Development of Jomda Interarc Basin in the North of Eastern Tibet

LI Jin gao; ZHOU Zu yi; PENG Yong min; YAO Peng

Jomda interare basin is located in the north part of Three-River area,eastern Tihet, and today covered by Triassic with about 10 000 m in thickness.Marine sediments predominated, and were characterized by the largely thick turhiditv rocks and arc volcanic rocks of cal。-alkalic suites that resulted from frequent volcanic events.The basin analvscs were on the bases of two sides:(1)utility of sequence stratigraphy, based on outcrop profiles, 10 three-order boundaries and sequcnccs were recognized by research of fine sediment facics and its models.Isochronous grillwork for Triassic sequence stratigraphy were established.The recognized marks of boundaries were built by the distinguished kcv sequence boundaries and geometric or superposed patterns of system traces and compared isochron of sedimentary and volcanic events.10 sequcncc stratigraphic boundaries were discriminated with marks of tectonic and strata including 6 Ⅰ-type and 4 Ⅱ-type boundaries.10 sequences were divided,.including 6 Ⅰ-type and 4 Ⅱ-type.These sequences developed during 37 Ma, the estimated average time of a sequence is 3-7Ma, with generally 1-2 Ma, the longest about lOMa. (2) Analvses of subsidence, the rebuilt of tectonic subsidence curves suggested that there were clearly two uplifts(at 250 Ma and 235 Ma) and two sinks.The estimated sedimentary rates were among 87-537 m/Ma. It is inferred that relations among tectonic suhsidence, water depth and high-frequency sedimentary velocities represented characteristics of depositional process in the arc area.It is concluded that evolution of Jomda basin were classificated into 6 depositional accumulation stages.The 6 stages were respectably: ①sedimentation of first shallow shelfs② formation of carbonate platforms ③development of the volcanic-terrigeous auhmarine fans④advancement of the volcanic-terrigeous shelfs③evolution of carbonate ramp and ⑥advancement of the terrigeous shelf to delta. It is pointed out that interarc basin of Jomda experienced processes of both early extensive deepness and late compressed shallowness.

1 Tongji University,Shanghai 200092;

2 Tibet Bureau of Geology and Mineral Resources,Lhasa 850000;

3 Chengdu Institute of Geology and Mineral Resources,Chengdu 610082

Received Date: 2000-03-07

Rev Recd Date: 2000-07-27

Key words:

Abstract: Jomda interare basin is located in the north part of Three-River area,eastern Tihet, and today covered by Triassic with about 10 000 m in thickness.Marine sediments predominated, and were characterized by the largely thick turhiditv rocks and arc volcanic rocks of cal。-alkalic suites that resulted from frequent volcanic events.The basin analvscs were on the bases of two sides:(1)utility of sequence stratigraphy, based on outcrop profiles, 10 three-order boundaries and sequcnccs were recognized by research of fine sediment facics and its models.Isochronous grillwork for Triassic sequence stratigraphy were established.The recognized marks of boundaries were built by the distinguished kcv sequence boundaries and geometric or superposed patterns of system traces and compared isochron of sedimentary and volcanic events.10 sequcncc stratigraphic boundaries were discriminated with marks of tectonic and strata including 6 Ⅰ-type and 4 Ⅱ-type boundaries.10 sequences were divided,.including 6 Ⅰ-type and 4 Ⅱ-type.These sequences developed during 37 Ma, the estimated average time of a sequence is 3-7Ma, with generally 1-2 Ma, the longest about lOMa. (2) Analvses of subsidence, the rebuilt of tectonic subsidence curves suggested that there were clearly two uplifts(at 250 Ma and 235 Ma) and two sinks.The estimated sedimentary rates were among 87-537 m/Ma. It is inferred that relations among tectonic suhsidence, water depth and high-frequency sedimentary velocities represented characteristics of depositional process in the arc area.It is concluded that evolution of Jomda basin were classificated into 6 depositional accumulation stages.The 6 stages were respectably: ①sedimentation of first shallow shelfs② formation of carbonate platforms ③development of the volcanic-terrigeous auhmarine fans④advancement of the volcanic-terrigeous shelfs③evolution of carbonate ramp and ⑥advancement of the terrigeous shelf to delta. It is pointed out that interarc basin of Jomda experienced processes of both early extensive deepness and late compressed shallowness.

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Development of Jomda Interarc Basin in the North of Eastern Tibet

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