Geochemistry and origin of Mesoproterozoic metavolcanic rocks from Fisher Massif, Prince Charles Mountains, East Antarctica
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Abstract:
Fisher Massif consists of Mesoproterozoic ( c. 1300 Ma) lower amphibolite-facies metavolcanic rocks and associated metasediments, intruded by a variety of subvolcanic and plutonic bodies (gabbro to granite). It differs in both composition and metamorphic grade from the rest of the northern Prince Charles Mountains, which were metamorphosed to granulite facies about 1000 m.y. ago. The metavolcanic rocks consist mainly of basalt, but basaltic andesite, andesite, and more felsic rocks (dacite, rhyodacite, and rhyolite) are also common. Most of the basaltic rocks have compositions similar to low-K island arc tholeiites, but some are relatively Nb-rich and more akin to P-MORB. Intermediate to felsic medium to high-K volcanic rocks, which appear to postdate the basaltic succession, have calc-alkaline affinities and probably include a significant crustal component. On the present data, an active continental margin with associated island arc was the most likely tectonic setting for generation of the Fisher Massif volcanic rocks.Keywords:
Felsic
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Hornblende
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Island arc
Lile
Diorite
Fractional crystallization (geology)
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Lile
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Island arc
Lile
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Back-arc basin
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The Mineral King pendant in the Sierra Nevada batholith (California, USA) contains at least four rhyolite units that record high-silica volcanism during magmatic lulls in the Sierran magmatic arc. U-Th-Pb, trace element (single crystal spot analyses via sensitive high-resolution ion microprobe–reverse geometry, SHRIMP-RG), and bulk oxygen isotope analyses of zircon from these units provide a record of the age and compositional properties of the magmas that is not available from whole-rock analysis because of intense hydrothermal alteration of the pendant. U-Pb spot ages reveal that the Mineral King rhyolites are from two periods, the Early Jurassic (197 Ma) and the Early Cretaceous (134–136 Ma). These two rhyolite packages have zircons with distinct compositional trends for trace elements and δ18O; the Early Jurassic rhyolite shows less evidence of crustal influences on the rhyolites and the Early Cretaceous rhyolite shows evidence of increasing crustal influences and crystal recycling. These rhyolites capture evidence of magmatism during two periods of low magmatic flux in the Sierran Arc; however, they still show that magmas were derived from interactions of maturing continental crust, increasing from the Early to Late Jurassic. This finding likely reflects the transition of the North America margin from one of docking island arcs in the Early Jurassic to one of a more mature continental arc in the Early Cretaceous. This also shows the utility in examining zircon spot ages combined with trace element and bulk isotopic composition to unlock the petrogenetic history of altered volcanic rocks.
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The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1961)
In this paper is presented a detailed subdivision of socalled gabbro-amphibolite zone of the Hidaka metamorphic belt, the axis of island of Hokkaido. It is composed of four tectonic units which are arranged in the following order from west to east, as is shown in figure I. 1) green schist zone, 2) epidote amphibolite zone, 3) green hornblende schistose amphibolite zone and 4) saussurite gabbro zone. Concerning zones 1), 2) and 3), their original rock facies are not clearly determinable. The zone of saussurite gabbro is composed of three varieties of amphibolite, a) hornblende schist facies, b) coarse grained amphibolite (=metasomatic) facies and c) compact amphibolite facies, all of which are derived from saussurite gabbro. In such a diverse metamorphic process, the different characters of tectonic forces and combined metasomatic effects have been the chief determinants.
