TY - JOUR

T1 - Formation of orthopyroxene-magnetite symplectites by reactive melt flow

T2 - Insights into the Shangzhuang layered intrusion in Beijing, China

AU - Wang, Sijia

AU - Hou, Tong

AU - Xie, Qiuhong

N1 - Publisher Copyright: © 2024 Elsevier Ltd

PY - 2024/9

Y1 - 2024/9

N2 - Interstitial microstructures in layered intrusions can provide crucial insights into the formation, transport, evolution, and solidification processes of magma. The symplectites commonly observed in the Shangzhuang layered intrusions in Beijing, China, can be classified into three types based on their occurrence and related primocryst minerals. Regardless of variation in types, the vermicular symplectites consistently exhibit a volume ratio of magnetite to orthopyroxene at approximately 1:4. Orthopyroxene in the symplectites shows no geochemical difference from those primocrysts. Inter-cumulus hornblende formed during the late stage after the formation of symplectites so that the symplectites are always enclosed by hornblende. By utilizing the hornblende geothermobarometer, we have also constrained that the symplectites have been formed within a relatively wide temperature range of 1040–915 °C through a reaction between the interstitial immiscible Fe-rich melt and the primocryst olivine and orthopyroxene. The reaction can be simplified as Ol/Opx (primocryst) + Fe-rich melt → Opx (symplectite) + Mt (symplectite). Besides, based on the mass balance and reaction results, the Si/O ratio of Fe-rich melt is estimated to be 1:3. The study of these symplectites contributes to refining the processes of reactive melt flow in mafic layered intrusions during late-stage magmatic crystallization.

AB - Interstitial microstructures in layered intrusions can provide crucial insights into the formation, transport, evolution, and solidification processes of magma. The symplectites commonly observed in the Shangzhuang layered intrusions in Beijing, China, can be classified into three types based on their occurrence and related primocryst minerals. Regardless of variation in types, the vermicular symplectites consistently exhibit a volume ratio of magnetite to orthopyroxene at approximately 1:4. Orthopyroxene in the symplectites shows no geochemical difference from those primocrysts. Inter-cumulus hornblende formed during the late stage after the formation of symplectites so that the symplectites are always enclosed by hornblende. By utilizing the hornblende geothermobarometer, we have also constrained that the symplectites have been formed within a relatively wide temperature range of 1040–915 °C through a reaction between the interstitial immiscible Fe-rich melt and the primocryst olivine and orthopyroxene. The reaction can be simplified as Ol/Opx (primocryst) + Fe-rich melt → Opx (symplectite) + Mt (symplectite). Besides, based on the mass balance and reaction results, the Si/O ratio of Fe-rich melt is estimated to be 1:3. The study of these symplectites contributes to refining the processes of reactive melt flow in mafic layered intrusions during late-stage magmatic crystallization.

KW - Fe-rich melt

KW - Interstitial liquid immiscibility

KW - Mafic layered intrusions

KW - Reactive melt flow

KW - Symplectite

UR - http://www.scopus.com/inward/record.url?scp=85199275128&partnerID=8YFLogxK

U2 - 10.1016/j.jseaes.2024.106262

DO - 10.1016/j.jseaes.2024.106262

M3 - Article

AN - SCOPUS:85199275128

VL - 273

JO - Journal of Asian earth sciences

JF - Journal of Asian earth sciences

SN - 1367-9120

M1 - 106262

ER -