Leucogranite Records Multiple Collisional Orogenies

Abstract

The history of the continental crust is the sum of processes of new crust generation and reworking of pre-existing crustal components (Cawood et al., 2021). Granite is a key component of the continental crust and is mainly formed at convergent continental margins in accretionary and collisional orogens (Sawyer et al., 2011;Zheng & Gao, 2021). Leucogranite, characterized by less than 5% of dark-colored minerals (e.g., biotite), is a minor but widely distributed component of most orogens in Western Europe (e.g.,

A zircon LA-ICPMS reverse depth profiling analysis method and its geological application

“…The traditional depth profiling LA-ICPMS U–Pb dating method has also been used to analyze 96 leucogranite zircons (DJ87) from Dinggye and obtained 128 valid data. 39 Among them, there are 67 single-age grains and 29 multi-age grains. 30% of randomly chosen zircon grains have core–rim age structures.…”

“…38 In this study, we applied our method to zircons from the Himalayas, Tibet, China. One is derived from a two-mica leucogranite located in the Dinggye area, 39 while the other is sourced from a garnet granitic gneiss in the Yadong area. 40…”

“…Leucogranites are characterized by low amounts (<5%) of dark minerals (e.g., biotite) and are mostly derived from anatexis of metasedimentary rocks in the late extension stage of orogeny. 39,[46][47][48][49] This feature results in the core-rim age of zircons being an important indicator for determining the magma source of leucogranite and deciphering orogenic events. Zircon U-Pb dating has always been the most important way to determine these leucogranites' ages.…”

“…According to the age distribution characteristics of leucogranite zircons, previous studies have delineated the rim age line of zircons as 50-6 Ma without considering the single-age or multi-age characteristics of zircons. 39,50 In this study of leucogranite zircons, we followed this denition and treated age proles exceeding 50 Ma as core age proles, a designation that remains unaffected by the presence or absence of grain overgrowth.…”

“…The MSWD values for the depth proling method (including traditional depth proling and reverse depth proling) exceed the acceptable range for the traditional LA-ICPMS method (0.2-2.2, depending on the grain count), 51 indicating a larger age range variation in the rims, which also suggests that traditional LA-ICPMS U-Pb dating method oen homogenizes the heterogeneous rims, underestimating the age differences in the sample. 39 3.1.2. Garnet granitic gneiss zircon of Yadong, Himalayas.…”