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Late Paleozoic- Early Mesozoic tectonics of Hainan Island: Key to understanding Paleotethyan geology
<p>In Southeast Asia, establishing the origin and associated tectonic setting of Late Paleozoic-Early Mesozoic igneous rocks is complicated by structural overprinting and the complex tectonic evolution of the Paleotethyan regime. Hainan Island, located at the south-eastern margin of the Paleotethys, and lacking significant tectonic overprints is a key to understand amalgamation history of the Indochina and South China blocks and to constraining the tectonic evolution of Paleotethys ocean in southeast Asia.</p><p>The Late Paleozoic-Early Mesozoic record of igneous rocks on Hainan Island includes the following. 1) ca. 350 Ma island arc andesites and ca. 330 Ma metabasites, the latter with both MORB- and arc-like geochemical affinities, positive &#949;<sub>Nd</sub>(t) values of +5.86 &#8211; +9.85 and rare inherited zircons with a zircon age of 1400 Ma inferred to be derived from a MORB source with the input of a slab-derived component. Together with the ~350 Ma island arc andesites, the Carboniferous tectonic environment is supposed to be a continental back-arc basin setting. 2) Late Permian gneiss granitoids (272-252 Ma) characterized by a gneissic foliation and calc-alkaline I-type geochemical affinities with negative Nb-Ta and Ti anomalies, related to metasomatized mantle wedge modified by the sediment-derived component in a continental arc setting. 3) ca. 257 Ma arc-like andesites, which further validate a subduction-related setting. 4) Peraluminious Early-Middle Triassic massive granitoids (251&#8211;243 Ma) with slightly high A/CNK ratios, &#948;<sup>18</sup>O values (up to 11.75 &#8240;) and Sr/Y ratios, inferred to have formed in a compressive regime from a mixed source of greywacke and metabasite. 5) Middle-Late Triassic (242&#8211;225 Ma) high-K calc-alkaline granitoids with high zircon temperatures (842&#8211;867&#176;C) and geochemical signatures of A-type granites. They show slightly low whole-rock &#949;<sub>Nd</sub>(t) and zircon &#949;<sub>Hf</sub>(t) values, suggestive of the derivation from a metabasite&#8211;greywacke source in an extensional setting. 6) ca. 240 Ma gabbro-dolerites showing enrichment in LILEs, depletion in HFSEs, negative &#949;<sub>Nd</sub> (t)-&#949;<sub>Hf</sub> (t) values (&#8722;8.45 to &#8722;1.05 and &#8722;5.9 to &#8722;2.7, respectively) and crustal-like &#948;<sup>18</sup>O values (7.26&#8211;8.70&#8240;), it is implied that the Hainan Island entered into post-collisional environment in response to the asthenosphere upwelling shortly after the closure of back-arc basin.</p><p>Thus, Hainan Island provides a record of Carboniferous back-arc basin opening, followed by an extended Permian&#8211;Triassic history of subduction-related consumption leading to orogenic assembly and extensional collapse between the South China and Indochina blocks. Such a tempo-spatial pattern is consistent with that along the Song Ma&#8211;Ailaoshan suture zone rather than the magmatic history of eastern South China and indicates that the Paleotethys extended west to at least Hainan Island in the Late Paleozoic-Early Mesozoic.</p>
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Abstract The Mesoproterozoic Granite‐Rhyolite Provinces in North America consist of A‐type granitic and rhyolitic rocks, and their formation is commonly ascribed to continental `extension' or `rifting'. The tectonic environment of the extension is, however, poorly understood. New Sm–Nd isotopic data from the Central Gneiss Belt, Grenville Province, Ontario, suggest that rocks compositionally and temporally similar to those in the Granite‐Rhyolite Provinces formed in and behind an active continental arc undergoing intra‐arc and back‐arc extension. Basaltic underplating accompanied extension, providing heat and juvenile material. Source rocks vary from juvenile within the arc, to more mature with increasing distance behind the arc. Recent investigations from SW Baltica show that the Rjukan Group, a proposed Granite‐Rhyolite Province correlative, also formed inboard of an active continental arc. A tectonically and temporally similar, and probably recurrent, evolution along the vast Laurentia–Baltica margin points to active continental‐margin processes as first‐order controls on back‐arc granite‐rhyolite magmatism.
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Using cathodoluminescence(CL)imaging and LA-ICP-MS in site U-Pb isotope dating technigue,this paper presents zircon U-Pb dating for the gabbro from the Baihua igneous complex in Tianshui area,eastern Gansu pvovince and reveals interesting tectonic implication.Baihua igneous complex consists mainly of pyroxenite-gabbro(diorite)-diorite-quartz diorite.They form a complete comagmatic evolutionary series.The tectonics environment discrimination of trace element geochemistry reveals the igneous complexs formed in an island-arc setting.The LA-ICP-MS single-zircons U-Pb age of the gabbro from Baihua igneous complex is(449.7±3.1)Ma(MSWD=1.9),which shows that the forming time of the island-arc type magmatite in northern zone of West Qinling is Late Ordovician,also reveals that the timing of subduction of paleo-ocean basin represented by the Guanzizhen ophiolite and resulting island-arc-type magmatic activities is probably Middle-Late Ordovician.
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