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The origin of enriched mantle beneath North China block: Evidence from young carbonatites

The origin of enriched mantle beneath North China block: Evidence from young carbonatites
The origin of enriched mantle beneath North China block: Evidence from young carbonatites
A swarm of Late Triassic (220 Ma) carbonatite dykes is emplaced into the deformed southern margin of the North China block (NCB) at Lesser Qinling, discontinuously extending for about 10 km. The carbonatites are volumetrically minor, and their formation is related to collision between the South China block (SCB) and Qinling orogen, which led to the amalgamation of the NCB and SCB. The carbonatites are intruded into different Archean and Mesoproterozoic wall-rocks, but are characterized by remarkably similar isotopic compositions [(87Sr/86Sr)i = 0.7048–0.7057; ?Nd = ? 4.3 to ? 10.1; 207Pb/206Pb = 0.878–0.889 and 208Pb/206Pb = 2.136–2.160], which approach, and trend toward slightly less radiogenic Sr and Nd values than, the enriched mantle component EM1. Proterozoic oceanic crust recycled through deep mantle is interpreted to be the principal source of carbon for the Lesser Qinling carbonatites. In comparison with most other young carbonatites (< 200 Ma) emplaced in a rift setting, the Lesser Qinling suite contains appreciably lower ?Nd and higher 207Pb/206Pb and 208Pb/206Pb values, which suggest the presence of an isotopically distinct additional component in its mantle source. The Pb isotopic signature of these carbonatites is significantly distinct from that of the Precambrian rocks in the North China block, but is similar to that of basement rocks in the South Qinling. On the basis of the available isotopic, geophysical and tectonic constraints, we suggest that the southern margin of the North China block was underthrust by crustal material derived from the South Qinling during their collision. The underthrusting contributed to thickening of the lower crust beneath the North China block and its conversion to dense eclogite. This process culminated in brittle delamination of the eclogitized material into the mantle and its metasomatic reworking by carbonate-rich melts derived from the EM1-type recycled Proterozoic crust. Carbonate metasomatism could produce an enriched sub-continental lithospheric source capable of yielding a variety of magma types.
North China block, Qinling orogen, Carbonatites, Enriched mantle, Subducted oceanic crust, Delamination
0024-4937
1-9
Xu, Cheng
af526865-aee4-4ef6-8174-def5c38149a2
Taylor, Rex N.
094be7fd-ef61-4acd-a795-7daba2bc6183
Kynicky, Jindrich
10bf66e4-dd34-4d0b-b92e-25215d5eeaf4
Chakhmouradian, Anton R.
193dd22f-0d7c-407c-9581-14983d9b3c50
Song, Wenlei
463b832c-69ff-4978-a605-e96c6f3b13be
Wang, Linjun
cdb148d7-1ab1-41b3-94bb-d5de855c6e83
Xu, Cheng
af526865-aee4-4ef6-8174-def5c38149a2
Taylor, Rex N.
094be7fd-ef61-4acd-a795-7daba2bc6183
Kynicky, Jindrich
10bf66e4-dd34-4d0b-b92e-25215d5eeaf4
Chakhmouradian, Anton R.
193dd22f-0d7c-407c-9581-14983d9b3c50
Song, Wenlei
463b832c-69ff-4978-a605-e96c6f3b13be
Wang, Linjun
cdb148d7-1ab1-41b3-94bb-d5de855c6e83

Xu, Cheng, Taylor, Rex N., Kynicky, Jindrich, Chakhmouradian, Anton R., Song, Wenlei and Wang, Linjun (2011) The origin of enriched mantle beneath North China block: Evidence from young carbonatites. Lithos, 127 (1-2), 1-9. (doi:10.1016/j.lithos.2011.07.021).

Record type: Article

Abstract

A swarm of Late Triassic (220 Ma) carbonatite dykes is emplaced into the deformed southern margin of the North China block (NCB) at Lesser Qinling, discontinuously extending for about 10 km. The carbonatites are volumetrically minor, and their formation is related to collision between the South China block (SCB) and Qinling orogen, which led to the amalgamation of the NCB and SCB. The carbonatites are intruded into different Archean and Mesoproterozoic wall-rocks, but are characterized by remarkably similar isotopic compositions [(87Sr/86Sr)i = 0.7048–0.7057; ?Nd = ? 4.3 to ? 10.1; 207Pb/206Pb = 0.878–0.889 and 208Pb/206Pb = 2.136–2.160], which approach, and trend toward slightly less radiogenic Sr and Nd values than, the enriched mantle component EM1. Proterozoic oceanic crust recycled through deep mantle is interpreted to be the principal source of carbon for the Lesser Qinling carbonatites. In comparison with most other young carbonatites (< 200 Ma) emplaced in a rift setting, the Lesser Qinling suite contains appreciably lower ?Nd and higher 207Pb/206Pb and 208Pb/206Pb values, which suggest the presence of an isotopically distinct additional component in its mantle source. The Pb isotopic signature of these carbonatites is significantly distinct from that of the Precambrian rocks in the North China block, but is similar to that of basement rocks in the South Qinling. On the basis of the available isotopic, geophysical and tectonic constraints, we suggest that the southern margin of the North China block was underthrust by crustal material derived from the South Qinling during their collision. The underthrusting contributed to thickening of the lower crust beneath the North China block and its conversion to dense eclogite. This process culminated in brittle delamination of the eclogitized material into the mantle and its metasomatic reworking by carbonate-rich melts derived from the EM1-type recycled Proterozoic crust. Carbonate metasomatism could produce an enriched sub-continental lithospheric source capable of yielding a variety of magma types.

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More information

Published date: November 2011
Keywords: North China block, Qinling orogen, Carbonatites, Enriched mantle, Subducted oceanic crust, Delamination
Organisations: Geochemistry

Identifiers

Local EPrints ID: 209909
URI: http://eprints.soton.ac.uk/id/eprint/209909
ISSN: 0024-4937
PURE UUID: 4e888ee8-bd22-4308-8926-21d21ee880cf
ORCID for Rex N. Taylor: ORCID iD orcid.org/0000-0002-9367-0294

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Date deposited: 02 Feb 2012 14:17
Last modified: 15 Mar 2024 02:50

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Contributors

Author: Cheng Xu
Author: Rex N. Taylor ORCID iD
Author: Jindrich Kynicky
Author: Anton R. Chakhmouradian
Author: Wenlei Song
Author: Linjun Wang

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