A noncognate relationship between megacrysts and host basalts from the Tuoyun basin, Chinese Tian Shan

• Published in: The Journal of Geology
• Main Authors: Han, Bao-fu, Liu, Jian-bo, Zhang, Lei
• Other Authors: Han, BF (reprint author), Peking Univ, Sch Earth & Space Sci, Minist Educ Key Lab Orogen Belts & Crustal Evolut, Beijing 100871, Peoples R China., Peking Univ, Sch Earth & Space Sci, Minist Educ Key Lab Orogen Belts & Crustal Evolut, Beijing 100871, Peoples R China.
• Format: Journal/Newspaper
• Language: English
• Published: journal of geology 2008
• Subjects: CENTRAL TIEN-SHAN; ALKALI BASALTS; LITHOSPHERIC MANTLE; KERGUELEN ISLANDS; ANORTHOCLASE MEGACRYSTS; SOUTHEASTERN AUSTRALIA; IHERZOLITE XENOLITHS; PERIDOTITE XENOLITHS; SOUTHWEST TIANSHAN; COGNATE INCLUSIONS; Kerguelen; Kerguelen Islands
• Online Access: https://hdl.handle.net/20.500.11897/312516; https://doi.org/10.1086/590136

Abundant kaersutite and alkali feldspar megacrysts occur together with mantle-derived and lower crustal xenoliths, including kaersutite hornblendite and syenite, in the Early Cretaceous alkaline basalts of the Tuoyun basin in the westernmost Chinese Tian Shan. Particularly, several kaersutite hornblendite cumulate xenoliths have the assemblage of kaersutite + alkali feldspar + titanian mica +/- titanomagnetite +/- clinopyroxene, in which kaersutite occurs as an early-stage cumulus phase crystallized from a parental magma and alkali feldspar occurs as a late-stage intercumulus phase from the evolved magma between accumulating kaersutite grains. The megacrystic and xenolithic kaersutite has much higher Mg# values (0.70-0.96) than the host basalt (0.47-0.60). The kaersutite and alkali feldspar megacrysts have similar initial Sr-87/Sr-86 ratios (0.7032-0.7033 and 0.7035-0.7038, respectively), significantly different from their host basalts (0.7047-0.7054). Xenolithic petrography and megacrystic Sr isotope geochemistry support a common origin for the kaersutite and alkali feldspar megacrysts and preclude the precipitation of the megacrysts from their host basalts. As the fragments of kaersutite hornblendite and syenite that may have crystallized from a trachytic parental magma and its evolved magma underplated earlier in the crust-mantle transition zone, these megacrysts, together with other xenoliths, were captured and brought to the surface by the Early Cretaceous basalts. http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000259502600005&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701 Geology SCI(E) 3 ARTICLE 5 499-509 116