Skip to Main Content
Skip Nav Destination
GEOREF RECORD

Petrogenesis of high-K calc-alkaline granodiorite and its enclaves from the SE Lhasa Block, Tibet (SW China); implications for recycled subducted sediments

Zhu Renzhi, Lai ShaocCong, Qin Jiangfeng, Zhao Shaowei and M. Santosh
Petrogenesis of high-K calc-alkaline granodiorite and its enclaves from the SE Lhasa Block, Tibet (SW China); implications for recycled subducted sediments
Geological Society of America Bulletin (February 2019) 131 (7-8): 1224-1238

Abstract

The genesis of high-K calc-alkaline rocks is important in evaluating subduction-related magmatism, particularly with regard to melts derived from recycled subducted sediments, which require unusually steep geothermal gradients. Here, we present high-precision laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb, bulk-rock geochemical, Sr and Nd isotopic, mineral chemical, and in situ zircon Hf isotope data for high-K calc-alkaline granodiorites and associated enclaves in the SE Lhasa Block, Tibet. The LA-ICP-MS zircon U-Pb data show that the granodiorites were emplaced at ca. 124.1-123.8 Ma, and the associated enclaves formed at ca. 132.7-129.6 Ma. The granodiorites are high-K, calc-alkaline, and slightly peraluminous, with A/CNK (= molar ratio of Al (sub 2) O (sub 3) /[CaO + Na (sub 2) O + K (sub 2) O]) values in the range 0.96-1.11. The high Th/La and La/Sm ratios, Th and Nb content, and low Nb/Ta, Ba/Th, U/Th, and Zr/Nb ratios are similar to rocks formed from sediment-derived melts. The uniformly high initial (super 87) Sr/ (super 86) Sr values (0.710277-0.712581), low epsilon Nd(t) (-8.3 to -11.2) values, and negative and variable zircon epsilon Hf(t) values (-11.71 to -0.96) imply continental crustal sources. The enclaves are basaltic to andesitic and have high MgO (3.82-5.48 wt%), and their zircon Hf isotopic compositions and presence of magnesian-hornblende and plagioclase with labradorite-bytownite composition indicate a possible mantle connection. In conjunction with regional geological features, we infer that these rocks were derived from melting of recycled subducted sedimentary materials in the mantle wedge during the southward subduction of the Bangong-Nujiang Tethyan Ocean. Our new data, together with those from the Bangong-Nujiang suture zone and its flanks, suggest that magmatic activity associated with the subduction of Bangong-Nujiang Tethyan oceanic lithosphere occurred from the Middle Triassic to Early Cretaceous.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 131
Serial Issue: 7-8
Title: Petrogenesis of high-K calc-alkaline granodiorite and its enclaves from the SE Lhasa Block, Tibet (SW China); implications for recycled subducted sediments
Affiliation: Northwest University, Department of Geology, State Key Laboratory of Continental Dynamics, Xi'an, China
Pages: 1224-1238
Published: 20190204
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 119
Accession Number: 2019-014788
Categories: Isotope geochemistryIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2019034
Illustration Description: illus. incl. geol. sketch maps
N27°40'00" - N27°49'60", E98°19'60" - E98°40'00"
Secondary Affiliation: China University of Geosciences-Beijing, CHN, China
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2022, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201910
Close Modal

or Create an Account

Close Modal
Close Modal