Terrane

About: Terrane is a research topic. Over the lifetime, 11025 publications have been published within this topic receiving 442596 citations. The topic is also known as: tectonostratigraphic terrane.

The hot southern continent: heat flow and heat production in Australian Proterozoic terranes

Abstract: Available surface heat-flow measurements from Australian Proterozoic terranes (83 ′ 18 mWm - 2 ) are significantly higher than the global Proterozoic average of -50 mWm - 2 . Seismic evidence for the presence of relatively cool mantle together with the lack of evidence for neotectonic processes normally associated with thermal transients suggests that anomalous heat flow must reflect crustal radiogenic sources (U, Th and K). This is supported by a compilation of more than 6000 analyses from 455 individual granites, granitic gneisses and felsic volcanics which shows that the present-day average heat production of these rock types is 4.6 μWm - 3 when normalised by area of outcrop (over more than 100 000 km 2 ); roughly twice that of 'average' granite. At the time of this felsic magmatism (ca 1850-1500 Ma) heat production rates were some 25-30% greater than the present day such that the total complement of U, Th and K in many parts of the Australian Proterozoic crust may have contributed as much as 60-85 mWm - 2 to the surface heat flow, or 2 to 3 times the present-day continental average. This extraordinary enrichment has played a key role in the tectonothermal evolution of the Australian Proterozoic crust, and has important implications for our understanding of the thermal budget of ancient continental crust.

Composition of the crust in the Grenville and Appalachian Provinces of North America inferred from V P /V S ratios

Abstract: We use the ratios between P and S wave velocities (VP/VS), derived from seismic refraction data, to infer the composition of the crust in the Grenville and the Appalachian Provinces of North America. The crust exhibits VP/VS increasing with depth from 1.64 to 1.84; there is a clear distinction between the Grenville Province (average VP/VS=1.81) and the Appalachian Province (average VP/VS=1.73) which persists at all depths. The boundary between these provinces is east dipping extending for 100 km east of the Champlain thrust. In the Appalachian Province the increase in VP/VS ratios with depth from 1.67 to 1.74±0.02 may reflect a normal decrease of silica content in the continental crust. In the Grenville Province beneath the Central Granulite Terrane, an anomalous VP/VS ratio of 1.82±0.02 is observed extending to a depth of 10 km; this correlates with the abundance of Ca-plagioclase in the Marcy Anorthosite. At greater depth (15–20 km), where seismic lamination and high electrical conductivity is observed, VP/VS is 1.84±0.02 and correlates with the Tahawus Complex, a layered mafic intrusion. Within the 25-km-thick lower crust of the Grenville Province the VP/VS is 1.84±0.02 and P-velocity is 7.0±0.1 km/s, which are typical for plagioclase-bearing rocks (gabbro-norite). The high VP/VS ratio in the Grenville Province has not been reported in crust of any other age. Since the Grenville Province contains 75% of the world's known anorthosites, high VP/VS ratio is related to high plagioclase. We suggest that the composition of the Grenville lower crust was significantly modified by the emplacement of the anorthosites in the mid-Proterozoic.

Structural continuity of the Ross and Delamerian orogens of Antarctica and Australia along the margin of the paleo-Pacific

Abstract: The Delamerian orogen (southeast Australia) and the Wilson terrane (northern Victoria Land, Antarctica) constitute a formerly continuous lower Paleozoic fold-and-thrust belt developed along the paleo-Pacific margin of eastern Gondwana. Major folds and thrust faults in these regions, rooted in mid-crustal detachment zones, transported Cambrian-Ordovician granites and high-temperature- low-pressure metamorphic rocks divergently toward their respective western craton margins and eastern orogen margins and associated cover sequences. The structural imprints are related to the accretion of lower Paleozoic terranes at the eastern margin of the Delamerian orogen and the Wilson terrane. The continuity of the contemporaneous structure patterns in Australia and Antarctica is evidence for continuous convergent tectonism along the lower Paleozoic-Pacific margin of Gondwana.

