Geochemistry of ultramafic–mafic rocks of Mesoarchean Sargur Group, western Dharwar craton, India: Implications for their petrogenesis and tectonic setting

The Canyon domain and the Banded complex in the Manicouagan area of the Grenville Province preserve a record of magmatic activity from ∼1.4 to 1 Ga. This study focuses on 1.4–1.2 Ga mafic rocks and 1 Ga ultrapotassic dykes. Geochemistry and Sm–Nd isotopic signatures were used to constrain the origin of these rocks and evaluate the changing role of the mantle with time and tectonic setting from the late evolution of the Laurentian margin to the Grenvillian orogeny, in the Manicouagan area. The mafic rocks include layers inferred to represent flows, homogeneous bodies in mafic migmatite, and deformed dykes, all of which were recrystallized under granulite-facies conditions during the Grenvillian orogeny. In spite of the complexities inherent in these deformed and metamorphosed mafic rocks, we were able to recognize suites with distinctive geochemical and isotopic signatures. Integration of this data along with available ages is consistent with a 1.4 Ga continental arc cut by 1.2 Ga non-arc basalts derived from depleted asthenospheric mantle, with varied degrees of crustal contamination and inferred to represent magmatism in an extensional environment. The 1 Ga ultrapotassic dykes postdate the Grenvillian metamorphism. They are extremely enriched in incompatible elements, have negative Nb anomalies, relatively unradiogenic Sr-isotopic compositions (initial 87Sr/86Sr ~ 0.7040) and εNd –3 to –15. Some dykes have compositional characteristics consistent with derivation from the mantle, ruling out crustal contamination as a major process in their petrogenesis. The most likely source region for the ultrapotassic dykes is a metasomatized subcontinental lithospheric mantle, with thermal input from the asthenosphere in association with post-orogenic delamination.

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Petrological and Tectonostratigraphic Evidence for a Mid Ordovician Rift Pulse on the Arabian Peninsula

GeoArabia ◽

10.2113/geoarabia0404467 ◽

1999 ◽

Vol 4 (4) ◽

pp. 467-500 ◽

Cited By ~ 5

Author(s):

W. Heiko Oterdoom ◽

Mike A. Worthing ◽

Mark Partington

Keyword(s):

Tectonic Setting ◽

Late Ordovician ◽

Mafic Rocks ◽

Early Ordovician ◽

Sedimentary Sequences ◽

Field Investigations ◽

Clastic Sediments ◽

Step Heating ◽

Well Data ◽

Uplift And Erosion

ABSTRACT During late Early Ordovician times an increase in the rate of subsidence in the Ghaba Salt Basin and western South Oman Salt Basin is suggested by the thick sequence of continental clastics of the Ghudun Formation. After a phase of rift-shoulder uplift and erosion, related to a renewed pulse of extension which may have initiated diapiric growth of salt structures in the Ghaba Salt Basin, sedimentation resumed again in the Mid Ordovician. During this period, the center of deposition shifted to the Saih Hatat area in North Oman. This paper documents seismic and well data, field investigations and petrological study of potassic mafic rocks from the Huqf area which were intruded in the eastern side of the Ghaba Salt Basin. A Mid Ordovician age of 461 ± 2.4 million years has been established for these rocks by the Argon-Argon step heating method. Analogy with the petrology and setting of similar potassic mafic rocks from the Rio Grande Rift in the western United States of America suggests that they were intruded into the shoulder of an intra-continental rift. The data provide the first clear evidence of a pulse of rift-shoulder uplift in the Huqf area during the Mid Ordovician. The 3-kilometer-thick Mid to Late Ordovician clastic sediments of the Amdeh Formation in North Oman, together with the occurrence of abnormally thick sedimentary sequences and volcanics in the Tabas Graben in Iran, are consistent with a period of break-up of eastern Gondwana. Together, the Ghaba-Saih Hatat and Tabas Basins are considered to be part of a failed rift arm. These observations further improve our regional knowledge of the Early to Late Ordovician tectonic setting of Oman and will assist in unlocking the hydrocarbon potential of classical rift-related structures consisting of early-rift Early Ordovician sand-prone reservoirs sealed by syn-rift Mid to Late Ordovician marine shales.

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Geochemical constraints on the tectonic setting of the mafic rocks of the Bathurst Camp, Appalachian Orogen

Canadian Journal of Earth Sciences ◽

10.1139/e90-125 ◽

1990 ◽

Vol 27 (9) ◽

pp. 1182-1193 ◽

Cited By ~ 2

Author(s):

A. Dogan Paktunc

Keyword(s):

Trace Element ◽

Gulf Of California ◽

Tectonic Setting ◽

Source Region ◽

Ocean Basin ◽

Mafic Rocks ◽

Middle Ordovician ◽

Element Abundances ◽

Fine Grained ◽

Back Arc

Abundant mafic rocks comprising basalts and gabbros occur in the Bathurst Camp, a complexly deformed Ordovician terrane in northeastern New Brunswick. The mafic rocks form a consanguineous suite of aphyric lavas, subvolcanic sills, and (or) dikes. Gabbros and basalts have somewhat similar major-element compositions but differ in terms of their trace-element contents. Medium-grained gabbros display tholeiitic compositions, whereas basalts and fine-grained gabbros have alkalic affinities. In general, trace-element abundances indicate an enriched source region for the Bathurst mafic rocks. Trace-element characteristics of the tholeiitic group point to a transitional setting going from back-arc to ocean basin, whereas the alkalic group has geochemical characteristics in common with within-plate basalts. Mixing between magmas of these contrasting settings could explain some of the trace-element characteristics of both groups. The back-arc-basin setting appears to be ensialic and is characterized by the absence of an underlying subducted slab during the formation of the basin. The tectonic reason for rifting in such a case could be the strike separation along a series of en echelon faults similar to those of the Gulf of California. Calc-alkaline characteristics of the upper mantle underlying the basin seem to have been inherited from southeasterly subduction of the proto-Atlantic Ocean in Early to Middle Ordovician times.

