I have seen overgrowths on zircon, both in igneous and sedimentary rocks
In igneous rocks it is assumed that...such zircons are as a result of S-type nature of the granite, but in sedimentary environment how overgrowths develop on zircon
Is there any particular process by which this is possible?
Asoori, it is not clear in your question if you want to know about growths of any mineral over zincon crystals or zircon mineral haloes grown over older zircons.
Overgrowths do happen on zircon during early diagenesis, but the overgrowths are usually phosphate minerals, specially xenotime. See classic article link below.
Article Early-diagenetic REE-phosphate minerals (florencite, gorceix...
Dear Dr. Latha,
There are still some open questions as to the intergrowth of two or more minerals. Is the host mineral different from the rim mineral or not? I know rims of euhedral coffinite [U(SiO4)1−x(OH)4x] around zircon ZrSiO4 , both of which are “almost” isotypic. Intergrowth of zircon with zircon is not anything out of the ordinary and known to geochronologists dealing with U/Pb systems. All of these examples are either from metamorphic or magmatic lithologies which evolved under temperatures far beyond those of near-ambient conditions used to be the case of sediments. Zircon pertains to the so-called ultrastable accessory/heavy minerals that are strongly resistant to chemical processes during supergene and hypogene alteration. Phosphate minerals such as APS minerals which precipitate on decreasing pH from the afore-mentioned solutions or REE phosphates such as xenotime or rhabdophane that become stable under higher pH conditions should not corrode zircon (pH > or = 7). With this in mind the sedimentary realm and low-T hydrothermal environments do not offer favorable conditions to foster such processes. Growth of minerals others than zircon on zircon grains in these low-T environments is possible as an interstitial pore filling, e.g., in clastic sediments. It is an in-situ process. I do not want to go any further and feel we will get closer to a solution if we deal with a case in point.
With kind regards
H.G.Dill
Thank you so much for all the valuable information provided.
It definitely enhanced my knowledge and helped me better understanding the process involved.
hi Amitava, thanks for this point/reference! I did not know that, but I guess, if you have good and clear CL pictures you can judge, whether or not the zircons are metamict.
Dear Professor Knittel,
Exactly, you are right. On the other hand, the BSI images will be helpful for textural observation.
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