes in the 3.48–3.43Ga Tsawela tonalite suite (Ancient Gneiss Complex, Swazilan…
2016
Abstract The ca. 3480–3430 Ma Tsawela Gneiss (TG) is a well-preserved coarse-grained diorite to tonalite suite within the Ancient Gneiss Complex of Swaziland, eastern Kaapvaal craton. These gneisses are texturally and compositionally distinct from the hosting oldest components of the ca. 3200–3660 Ma TTG-type Ngwane Gneisses (NG). Major and trace elements, in combination with whole-rock hafnium-neodymium isotopic data, were analyzed in the TG and in three samples of ca. 3450 Ma grey NG to constrain sources and magmatic processes. High-field-strength element data (HFSE) were combined with U-Pb SHRIMP II ages and Hf-in-zircon data for key samples to constrain their ages and petrogenesis. In c…
Petrogenesis of synorogenic diorite–granodiorite–granite complexes in the Damara Belt, Namibia: Constraints from U–Pb zircon ages and Sr–Nd–Pb isotop…
2015
The synorogenic Palmental complex (central Damara Belt, Nambia) consists of ca. 545 Ma old quartz diorites and rare granodiorites and ca. 520 Ma-old leucogranites, representing one of the earliest and most primitive phase of crustal plutonism predating the main high-T regional metamorphism. Most quartz diorites and one granodiorite evolved through multistage, polybaric evolutionary processes involving fractionation from a lithospheric mantle-derived melt, followed by fractional crystallization of mainly hornblende, plagioclase and apatite which is shown by decreasing MgO, FeO, CaO, TiO2 and P2O5 with increasing SiO2. Assimilation of felsic basement gneisses was also important during formati…
Impact of hydrologically driven hillslope erosion and landslide occurrence on soil organic carbon dynamics in tropical watersheds
2016
The dynamics of soil organic carbon (SOC) in tropical forests play an important role in the global carbon (C) cycle. Past attempts to quantify the net C exchange with the atmosphere in regional and global budgets do not systematically account for dynamic feedbacks among linked hydrological, geomorphological, and biogeochemical processes, which control the fate of SOC. Here we quantify effects of geomorphic perturbations on SOC oxidation and accumulation in two adjacent wet tropical forest watersheds underlain by contrasting lithology (volcaniclastic rock and quartz diorite) in the Luquillo Critical Zone Observatory. This study uses the spatially-explicit and physically-based model of SOC dy…
The complexities of zircon crystllazition and overprinting during metamorphism and anatexis: An example from the late Archean TTG terrane of western …
2017
Abstract There are different viewpoints on metamorphic and anatectic zircons recording ages of 2.45–2.48 Ga or even younger in some areas of the North China Craton where both late Neoarchean and late Paleoproterozoic tectono-thermal events are well developed. These are: 1) partial resetting of the U-Pb isotopic system in the late Neoarchean zircons, 2) metamorphism lasting from the late Neoarchean to the earliest Paleoproterozoic, and 3) earliest Paleoproterozoic metamorphism as separate different event. Western Shandong Province is an area where the late Neoarchean tectono-thermal event is widely developed but the late Paleoproterozoic event has not been identified. This provides an opport…
High-grade metamorphism and partial melting of basic and intermediate rocks
2016
Rocks of basic and intermediate bulk composition occur in orogenic terranes from all geological time periods and are thought to represent significant petrological components of the middle and lower continental crust. However, the former lack of appropriate thermodynamic models for silicate melt, amphibole and clinopyroxene that can be applied to such lithologies at high temperature has inhibited effective phase equilibrium modelling of their petrological evolution during amphibolite- and granulite facies metamorphism. In this work, we present phase diagrams calculated in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O2 (NCKFMASHTO) compositional system for a range of natural basic and interm…
Geochronology and Nd-Sr systematics of Lusatian granitoids: significance for the evolution of the Variscan orogen in east-central Europe
1994
A variety of pre-Variscan granitoids and two Variscan monzogranites occurring in the central and western parts of the Lusatian Granodiorite Complex (LGC), Saxonia were dated by the single zircon evaporation method, complemented by whole rock Nd isotopic data and Rb —Sr whole rock and mineral ages. The virtually undeformed pre-Variscan granitoids constitute a genetically related, mostly peraluminous magmatic suite, ranging in composition from two-mica granodiorite, muscovite-bearing biotite quartz diorite (tonalite) and granodiorite to biotite granodiorite and monozogranite.
Post-collisional adakite-like magmatism in the Ağvanis Massif and implications for the evolution of the Eocene magmatism in the Eastern Pontides (NE …
2011
In the Anatolia, the Caucasus and northwest Iran, the Eocene epoch is characterized by widespread basic to acidic magmatism, whose temporal and spatial evolutions and origin are poorly understood. In this paper, we provide geochronological and geochemical data on a suite of Early Eocene intrusions from northeast Turkey and discuss their origin within a regional tectonic framework. Post to late-collisional, moderate to small bodies of quartz diorite and leucogranodiorite as well as later dacite porphyries intrude Permo-Triassic low-grade metamorphic rocks in the southern part of the Eastern Pontides very close to the Neo-Tethyan Izmir-Ankara-Erzincan suture. In places, the intrusives display…
Dating of late Proterozoic ophiolites in Egypt and the Sudan using the single grain zircon evaporation technique
1992
Abstract Zircons from gabbro and plagiogranite in late Proterozoic ophiolites of the Arabian-Nubian Shield (ANS) in Egypt and the Sudan, as well as post-ophiolite granites have been dated using the stepwise evaporation method. Zircons from a plagiogranite in the Wadi Ghadir ophiolite, Eastern Desert of Egypt, yielded a mean 207Pb/206Pb age of 746±19 Ma, while a gabbro and diorite associated with the Abu Swayel ophiolite nappe ∼ 250 km southwest of Wadi Ghadir provided zircon 207Pb/206Pb ages of 729±17 and 736±11 Ma, respectively. Zircons from layered gabbro along the western margin of the Jabal Gerf ophiolite just north of 22°N were dated at 741±21 Ma, indistinguishable from the Wadi Ghadir…
Episodic mantle melting-crustal reworking in the late Neoarchean of the northwestern North China Craton: Zircon ages of magmatic and metamorphic rock…
2012
Abstract The Yinshan Block in the northwestern North China Craton comprises late Neoarchean greenstones, high-grade metamorphic rocks (granulite, charnockite, enderbite and amphibole gneiss), diorites (sanukitoid and Mg-adakite) and granitoids (predominantly trondhjemite-tonalite). A greenstone terrane comprises a volcanic sequence of predominant basalt and dacite, with minor andesite. Zircons from a high-Mg andesite and an andesite have weighted mean 207Pb/206Pb ages of 2533 ± 5 Ma and 2510 ± 7 Ma, respectively, which reflect the timing of two distinct volcanic episodes. These two either predated or postdated a major volcanic episode that formed a basalt-dacite bimodal suite during 2515 ± …