The petrogenesis of quartz-diorites from the Tatra Mountains (Central Western Carpathians): an example of magma hybridisation
Gaweda, Aleksandra; Doniecki, Tomasz; Burda, Jolanta; Kohut, Milan
published: Jan 21, 2005
ArtNo. ESP154018101009, Price: 29.00 €
Quartz diorites, one of four granitoid varieties distinguished in the Tatra Mts., were found as enclaves in the composite Tatra granite pluton and as small intrusions in the metamorphic envelope. The rocks display contrasting mineralogical and petrological features, suggesting the involvement of crustal and mantle magma sources in their genesis. The presence of monazite and xenotime, the prevalence of zircons with low IT indexes, and intermediate Nd/Th ratios all suggest a parental magma of crustal character. On the other hand, the presence of allanite, metaluminous subaluminous chemistry, and low Rb/Sr ratios (0.064 0.108) suggest a mantle influence. The isotopic (Nd and Sr) data are also typical of mantle-related magmas. The quartz diorites probably crystallised from hybrid magmas, with mingling of felsic (crustal) and mafic (mantle) magmas as a major process. The stabilisation of the mineral composition of the hybrid magma took place over a wide temperature interval from above 800 °C to below 600 °C. Though intrusion probably took place during decompression, pressure data from Al-in-hornblende geobarometry relate only to late magmatic overprinting (at about 4 kbars). The quartz diorites represent pre-plate collision magmas and could be mafic precursors of the felsic Tatra granitoids.