Genesis And Dynamic Significance Of The High Himalayan Leucogranites In The Region Of Dinjie, Tibet

The Higher Himalayan leucogranites in the region of Dinjie, Tibet, are closely near theinner South Tibet Detachments and occur in a series of small stocks. Most of them was emplacedinto the para-metamorphic rocks in the base, and abundant leucogranitic veins occurr as net,stratum or chamber in the para-metamorphic rocks, too. The leucogranites have apparently twoperiods: earlier two mica leucogranites, the mineral assemblages are biotite+muscovite±garnet(quartz+plagioclase+alkaline-feldspar); the later tourmaline leucogranites, the mineralassemblages are muscovite+tourmaline±biotite±garnet(quartz+plagioclase+alkaline-feldspar).According to petrography, muscovites are primary or secondary, and biotites are peraluminoussiderophyllites. Geochemical constraints show the leucogranites are rich in Si, K, (K+Na), Al, LREE, K, Rb,Ba, Th, Ta, and Nb, and poor in Ca and (Fe+Mg), HREE, Hf, Zr, Y and Yb. Tourmalineleucogranites are rich in Nb, Ta, Be and B and poor in Sr, Ba, Zr, Th and Co relative to two micaleucogranites. ε Nd of the leucogranites(-12.04 — -19.80) is small. In the whole theleucogranites are typical S-type granite. The para-metamorphic rocks in the base are abundant with Si and Al, and The REE of themis similar with that of the leucogranites. The characteristics of Rb, Sr and Ba indicates theleucogranites are formed from the dehydration melting of the micas. The geochemical feature ofthe leucogranites and the para-metamorphic rocks suggests two of them has genetic relations, sothe para-metamorphic rocks are the possible sources of the leucogranites. According to field geology, petrography, geochemistry and experimental petrology, theauthor think that the para-metamorphic rocks are the source rocks of the High Himalayanleucogranites, they are melted and formed leucogranites magma in condition of decompressionof the base, and The leucogranites magma were emplaced passively while the base was uplifting.Two mica leucogranites firstly melted and formed, and then tourmaline leucogranites in turn, andthis is the changing process of the structural environments.