Search results for "Batholith"
showing 10 items of 15 documents
Multiple intrusive phases in the Leinster Batholith, Ireland: geochronology, isotope geochemistry and constraints on the deformation history
2017
The formation of granite batholiths, commonly by incremental assembly of small magma batches, and their correlation with tectonic events, on both local and regional scales, is crucial to understanding the evolution of the Earth9s continental crust. However, these correlations often rely on assumptions about the detailed relationship and timing of mapped units. Here we report how an integrated geochronological, structural and isotope geochemical study in only one key locality from the late Caledonian Leinster Batholith in SE Ireland provides the potential for unravelling essential questions on batholith petrogenesis. The Northern Unit of the Leinster Batholith intruded incrementally, as demo…
A geotraverse across two paleo-subduction zones in Tien Shan, Tajikistan
2017
Abstract We present first LA-ICP-MS U–Pb zircon ages as well as geochemical and Sr–Nd–Pb isotope data for 14 magmatic rocks collected along ca. 400 km profile across the Chatkal-Kurama terrane in the Mogol-Tau and Kurama ranges and the Gissar Segment of the Tien Shan orogen in Tajikistan. These new data from supra-subduction and post-collisional magmatic rocks of two Late Paleozoic active margins constrain a tectonic model for terrane motions across two paleo-subduction zones: (1) The 425 Ma old Muzbulak granite of the Mogol-Tau range formed in a supra-subduction setting at the northern margin of the Turkestan Ocean. The north-dipping plate was subducted from the Early Silurian to the earli…
On shearing, magmatism and regional deformation in Neoarchean granite-greenstone systems: Insights from the Yilgarn Craton
2014
Abstract The structure of the Neoarchean Yilgarn Craton is dominated by craton-scale high-strain zones, mostly associated with highly-deformed elongate granitic bodies and transposed greenstone belts. These shear zones developed during widespread and prolonged magmatic activity that led to a nearly complete reworking of the felsic continental crust. The spatial, temporal and genetic relationships between such a voluminous and protracted event of crustal reworking and the development of the craton-scale shear zone network are unclear. Here, we combine new structural, geophysical and geochemical data to investigate the relationship between crustal-scale shear zones and large syntectonic pluto…
Zircon age and occurrence of the Adaatsag ophiolite and Muron shear zone, central Mongolia: constraints on the evolution of the Mongol–Okhotsk ocean,…
2005
The Adaatsag ophiolite in eastern Mongolia is situated in the Mongol–Okhotsk suture zone, which extends from central Mongolia through Transbaikalia to the Sea of Okhotsk and separates the Siberian and Amurian (Mongolian) plates. The ophiolite sequence passes upwards from serpentinite melange and serpentinized dunite and harzburgite, through layered gabbro (with leucogabbro pegmatite dykes), wehrlite and clinopyroxenite, to isotropic gabbro and leucogabbro, sheeted mafic dykes, and olivine-rich basaltic lavas, overlain by red chert and meta-clastic sediments. A single-zircon mean 207 Pb/ 206 Pb evaporation age of 325.4 ± 1.1 Ma for a leucogabbro pegmatite dyke records the time of igneous cry…
Evolution of the Mayo Kebbi region as revealed by zircon dating: An early (ca. 740Ma) Pan-African magmatic arc in southwestern Chad
2006
Abstract The Mayo Kebbi region in SW Chad is part of the NNE-SSW trending Neoproterozoic Central African Fold Belt (CAFB) and is made up of three calc-alkaline granitoid suites emplaced into a metavolcanic–metasedimentary sequence. The first suite is represented by mafic to intermediate rocks (gabbro-diorite and metadiorite) emplaced between 737 and 723 Ma during early Pan-African convergence. The second consists of the Mayo Kebbi batholith and includes tonalites, trondhjemites and granodiorites, emplaced during several magmatic pulses between 665 and 640 Ma. The third suite includes porphyritic granodiorite and hypersthene monzodiorite dated at ca. 570 Ma. The Mayo Kebbi domain extends sou…
The Mulgandinnah Shear Zone; an Archean crustal scale strike-slip zone, eastern Pilbara, Western Australia
1998
Abstract A large part of the deformation in the Archean Pilbara granitoid-greenstone terrain is localized in relatively narrow shear zones. The Mulgandinnah shear zone (MSZ) is a major one of these, with a width up to 8 km, that can be followed for over 70 km along strike in the Shaw Batholith in the eastern Pilbara. It forms part of the Mulgandinnah Lineament, that can be traced to the Lalla Rookh Basin and the Carlindi Batholith in the north, giving it a total length of over 150 km. The MSZ contains both mylonites and ultramylonites, both of which have foliations that are subvertical to steeply dipping, with the ultramylonitic foliation overprinting the mylonitic foliation to form more lo…
Geometric aspects of synkinematic granite intrusion into a ductile shear zone — an example from the Yunmengshan core complex, northern China
2005
The Cretaceous Yungmengshan core complex in northern China contains a large syntectonic granodiorite batholith that intrudes a slightly older diorite intrusion. A major gently dipping ductile decollement shear zone is developed along the contact of the diorite and granodiorite. The shear zone is invaded by a large volume of granitic and pegmatite veins associated with the main granodiorite batholith during activity of the shear zone under high-grade metamorphic conditions. Progressively older veins are more strongly deformed into tight cylindrical fold structures rotated into parallelism with the lineation and foliation in the shear zone. Parallelism of veins to the foliation is partly due …
Chapter 5.2 The Ancient Gneiss Complex of Swaziland and Environs: Record of Early Archean Crustal Evolution in Southern Africa
2007
Publisher Summary This chapter discusses the record of early Archean crustal evolution in Southern Africa. Southern Africa preserves one of the most complete and detailed records of early Precambrian crustal evolution, and the Ancient Gneiss Complex (AGC) of Swaziland and the related rocks along the southern margin of the 3.5–3.2 Ga Barberton Greenstone Belt (BGB) have played a prominent role in models for the early evolution of continental crust. The AGC is separated from the BGB by a large granitoid sheet-like pluton some 3 Ga in age and known as the Mpuluzi Batholith. In northwest Swaziland, however, small inliers of AGC gneisses occur in faulted and sheared contact with BGB rocks, and t…
Crustal age domains in the Kibaran belt of SW-Uganda: Combined zircon geochronology and Sm–Nd isotopic investigation
2008
Abstract Combination of geochemistry, Nd mean crustal residence ages and single zircon ages reveal distinct provinces not recognized previously within the Kibaran belt of SW-Uganda. Geochemical analyses (HFSE and REE) of four granitoids, namely the Ntungamo, Chitwe, Rwentobo and Kamwezi from the Karagwe Tinfield have been interpreted to be mainly composed of melt components from subduction modified parts of the continental lithospheric mantle. In addition we can demonstrate, from these distinctive batholiths crystallization ages that lead to the result of three age groups, one at around 1566 Ma, the second at 1444 Ma to and the third clusters between 1329 Ma and 1363 Ma. The eNd(t) values f…
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 ± …