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Jurassic Hornblende Gabbros in Dongga, Eastern Gangdese, Tibet: Partial Melting of Mantle Wedge and Implications for Crustal Growth
Author(s) -
XU Bo,
HOU Zengqian,
ZHENG Yuanchuan,
ZHOU Ye,
ZHOU Limin,
YANG Yu,
HAN Yanwei,
ZHEN Guo,
WU Changda
Publication year - 2017
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.13117
Subject(s) - geology , geochemistry , batholith , hornblende , gabbro , zircon , partial melting , plagioclase , magmatism , mantle wedge , diorite , petrogenesis , mantle (geology) , igneous rock , subduction , petrology , biotite , tectonics , paleontology , quartz
The Gangdese batholith, more than 2500 km in length, is composed mainly of Jurassic‐Miocene igneous rocks. This batholith is one of the most important constituents of the Tibetan orogenesis and provides an ideal place for study of Neo‐Tethyan ocean geodynamic evolution and plateau uplift. Recent studies on the Gangdese Jurassic felsic magmatism highlight its juvenile source. However, important aspects concerning the genesis of the juvenile magmatism and related deep geodynamic evolution are still unclear. Here, we report detailed petrological, geochronological, geochemical, whole‐rock Sr‐Nd isotopic, and in situ Sr‐Hf isotopic data for a recently identified hornblende gabbro in the Dongga area, southern Lhasa sub‐block. This hornblende gabbro is dominated by hornblende and plagioclase, dated at Early Jurassic (ca. 180–190 Ma), and characterized by a narrow compositional range in SiO 2 (49.38wt%–52.27wt%), MgO (4.08wt%–7.00wt%), FeO (10.43wt%–11.77wt%), Na 2 O (2.58wt%–3.51wt%), and K 2 O (0.48wt%–1.53wt%). It has depleted isotopic signatures, with whole‐rock ( 87 Sr/ 86 Sr) i ratios of 0.7033–0.7043, ε Nd ( t ) values of +4.90 to +6.99, in situ plagioclase ( 87 Sr/ 86 Sr) i ratios of 0.7034–0.7042, and zircon ε Hf ( t ) of +12.2 to +16.8. Our results integrated with published data suggest a model of Gangdese juvenile crustal growth by a subduction‐related water‐enriched mantle wedge. The hydrous partial melting of the lithosphere mantle was triggered by the dehydration of a Neo‐Tethyan oceanic slab. This mafic magmatism emplaced in the middle‐lower crust of intraoceanic arcs or active continental margins, leading to Jurassic juvenile crustal growth in southern Tibet.