During Carboniferous time,tremendous juvenile arc crust was formed in the southern Central Asian Orogenic Belt(CAOB),although its origin remains unclear.Herein,we presented zircon U-Pb-Hf and whole-rock geochemical an...During Carboniferous time,tremendous juvenile arc crust was formed in the southern Central Asian Orogenic Belt(CAOB),although its origin remains unclear.Herein,we presented zircon U-Pb-Hf and whole-rock geochemical and Sr-Nd isotopic data for a suite of volcanic and pyroclastic rocks from the Khan-Bogd area in southern Mongolia.These Carboniferous pyroclastic rocks generally have some early Paleozoic zircons,probably derived from the granitic and sedimentary rocks of the Lake Zone and the Gobi-Altai Zone to the north,indicative of a continental arc nature.In addition,they have a main zircon U-Pb age of ca.370–330 Ma,positive Hf and Nd isotopes,and mafic-intermediate arc affinity,similar to the coeval arc magmatism.Moreover,the pyroclastic rocks of the northern area have more mafic and older volcanic components with depositional time(ca.350–370 Ma;Visean and Bashkirian stages)earlier than that in the southern area(mainly ca.350–315 Ma;Serpukhovian and Bashkirian stages).Combining a preexisting northward subduction supported by the available magnetotelluric data with a slab rollback model of the main oceanic basin of the Paleo-Asian Ocean(PAO)during Carboniferous and Triassic times,we infer that the Carboniferous arc magmatism was probably derived from a backarc ocean triggered by slab rollback.Thus,the juvenile arc volcanism of Mongolia,together with other areas(e.g.,Junggar)in the southern CAOB,represented a significant lateral accretion that terminated after the Carboniferous due to a significant contraction of the PAO.展开更多
The total magmatic output in modern arcs,where continental crust is now being formed, is believed to derive from melting of the mantle wedge and is largely basaltic. Globally averaged continental crust, however, has a...The total magmatic output in modern arcs,where continental crust is now being formed, is believed to derive from melting of the mantle wedge and is largely basaltic. Globally averaged continental crust, however, has an andesitic bulk composition and is hence too silicic to have been derived directly from the mantle. It is well known that one way this imbalance can be reconciled is if the parental basalt differentiates into a mafic garnet pyroxenitic residue/cumulate(‘‘arclogite'') and a complementary silicic melt, the former foundering or delaminating into the mantle due to its high densities and the latter remaining as the crust.Using the Sierra Nevada batholith in California as a case study, the composition of mature continental arc crust is shown in part to be the product of a cyclic process beginning with the growth of an arclogite layer followed by delamination of this layer and post-delamination basaltic underplating/recharge into what remains of the continental crust.A model is presented, wherein continuous arc magmatism and production of arclogites in continental arcs are periodically punctuated by a delamination event and an associated magmatic pulse every *10–30 My. The recycling flux of arclogites is estimated to be *5 %–20 % that of oceanic crust recycling by subduction. Delaminated arclogites have the necessary trace-element compositions to yield time-integrated isotopic compositions similar to those inferred toexist as reservoirs in the mantle. Because of their low melting temperatures, such pyroxenites may be preferentially melted, possibly forming a component of some hotspot magmas.展开更多
基金financially supported by the National Natural Science Foundation of China(42102260,42172236,42072264,41902229,and 42072267)Hong Kong Research Grants Council General Research Fund(17307918)+1 种基金the Fundamental Research Funds for the Central Universities,Chang’an University,China(300102272204)Opening Foundation of State Key Laboratory of Continental Dynamics,Northwest University,China(21LCD09)。
文摘During Carboniferous time,tremendous juvenile arc crust was formed in the southern Central Asian Orogenic Belt(CAOB),although its origin remains unclear.Herein,we presented zircon U-Pb-Hf and whole-rock geochemical and Sr-Nd isotopic data for a suite of volcanic and pyroclastic rocks from the Khan-Bogd area in southern Mongolia.These Carboniferous pyroclastic rocks generally have some early Paleozoic zircons,probably derived from the granitic and sedimentary rocks of the Lake Zone and the Gobi-Altai Zone to the north,indicative of a continental arc nature.In addition,they have a main zircon U-Pb age of ca.370–330 Ma,positive Hf and Nd isotopes,and mafic-intermediate arc affinity,similar to the coeval arc magmatism.Moreover,the pyroclastic rocks of the northern area have more mafic and older volcanic components with depositional time(ca.350–370 Ma;Visean and Bashkirian stages)earlier than that in the southern area(mainly ca.350–315 Ma;Serpukhovian and Bashkirian stages).Combining a preexisting northward subduction supported by the available magnetotelluric data with a slab rollback model of the main oceanic basin of the Paleo-Asian Ocean(PAO)during Carboniferous and Triassic times,we infer that the Carboniferous arc magmatism was probably derived from a backarc ocean triggered by slab rollback.Thus,the juvenile arc volcanism of Mongolia,together with other areas(e.g.,Junggar)in the southern CAOB,represented a significant lateral accretion that terminated after the Carboniferous due to a significant contraction of the PAO.
文摘The total magmatic output in modern arcs,where continental crust is now being formed, is believed to derive from melting of the mantle wedge and is largely basaltic. Globally averaged continental crust, however, has an andesitic bulk composition and is hence too silicic to have been derived directly from the mantle. It is well known that one way this imbalance can be reconciled is if the parental basalt differentiates into a mafic garnet pyroxenitic residue/cumulate(‘‘arclogite'') and a complementary silicic melt, the former foundering or delaminating into the mantle due to its high densities and the latter remaining as the crust.Using the Sierra Nevada batholith in California as a case study, the composition of mature continental arc crust is shown in part to be the product of a cyclic process beginning with the growth of an arclogite layer followed by delamination of this layer and post-delamination basaltic underplating/recharge into what remains of the continental crust.A model is presented, wherein continuous arc magmatism and production of arclogites in continental arcs are periodically punctuated by a delamination event and an associated magmatic pulse every *10–30 My. The recycling flux of arclogites is estimated to be *5 %–20 % that of oceanic crust recycling by subduction. Delaminated arclogites have the necessary trace-element compositions to yield time-integrated isotopic compositions similar to those inferred toexist as reservoirs in the mantle. Because of their low melting temperatures, such pyroxenites may be preferentially melted, possibly forming a component of some hotspot magmas.
