The petrogenesis of granitoid rocks unusually rich in apatite in the Western Tatra Mts. (S-Poland, Western Carpathians)

Abstract

In the bottom part of the tongue-shaped, layered granitoid intrusion, exposed in the Western Tatra Mts., apatite-rich granitic rocks occur as pseudo-layers and pockets between I-type hybrid mafic precursors and homogeneous S-type felsic granitoids. The apatite-rich rocks are peraluminous (ASI01.12-1.61), with P 2 O 5 contents ranging from 0.05 to 3.41 wt.% (<7.5 vol.% apatite), shoshonitic to high-K calcalkaline. Apatite is present as long-prismatic zoned crystals (Ap 1 ) and as large xenomorphic unzoned crystals (Ap 2 ). Ap 1 apatite and biotite represent an early cumulate. Feldspar and Ap 2 textural relations may reflect the interaction of the crystal faces of both minerals and support a model based on local saturation of (P, Ca, F) versus (K, Na, Al, Si, Ba) in the border zones. Chondrite-normalized REE patterns for the apatite rocks and for pure apatite suggest apatite was a main REE carrier in these rocks. Minerals characteristics and the whole rock chemistry suggest both reduced S-type and I-type magma influenced the apatite-rich rocks. The field observations, mineral and rock chemistry as well as mass-balance calculations point out that the presence of apatite-rich rocks may be linked to the continuous mixing of felsic and mafic magmas, creating unique phosphorus-and aluminium-rich magma portions. Formation of these rocks was initially dominated by the complex flowagecontrolled and to some extent also gravity-driven separation of early-formed zoned minerals and, subsequently, by local saturation in the border zones of growing feldspar and apatite crystals. Slow diffusion in the phosphorus-rich magma pockets favoured the local saturation and simultaneous crystallization of apatite and feldspars in a crystal-ladden melt.

LA-ICP-MS U-Pb dating and REE patterns of apatite from the Tatra Mountains, Poland as a monitor of the regional tectonomagmatic activity

“…1b) an Early-Variscan hybridization episode is represented by I-type quartz-diorite hybrid precursors (368 ± 8 Ma by the U-Pb method on zircon; Gawęda et al, 2005;Burda et al, 2011), which occur as sills within the metamorphic envelope and at the base of the granodiorite-tonalite intrusion (360-345 Ma; . A suite of unusual apatite-rich rocks of cumulative origin is linked to this hybridization episode (Szopa et al, 2013). In the eastern part of the crystalline core (High Tatra Mountains) syenogranite-monzogranite is most abundant, locally with mafic microgranular enclaves (MME) and metasedimentary xenoliths (Gawęda, 2009 and references therein).…”

“…As these rocks have demonstrated to be genetically linked to the mixing and mingling of two different magmas, the zircon U-Pb age of the mingled hybrid (368 ± 8 Ma; Burda et al, 2011) is considered to constrain the age of these rocks. Apatite-rich cumulates show low degree of REE fractionation and negative Eu anomalies (Eu/Eu* = 0.4-0.7; Szopa et al, 2013; Fig. 3c).…”

“…For this study we used magmatic rock samples, that were previously dated by the LA-MC-ICP-MS zircon UPb method (Burda et al, 2011(Burda et al, , 2013a(Burda et al, , 2013b and one sample of an apatite-rich cumulate (Szopa et al, 2013). Petrographical analyses of thin sections were undertaken to check the apatite content and its morphological varieties.…”

“…Apatite is an important carrier of many trace elements (Sha and Chappell, 1999), and can control the budget of Y and REE, especially in rocks with high apatite contents (Dempster et al, 2003;Prowatke and Klemme, 2006;Szopa et al, 2013). Recently apatite has been used in high-temperature thermochronological studies, showing that the closure temperature of the uranium -lead (U-Pb) system is approximately 350-550°C (Chamberlain and Bowring, 2000;Schoene and Bowring, 2007;Cochrane et al, 2014).…”

Age and origin of fluorapatite-rich dyke from Baranec Mt. (Tatra Mts., Western Carpathians): a key to understanding of the post-orogenic processes and element mobility

“…Fluorapatite-rich rocks are present in the Tatra Mountains (Gawęda 2008;), however they are commonly associated with the oldest magmatic episode at ca. 368 Ma (Burda et al 2011;Szopa et al 2013) and show U-Pb apatite cooling age of ~ 340 Ma …”