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Derivation of A1-type granites by partial melting of newly underplated rocks related with the Tarim mantle plume

Geological Magazine ◽

10.1017/s0016756817000838 ◽

2017 ◽

Vol 156 (3) ◽

pp. 409-429 ◽

Cited By ~ 4

Author(s):

YUPING SU ◽

JIANPING ZHENG ◽

LILI LIANG ◽

HONGKUN DAI ◽

JUNHONG ZHAO ◽

...

Keyword(s):

Partial Melting ◽

Tectonic Setting ◽

Mafic Magma ◽

Alkali Feldspar ◽

Limited Range ◽

Granitic Rocks ◽

Large Igneous Province ◽

Mafic Rocks ◽

Mafic Intrusions ◽

Ultramafic Complex

AbstractThe granitic rocks of the Tarim large igneous province (LIP) are temporally and spatially related to mafic intrusions. However, their tectonic setting and genetic relationship are debated. Here, we report geochemical, and zircon U–Pb–Hf isotopic results for three alkali feldspar granitic plutons in the Halajun area, western margin of the Tarim Block. Zircon U–Pb ages suggest these plutons were emplaced at 268–275 Ma, coeval with the neighbouring mafic–ultramafic complexes and syenitic rocks. These granitic rocks have high contents of SiO2, alkalis, Rb, Th, Zr and REE (except Eu), and high ratios of FeO*/MgO and Ga/Al, and show strong depletions in Ba, Sr, Eu, which are commonly observed in the A1-type granites. Zircon Hf isotopes reveal a limited range ofεHf(t) values from −1.0 to +3.5 for different samples from three granitic plutons, obviously higher than those (mostly <0) of the mafic rocks. This distinct difference, along with a Daly gap and small volume of mafic rocks, argues against extreme fractionation of mafic magma as the main origin of the A1-type granites. Instead the A1-type granites were most likely derived from partial melting of newly underplated rocks triggered by the upwelling asthenosphere, followed by extensive fractionation. These A1-type granites were emplaced within an anorogenic setting during the late stage of the Tarim LIP, which possibly lasts for more than 30 Ma. The Piqiang mafic–ultramafic complex directly stemmed from asthenospheric mantle and Halajun A1-type granites represent two manners of vertical crustal growth.

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The Liuyuan complex in the Beishan, NW China: a Carboniferous–Permian ophiolitic fore-arc sliver in the southern Altaids

Geological Magazine ◽

10.1017/s0016756811000811 ◽

2011 ◽

Vol 149 (3) ◽

pp. 483-506 ◽

Cited By ~ 74

Author(s):

QIGUI MAO ◽

WENJIAO XIAO ◽

BRIAN F. WINDLEY ◽

CHUNMING HAN ◽

JUNFENG QU ◽

...

Keyword(s):

Tectonic Setting ◽

Weighted Average ◽

Geochemical Data ◽

Current Debate ◽

Mafic Rocks ◽

Nw China ◽

Tectonic History ◽

Icp Ms ◽

Ocean Ridge ◽

Basic Rocks

AbstractThe tectonic history and time of closure of the Palaeo-Asian ocean of the Altaids are issues of lively current debate. To address these issues, this paper presents detailed geological, petrological and geochemical data of the Liuyuan complex (LC) in the Beishan region in NW China, located in the southernmost Altaids, in order to constrain its age, origin and tectonic setting. The LC mainly comprises massive basalts, pillow basalts, basaltic breccias, gabbros and ultramafic rocks together with cherts and tuffs. Most prominent are gabbros and large volumes of basaltic lavas. These mafic rocks have high TiO2 contents, flat rare earth element (REE) patterns and show high-field-strength elements (HFSEs) similar to those of mid-ocean ridge basalts (MORB). The mafic rocks exhibit positive εNd(t) (6.6–9.0) values, representing magmas derived from the mantle. But these basic rocks are also enriched in Th relative to REEs, and are systematically depleted in Nb–Ta–(Ti) relative to REEs. There is also a large range in initial 87Sr/86Sr (0.7037–0.7093). All these variables indicate that mantle-derived magma was contaminated by fluids and/or melts from a subducting lithospheric slab, and formed in a supra-subduction zone (SSZ) setting. A gabbro intruded in the complex was dated by LA-ICP-MS on 20 zircons that yielded a 206Pb–238U weighted average age of 286 ± 2 Ma. Considering the fact that all these basalts are imbricated against Permian tuffaceous sediments and limestone, we propose that the LC formed as an ophiolite in a fore-arc in Carboniferous–Permian time. This indicates that the Palaeo-Asian ocean still existed at 286 ± 2 Ma in early Permian time, and thus the time of closure of the Palaeo-Asian ocean was in or after the late Permian.

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