Tectonothermal History of the Central Indian Tectonic Zone and Reactivation of Major FauIts/Shear Zones

Abstract: Central Indian Tectonic Zone (CITZ), which divides the Indian subcontinent into Bundelkhand Block in the north and the Deccan Block in the south, is represented by a collage of different lithotectonic terranes ranging in age from Archaean to Recent. It comprises two parallel structural domains, namely the Son-Narmada (SONA) subzone in the north and the Sausar mobile belt (SMB) in the south. The ancestry of the SONA subzone is indicated by the Neoarchaean - Palaeoproterozoic ages yielded by the rocks of Mahakoshal fold belt; the Sausar belt, on the other hand, has yielded Meso- to Neo-proterozoic ages. The present response of CITZ to accumulation of stress and attendant seismicity is governed by the structures generated due to early tectonic history of rocks within it, particularly the development of number of E-W to ENE-WSW striking, brittle and ductile shear zones. While the Sausar belt has remained more or less stable since the late Precambrian, the SONA and Tapti lineament zones have been reactivated several times. Two prominent ENE-WSW trending deep fautts, termed the Son-Narmada North Fault (SNNF) and Son-Narmada South Fault (SNSF) have been episodically active from Neoarchaean onwards. The SNSF in particular has witnessed protracted reactivation well into the Phanerozoic. Intraplate seismicity in continents is commonly concentrated along ancient fault zones. Reactivation of faults or shear zones is favoured over new fault generation, since the SNSF is in a high shear stress orientation. Although the Sausar mobile belt is marked by a number of E-W trending parallel ductile shears, mass transfer processes such as silicification, recrystallization and grain growth during Precambrian appear to have healed them.

Geology and thermochronometry of the east edge of the Median Batholith (Median Tectonic Zone): a new perspective on Permian to Cretaceous crustal growth of New Zealand

Abstract: We report new field, petrological and isotopic data and interpretations from one of New Zealand’s major basement geological boundaries, the contact between the east side of the Median Batholith (formerly Median Tectonic Zone) and the allochthonous Mesozoic terranes of the Eastern Province. In the Nelson and Hollyford–Eglinton areas this contact is a Cenozoic fault, the Median Tectonic Line of earlier workers. However, in the Longwood Range, unfaulted pre-Cenozoic geological relations are preserved intact. Our new Ar–Ar, U–Pb and isotopic data show that the Median Batholith in the Longwood Range consists of two suites. (i) Eastern, isotopically primitive (87Sr/86Sri = 0.702 to 0.703; ɛNdT = + 7 to + 8) trondhjemite and gabbroic rocks of Permian age that we believe are part of the intraoceanic Brook Street arc of the Eastern Province. (ii) Western, isotopically more evolved (87Sr/86Sri = 0.703 to 0.704; ɛNdT = + 3 to + 5) quartz diorites, quartz monzodiorites and rare granites of Middle Triassic to Early Jurassic age that we correlate with a pulse of magmatism elsewhere in the Median Batholith. Field observations in the Longwood Range indicate intrusive, not faulted, contacts between these units and constrain accretion of the Brook Street Terrane to Gondwana to have occurred 230–245 Ma. Intra-batholith shear zones (T ~ 600°C and P ~ 0.2–0.3 GPa) were active at approximately 220 Ma. Modelling of K-feldspar Ar incremental heating ages indicate that most of the Longwood Range had cooled below 175°C by the Middle Jurassic and experienced no subsequent reheating. Significant additional post-accretionary Early Cretaceous and Cenozoic thermotectonic activity in Median Batholith in the Hollyford-Eglinton area is indicated by a new 140 ± 2 Ma U-Pb zircon date on a Largs ignimbrite, as well as by Cenozoic K-feldspar Ar–Ar ages in the Middle Triassic Mistake Diorite.